JP2005150568A - Nitride semiconductor light emitting device and optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride semiconductor light-emitting device that suppresses light oozing into the p-layer region, has a good light output characteristic, and has a sufficiently low jitter, a method for manufacturing the same, and the nitride An object of the present invention is to propose an optical pickup device using a semiconductor light emitting element.
A nitride semiconductor light emitting device according to the present invention includes an active layer that emits light by trapping carriers, a carrier block layer that traps carriers in the active layer, and a gap between the active layer and the carrier block layer. In a nitride semiconductor light emitting device having an intermediate layer of 40 nm or more configured as follows, a graded layer in which an energy gap is continuously changed while being in contact with the carrier block layer is formed in a part of the intermediate layer. The graded layer is composed of an Al _x Ga _1-x N (0 ≦ x ≦ 1) layer. According to this configuration, since the material constituting the graded layer is AlGaN having good crystallinity, the recombination of hole carriers in the intermediate layer is reduced, and the efficiency of hole carrier injection into the active layer is increased. Jitter characteristics can be improved while maintaining the same level as before.
[Selection] Figure 2

Description

  The present invention relates to a nitride semiconductor light emitting device and an optical pickup device using the device.

  As a light-emitting element in the visible light short wavelength region, one using a compound semiconductor is known. In particular, gallium nitride based semiconductor light-emitting elements are attracting particular attention recently because they are direct transition type, have high luminous efficiency, and emit blue light, which is one of the three primary colors of light. In the gallium nitride based semiconductor light-emitting device, Mg is usually used as an impurity dopant to form a p-type layer, but the light absorption of this Mg-doped layer is very large, deteriorating the light output characteristics. However, it has been a problem in the past.

  In order to solve this problem, there has been proposed a laser device in which an intermediate layer is provided between a p-type AlGaN carrier block layer and a multiple quantum well structure active layer as in the band diagram structure shown in FIG. Patent Document 1). In FIG. 9, a multi-quantum well structure active layer 6 comprising three InGaN quantum well layers 8a, 8b and 8c and three InGaN barrier layers 7a, 7b and 7c, an n-type InGaN layer 9 and an n-type AlGaN. A layer 10, a p-type AlGaN carrier block layer 11, a p-type GaN guide layer 12, and a p-type AlGaN cladding layer 13 are shown, and Mg is usually doped into a layer laminated from the p-type AlGaN carrier block layer 11. As a result, an Mg doped region (p layer region) is formed. Here, the Al composition ratio of the p-type AlGaN carrier block layer 11 is usually about 0.2 to 0.3, and has an effect of preventing leakage of electron carriers to the p-layer region.

According to this structure, an intermediate layer composed of an n-type InGaN layer 9 and an n-type AlGaN layer 10 is provided between the p-type AlGaN carrier block layer 11 and the multiple quantum well structure active layer 6. The distance between the p-type AlGaN carrier block layer 11 and the multiple quantum well structure active layer 6 is expanded to 130 nm. Therefore, the bleeding of light into the p-layer region is greatly reduced, the light absorption loss is reduced, and the light output characteristic better than the conventional one is obtained.
IEICE Technical Report LQE2002-87 “Blue Purple High Power Semiconductor Laser”

  The technique according to the above-mentioned Reference 1 reduces the light leakage to the p-layer region by increasing the distance between the p-type AlGaN carrier block layer 11 and the multiple quantum well structure active layer 6, and improves the light output characteristics. It has been proposed to improve. However, as the distance between the p-type AlGaN carrier block layer 11 and the multiple quantum well structure active layer 6 is increased, the distance at which hole carriers diffuse as minority carriers increases. For this reason, when the laser element is pulse-driven, the rise time and fall time of the laser light output become long and the jitter becomes large. In particular, when the distance between the p-type AlGaN carrier block layer 11 and the multiple quantum well structure active layer 6 is 40 nm or more, such a problem becomes remarkable.

  The present invention provides a nitride semiconductor light-emitting device that suppresses light oozing into the p-layer region, has good light output characteristics, and has sufficiently low jitter, a method for manufacturing the same, and the nitride semiconductor light-emitting device An object of the present invention is to propose an optical pickup device using the above.

In order to achieve the above object, a nitride semiconductor light emitting device of the present invention includes an active layer that emits light by trapping carriers, a carrier block layer that traps carriers in the active layer, the active layer, and the carrier In a nitride semiconductor light emitting device having an intermediate layer of 40 nm or more formed between block layers, a graded layer in which the energy gap is continuously changed while being in contact with the carrier block layer at a part of the intermediate layer The graded layer comprises an Al _x Ga _1-x N (0 ≦ x ≦ 1) layer.

  According to this configuration, since the material constituting the graded layer is AlGaN having good crystallinity, the recombination of hole carriers in the intermediate layer is reduced, and the efficiency of hole carrier injection into the active layer is increased. Jitter characteristics can be improved while maintaining the same level as before.

  In such a nitride semiconductor light emitting device, the intermediate layer may be composed of the graded layer and an InGaN layer or a GaN layer. Furthermore, lattice strain between the active layer and the graded layer can be effectively prevented by setting the thickness of the InGaN layer or the GaN layer to 10 nm or more. In addition, when the thickness of the InGaN layer or the GaN layer is 40 nm or less, the hole carrier diffusion time can be sufficiently shortened.

  In such a nitride semiconductor light emitting device, the carrier block layer is made of AlGaN, and the difference x1 between the Al composition ratio value x1 in the carrier block layer and the maximum Al composition ratio value x2 in the graded layer. By setting −x2 to 0.1 or more, it is possible to effectively suppress the overflow of electron carriers into the p-layer region at a high temperature of 60 ° C. or more.

  In such a nitride semiconductor light emitting device, the difference x2-x3 between the maximum value x2 and the minimum value x3 of the Al composition ratio of the graded layer may be 0.02 or more.

  In such a nitride semiconductor light emitting device, a potential barrier is formed at the interface between the graded layer and the InGaN layer by setting the minimum value x3 of the Al composition ratio of the graded layer to 0.02 or more. It is possible to effectively suppress the overflow of electron carriers into the p-layer region at a high temperature of 60 ° C. or higher.

  In such a nitride semiconductor light emitting device, the graded layer may be formed by ramping growth in which growth is performed while continuously increasing the growth temperature. When this ramping growth is used, the graded layer can prevent deterioration due to desorption of In from the active layer and improve the crystallinity of the graded layer itself. Can improve. Furthermore, in each of the nitride semiconductor light emitting devices described above, the active layer is a quantum well structure active layer composed of a plurality of quantum well layers and a plurality of barrier layers.

The nitride semiconductor light emitting device of the present invention includes an active layer that emits light by trapping carriers, an Al _x Ga _1-x N carrier block layer that traps carriers in the active layer, the active layer, a Al _x Ga _1-x N intermediate layer above 40nm formed between the carrier block layer, the nitride semiconductor light emitting device including, in some or all of the Al _x Ga _1-x N carrier block layer, The Al composition ratio is provided with a portion that continuously decreases from the side in contact with the intermediate layer toward the opposite side.

According to such a configuration, the energy gap on the band diagram is continuously changed by continuously changing the Al composition ratio. Therefore, the potential barrier generated at the interface between the Al _x Ga _1-x N carrier block layer and the p-type guide layer is relaxed, and the hole carrier injection efficiency is improved.

In such a nitride semiconductor light emitting device, the Al _x Ga _1-x N carrier block layer has a layer thickness where the Al composition continuously decreases from the side in contact with the intermediate layer to the opposite side. By setting the thickness to 5 nm or more, the hole carrier injection efficiency can be sufficiently increased.

Further, in such a nitride semiconductor light emitting device, the maximum value of the Al composition ratio of the Al _x Ga _1-x N carrier block layer is set to 0.1 or more, so that the p layer is formed at a high temperature of 60 ° C. or more. Overflow of electron carriers into the region can be effectively suppressed.

Further, in such a nitride semiconductor light emitting device, by making the thickness of the Al _x Ga _1-x N carrier block layer 10 nm or more, the outflow of electron carriers to the p layer region due to the tunnel effect is effectively prevented. Can be suppressed.

  Further, in such a nitride semiconductor light emitting device, a graded layer that is in contact with the carrier block layer and whose energy gap continuously changes may be provided in a part of the intermediate layer.

  The optical pickup device according to the present invention uses light emitted from each of the nitride semiconductor light emitting elements described above.

  According to the nitride semiconductor light emitting device according to the present invention, since the Al composition of the graded layer is continuously changed, the energy gap is also continuously changed to generate a potential gradient. For this reason, since the diffusion time of holes from the p-layer region to the active layer is shortened as compared with the conventional case, jitter characteristics are improved when the laser element is pulse-driven. Further, since the graded layer is configured to be in contact with the carrier block layer, a potential groove formed at the interface with the n-type layer can be eliminated. Therefore, the injection of hole carriers into the active layer is promoted and the jitter characteristics are improved. Further, as the hole diffusion time is shortened and the injection into the active layer is promoted, the threshold at which the laser oscillates is reduced and the slope efficiency is improved. Further, the graded layer can effectively prevent the lattice distortion between the carrier block layer and the active layer, and the life characteristics are improved.

  According to the nitride semiconductor light emitting device of the present invention, an InGaN layer or a GaN layer is formed between the graded layer and the quantum well layer, so that the lattice strain between the graded layer and the active layer is reduced. In order to prevent it more effectively, the life characteristics are improved. Furthermore, lattice strain can be particularly effectively prevented by setting the thickness of the InGaN layer or the layer made of the GaN layer to 10 nm or more. Moreover, the hole diffusion time can be sufficiently shortened by setting the film thickness of the InGaN layer or the layer made of the GaN layer within 40 nm.

  According to the nitride semiconductor light emitting device of the present invention, when the Al composition ratio of the material AlGaN constituting the carrier block layer is x1, and the maximum Al composition ratio of the graded layer is x2, the difference x1 between x1 and x2 is x1. By setting −x2 to 0.1 or more, it is possible to effectively suppress the overflow of electron carriers to the p-layer region at a high temperature of 60 ° C. or more. In addition, the difference between the maximum value x2 and the minimum value x3 of the graded layer x2 and the minimum value x3 is set to 0.02 or more, and the gradient of the energy gap makes the hole carrier diffusion time shorter and jitter is effective. Improved.

  According to the nitride semiconductor light emitting device of the present invention, by setting the minimum value x3 of the Al composition ratio of the graded layer to 0.02 or more, the energy gap is reduced at the interface between the graded layer and the InGaN layer or the GaN layer. When the value is discontinuously changed to form an energy diagram having a stepped structure, a potential barrier against electron carriers is formed at the interface between the graded layer and the InGaN layer or the GaN layer, and p at a high temperature of 60 ° C. or higher. The overflow of electron carriers into the layer region can be effectively suppressed.

  According to the nitride semiconductor light emitting device of the present invention, the graded layer is formed by ramping growth, thereby effectively preventing deterioration due to In desorption from the active layer, and the graded layer itself. Since the crystallinity can also be good, the life characteristics can be improved.

According to the nitride semiconductor light emitting device according to the present invention, since the Al composition ratio in the Al _x Ga _1-x N carrier block layer continuously changes, the energy gap of the Al _x Ga _1-x N carrier block layer Changes continuously, the potential barrier generated at the interface between the Al _x Ga _1-x N carrier blocking layer and the p-type guide layer is relaxed, and the efficiency of hole carrier injection into the intermediate layer is improved. Further, compared to a nitride semiconductor light emitting device having a conventional structure, the voltage applied to the pn junction can be lowered, so that the operating voltage can be improved and the Al _x Ga _1-x N carrier block layer and the n-type can be improved. It is possible to relax a potential groove that has been conventionally formed at the layer interface, and to improve the efficiency of hole carrier injection from the intermediate layer to the active layer. Due to the above effects, the jitter characteristics could be improved.

According to the nitride semiconductor light emitting device of the present invention, hole carrier injection is achieved by setting the layer thickness of the Al _x Ga _1-x N carrier block layer where the Al composition ratio is continuously changed to 5 nm or more. Efficiency is high enough. In addition, by setting the maximum Al composition ratio of the Al _x Ga _1-x N carrier block layer to 0.1 or more, it is possible to effectively suppress the overflow of electron carriers to the p layer region at a high temperature of 60 ° C. or higher. Furthermore, the outflow of electron carriers to the p-layer region due to the tunnel effect is effectively suppressed by setting the thickness of the Al _x Ga _1-x N carrier block layer to 10 nm or more.

  According to the optical pickup device equipped with the nitride semiconductor light-emitting element of the present invention, jitter due to the nitride semiconductor light-emitting element is reduced, so that good frequency characteristics can be obtained.

<First Embodiment>
A first embodiment of the present invention will be described with reference to the drawings. As an example of the nitride semiconductor light emitting device, a gallium nitride based semiconductor laser device will be described. FIG. 1 is a schematic cross-sectional view showing the configuration of a gallium nitride based semiconductor laser device according to this embodiment.

First, the structure of the gallium nitride based semiconductor laser device will be described. 1 includes a sapphire substrate 1 having a c-plane surface, a GaN buffer layer 2, an n-type GaN contact layer 3, an n-type Al _0.1 Ga _0.9 N cladding layer 4, and an n-type GaN guide layer 5. Multiple quantum well structure active layer comprising three layers of In _0.2 Ga _0.8 N quantum well layers 8a, 8b and 8c (FIG. 2) and three layers of In _0.01 Ga _0.99 N barrier layers 7a, 7b and 7c (FIG. 2) 6, n-type In _0.01 Ga _0.99 N layer 9a, n-type Al _x GaN _1-x graded layer 10a, p-type Al _0.2 Ga _0.8 N carrier block layer 11a, p-type GaN guide layer 12, p-type Al _0.1 Ga _0.9 The N clad layer 13 a, the p-type GaN contact layer 14, the p-side electrode 15, the n-side electrode 16, and the SiO ₂ insulating film 17 are configured. Reference numeral 18 denotes the entire laser device.

  In each of the following embodiments including this embodiment, the cavity length of the gallium nitride based semiconductor laser element is set to 500 μm, and the front surface reflectance and the rear surface reflectance of the resonator are respectively set to 20% and 90%. . Further, the surface orientation of the surface of the sapphire substrate 1 is not limited to the c-plane, and may be other surface orientations such as a-plane, r-plane, and m-plane.

  Next, a method for manufacturing a gallium nitride based semiconductor laser device will be described with reference to FIG. The following description shows the case where the MOCVD method (metal organic vapor phase epitaxy) is used. However, the growth method is not limited to the MOCVD method as long as it can epitaxially grow GaN, and the MBE method (molecular beam epitaxial growth). Other vapor phase epitaxy methods such as HDVPE (hydride vapor phase epitaxy).

First, the GaN buffer layer is grown on a sapphire substrate 1 having a c-plane as a surface placed in a predetermined growth furnace, using trimethylgallium (TMG) and ammonia (NH ₃ ) as raw materials at a growth temperature of 550 ° C. 2 is grown to 35 nm. Next, the growth temperature is raised to 1050 ° C., and the Si-doped n-type GaN contact layer 3 having a thickness of 3 μm is grown using TMG, NH ₃ , and silane gas (SiH ₄ ) as raw materials. Subsequently, trimethylaluminum (TMA) is added to the raw material and the growth temperature is maintained at 1050 ° C., and the Si-doped n-type Al _0.1 Ga _0.9 N cladding layer 4 having a thickness of 0.7 μm is grown. Subsequently, TMA is excluded from the raw material, and the growth temperature is kept at 1050 ° C. to grow the Si-doped n-type GaN guide layer 5 having a thickness of 50 nm.

Next, the growth temperature is lowered to 750 ° C., TMG, NH ₃ , and trimethylindium (TMI) are used as raw materials, and the three In _0.2 Ga _0.8 N quantum well layers 8a, 8b, 8c, the three layers are formed. The In _0.01 Ga _0.99 N barrier layers 7a, 7b and 7c are successively grown alternately to produce the multiple quantum well structure active layer 6. Each layer thickness is 5 nm.

Next, the growth temperature is maintained at 750 ° C., and the n-type In _0.01 Ga _0.99 N layer 9a is grown to 20 nm. Subsequently, TMG, TMA, and NH ₃ are used as raw materials, and the supply amounts of these raw material gases are changed. Then, the n-type Al _x GaN _1-x graded layer 10a having a changed Al composition ratio is formed to 20 nm. At this time, the Al composition ratio is changed, for example, by continuously increasing the content of TMA. This Al composition distribution is such that the Al composition ratio x is 0 at the interface in contact with the n-type In _0.01 Ga _0.99 N layer 9a, and the Al composition ratio x is at the interface in contact with the p-type Al _0.2 Ga _0.8 N carrier block layer 11. Prepare to be 0.1.

Subsequently, TMG, TMA, NH ₃ , and cyclopentadienyl magnesium (Cp 2 Mg) are used as raw materials, the growth temperature is maintained at 750 ° C., and the p-type Al _0.2 Ga _0.8 N carrier block layer having a thickness of 10 nm. 11a is grown. Next, the growth temperature is increased to 1050 ° C., and the Mg-doped p-type GaN guide layer 12 having a thickness of 50 nm is formed using TMG, NH ₃ , and cyclopentadienyl magnesium (Cp ₂ Mg) as raw materials. Grow.

The n-type Al _x GaN _1-x graded layer 10a, the p-type Al _0.2 Ga _0.8 N carrier blocking layer 11a, and the p-type GaN guide layer 12 can also be formed by the following method. Using TMG, TMA, and NH ₃ as raw materials, the growth rate of the multi-quantum well structure active layer 6 and the n-type In _0.01 Ga _0.99 N layer 9a from 750 ° C. Growth is performed while continuously increasing the growth temperature to 1050 ° C. This growth method is called ramping growth. By the above method, the n-type Al _x GaN _1-x graded layer 10a whose Al composition ratio is continuously changed is formed.

Subsequently, the p-type Al _0.2 Ga _0.8 N carrier blocking layer 11a having a thickness of 10 nm is grown with the growth temperature kept at 1050 ° C., and TMG, NH ₃ , and cyclopentadienyl magnesium (Cp ₂ Mg) are grown. ) Is used as a raw material to grow the Mg-doped p-type GaN guide layer 12 having a thickness of 50 nm. When such a growth method is used, the n-type Al _x GaN _1-x graded layer 10a formed by ramping growth serves to prevent deterioration due to In desorption from the multiple quantum well structure active layer 6. In addition to the effective performance, the crystallinity of the n-type Al _x GaN _1-x graded layer 10a can be improved, so that the life characteristics can be improved.

When the n-type Al _x GaN _1-x graded layer 10a, the p-type Al _0.2 Ga _0.8 N carrier block layer 11a, and the p-type GaN guide layer 12 are formed as described above, TMA is added to the raw material, The growth temperature is maintained at 1050 ° C., and the Mg-doped p-type Al _0.1 Ga _0.9 N cladding layer 13a having a thickness of 0.7 μm is grown. Further, while maintaining the growth temperature at 1050 ° C., TMA is excluded from the raw material, and the Mg-doped p-type GaN contact layer 14 having a thickness of 0.2 μm is grown to complete a gallium nitride epitaxial wafer. To do. Thereafter, the gallium nitride-based epitaxial wafer is annealed in a nitrogen gas atmosphere at 800 ° C. to reduce the resistance of the Mg-doped p-type layer.

When the layers are stacked on the sapphire substrate 1 in this manner, first, the n-type GaN is formed from the outermost surface of the p-type GaN contact layer 14 in a stripe shape having a width of 200 μm by using a normal photolithography and dry etching technique. Etching is performed until the contact layer 3 is exposed. Then, using the same photolithography and dry etching technique, the ridge structure is formed in a stripe shape having a width of 5 μm on the outermost surface of the p-type GaN contact layer 14 remaining without being etched. The p-type GaN contact layer 14 and the p-type Al _0.1 Ga _0.9 N cladding layer 13a are etched. Subsequently, on the side surface of the ridge (side surface of the p-type GaN contact layer 14) and the surface of the p-type layer other than the ridge (the surface of the p-type Al _0.1 Ga _0.9 N cladding layer 13a), the SiO having a thickness of 200 nm is formed. _{2 The} insulating film 17 is formed. The p-side electrode 15 made of nickel and gold is formed on the surfaces of the SiO ₂ insulating film 17 and the p-type GaN contact layer 14, and titanium and aluminum are formed on the surface of the n-type GaN contact layer 3 exposed by etching. The n-side electrode 16 is formed, and a wafer on which a gallium nitride based semiconductor laser device is fabricated is completed.

  Thereafter, the wafer is cleaved in a direction perpendicular to the ridge stripe to form a laser cavity end face, and further divided into individual chips. Then, each chip is mounted on the stem, and each electrode and the lead terminal are connected by wire bonding to complete the gallium nitride based semiconductor laser element 18.

FIG. 2 shows a partial band diagram of the gallium nitride based semiconductor laser device of the present embodiment manufactured by the above method. In FIG. 2, the multi-quantum well structure active layer 6 composed of the three In _0.2 Ga _0.8 N quantum well layers 8a, 8b and 8c and the three In _0.01 Ga _0.99 N barrier layers 7a, 7b and 7c. The n-type In _0.01 Ga _0.99 N layer 9a, the n-type Al _x GaN _1-x graded layer 10a, the p-type Al _0.2 Ga _0.8 N carrier blocking layer 11a, the p-type GaN guide layer 12, and the p-type The Al _0.1 Ga _0.9 N clad layer 13a and the respective energy gaps are shown. Here, in the n-type Al _x GaN _1-x graded layer 10a, the Al composition x is the lowest on the multi-quantum well structure active layer 6 side, and the Al composition ratio continuously increases as the distance from the active layer increases. Thus, it is configured to be highest at a portion in contact with the p-type Al _0.2 Ga _0.8 N carrier block layer 11a.

In the above configuration, since the Al composition of the n-type Al _x GaN _1-x graded layer 10a continuously changes, its energy gap also changes continuously as shown in FIG. Produce. Therefore, the hole diffusion time from the p-layer region to the multiple quantum well structure active layer 6 is shortened as compared with the conventional case, so that the jitter characteristics are improved when the laser element is pulse-driven. In the conventional structure, at the interface between the p-type AlGaN carrier block layer 11 and the n-type layer, the band of the n-type layer bends to the positive energy side when a voltage is applied, and at the interface with the p-type AlGaN carrier block layer 11. A potential groove was formed. Electron carriers accumulated in this potential groove, and injection of hole carriers into the multiple quantum well structure active layer 6 was prevented. However, in the present embodiment, the n-type Al _x GaN _1-x graded layer 10a is configured to be in contact with the p-type Al _0.2 Ga _0.8 N carrier blocking layer 11a, and thus formed at the interface with the n-type layer. The potential groove can be eliminated. Therefore, the injection of hole carriers into the active layer is promoted and the jitter characteristics are improved.

Further, as the hole diffusion time is shortened and the injection into the multiple quantum well structure active layer 6 is promoted, the threshold for laser oscillation is reduced and the slope efficiency is improved. Further, the n-type Al _x GaN _1-x graded layer 10a can effectively prevent lattice distortion between the p-type Al _0.2 Ga _0.8 N carrier blocking layer 11a and the multiple quantum well structure active layer 6. , Life characteristics are improved. Even when the n-type Al _x GaN _1-x graded layer 10a is made of n-type In _x GaN _1-x , a band diagram similar to that of the present embodiment can be obtained. However, since all the intermediate layers are composed of InGaN layers with poor crystallinity, the hole injection efficiency is extremely lowered, the light output characteristics are deteriorated, and the jitter characteristics are not improved as a result. . That is, the improvement in characteristics in the present embodiment is configured such that the n-type Al _x GaN _1-x graded layer 10a made of an AlGaN material with good crystallinity is in contact with the p-type Al _0.2 Ga _0.8 N carrier block layer 11a. This is considered to be achieved.

Furthermore, the n-type In _0.01 Ga _0.99 N layer 9a is formed between the n-type Al _x GaN _1-x graded layer 10a and the In _0.2 Ga _0.8 N quantum well layer 8c, In order to more effectively prevent the lattice strain between the n-type Al _x GaN _1-x graded layer 10a and the multi-quantum well structure active layer 6, the lifetime characteristics are improved. The same effect can be obtained by providing a layer made of GaN instead of InGaN used as a material for the n-type In _0.01 Ga _0.99 N layer 9a. At this time, it is preferable to make the film thickness of the n-type In _0.01 Ga _0.99 N layer 9a or the layer made of GaN 10 nm or more because lattice strain can be particularly effectively prevented. The film thickness of the n-type In _0.01 Ga _0.99 N layer 9a or the layer made of GaN is preferably set within 40 nm in order to sufficiently shorten the hole diffusion time.

The p-type Al _0.2 Ga _0.8 N carrier block layer 11a can use Mg as a p-type dopant. At this time, the Mg concentration is usually 10 ¹⁹ cm ⁻³ or more and 10 ²¹ cm ⁻³ or less. When the Mg concentration is 10 ¹⁹ cm ⁻³ or less, the p-type Al _0.2 Ga _0.8 N carrier block layer 11a has a high resistance, leading to an increase in operating voltage. On the other hand, when the Mg concentration is 10 ²¹ cm ⁻³ or more, the crystallinity of the p-type Al _0.2 Ga _0.8 N carrier block layer 11a is deteriorated, resulting in a decrease in yield. When the thickness of the p-type Al _0.2 Ga _0.8 N carrier blocking layer 11a is less than 5 nm, electrons are injected into the p-type layer region due to the tunnel effect, whereas when the thickness is greater than 30 nm, The influence of crystal distortion on the multi-quantum well structure active layer 6 increases, resulting in a decrease in yield. Therefore, the thickness of the p-type Al _0.2 Ga _0.8 N carrier block layer 11a is preferably 5 nm or more and 30 nm or less.

  With the configuration as described above, in the gallium nitride semiconductor laser device according to the present embodiment, it is possible to obtain good jitter characteristics as well as good light output characteristics.

In this embodiment, the Al composition ratio of the material Al _x Ga _1-x N constituting the p-type carrier block layer is x1, and the maximum value of the Al composition ratio of the n-type Al _x GaN _1-x graded layer is When x2, the difference x1-x2 between x1 and x2 is 0.1 or more, so that the overflow of electron carriers into the p-layer region at a high temperature of 60 ° C. or higher can be effectively suppressed. preferable. Further, the Al composition ratio of the n-type Al _x GaN _1-x graded layer may be changed stepwise instead of continuously.

<Second Embodiment>
A second embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a band diagram of the gallium nitride based semiconductor laser device of this embodiment. The configuration of the gallium nitride based semiconductor laser device in this embodiment is as shown in FIG. However, in FIG. 1, the n-type Al _x GaN _1-x graded layer 10a corresponds to an n-type Al _x GaN _1-x graded layer 10b described later in the present embodiment. In addition, since the manufacturing method of the gallium nitride based semiconductor laser device in this embodiment is the same as that in the first embodiment, the detailed description thereof will be omitted with reference to the first embodiment.

In the gallium nitride based semiconductor laser device of this embodiment, unlike the first embodiment, the minimum value x3 of the Al composition ratio of the n-type Al _x GaN _1-x graded layer 10b is set to 0.02 or more. As shown in FIG. 3, at the interface between the n-type Al _x GaN _1-x graded layer 10b and the n-type In _0.01 Ga _0.99 N layer 9a, the energy gap value is changed discontinuously to provide a step. The energy diagram of the structure. As a result, an energy diagram having such a structure forms a potential barrier against electron carriers at the interface between the n-type Al _x GaN _1-x graded layer 10b and the n-type In _0.01 Ga _0.99 N layer 9a. , It is possible to effectively suppress the overflow of electron carriers into the p-layer region at a high temperature of 60 ° C. or higher. In addition, the difference x2-x3 between the maximum value x2 and the minimum value x3 of the Al composition ratio of the n-type Al _x GaN _1-x graded layer 10b is set to 0.02 or more, and the energy gap is given a gradient, whereby hole carriers Diffusion time is reduced, and jitter is effectively improved.

<Third Embodiment>
A third embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a schematic cross-sectional view showing the configuration of the gallium nitride based semiconductor laser device in the present embodiment. In the present embodiment, the intermediate layer composed of the n-type In _0.01 Ga _0.99 N layer 9a and the n-type Al _x GaN _1-x graded layer 10a and the p-type Al in the first embodiment described above. _The portion composed of the _0.2 Ga _0.8 N carrier block layer 11a is changed. Except for these portions, the configuration is the same as that of the first embodiment. Therefore, in FIG. 4, the same reference numerals are given, and the detailed description thereof is omitted with reference to the first embodiment. .

The gallium nitride based semiconductor laser device shown in FIG. 4 includes the n-type In _0.01 Ga _0.99 N layer 9a, the n-type Al _x GaN _1-x graded layer 10a and the p-type Al _0.2 Ga in the gallium nitride based semiconductor laser device of FIG. An n-type In _0.01 Ga _0.99 N layer 9b having a layer thickness of 40 nm and a p-type Al _x Ga _1-x N carrier block layer 11b are formed in a portion corresponding to the _0.8 N carrier block layer 11a. At this time, in the p-type Al _x Ga _1-x N carrier block layer 11b, the Al composition ratio x is the highest on the side of the multi-quantum well structure active layer 6 and continuously as the p-type GaN guide layer 12 is approached. In particular, the Al composition ratio is low, and the Al composition ratio is lowest at the portion in contact with the p-type GaN guide layer 12. For example, in the p-type Al _x Ga _1-x N carrier block layer 11b, the Al composition ratio x is 20% on the multiple quantum well structure active layer 6 side, and on the p-type GaN guide layer 12 side. The Al composition ratio is 0%.

Next, with reference to FIG. 4, a method for manufacturing the gallium nitride based semiconductor laser of this embodiment will be described. The GaN buffer layer 2, the n-type GaN contact layer 3, the n-type Al _0.1 Ga _0.9 N cladding layer 4, the n-type GaN guide layer 5, the three In _0.2 Ga _0.8 N quantum well layers 8a and 8b, The fabrication method up to the multiple quantum well structure active layer 6 composed of 8c and the three layers of In _0.01 Ga _0.99 N barrier layers 7a, 7b and 7c is the same as in the first embodiment. When the multi-quantum well structure active layer 6 is configured, the n-type In _0.01 Ga _0.99 N layer 9b is grown to 40 nm at a growth temperature of 750 ° C.

Then, while maintaining the growth temperature of 750 ° C., using TMG, TMA, and NH ₃ as raw materials, while changing the supply amount of these raw material gases, the p-type is changing continuously. An Al _x Ga _1-x N carrier block layer 11b is grown. At this time, for example, the Al composition ratio is changed by continuously increasing the content of TMA. The value of the Al composition ratio in the p-type Al _x Ga _1-x N carrier block layer 11b is 0.2 on the interface side in contact with the n-type In _0.01 Ga _0.99 N layer 9b, and the p-type GaN guide layer It is manufactured so as to have a distribution configuration that continuously changes from 0.2 to 0 toward the 12 side. The subsequent manufacturing method is the same as that of the first embodiment.

FIG. 5 shows a band diagram of a part of the gallium nitride based semiconductor laser device according to this embodiment. In the present embodiment, the energy gap of the p-type Al _x Ga _1-x N carrier blocking layer 11b is the largest on the multiple quantum well structure active layer 6 side, and continuously as it approaches the p-type GaN guide layer 12 side. Has decreased. The band diagram has a structure in which the Al composition ratio in the p-type Al _x Ga _1-x N carrier blocking layer 11b takes the largest value on the multiple quantum well structure active layer 6 side, and the p-type GaN guide layer It was obtained by constituting so as to decrease continuously as approaching the 12 side.

As mentioned above the structure, the Al composition ratio in the p-type Al _x Ga _1-x N carrier block layer 11b is continuously changed, as shown in FIG. 5, the p-type Al _x Ga The energy gap of the _1-x N carrier block layer 11b changes continuously, and the potential barrier generated at the interface between the p-type Al _x Ga _1-x N carrier block layer 11a and the p-type GaN guide layer 12 is relaxed. Thus, the efficiency of hole carrier injection into the intermediate layer is improved. In addition, the voltage applied to the pn junction can be lowered, the operating voltage can be improved, and the Al _x Ga _1-x N carrier block layer and the n-type can be compared with the nitride semiconductor light emitting device having the conventional structure. It is possible to relax a potential groove that has been conventionally formed at the layer interface, and to improve the efficiency of hole carrier injection from the intermediate layer to the active layer. Due to the above effects, the jitter characteristics could be improved.

<Fourth Embodiment>
A fourth embodiment of the present invention will be described below with reference to the drawings. In the present embodiment, the cross-sectional structure of each layer of the gallium nitride based semiconductor laser device is as shown in FIG. However, in FIG. 4, the p-type Al _x Ga _1-x N carrier block layer 11b corresponds to a p-type Al _x Ga _1-x N carrier block layer 11c (FIG. 6) described later in the present embodiment. Since other parts are the same as those in the third embodiment, detailed description thereof is omitted with reference to the third embodiment.

The manufacturing method of the gallium nitride based semiconductor laser device in this embodiment is the same as that in the third embodiment except for the p-type Al _x Ga _1-x N carrier block layer 11c. The p-type Al _x Ga _1-x N carrier block layer 11c uses TMG, TMA, and NH ₃ as raw materials at a growth temperature of 750 ° C., and changes the Al composition while changing the supply amounts of these raw material gases. The p-type Al _x Ga _1-x N carrier block layer 11c is formed. In the present embodiment, the TMA content is kept constant until the carrier block layer grows to 10 nm, and then the Al composition ratio is changed by continuously increasing the TMA content. In the p-type Al _x Ga _1-x N carrier block layer 11c, the Al composition ratio distribution is constant at 0.2 at 10 nm on the interface side in contact with the n-type In _0.01 Ga _0.99 N layer 9b. At the same time, the Al composition ratio is continuously reduced from 0.2 to 0 at 5 nm on the p-type GaN guide layer 12 side.

FIG. 6 shows a band diagram of a part of the gallium nitride based semiconductor laser device of this embodiment. In this embodiment, the p-type Al _x Ga _1-x N carrier blocking layer 11c includes a layer having the same band gap and a layer having a smaller band gap toward the p-type GaN guide layer 12, as shown in FIG. It becomes the composition provided. As in the third embodiment, an energy gap is continuously reduced toward the p-type GaN guide layer 12 in a part of the p-type Al _x Ga _1-x N carrier block layer 11c. The effect of can be obtained.

In order to sufficiently increase the hole carrier injection efficiency, the layer thickness of the portion where the Al composition ratio in the p-type Al _x Ga _1-x N carrier block layer 11c continuously changes should be 5 nm or more. Is preferred. In order to effectively suppress the overflow of electron carriers into the p layer region at a high temperature of 60 ° C. or higher, the maximum Al composition ratio of the p-type Al _x Ga _1-x N carrier block layer 11c is 0.1 or higher. It is preferable that In order to effectively suppress the outflow of electron carriers to the p-layer region due to the tunnel effect, it is preferable that the p-type Al _x Ga _1-x N carrier block layer 11c has a thickness of 10 nm or more.

  In the third embodiment and the fourth embodiment, the configuration without the graded layer has been described as an example. For example, as in the first embodiment, from the active layer side toward the carrier block side. Alternatively, a graded layer that widens the band gap may be provided.

  As an example, FIG. 7 shows a partial band diagram of a gallium nitride based semiconductor laser device. As described above, by combining the structure of the first or second embodiment and the structure of the third or fourth embodiment, it has good light output characteristics and sufficiently reduces jitter. A greater effect can be obtained.

  In each of the above-described embodiments, the sapphire substrate is used. However, the material used for the substrate is not limited to the sapphire substrate, and an SiC substrate, spinel substrate, MgO substrate, Si substrate, or GaAs substrate may be used. At this time, particularly in the case of a SiC substrate, since it is easier to cleave than a sapphire substrate, there is an advantage that it is easy to form the end face of the laser resonator by cleavage. The material used for the buffer layer on the sapphire substrate is not limited to GaN as long as it can epitaxially grow a gallium nitride based semiconductor on the substrate, but other materials such as AlN and AlGaN ternary mixed crystals may also be used. I do not care. Further, instead of the sapphire substrate and the GaN buffer layer, a GaN substrate may be substituted. In order to prevent cracks, an InGaN layer may be stacked on the sapphire substrate.

In each of the above-described embodiments, the AlGaN ternary mixed crystal having an Al composition ratio of Al _0.1 Ga _0.9 N is used as the composition material of the two cladding layers. For example, 4 4 containing other elements in a trace amount. Other materials such as an original mixed crystal semiconductor or higher may be used. Further, in the cladding layer, the mixed crystal composition may be changed so that the mixed crystal composition ratios of the two cladding layers are different.

  For the two guide layers, the energy gap value of the three quantum well layers constituting the active layer of the multiple quantum well structure and the energy gap value of the n-type cladding layer and the p-type cladding layer If there is a value of the energy gap between them, for example, a ternary mixed crystal such as InGaN or AlGaN or a quaternary mixed crystal such as InGaAlN may be used.

  Further, the composition ratio of the quantum well layer and the barrier layer constituting the multi-quantum well structure active layer is set according to a necessary laser oscillation wavelength. When it is desired to increase the oscillation wavelength, the value of the In composition ratio of the quantum well layer is increased, and when it is desired to decrease the wavelength, the value of the In composition ratio of the quantum well layer is decreased. Further, the quantum well layer and the barrier layer may be a quaternary mixed crystal semiconductor in which other elements are contained in a trace amount in the InGaN ternary mixed crystal. In addition, the constituent material of the barrier layer may be replaced with GaN.

  Furthermore, both the quantum well layer and the barrier layer constituting the multi-quantum well structure active layer may have a layer thickness other than 5 nm. Each layer thickness does not need to be the same, and may be different. Further, the number of quantum well layers may be other than three.

<Example of optical pickup device using gallium nitride based semiconductor laser element>
FIG. 8 shows a configuration diagram of an optical pickup portion of an optical pickup device using the gallium nitride based semiconductor laser element obtained by the present invention. The light emitted from the gallium nitride based semiconductor laser element 19 is divided into three light beams of two tracking sub-beams and a signal readout main beam by a tracking beam generating diffraction grating 20. The light passes through the hologram element 21 as zero-order light, is converted into parallel light by the collimator lens 22, and then condensed on the disk surface 24 by the objective lens 23.

  The condensed light is reflected by the light intensity modulated by the pits formed on the disk surface, passes through the objective lens 23 and the collimating lens 22, and is diffracted by the hologram element 21. The next light component is incident on the split type light receiving element 25 having a light receiving surface divided into five parts D1 to D5. By adding and subtracting the outputs from the five-divided light receiving surfaces, signal reading and tracking signals can be obtained.

  By using the gallium nitride based semiconductor laser element with reduced jitter described in the present invention for such an optical pickup device having an optical pickup section, good frequency characteristics can be obtained. The application of the gallium nitride based semiconductor laser device obtained in the present invention is not limited to the optical system described in this example, but the light composed of another optical system and an optical pickup unit using the optical system. It is possible to adapt to a pickup device.

It is a schematic sectional drawing which shows the structure of the gallium nitride semiconductor laser element in the 1st Embodiment or 2nd Embodiment of this invention. 1 is a band diagram of a part of a gallium nitride based semiconductor laser device according to a first embodiment of the present invention. FIG. 5 is a band diagram of a part of a gallium nitride based semiconductor laser device according to a second embodiment of the present invention. It is a schematic sectional drawing which shows the structure of the gallium nitride semiconductor laser element in the 3rd Embodiment or 4th Embodiment of this invention. FIG. 6 is a band diagram of a part of a gallium nitride based semiconductor laser device according to a third embodiment of the present invention. It is a one part band diagram figure of the gallium nitride semiconductor laser element in the 4th Embodiment of this invention. FIG. 6 is a band diagram of a part of a gallium nitride based semiconductor laser device that combines the structure of the first or second embodiment of the present invention and the structure of the third or fourth embodiment. It is an optical pick-up apparatus figure using the gallium nitride based semiconductor laser element by this invention. FIG. 5 is a band diagram of a part of a conventional gallium nitride based semiconductor laser device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sapphire substrate 2 GaN buffer layer 3 n-type GaN contact layer 4 n-type Al _0.1 Ga _0.9 N cladding layer 5 n-type GaN guide layer 6 Multi-quantum well structure active layer 7a In _0.01 Ga _0.99 N barrier layer 7b In _0.01 Ga _0.99 N Barrier layer 7c In _0.01 Ga _0.99 N barrier layer 8a In _0.2 Ga _0.8 N quantum well layer 8b In _0.2 Ga _0.8 N quantum well layer 8c In _0.2 Ga _0.8 N quantum well layer 9 n-type InGaN layer 9a n-type In _0.01 Ga _0.99 N Layer 9b n-type In _0.01 Ga _0.99 N layer 10 n-type AlGaN layer 10a n-type Al _x GaN _1-x graded layer 10b n-type Al _x GaN _1-x graded layer 11 p-type AlGaN carrier block layer 11a p-type Al _0.2 Ga _0.8 N carrier block layer 11b p-type Al _x Ga _1-x N carrier block layer 11c p-type Al _x Ga _1-x N carry Blocking layer 12 p-type GaN guide layer 13 p-type AlGaN cladding layer 13a p-type Al _0.1 Ga _0.9 N cladding layer 14 p-type GaN contact layer 15 p-side electrode 16 n-side electrode 17 SiO ₂ insulating film 18 gallium nitride semiconductor laser device 19 Gallium Nitride Semiconductor Laser Element 20 Diffraction Grating 21 Hologram Element 22 Collimating Lens 23 Objective Lens 24 On Disk Surface 25 Divided Light Receiving Element D1 5 Divided Light Receiving Surface D2 5 Divided Light Receiving Surface D3 5 Divided Light Receiving Surface D4 5 Divided Light Receiving Surface Light receiving surface D5 5 light receiving surface

Claims (14)

Nitriding comprising an active layer that emits light by trapping carriers, a carrier block layer that traps carriers in the active layer, and an intermediate layer of 40 nm or more formed between the active layer and the carrier block layer In a semiconductor light emitting device,
A graded layer in which an energy gap continuously changes is formed on a part of the intermediate layer, while being in contact with the carrier block layer.
The nitride semiconductor light emitting device, wherein the graded layer is composed of an Al _x Ga _1-x N (0 ≦ x ≦ 1) layer.   The nitride semiconductor light emitting element according to claim 1, wherein the intermediate layer includes the graded layer and an InGaN layer or a GaN layer.   The nitride semiconductor light emitting device according to claim 2, wherein the InGaN layer or the GaN layer has a thickness of 10 nm or more.   The nitride semiconductor light emitting device according to claim 2, wherein the InGaN layer or the GaN layer has a thickness of 40 nm or less.   The carrier block layer is made of AlGaN, and the difference x1-x2 between the Al composition ratio value x1 in the carrier block layer and the maximum Al composition ratio value x2 in the graded layer is 0.1 or more. The nitride semiconductor light emitting device according to any one of claims 1 to 4, characterized in that:   The nitride according to any one of claims 1 to 5, wherein a difference x2-x3 between a maximum value x2 and a minimum value x3 of the Al composition ratio of the graded layer is 0.02 or more. Semiconductor light emitting device.   The nitride semiconductor light emitting device according to any one of claims 1 to 6, wherein the minimum value x3 of the Al composition ratio of the graded layer is 0.02 or more.   The nitride semiconductor light-emitting device according to claim 1, wherein the graded layer is formed by a ramping growth that is performed while increasing a growth temperature. An active layer that emits light by trapping carriers, an Al _x Ga _1-x N carrier block layer that traps carriers in the active layer, and between the active layer and the Al _x Ga _1-x N carrier block layer In a nitride semiconductor light emitting device comprising an intermediate layer of 40 nm or more configured as follows:
A part or the whole of the Al _x Ga _1-x N carrier block layer includes a portion in which the Al composition ratio continuously decreases from the side in contact with the intermediate layer toward the opposite side. Nitride semiconductor light emitting device. In the Al _x Ga _1-x N carrier block layer, the layer thickness of the portion where the Al composition continuously decreases from the side in contact with the intermediate layer toward the opposite side is 5 nm or more, The nitride semiconductor light emitting device according to claim 9. 11. The nitride semiconductor light emitting device according to claim 9, wherein a maximum value of an Al composition ratio of the Al _x Ga _1-x N carrier block layer is 0.1 or more. The nitride semiconductor light emitting device according to any one of claims 9 to 11, wherein a thickness of the Al _x Ga _1-x N carrier block layer is 10 nm or more. A graded layer in which the energy gap continuously changes while being in contact with the Al _x Ga _1-x N carrier block layer is formed on a part of the intermediate layer, and the Al _x Ga _1-x N carrier block layer The part according to any one of claims 9 to 12, further comprising a part in which the Al composition ratio continuously decreases from the side in contact with the intermediate layer toward the opposite side. The nitride semiconductor light emitting device described.   14. An optical pickup device, wherein the nitride semiconductor light emitting element according to claim 1 is used as a laser element that emits laser light to a recording medium.

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