JP2004297060A - Light emitting diode element and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a light emitting diode element having a high luminance in the wavelength band of yellow-green, in which the drop in the output strength used to be marked conventionally, by forming a window layer in a process in which the temperature is higher than before in order to improve the electric conductivity of the window layer and by changing the structure thereof to prevent the changes due to the process under high temperatures. <P>SOLUTION: In a light emitting diode of a double-hetero type having an AlGaInP active layer, a clad layer on the positive electrode side is made up of an undoped AlInP layer that has grown to have a thickness of 0.5 μm or more and an intermediate layer having an energy band gap between the window layer and the undoped AlInP layer and to which a p-type doping has been conducted. In the above-mentioned window layer, a GaP layer grows at temperatures equal to 730°C or higher , the growth rate is equal to 7.8 μm per hour or greater, and the dopant is zinc. An undoped AlInP layer having a thickness of 0.1 μm or greater is attached to a clad layer on the negative electrode side. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a light emitting diode (LED) element having an active layer made of AlGaInP and having a high luminance in a yellow-green wavelength band, for example, and a method of manufacturing the same.

  Light emitting diodes are used in various types of display devices. As is well known, there are LEDs using InGaN, AlGaInP, GaAlAs, or GaInAsP in the order of short emission wavelength. Further, the luminance has been improved year by year, and recently, it has been used for illumination and backlight of a liquid crystal display device. However, research for further improvement is being conducted.

  As an LED having excellent luminous efficiency, an LED having a structure having a double hetero (DH) junction shown in FIG. 5 or FIG. 6 is known as described in Patent Document 1 or Patent Document 2. The feature of this LED is that it has a structure in which an active layer for recombining electrons and holes to emit light is sandwiched, and a binding layer for confining electrons and holes in the active layer. The confinement layer has a larger band gap than the active layer and functions as a cladding layer that does not absorb the emitted light.

It is well known that the emission wavelength of the LED having the above structure is determined by the composition of the active layer. For example, in the LED shown in FIG. 7 using AlGaInP having a structure having a double hetero (DH) junction as an active layer, when the composition is expressed as (Al _x Ga _1-x ) _0.5 In _0.5 P The bandgap energy (Eg) of Eg changes from Eg = 1.91 + 0.61x (eV) to x within the range of 0 ≦ x ≦ 0.6. Therefore, the emission wavelength of the LED changes from 650 nm to 545 nm depending on the band gap energy of the active layer, that is, the composition of the active layer. It is also known that, with the increase of x, the output light of the LED has a short wavelength and its intensity is considerably reduced.

  It has been clarified that the cause of the decrease in the intensity of the output light is as follows. That is, in order to emit light at a short wavelength, it is necessary to increase the band gap of the active layer. Therefore, the active layer has a reduced gallium (Ga) composition ratio. However, the decrease in the composition ratio reduces the band gap difference between the active layer and the confinement layer. As a result, the potential barrier when holes are injected into the active layer becomes larger, and the hole injection efficiency decreases. Further, the barrier of the cladding layer for electrons confined in the active layer is reduced, and confinement of electrons is reduced. As a result, recombination of electrons and holes is reduced, and the light emission output is reduced.

  For this reason, Non-Patent Document 1 discloses an LED in which the cladding layer is made of AlInP and the hole injection efficiency and the electron confinement effect are improved.

  Further, Patent Document 3 discloses an LED in which a part of a p-cladding layer in contact with an active layer has an undoped layer with a thickness of about 0.005 to 0.2 μm.

  The undoped layer has a similar structure in the present invention, but differs from the above disclosure in that a thicker undoped layer is required for essential reasons.

  Further, in order to suppress a notch generated due to band discontinuity between the p-GaP window layer and the p-AlGaInP layer, or between the p-AlGaInP clad layer and the AlGaInP active layer, these layers are formed. Patent Document 4 discloses a configuration in which a layer having an intermediate band gap is newly inserted to reduce the resistance value to a current flowing in the forward direction.

  In addition, attention is paid to the structure of the cladding layer, and as shown in FIG. 8, an active layer, an n-type cladding layer disposed on one side of the active layer, and an active layer disposed on the other side of the active layer. A n-type cladding layer adjacent to the active layer and an n-type second cladding layer adjacent to the first cladding layer. A cladding layer, wherein the first cladding layer has a lower carrier concentration than the second cladding layer and is thinner than the second cladding layer but thicker than a thickness at which quantum mechanical tunneling occurs. A height of a potential barrier between the active layer formed in a valence band and the second cladding layer, the height of a potential barrier between the active layer formed in the valence band and the first cladding layer; The height is set higher than the height of the potential barrier between the first and second potential barriers. The semiconductor light emitting device is characterized in that the cladding layer is made of AIGaInP, and the ratio of In to AlGa in the first cladding layer is set lower than the ratio of In to AlGa in the second cladding layer. It is disclosed in reference 5.

  Further, as shown in FIG. 9, an n-type cladding layer made of an AlGaInP-based compound semiconductor, an active layer made of an AlGaInP-based compound semiconductor having a composition smaller in band gap energy than the n-type clad layer, A light-emitting element in which an electrode is provided in a laminate in which a clad layer made of a p-type AlGaInP-based compound semiconductor having a large energy composition and a p-type window layer made of GaP are further provided. Patent Document 6 discloses that an intervening layer made of a material having a band gap energy smaller than that of the p-type cladding layer is provided between the p-type window layer and the p-type window layer.

  In addition, as shown in FIG. 10, in the LED having the double hetero junction structure, in order to obtain high characteristics without lowering the luminous efficiency without p-type impurities being diffused into the non-doped active layer, A method for producing a light emitting diode having a light emitting layer of a double hetero junction comprising an n-type cladding layer, an active layer and a p-type cladding layer on a semiconductor substrate, wherein a part of the p-type cladding layer on the side of the active layer is substantially formed. Patent Document 7 discloses a method for manufacturing a light-emitting diode in which each semiconductor layer is sequentially stacked as a non-doped layer.

  Patent Document 1 discloses an LED having a structure in which a GaP window layer is provided on AlGaInP. Non-Patent Document 2 describes a manufacturing method of stacking this GaP window layer on AlGaInP and suppressing crystal defects by growing at a high temperature of 800 ° C. or more when manufacturing the LED of FIG. I have.

  Generally, it is known that the electrical conductivity of p-AlGaInP or p-AlInP is very small. As a countermeasure, a window layer (or a current diffusion layer) is used to increase the area of the light emitting portion so that the current is diffused without being locally concentrated. However, when the resistance value of this window layer is large, the voltage required to flow a rated current through the LED becomes large. Therefore, it is desirable to use a material having a resistivity as small as possible for the window layer.

U.S. Pat. No. 5,008,718 JP-A-3-270186 JP-A-8-321633 Japanese Patent No. 3233369 Japanese Patent No. 3024484 JP 2000-312030 A JP-A-8-293623

G.B.Stringfellow et al. “High Brightness Light Emitting Diode”, pp. 108, 162, and, 168, 1996. J. Lin, et al., J. Crys. Growth, 142, pp. 15-20, 1994.

  In order to reduce the specific resistance of the window layer (or the current diffusion layer), it is effective to increase the crystallinity of the window layer. However, if the growth temperature of the window layer is increased to increase the crystallinity of this portion, the entire device is exposed to a high-temperature process, causing inconvenience in portions other than the window layer, and a light emitting diode having a large output intensity. The element cannot be realized.

  The present invention has been proposed in view of the above, and a window layer is formed by a process at a higher temperature than in the prior art to provide a window layer with improved electrical conductivity. By changing this, it is possible to realize a light-emitting diode element having high luminance in the yellow-green wavelength band where the output intensity has been significantly reduced in the past.

  A first feature of the present invention for achieving the above object is that an active layer of AlGaInP, an anode-side cladding layer and a cathode-side cladding layer each having an energy band gap larger than that of the active layer sandwiching the active layer. And a window layer having a larger energy band gap than the active layer formed on the anode-side cladding layer, wherein the anode-side cladding layer has a thickness of 0.5 μm or more in contact with the active layer. The undoped AlInP layer thus grown and 2) a P-type doped intermediate layer having an energy band gap intermediate between that of the undoped AlInP layer and that of the window layer and in contact with the window layer. It is to include.

  A second feature of the present invention is that an active layer of AlGaInP, an anode-side cladding layer, a cathode-side cladding layer and an anode-side cladding layer each having an energy band gap larger than that of the active layer with the active layer interposed therebetween. A light emitting diode comprising a window layer having a larger energy band gap than an active layer formed thereon, wherein said window layer is obtained by growing a GaP layer at a temperature of 730 ° C. or higher, and its growth rate. Is 7.8 μm / hr or more, and the dopant is zinc.

  A third feature of the present invention is that, in addition to the second feature, the anode-side cladding layer includes: 1) an undoped AlInP layer grown to a thickness of 0.5 μm or more in contact with the active layer; It has an energy band gap between the energy band gap of the AlInP layer and that of the window layer, and includes a P-type doped intermediate layer in contact with the window layer.

  A fourth feature of the present invention is that an active layer of AlGaInP, an anode-side cladding layer, a cathode-side cladding layer and an anode-side cladding layer each having an energy band gap larger than that of the active layer sandwiching the active layer therebetween A light emitting diode device comprising a window layer having an energy band gap larger than an active layer formed thereon, wherein the cathode side cladding layer includes an undoped AlInP layer having a thickness of 0.1 μm or more in contact with the active layer. is there.

  A fifth feature of the present invention is that, in addition to the fourth feature, the cathode-side cladding layer includes an n-type cladding layer in contact with the undoped AlInP layer on the cathode side, and the dopant of the n-type cladding layer is It is silicon.

  According to a sixth aspect of the present invention, there is provided a method of manufacturing a light emitting diode device, comprising the steps of: 1) depositing a buffer layer on a gallium arsenide (GaAs) substrate; and 2) reflecting light onto the buffer layer. Forming an n-type reflective layer as a layer; 3) depositing a silicon-doped n-type clad layer on the reflective layer; and 4) depositing an n-type clad layer on the n-type clad layer. A) providing an undoped AlInP layer; 5) providing an AlGaInP active layer on the undoped AlInP layer; 6) providing an undoped AlInP layer on the active layer; A) providing a p-type intermediate layer on the undoped AlInP layer; and 8) forming a zinc-doped p-type GaP layer as a window layer above 730 ° C. on the p-type intermediate layer. 7.8 per hour at temperature A step of growing at m or more growth rate, a is the inclusion.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram showing an example of a preferred embodiment of the present invention. In the configuration shown in FIG. 1, a film is formed on a gallium arsenide (GaAs) substrate 10 by a reduced pressure MOCVD growth method. The substrate 10 used is a gallium arsenide (GaAs) substrate (15 ° off) doped with silicon (Si). This substrate, trimethyl gallium _{(Ga (CH 3) 3)} , trimethyl indium _{(In (CH 3) 3)} , trimethyl aluminum _{(Al (CH 3) 3)} , dimethyl zinc _{(Zn (CH 3) 2)} , disilane ( Films are formed as shown in Table 1 using Si ₂ H ₆ ), arsine (AsH ₃ ), and phosphine (PH ₃ ). Note that the AlGaInP layer and the AlInP layer are preferably formed so as to be lattice-matched to the GaAs substrate.

Therefore, the outline of the example of the manufacturing process of the present invention is as follows.
1) An n-type GaAs layer doped with silicon is deposited as a buffer layer 9 on a GaAs substrate 10 to a thickness of 0.5 μm.
2) the reflective layer 8 (DBR: a Distributed Bragg Reflector), put an n-type _{Si-Al 0.5 Ga 0.5 As /} Al 0.9 Ga 0.1 As multilayer film. When this reflective layer is not provided, the output light decreases.
3) An AlInP layer doped with silicon is provided as an n-type cladding layer 7 on the reflection layer 8.
4) On the n-type cladding layer 7, an undoped AlInP layer 6 is provided as the undoped cladding layer 7. The thickness of this layer is desirably 0.1 μm or more. When this layer is not provided, the output light decreases. The n-type cladding layer 7 and the undoped AlInP layer 6 constitute a cathode-side cladding layer.

5) On the undoped AlInP layer 6, an active layer 5 made of undoped AlGaInP is provided. This active layer has a double hetero (DH) structure advantageous for light emission due to a structure sandwiched between the undoped AlInP layer 6 described above and the undoped AlInP layer 4 described below.
6) On the active layer 5, an undoped AlInP layer 4 is provided as an undoped cladding layer. This thickness is desirably 0.5 μm or more.
7) On the undoped AlInP layer 4, a p-type intermediate layer 3 made of (Al _0.6 Ga _0.4 ) InP doped with zinc (Zn) is provided. Since this (Al _0.6 Ga _0.4 ) InP has a band gap between GaP and AlInP, there are two band gaps with small discontinuity between the window layer 2 and the undoped AlInP layer 4. The resistance value caused by the discontinuous band gap is suppressed as compared with the case where one band gap is discontinuous. Further, the composition of the p-type intermediate layer 3 is not necessarily limited to (Al _0.6 Ga _0.4 ) InP. As shown in Table 2, output light can be obtained even with (Al _0.7 Ga _0.3 ) InP. When (Al _0.6 Ga _0.4 ) InP or (Al _0.7 Ga _0.3 ) InP is used for the intermediate layer, the forward voltage (Vf) is about half and the luminance is 2 in each case, as compared with the case where AlInP is used. It is about double. The distribution of data used to derive the results in Table 2 is shown in FIGS. In particular, when (Al _0.6 Ga _0.4 ) InP is used, Vf is smaller by 0.15 V and the luminance is 8.5% larger than when (Al _0.7 Ga _0.3 ) InP is used, which is preferable. Note that the undoped AlInP layer 4 and the p-type intermediate layer 3 constitute an anode-side cladding layer.

8) On the p-type intermediate layer 3, a window layer 2 made of p-type GaP doped with zinc is provided. This layer preferably has a thickness of 5 μm or more. This layer is preferably grown at 730 ° C. or above. Although zinc is doped during film growth, it is desirable to grow the film at a higher speed in order to increase the density of the dopant. As shown below, the brightness was improved by 70% by growing at 7.8 μm / hr or more.
9) The p-electrode 1 is formed on the surface of the window layer 2 and the n-electrode 11 is formed on the back of the GaAs substrate 10.

  The dependence of Vf and luminance on the configuration of the cathode-side cladding layer will be described. Table 3 shows Vf and luminance when the thickness of the undoped AlInP layer of the cathode-side cladding layer was changed. As can be seen from this table, when there is an undoped AlInP layer of 0.1 μm to 0.2 μm in comparison with the case without the undoped AlInP layer, the Vf of the undoped AlInP layer is reduced by about 0.2 V, and the luminance almost doubles. Further, when the undoped AlInP layer is 0.2 μm, the luminance is improved by 6% as compared with the case where the undoped AlInP layer is 0.1 μm. The distribution of data used to derive the results in Table 3 is shown in FIGS.

    The dependence of Vf and luminance on the growth conditions of the window layer will be described. Table 4 shows Vf and luminance when the growth temperature of the window layer was changed. As can be seen from this table, when the window layer was grown at a rate of 7.8 μm / h at 700 ° C., the Vf and the luminance were lower than when the window layer was grown at a rate of 2.8 μm / h at 700 ° C. Although almost the same, when grown at 730 ° C. at a rate of 7.8 μm / hour, Vf decreases by about 0.16 V and luminance increases by 88%. In this case, the thickness of the cathode-side undoped AlInP layer is 0.2 μm. From the values in Table 3, the contribution due to this difference is 6%. Therefore, even if this is subtracted, the luminance is improved by 80% or more. I understand. The distribution of data used to derive the results in Table 4 is shown in FIGS.

  Since the present invention has the above-described configuration, the following effects can be obtained.

  In the double-hetero type light-emitting diode device having the AlGaInP active layer of the present invention, as described above, the anode-side cladding layer is composed of 1) an undoped AlInP layer grown to a thickness of 0.5 μm or more in contact with the active layer. 2) Vf is reduced by half since the undoped AlInP layer has an energy band gap intermediate between that of the window layer and that of the window layer, and includes an intermediate layer which is in contact with the window layer and has been subjected to p-type doping. , And the luminance can be doubled.

  It is also possible to improve the crystallinity by growing the window layer at a high temperature, and at the same time, to grow the window layer at a high speed while doping, thereby lowering Vf by about 0.16 V and improving the luminance by 80% or more. it can.

  In addition, by providing an undoped layer on the cathode-side cladding layer active layer side, Vf can be reduced by about 0.2 V, and the luminance can be almost doubled.

  In addition, by using silicon as the dopant of the cathode-side semiconductor layer, the problem caused by increasing the process temperature is suppressed and does not occur.

FIG. 1 is a schematic diagram illustrating an example of an embodiment of the present invention. The figure which shows the intermediate layer composition dependence of LED of this invention. The figure which shows the cathode side undoped AlInP layer thickness dependence of LED of this invention. The figure which shows the window layer growth condition dependency of this invention LED. FIG. 9 is a schematic view showing a cross section of a conventional light emitting diode. FIG. 9 is a schematic view showing a cross section of a conventional light emitting diode. FIG. 9 is a schematic view showing a cross section of a conventional light emitting diode. FIG. 9 is a schematic view showing a cross section of a conventional light emitting diode. FIG. 9 is a schematic view showing a cross section of a conventional light emitting diode. FIG. 9 is a schematic view showing a cross section of a conventional light emitting diode. FIG. 9 is a schematic view showing a cross section of a conventional light emitting diode.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 p-electrode 2 window layer 3 p-type intermediate layer 4 undoped AlInP layer 5 active layer 6 undoped AlInP layer 7 n-type cladding layer 8 reflection layer 9 buffer layer 10 substrate 11 n-electrode

Claims (6)

The active layer of AlGaInP and the anode-side cladding layer, which has a larger energy band gap than this active layer sandwiching the active layer in the middle, the energy band than the active layer formed on the anode-side cladding layer and the anode-side cladding layer A light emitting diode element comprising a window layer having a large gap,
The anode-side cladding layer has 1) an undoped AlInP layer grown to a thickness of 0.5 μm or more in contact with the active layer, and 2) an energy band gap intermediate between that of the undoped AlInP layer and that of the window layer, And a P-type doped intermediate layer in contact with the window layer. The active layer of AlGaInP and the anode-side cladding layer, which has a larger energy band gap than this active layer sandwiching the active layer in the middle, the energy band than the active layer formed on the anode-side cladding layer and the anode-side cladding layer A light emitting diode comprising a window layer having a large gap,
The above-mentioned window layer is obtained by growing a GaP layer at a temperature of 730 ° C. or more, has a growth rate of 7.8 μm / hour or more, and has a dopant of zinc. The anode-side cladding layer has 1) an undoped AlInP layer grown to a thickness of 0.5 μm or more in contact with the active layer, and 2) an energy band gap between the energy band gap of the undoped AlInP layer and that of the window layer, 3. The light-emitting diode device according to claim 2, further comprising a P-type doped intermediate layer in contact with the window layer. The active layer of AlGaInP and the anode side cladding layer, which has a larger energy band gap than this active layer sandwiching the active layer in the middle, the energy band than the active layer formed on the anode side cladding layer and the anode side cladding layer A light emitting diode element comprising a window layer having a large gap, wherein the cathode-side cladding layer includes an undoped AlInP layer having a thickness of 0.1 μm or more in contact with the active layer. 5. The light emitting diode device according to claim 4, wherein the cathode-side cladding layer includes an n-type cladding layer in contact with the undoped AlInP layer on the cathode side, and a dopant of the n-type cladding layer is silicon. A method for manufacturing a light emitting diode element,
On a gallium arsenide (GaAs) substrate,
1) depositing a buffer layer;
2) a step of providing an n-type reflection layer as a reflection layer on the buffer layer;
3) depositing an n-type clad layer doped with silicon on the reflective layer;
4) forming an undoped AlInP layer on the n-type cladding layer;
5) providing an active layer of AlGaInP on the undoped AlInP layer;
6) providing an undoped AlInP layer on the active layer;
7) providing a p-type intermediate layer on the undoped AlInP layer;
8) a step of growing a zinc-doped p-type GaP layer as a window layer at a temperature of 730 ° C. or more at a growth rate of 7.8 μm or more per hour on the p-type intermediate layer;
The manufacturing method of the light emitting diode element characterized by including.

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