JPH07111339A - Surface emitting semiconductor light emitting device - Google Patents

Abstract

(57) [Summary] [Object] To provide a surface emitting semiconductor light emitting device having high external conversion efficiency. [Structure] n ⁺ InGa is formed on the semi-insulating InP substrate 11.
The As layer 12 is formed. And this n ⁺ InG
The first cladding layer 13 of n-InP, the active layer 14 of In _0.72 Ga _0.28 As _0.33 P _0.67 are formed on a portion of the aAs layer 12.
The second cladding layer 15 of p-InP is sequentially epitaxially grown to form a light emitting layer having a DH structure. further,
A p ⁺ InGaAs layer 17 is formed on the second cladding layer 15. A square p-type ohmic electrode 18 is formed on a portion of the p ⁺ InGaAs layer 17 and is formed on the n ⁺ InGaAs layer.
A rectangular n-type ohmic electrode 19 is formed on another portion of the layer 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device capable of efficiently extracting light output.

[0002]

2. Description of the Related Art Conventionally, in a surface emitting type light emitting device such as a light emitting diode, a p-type ohmic electrode provided in a light emitting portion on a semiconductor substrate is used as an output window having a circular or rectangular closed shape, and an n type The ohmic electrode was provided on the lower surface of the semiconductor substrate. For details of such technology, see IEEE Photo.
onics Technology Letters,
Vol. 4, No 5, pp. 409-411, 1992
It is described in.

[0003]

However, when an electric current is applied between the p-type and n-type ohmic electrodes of this type of light emitting device, the output region (light emitting region) in the output window will be described.
A phenomenon was observed in which light was emitted to the outside of or the part directly below the electrode. This is because the carriers flowing between the p-type and n-type ohmic electrodes flow outside the output region in the output window or immediately below the electrodes and are recombined there. If light emission occurs in such an area, the current-to-light conversion efficiency in the original output area is low, and light cannot be efficiently extracted in the direction perpendicular to the substrate surface.

In view of the above problems, it is an object of the present invention to provide a surface emitting semiconductor light emitting device which can efficiently extract light in a direction perpendicular to the substrate surface and can obtain high external quantum efficiency. To do.

[0005]

In order to solve the above problems, the present invention sandwiches a semiconductor light emitting layer, which emits light when carriers are injected, with two semiconductor conductive layers of different conductivity types in the thickness direction. The present invention is directed to a surface-emitting type semiconductor light emitting device in which a light structure is output from a light output region through at least one of two semiconductor conductive layers in the thickness direction. Are supplied with carriers from a first region adjacent to the light output region, and carriers are supplied to the other of the two semiconductor conductive layers via a second region opposite to the first region with the light output region interposed therebetween. It was decided to be supplied.

[0006]

According to the present invention, when carriers are supplied to the first region and the second region, the light output region is sandwiched between the first region and the second region. The current and electric field can be concentrated. Thereby, light can be emitted mainly in the light output region. Since it is not necessary to form an electrode or the like for supplying carriers on the light output region, when light is output from the light output region in the thickness direction, the light emitted by these electrodes or the like is absorbed. Never be done. As a result, the external quantum efficiency of such a surface emitting semiconductor light emitting device can be dramatically improved.

Alternatively, the present invention has a structure in which a semiconductor light emitting layer which emits light when carriers are injected is sandwiched in the thickness direction by first and second semiconductor conductive layers of different conductivity types, and A surface-emitting type semiconductor light emitting device in which light is output in a thickness direction from a light output region via a second semiconductor conductive layer on the side opposite to a first semiconductor conductive layer in contact with the second semiconductor conductive layer. A first electrode is formed in a region adjacent to the light output region, and the first semiconductor conductive layer is exposed on the substrate in a region opposite to the first electrode with the light output region sandwiched therebetween. The second electrode may be formed on the.

With such a structure, when a current is applied between the first electrode and the second electrode, the carrier causes a light output region located between the first electrode and the second electrode. Emission occurs primarily in the light output region as it flows through.
Therefore, it is possible to suppress light emission immediately below the first electrode, which is out of the path from the first electrode to the second electrode, and it is possible to efficiently extract the light emitted in the thickness direction. In such a surface emitting semiconductor light emitting device,
In particular, when the ratio of the sheet resistances of the two semiconductor conductive layers sandwiching the semiconductor light emitting layer is 0.1 to 10, it is possible to obtain a practically effective high light output.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a surface emitting semiconductor light emitting device according to the present invention will be described below with reference to the accompanying drawings. The same elements will be denoted by the same reference symbols, without redundant description.

FIG. 1 shows the structure of a light emitting diode according to the first embodiment of the present invention. First, as is clear from the longitudinal sectional view of FIG.
An n ⁺ InGaAs layer 12 (carrier concentration 2 × 10 ¹⁹ cm ⁻³ , layer thickness 0.2 μm) is formed on the substrate 11. Then, the n-InP first cladding layer 13 (carrier concentration 5 × 1) is formed on a part of the n ⁺ InGaAs layer 12.
0 ¹⁷ cm ^-3 , layer thickness 2 μm), In _0.72 Ga _0.28 As _0.33
P _0.67 active layer 14 (non-doped, layer thickness 0.2 μm),
p-InP second cladding layer 15 (carrier concentration 7 × 1
0 ¹⁷ cm ^-3 and a layer thickness of 2 μm) are sequentially epitaxially grown to form a light emitting layer having a DH structure. Further, ap ⁺ InGaAs layer 17 (carrier concentration 1 × 10 ¹⁹ cm ⁻³ , layer thickness 0.2 μm) is formed on the second cladding layer 15.

A square p-type ohmic electrode 18 is formed on a part of the p ⁺ InGaAs layer 17.
Similarly, a rectangular n-type ohmic electrode 19 is formed on the other part of the n ⁺ InGaAs layer 12. Note that Ti / Pt / Au is used for the p-type ohmic electrode 18,
Ge / AuGe / Ni is used for the n-type ohmic electrode 19, and these are deposited on the p ⁺ InGaAs layer 17 and the n ⁺ InGaAs layer 12, respectively, and then 450 ° C., 6
It was formed by alloying for 0 seconds.

As is apparent from the plan view of the light emitting diode shown in FIG. 1B, when such a light emitting diode is viewed from above, the p-type ohmic electrode 18 and the n-type ohmic electrode 19 have an output region 20 therebetween. Are provided facing each other. The output area 20 in FIG. 9B corresponds to the range designated by the arrow in FIG.
It is μm × 10 μm.

After realizing the light emitting diode having such a structure, the p-type ohmic electrode 18 and the n-type ohmic electrode 1 are formed.
9 and 9, a forward voltage is applied, and electrons and holes injected into the active layer 14 are recombined with each other, and light emission is observed in the output region 20. This is because there is the active layer 14 in the path of the current when the current flows from the p-type ohmic electrode 18 to the n-type ohmic electrode 19, and most of the part of the active layer 14 that corresponds to this path is in the output region 20. Is present in the.

For comparison, a light emitting diode having the following structure was manufactured. A longitudinal sectional view and a plan view of this light emitting diode are shown in FIGS. 2 (a) and 2 (b), respectively.

Similar to the first embodiment of the present invention, semi-insulating In
On the P substrate 21, an n ⁺ InGaAs layer 22, a first clad layer 23, an active layer 24, a second clad layer 25, and p ⁺ InP are formed.
The layer 26 and the p ⁺ InGaAs layer 27 are sequentially formed. The composition, carrier concentration and layer thickness of each of these layers have the same values as in the first embodiment. And p ⁺ InGa
A rectangular ring-shaped p-type ohmic electrode 28 provided with an output region 30 inside is formed on the upper surface of the As layer 27, and the p-type ohmic electrode 2 is formed on the lower surface of the semi-insulating InP substrate 21.
An n-type ohmic electrode 29 having a structure similar to that of No. 8 and having a slightly larger size is formed so as to include the output region 30 in the opening region thereof. The size of the output area 30 is the same as that of the output area 20 of the first embodiment. The semi-insulating InP substrate 2
No. 1 is etched from the lower surface so that the light generated in the active layer 24 is not absorbed by the semi-insulating InP substrate 21. The output area 30 in FIG. 11B corresponds to the range designated by the arrow in FIG. 9A and has dimensions of 10 μm × 10 μm.

After realizing the light emitting diode having such a structure, the p-type ohmic electrode 28 and the n-type ohmic electrode 2 are formed.
9 is applied with a forward voltage, the electrons and holes injected into the active layer 24 are recombined, and the output region 30 is surrounded by the p-type ohmic electrode 28 and surrounded by the p-type ohmic electrode 28. Luminescence was observed outside of. This is because the active layer 24 is in the path of the current when the current flows from the p-type ohmic electrode 28 to the n-type ohmic electrode 29, and most of the part of the active layer 24 that corresponds to this path is the p-type ohmic electrode 28. It means that it exists just below.

FIG. 3 shows a structure of a light emitting diode according to a second embodiment of the present invention. As a p ⁺ contact layer of the light emitting diode of FIG. 1, p ⁺ InGaA in FIG. 1 is used.
Instead of the s layer 17, the p ⁺ InP layer 36 (carrier concentration 5 × 10 ¹⁷ cm ⁻³ , layer thickness 0.3 μm) is formed on the second cladding layer 15.
m), p ⁺ InGaAs layer 37 (carrier concentration 5 × 10
¹⁹ cm ⁻³ and a layer thickness of 0.2 μm) are laminated and epitaxially grown. With such a structure, the resistance between the second cladding layer 15 and the p-type ohmic electrode 18 can be reduced, and light emission can be concentrated in the output region 20.

FIG. 4 is a diagram showing the relationship between the drive current and the light output of the light emitting diodes of the first and second embodiments as well as the comparative example. As is clear from the figure, the light output monotonically increases as the drive current increases. Then, for the same driving current, the light emitting diodes of the first and second embodiments can obtain higher light output than the light emitting device of the structure of the comparative example shown in FIG. That is, the external quantum conversion efficiency of the light emitting diodes of the first and second examples is 0.8%, and the external quantum conversion efficiency of the comparative example is 0.2.
It shows a high value compared to%. Note that the sheet resistance Rsh (p) of the p-type semiconductor of the first and second embodiments.
Of the sheet resistance of the n-type semiconductor Rsh (n) Rsh
(P) / Rsh (n) are 0.33 and 0.07, respectively.

Further, Rsh (p) / Rsh of the first embodiment
The relationship between (n) and light output was investigated. The result is shown in FIG. As is clear from the figure, Rsh (p) / Rsh
It can be seen that when (n) is between 0.1 and 10, the electric field and the current are concentrated in the active layer 14 in the output region 20 of FIG. 1, and the external quantum conversion efficiency is excellent. Note that Rsh (p) / Rsh (n) in the first and second embodiments are 0.33 and 0.07, respectively. Then, a result substantially similar to the result shown in FIG. 5 was obtained in the second embodiment.
As described above, the output region 20 having the same aspect ratio (the interval between the p-type ohmic electrode 18 and the n-type ohmic electrode 19 of the output region 20 is vertical and the direction perpendicular to this is horizontal) and the area are used. If there is, Rsh (p) / Rsh
It can be seen that the external quantum conversion efficiency is excellent when (n) is between 0.1 and 10. Note that the sheet resistances of the p-type semiconductor and the n-type semiconductor are the sheet resistance of the p-type semiconductor and the sheet resistance of the n-type semiconductor as a whole when there are a plurality of layers constituting them. However, in practice, the sheet resistance of these p-type semiconductors and the sheet resistance of the n-type semiconductors are p ⁺ InGaA
s layer 17, 37, 36 ... p ⁺ InP layer and n ⁺ InGaA
It strongly depends on the carrier concentration of the s layer 12.

As described above, according to the first and second embodiments of the present invention, since most of the current passing portion of the active layer 14 is included in the output region 20, light is generated in the output region 20. Can be made. Accordingly, it is possible to mainly emit light in the output region 20, and it is possible to suppress light emission outside the output region 20 or immediately below the electrodes. Further, since the n-type ohmic electrode 19 is not formed below the output region 20, the light emitted downward is not absorbed by the n-type ohmic electrode 19. In particular, when the ratio of the sheet resistance of the p-type semiconductor and the sheet resistance of the n-type semiconductor is 0.1 or more and 10 or less, it is possible to obtain a sufficiently high practical optical output.

As described above, the reason why the high external quantum efficiency is obtained is that the portion corresponding to the passage of the current in the active layer 14 is formed in a region other than immediately below the p-type ohmic electrode 18, and therefore the active layer 14 is directed upward. It is considered that the generated light is not absorbed by the p-type ohmic electrode 18 as in the conventional case. That is, the present invention relates to the active layer 14
The present invention is not limited to the above-mentioned first and second embodiments as long as the portion corresponding to the passage of the current inside is not formed immediately below the electrode.

That is, the light emitting diode of the present invention may have the structures shown in the following third to fifth embodiments. Third to
In the fifth embodiment, the shapes of the p-type ohmic electrode 18 and the n-type ohmic electrode 19 are changed. The third
~ The components of the light emitting diode according to the fifth embodiment (materials and carrier concentration thereof, layer structure, layer thickness and area) are
Unless otherwise specified, it is equivalent to the first embodiment.

FIG. 6B is a plan view of the light emitting diode according to the third embodiment of the present invention as seen from above. In this light emitting diode, an output region 20 is provided in a square ring-shaped n-type ohmic electrode 19 having an opening at the center, and a square p-type ohmic electrode 18 is formed inside the output region. It should be noted that FIG. 3A is a diagram showing a vertical cross-sectional structure of this light emitting diode. With such a configuration, not only the same operation as described above can be achieved, but also the light emission output can be stabilized.

FIG. 7B is a plan view of the light emitting diode according to the fourth embodiment of the present invention as seen from above. This light emitting diode is the n-type ohmic electrode 1 of the third embodiment.
9 has a circular ring shape, and the p-type ohmic electrode 18 has a disk shape. It should be noted that FIG. 3A is a diagram showing a vertical cross-sectional structure of this light emitting diode. With such a structure, not only the same effects as those of the first to third embodiments are obtained, but also the intervals between the p-type ohmic electrode 18 and the n-type ohmic electrode 19 are set to be substantially equal. Further, the light emission output can be stabilized and the reliability of the light emitting diode can be improved.

FIG. 8B is a plan view of the light emitting diode according to the fifth embodiment of the present invention as seen from above. In this light emitting diode, an n-type ohmic electrode 19 is formed in a lattice shape, an output region (light emitting region) 20 is set in the eyes of the lattice, and a rectangular p-type ohmic electrode 1 is provided in the output region 20.
8 is formed. It should be noted that FIG. 3A is a diagram showing a vertical cross-sectional structure of this light emitting diode. With such a structure, not only the same effects as those of the first to fourth embodiments are achieved, but also when the size is reduced to have a large number of grids, the in-plane uniformity of the light emission output is improved. It is possible to improve.

In the third to fifth embodiments, the structure of the light emitting diode in the vertical direction is the same as that of the first embodiment, but the same operation as that of the second embodiment can be achieved.

In the first to fifth embodiments, the semi-insulating InP substrate 11 is formed under the output region 20, but
This may be removed by etching the semi-insulating InP substrate 11 below the output region 20 as in Comparative Example 2. As a result, the absorption of light by the semi-insulating InP substrate 11 disappears, and the emitted light is n ⁺ In
Since the light is reflected at the interface between the GaAs layer and the outside, it is possible to further increase the light emission output.

[0028]

As described above, according to the present invention, when the surface emitting semiconductor light emitting device is energized, the electric field and the electric current are concentrated in the light output region, so that the emitted light can be efficiently extracted. When carriers are injected from the first and second electrodes, it is possible to suppress light emission outside the light output region or directly below the first or second electrode. If the output light extraction efficiency is high in this way, the power consumption can be kept low. Therefore, since it is possible to reduce the generation of heat, it is possible to suppress fluctuations in operating characteristics due to temperature changes. Further, when the first and second electrodes are formed on the same surface side of the substrate, integration is easy. Therefore, the present invention can be applied to a light source in optical communication or a light source forming a display device or the like.

[Brief description of drawings]

FIG. 1A is a vertical sectional view and FIG. 1B is a plan view of a semiconductor light emitting device according to a first embodiment of the invention.

FIG. 2A is a longitudinal sectional view and FIG. 2B is a plan view of a semiconductor light emitting device of a comparative example.

FIG. 3A is a vertical sectional view and FIG. 3B is a plan view of a semiconductor light emitting device according to a second embodiment of the invention.

FIG. 4 is a diagram showing drive current-optical output characteristics of a comparative example, a first example, and a second example.

FIG. 5 shows Rsh of the first and second embodiments of the present invention.
It is a figure which shows (p) / Rsh (n) -optical output characteristic.

6A is a vertical sectional view and FIG. 6B is a plan view of a semiconductor light emitting device according to a third embodiment of the invention.

FIG. 7A is a vertical sectional view and FIG. 7B is a plan view of a semiconductor light emitting device according to a fourth embodiment of the invention.

FIG. 8 is (a) a vertical sectional view and (b) a plan view of a semiconductor light emitting device according to a fifth embodiment of the present invention.

[Explanation of symbols]

11, 21 ... Semi-insulating InP substrate, 12, 22 ... n ⁺ I
nGaAs layer, 13, 23 ... First clad layer, 14, 2
4 ... Active layer, 15, 25 ... Second cladding layer, 26, 36
... p ⁺ InP layer, 17, 27, 37 ... p ⁺ InGaAs
Layer, 18, 28 ... p-type ohmic electrode, 19, 29 ... n
Type ohmic electrode, 20, 30 ... Output region.

Claims (3)

[Claims] 1. A structure is provided in which a semiconductor light emitting layer that emits light when carriers are injected is sandwiched in the thickness direction by two semiconductor conductive layers having different conductivity types, and at least one of the two semiconductor conductive layers is interposed. Is a surface-emitting type semiconductor light emitting device in which light is output from the light output region in the thickness direction, and carriers are supplied to one of the two semiconductor conductive layers from a first region adjacent to the light output region. And a carrier is supplied to the other of the two semiconductor conductive layers via a second region opposite to the first region with the light output region interposed therebetween. apparatus. 2. A semiconductor light emitting layer, which emits light when carriers are injected, has first and second conductivity types different from each other.
A structure sandwiched between the semiconductor conductive layers in the thickness direction is provided on the substrate, and the second semiconductor conductive layer opposite to the first semiconductor conductive layer in contact with the substrate is interposed between the light output region and the thickness direction. A surface emitting semiconductor light emitting device that outputs light to the first semiconductor conductive layer, wherein a first electrode is formed on a region of the second semiconductor conductive layer adjacent to the light output region. The surface emitting semiconductor light emitting device, wherein the layer is exposed on the substrate in a region opposite to the first electrode across the light output region and a second electrode is formed in this region. 3. The surface-emitting type according to claim 1, wherein a ratio of sheet resistances of the two semiconductor conductive layers sandwiching the semiconductor light emitting layer is 0.1 to 10. Semiconductor light emitting device.