JPS6255985A - Semiconductor light emitting element - Google Patents

Abstract

PURPOSE:To reduce the adverse influence of a lattice mismatch to the quality of a crystal without loss of low threshold laser function and to readily form a light emitting element by forming a 2-element or 3-element compound semiconductor between an active layer and a clad layer. CONSTITUTION:An undoped Ga0.5In0.5P active layer 104, and clad layers 102, 106 such as n-type (Al0.3Ga0.7)0.5In0.5P, P-type (Al0.6Ga0.4)0.5In0.5P are formed on an n-type GaAs substrate 101. Guide layers 103, 105 such as n-type Al0.5Ga0.5 As, p-type Al0.3Ga0.5As lattice-matched to a substrate 1 are formed of 2-element or 3-element compound semiconductor having Ga and A as III group elements and larger energy gap and smaller refractive index than the layer 104. Accordingly, the adverse influence of lattice mismatch to the crystal is prevented without loss of the low threshold laser function, the light is emitted over a wide wavelength range to enhance the performance, function and reliability and the formation is ready due to simple multilayer structure.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor light emitting device that emits light or emits laser light.

(Prior art and its problems) A multi-component mixed crystal compound semiconductor can change its energy gap and refractive index over a wide range depending on the combination of its constituent elements. Taking advantage of this property, high-efficiency light emitting diodes and laser diodes are manufactured by laminating multiple semiconductor layers of multi-component mixed crystal compounds to form a double heterostructure. However, in order to obtain these semiconductor light emitting devices with excellent characteristics and high reliability, it is necessary to make the lattice constant of each semiconductor layer match or be extremely close to the value of the substrate. AI that has been widely used in the past! xGa, -xAs (Q≦X≦1)
The lattice constant of the based compound conductor is almost constant regardless of the aluminum composition X. For this reason, AI! xGat-xA
In the case of the s-system, when forming the double heterostructure described above, the aluminum composition of each layer can be set while always satisfying the condition of lattice constant matching. In addition, a layer for optical waveguide (called an optical waveguide layer) is sandwiched between the cladding layer and the active layer of a semiconductor light emitting device, or the aluminum composition in the optical waveguide layer is changed continuously in the direction perpendicular to the layer surface. Even if the change is made, the problem of lattice constant mismatch does not occur.

However, in recent years, AI! Emission or laser excavation in a wider wavelength range (from visible light to infrared) than that obtained with the xGas-xAs system is required, and compound semiconductors made of other constituent elements are being used to fabricate light-emitting devices. became. In the visible light range (A l x Gas -x)6
, 5I no-s P system, GaxInl-x PyAs
Compound semiconductors such as I-y, and Ga in the infrared region.
xIns-x AsySbl-y system, GaxIrz
-xPykss-y compound semiconductors (any x
, ymaO<x≦1.0<y≦l) is used. Semiconductors for substrates include GaAs, Garb,
InP, etc. are used, and vapor phase growth methods (organic bulk pyrolysis (MOVPB), - Rodan transport method (1
-ITVPR)), liquid phase epitaxy (LPE), molecular beam method (MBE), etc., the double heterostructure is formed. At this time, each composition of the multi-component mixed crystal must be precisely controlled to achieve lattice matching with the substrate.

In Figure 3 (A /
1. A conventional example of a double heterostructure laser diode using S P system with Ga, )4 I n04 P as the active layer is shown (Applied Physics Letters).
-Phys-Let t-) Volume 43 pp987-98
9 (1983). On the n-type GaAs substrate 501, for example, an n-type Aj6.3 Ga(1,
7) (, -5In64P cladding layer 5021 undoped Ga6.5I''0.SP active layer 503, p-type (A
I! o,sG ao,? ) 6.5 I n9.5
A P cladding/* 504 and a p-type GaAs layer 505 for ohmic contact are sequentially formed, and then A u /
An electrode 507 for p-type such as Zn is formed on the back surface of the substrate 501, and an electrode 508 for n-type such as AuGe is formed on the back surface of the substrate 501. , this is a normal double heterostructure, but even with such a relatively simple structure, A
I! What can be achieved with the GaInP system is A j G a A
This is extremely difficult compared to the s-series. The reason for this is explained below. In the A/G a As system, aluminum (A
Regardless of the composition ratio of I and gallium (Ga), any composition is almost lattice matched to the GaAs substrate, but A I G
In the a I n P system, a large lattice mismatch occurs unless the ratio of the sum of the mole fractions of AI and Ga to the mole fraction of indium (In) is maintained at about 1:IK. When lattice mismatch occurs, crystallinity deteriorates, and therefore device characteristics deteriorate. In this way, when the AIGaInP system has a multilayer structure and the composition is continuously changed during growth, it is extremely difficult to change the composition while maintaining the lattice matching conditions.

Figure 4 fa) shows AI! Gradient refractive index separated optical waveguide heterostructure (GRIN-8CH) realized in GaAs system Radiation Applied Fixtures Letters (Appl・Phy
s-Let, t-) Volume 40 ppzx7-219 (19
82)) is a cross-sectional view. Figure 4(b) shows a diagram of the energy band perpendicular to the substrate surface and the refractive index.
.

It is also shown in (C). nfiGaAs substrate 521
Type A/6.5Ga, , As cladding layer 522, A/composition of 0.5Ga, As from cladding layer 522 to active layer 524.
N-type Al continuously reduced from 4 to 0.2! GaAs
AI! from the graded layer 523, the undoped active layer 524, and the active layer 524 to the cladding layer 526! p-type A I with increasing composition from 0.2 to continuous K O,4
G a As gray T-rad layer 525, p-type A10
．． After sequentially forming a 5Ga6.5As cladding 4526 and a p-type GaAs layer 527 for ohmic contact,
sio with striped openings 531, A on the membrane 528.
For p-type such as U/Zn, connect the pole 529 to the substrate 52.
An n-type electrode 530 such as AuGe is formed on the back surface of each of the two electrodes. The thickness of active N524 is 50
By setting the value to 0 A or less and having graded layers 523 and 525 with A/composition gradients, the laser oscillation threshold can be significantly lowered compared to the conventional double heterostructure. The possible wavelength range is 0.
There is a drawback that the thickness is limited to 7 to 0.87 μm. To obtain oscillations in the visible and infrared wavelength ranges, use AI!
AI using GaAs thread! A material other than A, gGaAs type, such as GaInP60aInAsSb type, must be used. However, these materials require strict control of their composition in order to achieve lattice matching with the substrate, making it extremely difficult to form complex multilayer structures that require high functionality and performance.

(Objective of the Invention) An object of the present invention is to eliminate such conventional drawbacks, to provide a semiconductor light emitting device that emits light over a wide wavelength range, and has high performance, high functionality, and high reliability.

(Structure of the Invention) According to the present invention, an active layer made of a multi-component compound semiconductor is provided on a binary or ternary m-v compound semiconductor substrate having one or both of gallium and aluminum as group elements; In a semiconductor light emitting device having cladding layers made of a multi-component compound semiconductor having a larger energy gap and a smaller refractive index than the active layer provided on both the upper and lower surfaces of the active layer, the active layer and one cladding layer or both cladding layers A semiconductor light emitting device having a structure including a binary or ternary compound semiconductor layer having one or both of gallium and aluminum as a group element and having a larger energy gap and a smaller refractive index than the active layer. is obtained. Furthermore, the aforementioned semiconductor light emitting device is obtained in which the aluminum composition of the compound semiconductor layer formed between the active layer and the cladding layer increases from the side in contact with the active layer to the side in contact with the cladding layer.

(Example) The present invention will be described in detail below using one drawing.

An embodiment of M-41 of the present invention is shown in FIG. Figure 1 (a
> is a schematic diagram of the first embodiment, and FIG. 1 (bl is an energy band diagram of the first embodiment, and FIG. 1 IC) is a refractive index diagram of the first embodiment. 1st
Common parts in Figures (al, bl, and (C) are given the same numbers. This example shows the structure of a red visible light semiconductor laser that oscillates at a wavelength of 0.65 μm, and its formation method is as follows. A 1.0 μm thick n-type (A
la, s G 3o, r ) o, s I no, i
P cladding layer 102゜thickness 0.4μm n-type Al! 6
．． 50a (1,5As guide layer 103, thickness 0.0: (
μm undoped Ga6,5 In6.5 P active layer 1
04, p-type Al with a thickness of 0.4 μm! o,sGa□,5
As guide layer 105, p-type (k16
．． s Ga(,,7)o,5In(1,5P cladding layer 106 and a p-type GaAs layer 107 with a thickness of 1 and 93 m are successively grown. The epitaxial growth method may be either MOVPE, MBE, etc. Striped opening (width lOμm) - A on the Ga As substrate 101
Complete by forming n electrode 1)0 by u/G e alloy. Current is injected into the active layer 104 in a stripe pattern and excited, allowing efficient oscillation. The energy band diagram and refractive index diagram with respect to the distance small Ga a6.5
I no and S P are confined in the active layer 104 and contribute to laser oscillation. In this embodiment, the active layer 104 is designed to increase the carrier density in the active layer and lower the laser oscillation threshold current value.
Since the thickness of the active layer 104 is as thin as 0.03 μm, the light is not confined only in the active layer 104, and the amount of light guided is 103°10.
It also spreads during the 5th. As can be seen in the refractive index diagram FIG. 1(C), the guide layers 103, 105 and the active layer 1
Since the refractive index of 04 is larger than that of the cladding layers 102 and 106, the laser oscillation light is confined in the active layer 104 and the light guide layers 103 and 105. In order to sufficiently confine light and injected carriers, the active layer must be sandwiched between cladding layers having the necessary refractive index difference and energy gap difference. The person who plays this role is (A
lo, 5Ga0,7) (, 5I no, Is P cladding layers 102 and 106. As shown in Figure 1(b) and (C1), the energy gap is 105, cladding layers 102 and 106, and the refractive index decreases in this order.In the A 71 Ga As system, there is a sufficient energy gap difference and refractive index difference with respect to Ga In P. Since it is not possible to take
It is necessary to use AlGa-nP as the cladding layer. However, for the guide layer, A I G a A s
The effect can be fully achieved by using a system with an appropriate AI composition as in this example. It is also possible to use an AlGaInP system with an appropriate composition as the guide layer, but in this case, it is necessary to maintain a lattice match with the substrate, and the degree of difficulty during crystal growth and reliability maintenance when used as a device are important. The difficulty becomes a problem, and the device yield also decreases. Therefore, by using AIGaAs, which has lattice matching with the substrate regardless of its composition, as in this embodiment, these disadvantages can be solved and desired device characteristics can be obtained.

A second embodiment of the invention is shown in FIG. FIG. 2(a) is a schematic diagram of the second embodiment, FIG. 2(b) is an energy band diagram of the second embodiment, and FIG. 2(C) is a refractive index diagram of the second embodiment. Each is shown below. Figure 2 (
Common parts in a), (b), and (C) are given the same numbers. This example shows the structure of a low oscillation threshold red visible light semiconductor laser that oscillates at a wavelength of 0.636 nm, and a method for forming the same will be described next. As the epitaxial crystal growth method, MBE method or MOVPE method is used. First, a layer with a thickness of 1,0,! is formed on an n-type GaAs substrate 201. 1
m n-type (A16.e Gao, 4) o, s I
No. 5P cladding layer 202 is grown. On top of this, an AlxGax-xAs graded layer 203 whose Al composition decreases continuously from 0.7 to 0.05 in the growth direction is formed.
Grows by μm.

Next, undoped (Alo, IOa) with a thickness of 0.01 μm
O, 9) o, sIn, JP active layer 204 is grown, and a kl x Ga 1-, As graded 20 is grown thereon, with the A1 composition increasing continuously from 0.5 to 0.07 in the growth direction.
5 to a thickness of 0.4 μm. Furthermore, the thickness is 1.0
μm p-type (Alo, s Ga6.4 ) o, s I
No. S P cladding N206 and a p-type GaAs layer 207 with a thickness of 1.0 μm are sequentially grown.

Subsequently, an n-electrode 209 made of an Au/Zn alloy is formed on a Si pseudo-insulating film 208 having striped openings (10 μm) 21), and an Au-electrode 209 is formed on an n-GaAs substrate 201.
/ An n-electrode 210 made of Ge alloy is formed.

FIG. 2(b) shows an energy band diagram and a refractive index diagram for the distance Mix in the growth layer direction.

Each is shown in (C). The injected carriers are shown in Figure 2 (
As shown in b), (Alo, t GaO, s) o, s In6. B
It is confined in the P active layer 204 and contributes to laser oscillation. In this embodiment, the active layer is made extremely thin with a thickness of 0.01 μm, the carrier density is increased compared to the first embodiment, and a quantum well effect is produced to lower the oscillation threshold. At this time, graded layers 203° and 205 are provided to efficiently collect injected carriers in the active layer 204 and to confine light between the cladding layers 202 and 206°. As shown in FIG. 2(b), the injected carriers are collected in the active layer 204 by the electric field created in the brella dirad layers 203 and 205, and the refractive index distribution is as shown in FIG. 2(c). The light is confined around the active layer 204 and across the graded layers 203 to 205. In this case, the graded layers 203 and 205 are required to have their compositions continuously changed. From the viewpoint of refractive index and energy gap values, AlGaInP systems are also satisfactory, but when used as a laser device, it is necessary to maintain lattice matching with the substrate. Generally, materials such as A I G aInP whose lattice constant changes when the composition is changed,
It is extremely difficult to change the composition while keeping the lattice constant constant. However, when an AlGaAs-based material is used as the graded layer as in this embodiment, the lattice constant almost matches that of GaAs even if the composition is continuously changed. Also, A I G a A S is AlGa
Even for a 1nP laser, it is possible to obtain a composition that satisfies the requirements for the energy gap value and refractive index as in this embodiment. The device manufactured in this manner was able to significantly reduce the oscillation threshold compared to the conventional double heterostructure device. This means that the same effect as that of the conventional 0RIN-8CH laser obtained with the AlGaAs system can be obtained with the structure of this embodiment. The parameters such as the compound composition, double layer thickness, conductivity type, etc. mentioned in the first and second examples are not limited to the values described here.

The present invention is also applicable to combinations of other compounds.

- For example, 1 μm thick n-type Al on n-type Garb substrate
o, s Gao, 5S b, 0.4 tt m thick n-type 14.1x Gai-xsb graded layer (
X: 0.4→0.2), 0.01 μm thick undoped Ga. , 4 I n. ,6 As0,5Sbo,s s
0.4βm thick p-type Al x()a s-x S
b graded layer (x: o, 2→0.4), 1
A semiconductor laser that emits infrared light at a wavelength of 2.5 μm is obtained by a multilayer structure in which p-type klo, s GaO, and 5S b cladding layers of μm thickness are sequentially formed.

(Effects of the Invention) As described above, according to the present invention, light and carrier confinement can be achieved using a conventional laser with a light guide layer or a gradient refractive index separated light 4-wave heterostructure (GRIN-8C).
It is possible to provide a semiconductor light-emitting device that does not impair the function of a low-threshold laser such as H), greatly reduces the adverse effects of lattice mismatch on crystal quality, and is easy to manufacture.

[Brief explanation of drawings]

Figures 1 (a), (b), (d are diagrams showing the structure, energy band diagram, and refractive index diagram of the first embodiment of the present invention, respectively, Figure 2 (a), (d)
b) and (C) are diagrams showing the structure, energy diagram, and refractive index diagram of the second embodiment, and the third diagram, respectively.
The figure is a schematic structural diagram showing a conventional example.
), (cl shows the cross-sectional view, energy diagram, and refractive index dichogram of other conventional examples. 101.201.501,521.--n-()aA
s substrate, 102, 502="・n (Alo, s
Ga0.7)0.8 In(,,5P cladding layer, 10
3...n-Alo4 Ga,, 5 As guide layer, 104,503--...-Undoped Ga0,5
In, 5F active layer, 105...-p-Al, ,
50a64 As guide layer, 106t504"""p
(AJo, 5Gao, y) o, s In. , 5P cladding layer, 202-- n-(Alo, s GaQ, 4)
0.5InO, SP cladding layer, 203, 523-.
” n AlxGat-xis graded layer, 20
4...Undoped (Alo, tGao, 9) 6
．． 5 I n6. BP active layer, 205,525...
・-p-klxGa 1-xAsAs-did layer, 2
06----・-p-(Alo, 6G ao, 4)o,
s I no, 5P cladding layer, 522...---n
-A10.5 ()a6,5 As cladding layer, 524
...Undoped GaAs active layer, 526 ・-
” p Alo, s Ga(,,5As cladding layer, 1
07,207,505,527...--p-GaA
s layer, 108,208. '506,528-...5iO
z film, 109,209,507,529...p
Electrode, 1) 0,210,508,53 (1...=n electrode, 1) 1.21),509,531...Stripe opening 0 Agent Patent attorney Susumu Uchihara Enel v 1. −q” − <C> Figure 2

Claims (2)

[Claims] (1) Binary or ternary III- element containing one or both of gallium and aluminum as Group III elements
A semiconductor having, on a V compound semiconductor substrate, an active layer made of a multi-component compound semiconductor, and cladding layers made of a multi-component compound semiconductor having a larger energy gap and a smaller refractive index than the active layer provided on both upper and lower surfaces of the active layer. In the light emitting device, the active layer and one or both cladding layers contain one or both of gallium and aluminum as a group III element, and have a larger energy gap and a smaller refractive index than the active layer. 1. A semiconductor light emitting device comprising a binary or ternary compound semiconductor layer. (2) A patent claim characterized in that the aluminum composition in the compound semiconductor layer formed between the active layer and the cladding layer increases from the side in contact with the active layer to the side in contact with the cladding layer. A semiconductor light emitting device according to range (1).