JPH0440872B2 - - Google Patents

Description

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

(Prior art and its problems) Multi-component mixed crystal compound semiconductors can change their energy gap and refractive index over a wide range depending on the combination of their 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. Conventionally widely used Al _x Ga _1-x As (0x1)
The lattice constant of the compound semiconductor is almost constant regardless of the aluminum composition x. For this reason, Al _x
In the Ga _1-x As 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 within the optical waveguide layer is continuously changed in the direction perpendicular to the layer surface. However, the problem of lattice constant mismatch does not occur. Furthermore, in general, if the group consists of aluminum and gallium and the types of group V elements and the composition ratio of group V elements are constant, the lattice constant of the compound does not depend on the aluminum composition of the group, so the problem of lattice constant mismatch occurs. do not have.

However, in recent years, there has been a demand for light emission or laser oscillation in a wider wavelength range (from visible light to infrared light) than can be obtained with the Al _x Ga _1-x As system, and compound semiconductors made of other constituent elements are being used to fabricate light-emitting devices. It came to be used to In the visible light range (Al _x Ga _1-x ) _0.5
Compound semiconductors such as In _0.5 P system, Ga _X In _1-x P _y As _1-y system, and Ga _x In _1-x As _y Sb _1-y system, Ga _x
A compound semiconductor such as an In _1-x P _y As _1-y system (both x and y take values of 0x1 and 0y1) is used. GaAs,
GaSb, InP, etc. are used, and vapor phase epitaxy (metal organic pyrolysis (MOVPE), halogen transport method (HTVPE)), liquid phase epitaxy (LPE),
Alternatively, a double heterostructure is formed by molecular beam method (MBE) or the like. In general, these multi-component mixed crystals have different lattice constants depending on the composition of their constituent elements. Therefore, in order to obtain the same lattice constant value as that of the substrate, that is, to achieve lattice matching, each composition of the multi-component mixed crystal must be precisely controlled.

Figure 3 shows (Al _x Ga _1-x ) _0.5 In _0.5 P system and Ga _0.5
A conventional example of a double heterostructure laser diode with In _0.5 P as the active layer (Applied Physics Letters, Vol. 43)
pp987−989 (1983). An n-type Al _0.3 Ga _0.7 ) _0.5 In _0.5 P is deposited on an n-type GaAs substrate 501 by, for example, MOCVD.
Clad layer 502, undoped Ga _0.5 In _0.5 P active layer 503, p-type (Al _0.3 Ga _0.7 ) _0.5 In _0.5 P clad layer 504, p-type GaAs layer 5 for ohmic contact
05 are sequentially formed, and further striped openings 50 are formed.
A p-type electrode 507 made of Au/Zn or the like is formed on a SiO ₂ film 506 having a silicon oxide film 506, and an n-type electrode 508 made of AuGe or the like is formed on the back surface of the substrate 501. This is a normal double heterostructure, but
Even with a relatively simple structure like this
It is much more difficult to achieve this with AlGaInP systems than with AlGaAs systems. The reason for this is explained below.
In the AlGaAs system, GaAs can be used regardless of the composition ratio of aluminum (Al) and gallium (Ga).
It is almost lattice matched with the substrate, but in AlGaInP system, Al
Unless the ratio of the sum of the mole fractions of Ga and Ga to the mole fraction of Indium (In) is kept at about 1:1, a large lattice mismatch will occur. When lattice mismatch occurs, crystallinity deteriorates, and therefore device characteristics deteriorate. As described above, when AlGaInP systems are formed into a multilayer structure, and furthermore when the composition is continuously changed during growth, it is extremely difficult to change the composition while maintaining lattice matching conditions.

Figure 4a shows a graded index separated optical waveguide heterostructure (GRIN-SCH) laser realized in AlGaAs system (Applied Physics Letters).
40, pp. 217-219 (1982)). Diagrams of the energy band perpendicular to the substrate surface and the refractive index are shown in Figure 4 b and c.
It is also shown in . n-type GaAs substrate 521
Al _0.5 Ga _0.5 As cladding layer 522, cladding layer 52
An n-type AlGaAs graded layer 523 in which the Al composition is successively reduced from 0.4 to 0.2 from 2 to the active layer 524; an undoped active layer 524; p-type AlGaAs increased to 0.4
Graded layer 525, p-type Al _0.5 Ga _0.5 As cladding layer 526, p-type for ohmic contact
After sequentially forming the GaAs layer 527, a p-type electrode 529 such as Au/Zn is formed on the back surface of the substrate 521 on the SiO ₂ film 528 having the striped openings 531.
An n-type electrode 530 made of AuGe or the like is formed respectively. By setting the thickness of the active layer 524 to 500 Å or less and having graded layers 523 and 525 with gradient Al compositions, the laser oscillation threshold can be significantly reduced compared to the conventional double heterostructure. However, it has the disadvantage that the wavelength range in which it can oscillate is limited to 0.7 to 0.87 μm. In order to obtain oscillation in the visible and infrared wavelength ranges other than this, it is not possible to use AlGaAs.
Materials other than AlGaAs-based, such as AlGaInP-based and GaInAsSb-based, must be used. However, these materials require strict control of their composition in order to achieve lattice matching with the substrate, and it has been extremely difficult to form complex multilayer structures for high functionality and performance.

(Purpose of Generation) The purpose 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, on a binary or ternary-V compound semiconductor substrate having one or both of gallium and aluminum as a group element, an active layer made of a multi-component compound semiconductor, and this active layer are formed. In a semiconductor light-emitting device, the active layer and one or both of the cladding layers have a cladding layer made of a multi-component compound semiconductor having a larger energy gap and a smaller refractive index than the active layer. between which one or both of gallium and aluminum are group elements;
A binary or ternary compound semiconductor layer having a group V element of the same type and composition as the group V element of the semiconductor substrate, and having a larger energy gap and a smaller refractive index than the active layer. A semiconductor light-emitting device having a structure having the following properties can be 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) Hereinafter, the present invention will be explained in detail using the drawings.
A first embodiment of the invention is shown in FIG. Figure 1a
is a schematic diagram of the first embodiment, FIG. 1b is an energy band diagram of the first embodiment, and FIG. 1c is a refractive index diagram of the first embodiment. Common parts in FIGS. 1a, b, 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. n-type GaAs substrate 10
1, an n-type (Al _0.3 Ga _0.7 ) _0.5 In _0.5 P cladding layer 102 with a thickness of 1.0 μm, an n-type Al 0.5 Ga 0.5 As guide layer 103 with a thickness of 0.4 μm, and a 0.03 μm-thick n-type (Al _0.5 Ga _0.5 As guide layer 103 with a thickness of 0.03 μm) are formed on the top layer 1 by epitaxial growth. undoped Ga _0.5 In _0.5 P active layer 104,
p-type Al _0.5 Ga _0.5 As guide layer 105 with a thickness of 0.4 μm,
A p-type (Al _0.3 Ga _0.7 ) _0.5 In _0.5 P cladding layer 106 with a thickness of 0.1 μm and a p-type GaAs layer 107 with a thickness of 1.0 μm are successively grown. As an epitaxial growth method
Either MOVPE method, MBE method, etc. may be used. Furthermore, it has a striped opening (width 10 μm) 111.
A SiO ₂ insulating film 108 is provided, a p-electrode 109 made of Au/Zn alloy is formed thereon, and the n-GaAs substrate 1
An n-electrode 110 made of Au/Ge alloy is formed on 01 to complete the process. Current is injected into the active layer 104 in a stripe pattern and excited, allowing efficient oscillation. An energy band diagram and a refractive index diagram with respect to distance x in the growth layer direction are shown in FIGS. 1b and 1c, respectively. As shown in FIG. 1b, the injected carriers are confined in the Ga _0.5 In _0.5 P active layer 104 with the smallest energy gap and contribute to laser oscillation. In this example, the thickness of the active layer 104 is 0.03 μm in order to increase the carrier density in the active layer and lower the laser oscillation threshold current value.
Since the active layer 104 is made thin, the light is not confined only in the active layer 104 but also spreads into the light guide amounts 103 and 105. As can be seen in the refractive index diagram FIG. 1c, the guide layers 103, 105 and the active layer 1
Since the refractive index of the active layer 104 is larger than that of the cladding layers 102 and 106, the laser oscillation light is transmitted to the active layer 104.
and is confined in the light guide layers 103 and 105. In order to achieve sufficient confinement of light and injected carriers, the active layer must be sandwiched between cladding layers having the necessary refractive index difference and energy gap difference. (Al _0.3 Ga _0.7 ) plays this role.
_0.5 In _0.5 P cladding layers 102 and 106.
As shown in FIGS. 1b and 1c, the energy gap increases in the order of active layer 104, guide layers 103 and 105, and cladding layers 102 and 106, and the refractive index decreases in this order. In the AlGaAs system, it is not possible to have a sufficient energy gap difference and refractive index difference with respect to GaInP, so AlGaInP is used as the cladding layer.
It is necessary to use However, if the guide layer is made of AlGaAs, but has an appropriate Al composition as in this embodiment, the effect can be sufficiently achieved. (Al _x
Ga _1-x ) _y In _1-y P (0≦x≦1, 0≦y≦1) can also be used, but in this case, the value of y (i.e., In
Since the lattice constant differs depending on the composition ratio 1-y),
In order to achieve lattice matching with the substrate, it is necessary to precisely control the value of y, which increases the difficulty of crystal growth and the difficulty of maintaining reliability when used as a device.
Device yield also decreases. Therefore, as in this example,
Lattice matched to the substrate regardless of composition
By using AlGaAs, these disadvantages can be resolved and desired device characteristics can be obtained.

A second embodiment of the invention is shown in FIG. Fig. 2a is a schematic diagram of the second embodiment, Fig. 2b is an energy band diagram of the second embodiment, Fig. 2c
respectively show refractive index diagrams of the second example. Common parts in FIGS. 2a, 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 its formation method will be described next. Epitaxial crystal growth methods include MBE method or MOVPE.
Use the law. First, on the n-type GaAs substrate 201,
1.0μm n-type (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P cladding layer 2
Grow 02. Continuously in the growth direction on top of this
An Al _x Ga _1-x As graded layer 203 whose Al composition is reduced from 0.7 to 0.5 is grown to a thickness of 0.4 μm. Subsequently, an undoped (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P active layer 204 with a thickness of 0.01 μm is grown, and a layer is continuously grown on it in the growth direction.
Al _x Ga _1-x As graded 205 with an Al composition increasing from 0.5 to 0.7 is grown to a thickness of 0.4 μm. Furthermore, a p-type (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P cladding layer 206 with a thickness of 1.0 μm and a p-type GaAs layer 207 with a thickness of 1.0 μm are further formed on it.
grow sequentially. Next, striped openings (width
Au _/
An n-electrode 210 made of an Au/Ge alloy is formed on a p-electrode 209 made of a Zn alloy and an n-electrode 210 made of an n-GaAs substrate 201 . An energy band diagram and a refractive index diagram with respect to distance x in the growth layer direction are shown in FIGS. 2b and 2c, respectively. The injected carriers are confined in the (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P active layer 204 with the smallest energy gap, as shown in FIG. 2b, and contribute to laser oscillation. In this example, the active layer is made extremely thin with a thickness of 0.01 μm,
The carrier density is higher than that of the first embodiment, and a quantum well effect is produced, thereby lowering the oscillation threshold. At this time, the injected carriers are efficiently collected in the active layer 204 and the light is transferred to the cladding layer 204.
Graded layers 203 and 205 are provided to confine the light between 2 and 206. As shown in Figure 2b, the injection carrier is in the grated layer 2.
The active layer 20 due to the electric field created at 03,205
4, and the light is confined across the graded layers 203 and 205 with the active layer 204 as the center due to the refractive index distribution as shown in FIG. 2c. In this case, the gray dated layers 203, 205
requires continuous changes in composition. In terms 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. AlGaInP is a material whose lattice constant generally changes when its composition is changed, and it is extremely difficult to change its 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 formation is continuously changed. Furthermore, AlGaAs can be used to obtain a composition that satisfies the requirements for the energy gap value and refractive index, as in this embodiment, even for AlGaInP-based lasers. The device manufactured in this way was able to significantly reduce the oscillation threshold compared to the conventional double heterostructure device. This is conventional
This means that the same effect as the GRIN-SCH laser obtained with the AlGaAs system can be obtained with the structure of this example. The parameters such as compound composition, 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. As an example, on an n-type GaSb substrate
1μm thick n-type Al _0.5 Ga _0.5 Sb, 0.4μm thick n-type
Al _x Ga _1-x Sb graded layer (x: 0.4→0.2),
0.01μm thick undoped Ga _0.4 In _0.6 As _0.5 Sb _0.5 ,
A multilayer structure consisting of a 0.4 μm thick p-type Al _x Ga _1-x Sb graded layer (x: 0.2→0.4) and a 1 μm thick p-type Al _0.5 Ga _0.5 Sb graded layer produces a wavelength of 2.5 μm.
An infrared-emitting semiconductor laser is obtained.

(Effects of the Invention) As described above, according to the present invention, light and carrier confinement can be achieved by reducing the threshold of conventional lasers with optical guide layers or graded refractive index separated optical waveguide heterostructures (GRIN-SCH). It is possible to provide a semiconductor light emitting device that does not impair the functionality of the laser at all, greatly reduces the adverse effects of lattice mismatch on crystal quality, and is easy to manufacture.

[Brief explanation of drawings]

Figures 1a, b, and c are diagrams showing the structure, energy band diagram, and refractive index diagram of the first embodiment of the present invention, respectively; Figures 2a, b, and c are diagrams showing the structure of the second embodiment, respectively; FIG. 3 is a schematic structural diagram showing a conventional example, and FIGS. 4 a, b, and c are sectional views, energy diagrams, and refractive index dichograms of other conventional examples. 101, 201, 501, 521...n-
GaAs substrate, 102,502...n-(Al _0.3 Ga _0.7 )
_0.5 In _0.5 P clad layer, 103...n-Al _0.5 Ga _0.5
As guide layer, 104,503...undoped
Ga _0.5 In _0.5 P active layer, 105...p-Al _0.5 Ga _0.5 As
Guide layer, 106,504...p-(Al _0.3 Ga _0.7 ) _0.
5 In _0.5 P cladding layer, 202...n-(Al _0.6 Ga _0.4 )
_0.5 In _0.5 P clad layer, 203,523...n-
Al _x Ga _1-x As graded layer, 204...Undoped (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P active layer, 205,5
25...p-Al _x Ga _1-x As graded layer, 2
06...p-(Al _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer,
522... n-Al _0.5 Ga _0.5 As cladding layer, 524
...Undoped GaAs active layer, 526...p-
Al _0.5 Ga _0.5 As cladding layer, 107,207,50
5,527...p-GaAs layer, 108,208,
506,528...SiO ₂ film, 109,209,
507,529...p electrode, 110,210,5
08,530...n electrode, 111,211,50
9,531...Striped opening.

Claims (1)

[Scope of Claims] 1. An active layer made of a multi-component compound semiconductor on a binary or ternary-V compound semiconductor substrate having one or both of gallium and aluminum as a group element, and an active layer on both upper and lower surfaces of the active layer. In a semiconductor light emitting device having a cladding layer made of a multicompound semiconductor having a larger energy gap and a smaller refractive index than an active layer provided in the semiconductor light emitting device,
One or both of gallium and aluminum is used as a group element between the active layer and one clad layer or both clad layers, and the group V element is the same type and has the same composition as the group V element of the semiconductor substrate. 1. A semiconductor light emitting device, comprising a binary or ternary compound semiconductor layer having a compound semiconductor layer as an element and having a larger energy gap and a smaller refractive index than the active layer. 2. Claim No. 2, 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. The semiconductor light emitting device according to item 1.