JPH0821761B2 - Semiconductor light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relaxes internal stress generated between a semiconductor crystal and an insulating film, a metal, etc., having different thermal expansion coefficients, and dislocations of defects caused by the internal stress. The present invention relates to a semiconductor light emitting device.

[Conventional technology]

FIG. 4 is a sectional view showing a conventional electrode stripe laser device. In this figure, 1 is an n-type GaAs substrate (hereinafter simply referred to as a substrate, other symbols are also abbreviated), and 2 is n-type Al.
GaAs lower clad layer, 3 p-type GaAs active layer, 4 p-type AlGa
As upper cladding layer, 5 is a p-type GaAs contact layer, 7 is an insulating (SiO ₂ ) film, 8 is a p-side electrode, and 9 is an n-side electrode.

 Next, the operation will be described.

In the semiconductor laser device shown in FIG. 4, the p-side electrode 8
When a voltage is applied to (+) and (−) to the n-side electrode 9, the current flows through the p-side electrode 8 → contact layer 5 → upper cladding layer 4 → active layer 3 → lower cladding layer 2 → substrate 1. Flowing. As a result, electrons are injected into the active layer 3 and light is generated by recombination of electrons and holes. Increasing the current increases electron injection and also increases recombination light. When the current exceeds the threshold value, laser oscillation starts and laser light is emitted to the outside of the device.

The insulating film 7 has a function of confining the current to a narrow region and locally increasing the current density to cause laser oscillation with a lower threshold current.

[Problems to be solved by the invention]

The conventional electrode stripe laser device is configured as described above, and in this kind of electrode stripe laser device, the insulating film 7 is indispensable for lowering the threshold current. However, the thermal expansion coefficient of the insulating film 7 is different from that of the GaAs crystal. Therefore, when the temperature at the time of forming the insulating film 7 is room temperature or higher, when the temperature of the insulating film 7 is returned to room temperature, stress is generated between the insulating film 7 and the GaAs crystal due to the difference in thermal expansion coefficient. Even when the insulating film 7 is formed at room temperature, similar stress is generated when the semiconductor laser is used at a temperature other than room temperature as in the high temperature aging test.
When stress is applied to the crystal, defects and dislocations in the crystal are activated, and the dislocations are extended while repeating emission and absorption of point defects to form a dislocation network. When the dislocation reaches the active layer 3,
Since the dislocation becomes a non-light emitting region in the active layer 3, it causes an increase in threshold value and operating current. When the dislocation network develops in the active layer 3, the laser oscillation is finally impossible. Therefore, in the semiconductor laser device having the structure using the insulating film 7,
Reliability has always been a problem.

The present invention has been made to solve the above problems. Even if a film having a coefficient of thermal expansion different from that of a crystal, such as an insulating film, is formed on the crystal, stress and defects It is an object to obtain a semiconductor device in which dislocations do not reach.

[Means for solving problems]

The first invention relating to the semiconductor light emitting device of the present invention is a semiconductor device in which a semiconductor crystal and an insulating film or a metal layer made of a substance having a coefficient of thermal expansion different from that of the semiconductor crystal are bonded together, A strained superlattice layer composed of two or more types of thin layers having different lattice constants is formed on the surface of the semiconductor crystal on the side in contact with the insulating film or the metal layer. In the first invention, the surface of the semiconductor crystal forming the strained superlattice layer is on the surface side of the semiconductor device, and the third invention is the insulation method according to the first and second inventions. The semiconductor crystal forming the strained superlattice layer on the surface in contact with the film or the metal layer is a contact layer.

[Action]

In the present invention, since the strained superlattice layer is formed on the surface of the semiconductor crystal to which the semiconductor crystal and the film made of the material having a different thermal expansion coefficient from the semiconductor crystal are bonded, Since the stress generated by the adhesion with the film is relaxed by the strained superlattice layer, it is not transmitted to the inside of the crystal. Further, even if dislocations of defects due to stress occur at the interface between the strained superlattice layer and the substance to be adhered, the dislocations have the property of extending within the plane of each layer forming the strained superlattice layer. Therefore, dislocations do not extend below the strained superlattice layer.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

1 (a) and 1 (b) are a sectional view and a partially enlarged sectional view of a semiconductor laser device showing an embodiment of the present invention.

In FIG. 1, the same symbols as those in FIG. 4 indicate the same things, and 6 is a strained superlattice layer formed on the outermost surface of the contact layer 5 in contact with the insulating film 7. The strained superlattice layer 6 is configured by alternately laminating two or more kinds of thin layers different from each other.

 First, the function of the strained superlattice layer 6 will be described.

Generally, in a heterojunction of different materials, if there is a lattice mismatch between both layers, internal stress occurs in the layers. When the layer thickness increases, the internal stress exceeds the elastic limit and dislocations due to lattice mismatch occur. However, in the strained superlattice layer 6, since each layer is thin, strain due to lattice mismatch does not occur. This aspect will be described with reference to FIG.

FIG. 2 is a diagram showing a state of internal stress of the strained superlattice layer 6 composed of two types of strained superlattice layers 6a and 6b. The arrows in the figure indicate the magnitude and direction of the stress, and the dotted lines indicate the positions occupied by the respective layers in the bulk. Strained superlattice layer 6a, 6
Each layer of b expands and contracts mutually due to internal stress, and the lattice mismatch is absorbed.

When a layer such as an insulating film 7 which applies an internal stress to the crystal is formed in contact with the strained superlattice layer 6, the strained superlattice layer 6 is strained as shown in FIG. Lattice layer 6
The internal stress in the inside changes to relieve the internal stress applied by the insulating film 7. As a result, the internal stress applied by the insulating film 7 is not transmitted inside the crystal. Further, the strained superlattice layer 6 has the property of stopping threading dislocations. This will be explained below.

In crystals often used in optical devices such as GaAs and InP, dislocations extend along the (111) plane. When a (100) crystal substrate is used, dislocations repeatedly move up and down within a plane inclined by 55 ° with respect to the substrate plane. Therefore, the dislocations generated by the internal stress at the interface between the conventional insulating film and the GaAs crystal behave as if they extend downward when viewed from the (110) plane.

In the strained superlattice layer 6, the strained superlattice layer 6 is formed 2
Internal stress due to the difference in lattice constants is working at the hetero-interface of different types of layers. In general, the behavior of dislocations is strongly influenced by the internal stress at the hetero interface, and in the region where the internal stress is large near the interface, the dislocation tends to extend parallel to the interface rather than penetrating the interface. Therefore, dislocations cannot easily penetrate in the strained superlattice layer 6 formed by stacking dozens of layers. Therefore, there is almost no possibility that dislocations generated at the interface between the insulating film 7 and the strained superlattice layer 6 extend into the inside of the crystal.

As described above, because of the strained superlattice layer 6, the active layer 3 inside the crystal is not affected by internal stress or dislocation, so that a highly reliable semiconductor laser device can be obtained.

Although only the case of the insulating film 7 and the semiconductor laser device is shown in the above embodiment, when the semiconductor crystal is bonded to a film made of a substance having a different coefficient of thermal expansion from the semiconductor crystal, for example, the semiconductor laser device is used as a heat sink. It can also be applied when adhering.

Further, the present invention is not limited to the semiconductor laser device, and can be applied to all semiconductor devices made of semiconductor crystals that adhere to substances having different thermal expansion coefficients.

Further, although only the GaAs crystal is shown in the above embodiment, the present invention can be applied to a semiconductor device composed of all crystals capable of forming other strained superlattice layers.

〔The invention's effect〕

As described above, according to the present invention, the strain formed by two or more kinds of thin layers having different lattice constants is formed on the surface of the semiconductor crystal that is in contact with the insulating film or the metal layer made of a substance having a different thermal expansion coefficient from that of the semiconductor crystal. Since the superlattice layer is formed, even if a substance having a different thermal expansion coefficient is bonded to the semiconductor crystal, the internal stress is relaxed by the strained superlattice layer that is in contact with this substance, and at the same time, the strained superlattice is Even if dislocations occur at the interface of the lattice layer, they cannot penetrate the strained superlattice layer, so that internal stress and dislocations are not transmitted to the inside of the crystal, and a semiconductor device having excellent reliability can be obtained.

[Brief description of drawings]

1 (a) and 1 (b) are a sectional view and a partially enlarged sectional view of a semiconductor laser device showing an embodiment of the present invention, and FIG. 2 is a state of internal stress of a strained superlattice layer without an insulating film. FIG. 3 is a diagram showing the state of internal stress when the insulating film is in contact with the strained superlattice layer, and FIG. 4 is a sectional view of a conventional electrode stripe laser device. In the figure, 1 is a substrate, 2 is a lower cladding layer, 3 is an active layer, 4 is an upper cladding layer, 5 is a contact layer, 6 is a strained superlattice layer, 7 is an insulating film, 8 is a p-side electrode, and 9 is n. It is a side electrode. The same reference numerals in each drawing indicate the same or corresponding parts.

Claims (3)

[Claims] 1. A semiconductor device constituted by adhering a semiconductor crystal and an insulating film or a metal layer made of a substance having a different thermal expansion coefficient from that of the semiconductor crystal, on a side in contact with the insulating film or the metal layer. A semiconductor light emitting device, wherein a strained superlattice layer composed of two or more kinds of thin layers having different lattice constants is formed on the surface of the semiconductor crystal. 2. The semiconductor light emitting device according to claim 1, wherein the surface of the semiconductor crystal forming the strained superlattice layer is the surface side of the semiconductor device. 3. A semiconductor crystal forming a strained superlattice layer on the surface in contact with an insulating film or a metal layer is a contact layer, and the semiconductor crystal is a contact layer. The semiconductor light-emitting device described.