JP2871295B2 - Surface type optical semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor optical device used for optical interconnection between devices.

[0002]

2. Description of the Related Art A surface optical device is a device that emits light in a direction perpendicular to a semiconductor substrate, and is a vertical cavity surface emitting laser (VCSELD) or a distributed reflector (multilayer semiconductor). DBR) and a vertical cavity surface input / output photoelectric fusion device (VC-VSTEP) having a pnpn structure formed between them. In the surface optical device, light can be extracted in a direction perpendicular to the substrate, and the device size itself can be reduced. Therefore, the feature of the surface optical device is that two-dimensional integration is possible. As a material system of VCSELD and VC-VSTEP, a GaAs system is mainly used, but an InP-based VCSELD has begun to be prototyped.

FIG. 3 shows an element structure of a VCSELD made of InP. Technical Committee on Optical Switching (PST9)
1-12, 1991).
If an InP-based material is used as a material system, a wavelength band of 1 μm, which is important as a light source for optical communication, can be covered by this, and is therefore of interest in various places.

In FIG. 3, reference numeral 31 denotes n-InP,
Numeral 32 denotes an n-InGaAsP / InP-DBR whose number of periods is 30.5 pairs. 33 is an n-InP cladding layer, 3
4 is an active layer of p-InGaAsP, 35 is a cladding layer of p-InP, 36 is a contact layer of p-InGaAsP, and 37 is an α-Si / SiO ₂ multilayer film which functions as a p-side reflector. 38 and 39 are a p electrode and an n electrode, respectively. Numerals 40 and 41 serve to block the current flowing in this portion with p-InP and n-InP, respectively.

[0005]

A problem with the conventional InP-based surface optical device is that it is difficult to manufacture a DBR having a high reflectivity of 99.9%. The reason is that the refractive index difference between InP and InGaAsP is small in the InP / InGaAsP system.
Of course, the reflectivity can be increased by increasing the number of layers of the DBR. However, since the thickness is increased, the growth takes time and the process becomes difficult due to a step.

For example, in the GaAs system, a sufficient reflectivity can be realized with 15-20 pairs, whereas in the InP system, about 40 pairs of semiconductor multilayer films are required. In addition, the 1 μm band In
The thickness of one layer (λ / 4 wavelength) in the P system is larger than that of the GaAs system in the 0.8 μm band, so that the thickness is excessive. At present, the performance of the InP-based VCSELD is not as good as that of the GaAs-based one, and continuous oscillation (threshold current is 6 mA) is realized at 77 K, but pulse oscillation (threshold current is 150 mA) at room temperature. This is a short-wavelength VCSELD having an active layer of a GaAs layer or an InGaAs layer in which a small amount of In is added to the GaAs layer.
Thus, it can be said that this is significantly delayed as compared with the case where room temperature continuous oscillation is realized with a threshold current of about 1 mA.

[0007]

According to the present invention, there is provided a conventional one in which the number of layers of the DBR is increased and the growth and the process become difficult.
An object of the present invention is to solve the problem of the surface optical semiconductor device in the μm band. The surface type optical semiconductor device according to the present invention is made of GaAs.
Alternatively, Al _x Ga _{1 -x} As (0 <
x <1) and Al _y Ga _1-y As (0 <y <1) are alternately stacked, and a semiconductor distributed reflector is grown thereon.
The buffer layer and the In _z Ga ₁ -z _Asw P _{1 -w} active layer (0
In the surface type optical semiconductor device in which the intermediate layer including <z, w <1) is grown and the multilayer mirror is formed thereon, after the semiconductor distributed reflector is grown, the dielectric material is grown thereon. A film is formed, a part of the film is opened, and the I
An nP buffer layer and the intermediate layer are grown.

[0008]

Since the DBR on the substrate side is made of a GaAs-based structure, a large difference in the refractive index can be obtained for a wavelength in the 1 μm band. This makes it possible to reduce the number of layers required to obtain a high reflectivity as compared with the case where a DBR is manufactured using an InP system. However _{Al x Ga 1-x As /} Al y Ga 1-y
It is generally not easy to grow an InP layer on an As-DBR. AlGaAs / GaAs system and InGa
This is because there is a problem of lattice mismatch with the AsP / InP system, dislocations are generated, and it is difficult to obtain a mirror-like surface.

[0009] In the present invention _{Al x Ga 1-x As /} Al y G
After growing a _1-y As-DBR, a dielectric film is formed thereon, a part of the film is opened, and InGaAsP is selectively formed therein.
A / InP-based intermediate layer is grown. When selectively grown in this way, dislocations are initially generated, but stop there when they reach the side wall of the selectively grown layer. Further, the upward progress is suppressed. The reason why the dislocation stops there when reaching the side wall of the selective growth layer is that strain can be released.

[0010]

FIG. 1 shows an embodiment according to the present invention. In the figure, 101 is n-GaAs, 102 is n of λ / 4 thickness.
-AlAs (Si doping, doping concentration N = 2 × 10
¹⁸ cm ⁻³ ) 114, n-GaAs (Si-doped, N = 2)
x10 ¹⁸ cm ^-3 ) 113 is an n-type DBR formed by alternately stacking. λ represents the wavelength in AlAs (or GaAs) corresponding to the oscillation (wavelength 1.5 μm) by the InGaAs active layer 106. The number of periods is 24.5, which can achieve a reflectivity of 99.9%.

Reference numeral 103 denotes an n-InP buffer layer (N = 2
x10 ¹⁸ cm ^-3 , layer thickness 2.5 μm).
Growing at 0 ° C. Although the MOCVD method was used for the growth, the others were grown at 650 ° C.

The growth of the n-InP buffer layer 103 is n
Dielectric film 120 made of SiO ₂ on DBR 102
The opening 121 was selectively grown. The opening 121 has a circular shape and a diameter of 2.5 μm. The dielectric film 120 was formed at a thickness of 1000 A by a thermal CVD method.

The n-InP buffer layer 103 is heated to 500 ° C.
The reason for growing at a relatively low temperature will be described below. InP
When a buffer layer is grown on a GaAs-based semiconductor at a normal temperature of 600 to 700 ° C., In
The growth of P proceeds and the surface becomes uneven. On the other hand, if the InP buffer layer is grown at a low temperature of 550 ° C. or less, the size of the islands becomes small, and the islands come together in a short time to flatten the growth surface. By interposing such an InP buffer layer, an InP-based semiconductor can be grown in a mirror-like manner on a GaAs-based semiconductor having a different lattice constant.

Reference numeral 104 denotes n-InP (Si-doped, N = 2
× 10 ¹⁸ cm ^-3 , layer thickness 500A). InGaAs
The layer thickness of the active layer 106 is 100 A and is undoped.
105 and 107 are n-InGaAsP and p-I, respectively.
nGaAsP, both having a layer thickness of δ and a doping concentration of 2 × 10 ¹⁸ cm ⁻³ (105 is Si-doped, 1
07 is Zn-doped). n-InGaAsP10
5, the composition of p-InGaAsP 107 is parabolically changed, the band gap wavelength on the side in contact with the active layer 106 is 1.3 μm, and the band gap wavelength on the opposite side is In.
Same as P. Reference numeral 108 denotes n-InP (Zn-doped, N = 2 × 10 ¹⁸ cm ⁻³ , layer thickness 5000A).
Reference numeral 109 denotes p-InGaAsP having a thickness of 1000 A (bandgap wavelength is 1.3 μm, Zn-doped, N = 2 × 10
¹⁸ cm ^-3 ) and works as a contact layer. n-In
P-InGaAsP on the top of the P buffer layer 103
The layer thickness up to 109 is 7λ (λ is the oscillation wavelength, about 1.5 μm
(Wavelength in the InGaAsP / InP-based intermediate layer).

FIG. 2 is a sectional view of a VCSELD having a mesa diameter of 10 μm manufactured using the wafer of FIG. 111
Reference numeral 5 denotes a p-type DBR, which has a λ / 4 thickness of α-Si116 and SiO
₂ 117 are repeatedly formed in three cycles. 110 is Cr / Au, 111 is n-GaAs 113
AuGe-Ni / Au formed on the substrate, and serves as a p-type electrode and an n-type electrode, respectively. Light output is obtained from the substrate side. The oscillation threshold current was about 100 μA. n-type DBR
Although the number of periods of 102 is 24.5, a reflectivity of 99.9% is realized, but in order to obtain the same reflectivity in the InP system, 40 periods are required, so that the growth layer thickness can be reduced. In FIG. 2, the entire height of the element could be suppressed to about 5 μm.

[0016]

According to the present invention, laser light can be obtained in a wavelength band of 1 μm, which is important as a light source for optical communication, and a surface optical semiconductor device operating at a low threshold can be realized. In this embodiment, V
Although CSELD has been described, it goes without saying that application to VSTEP is also possible.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a sectional view of a surface emitting laser manufactured using the wafer of FIG. 1;

FIG. 3 is a perspective view showing a conventional surface emitting laser.

[Explanation of symbols]

101 n-GaAs 102 n-type DBR 103 n-InP buffer layer 104, 31, 33, 41 n-InP 105 n-InGaAsP 106 InGaAsP active layer 107, 109, 34, 36 p-InGaAsP 108, 35, 40 p-InP 110 Cr / Au 111 AuGe-Ni / Au 112 SiN 113 n-GaAs 114 p-GaAs 116 α-Si 117 SiO ₂ 115 p-type DBR 32 n-InGaAsP / InP-DBR 37 α-Si / SiO ₂ multilayer film 38 p Electrode 39 n-electrode 120 SiO ₂ dielectric film 121 opening

Claims (1)

(57) [Claims] 1. A method in which A is placed on a GaAs or AlGaAs substrate.
_{l x Ga 1-x As (} 0 <x <1) and Al _y Ga _1-y As
A semiconductor distributed reflector in which (0 <y <1) is alternately stacked is grown, and an InP buffer layer and In _z Ga ₁ -z are formed thereon.
In the surface type optical semiconductor device in which an intermediate layer including an As _w P _1-w active layer (0 <z, w <1) is grown and a multilayer reflector is further formed thereon, the semiconductor distributed reflector A surface type optical semiconductor device, wherein a dielectric film is formed thereon, a part of the film is opened, and the InP buffer layer and the intermediate layer are selectively grown thereon.