JPH0521898A - Surface emitting type laser - Google Patents

Abstract

PURPOSE:To ensure a single mode with lower threshold by specifying the diameter of a first optical reflection layer formed on the principal surface of a semiconductor and the refractive index of a cavity layer. CONSTITUTION:Assumed refractive indexes of cavity layers (undoped GaAs layers) 3, 5 to be n1 and that of a third semiconductor to be n3, and a laser oscillation wavelength to be lambda0 those reflectivity satisfy: 0<2pin1a(2DELTA<1/2>/lambda0)<=2.405(DELTA=(n1<2>-n3<2>)/2/n1<2>). Further, a p/n Al0.43Ga0.57As is buried so as to form a reverse pn junction using p Al0.43Ga0.57As and hence ensure a higher light confinement coefficient, and a P<++>-GaAs layer 9 is grown as a contact layer. Finally, a p electrode 10 is deposited on the upper portion of the device and an n electrode 11 is deposited on the lower portion of the same. Hereby, there is ensured a single transverse mode with a lowest threshold.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a side surface of a convex portion after a first light reflecting layer, a cavity layer and a second light reflecting layer having a diameter of 2a are formed on the main surface of a semiconductor substrate in a convex shape. In a surface-emitting laser having a structure in which a convex portion is embedded by a third semiconductor in contact with, the refractive index of the cavity layer is n ₁ ,
0 <2πn ₁ a (2Δ) ^1/2 / λ ₀ ≦ 2.405, where n _{3 is} the refractive index of the third semiconductor and λ ₀ is the laser oscillation wavelength.
(Where, Δ = (n ₁ ² −n ₃ ² ) / 2 / n ₁ ² ) has a diameter 2a and a refractive index n ₁ which satisfy the condition, so that the optical confinement is higher than that of the prior art. The present invention relates to a surface-emitting laser that maintains a single lateral mode and obtains a low threshold value.

[0002]

2. Description of the Related Art Generally, a III-V group compound semiconductor laser typified by GaAs forms an optical resonator in a direction parallel to a substrate, and a laser beam is emitted from an end surface (usually a cleavage plane) of the optical resonator. Are taking out. In this case, it is very difficult to two-dimensionally integrate the laser on the wafer surface at a high density because of the structural problem. That is, since the length of the optical resonator of each laser is as long as 100 to 300 μm, there is a limit to the number of lasers that can be integrated in a wafer per unit area, and the laser light is emitted parallel to the substrate. So
It has a drawback that a 45 ° high-reflecting mirror must be formed by etching separately from the laser portion in order to extract light in a direction perpendicular to the substrate. On the other hand, a so-called surface-emitting laser that emits laser light perpendicularly to the growth substrate can be easily and two-dimensionally integrated with high density because of its structure. Moreover, as the surface emitting laser, a laser having an extremely low threshold value of less than 1 mA can be realized as compared with a normal laser. FIG. 3 shows the structure of this type of surface emitting laser. In the figure, 1 is an n-type G
aAS substrate, 10 is AuZnNi / Au p-electrode, 11
Is an n-electrode of AuGeNi / Au, 22 is n-AlAs /
GaAs DBR, 23 is a GaAS layer, 24 is InGa
As SQW, 26 is p-AlAs / GaASDBR,
30 is a polyimide.

[0003]

Conventionally, in surface emitting lasers, when the injection current is increased, the transverse mode suddenly changes, and as a result, the optical output and the spatial distribution of light fluctuate, and a stable single lateral laser is obtained. It is confirmed that the mode does not oscillate. This is because the surface emitting laser that has been generally reported has a cylindrical shape with a diameter of about 10 μm surrounded by air or polyimide, and has a single transverse mode considering the optical waveguide structure in the cavity structure. This is considered to be because it is two orders of magnitude larger than the condition for becoming. Considering the confinement of light against the above facts, it is difficult to reduce the cylindrical diameter of the surface emitting laser from the viewpoint of the process,
Further, as the diameter is made smaller, the contribution of loss due to surface recombination on the side surface cannot be ignored in the surface emitting laser, and eventually laser oscillation cannot be achieved. For this reason, it has been impossible to obtain a stable single transverse mode laser with a low threshold by reducing the device shape. An object of the present invention is to obtain a surface emitting laser having a single transverse mode and a low threshold value.

[0004]

To achieve the above object, a first light reflecting layer, a cavity layer, and a second light reflecting layer having a diameter of 2a are formed in a convex shape on the main surface of a semiconductor substrate. In a surface emitting laser having a structure in which a convex portion is buried with a third semiconductor which comes into contact with the side surface of the convex portion later, in the surface emitting laser, the refractive index of the cavity layer is n ₁ , the refractive index of the third semiconductor is n ₃ ,
0 <2πn ₁ a (2Δ) where lasing wavelength is λ ₀
^1/2 / λ ₀ ≦ 2.405 (where Δ = (n ₁ ² −n ₃ ² )
The diameter 2a and the refractive index n ₁ satisfying the condition of / 2 / n ₁ ² ) are selected. As a result, higher optical confinement that satisfies the single transverse mode is realized as compared with the conventional technique, and surface recombination is suppressed in the surface emitting laser by the embedding with the third semiconductor, so that the single transverse mode is achieved. A low-threshold surface-emitting laser can be obtained.
That is, according to the present invention, the third semiconductor contacting the side surface of the convex portion is formed after the first light reflecting layer, the cavity layer, and the second light reflecting layer having the diameter of 2a are formed on the main surface of the semiconductor substrate in a convex shape. In a surface emitting laser having a structure in which a convex portion is embedded by, the refractive index of the cavity layer is n ₁ , the refractive index of the third semiconductor is n ₃ , the laser oscillation wavelength is λ ₀ , and 0 <2πn ₁
a (2Δ) ^1/2 / λ ₀ ≦ 2.405 (where Δ = (n
_The diameter 2a and the refractive index n ₁ satisfying the condition of ₁ ² −n ₃ ² ) / 2 / n ₁ ² ) are selected.

[0005]

As a result of selecting the diameter 2a and the refractive index n ₁ satisfying the above conditions, a surface emitting laser with a single transverse mode and a low threshold value can be realized.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a structural diagram showing an embodiment of a surface emitting laser according to the present invention, which uses an InGaAs / GaAs strained superlattice having an well layer width of 10 nm as an active layer.
This is an example of a 0 μm surface emitting laser. Note that this embodiment is 1
It is needless to say that various modifications and improvements can be made without departing from the spirit of the present invention.
In FIG. 1, first, MO is first formed on an n-type GaAs substrate.
The optical film thickness of each layer is sequentially set to λ / of the oscillation wavelength using the CVD method.
4 (250 nm) 30 pairs of n-AlAs / GaA
After forming a cavity layer consisting of an s-reflecting layer, an undoped GaAs layer, a 10 nm undoped In _0.2 Ga _0.8 As layer as an active layer, and an undoped GaAs layer having a thickness of the oscillation wavelength as a whole, the optical thickness of each layer oscillates. Λ / 4 of wavelength
(250 nm) 20.5 pairs of p-AlAs / Ga
Crystallize the As reflective layer. Subsequently, SiO ₂ is formed to a thickness of 200 nm by sputtering, and a mask is formed by resist patterning. Then, after the outside of the mask is dry-etched by RIE using C ₂ F ₆ and SF ₆ , ECR etching with chlorine gas is used until the middle of the n-AlAs / GaAs reflective layer is dry-etched and a sulfuric acid-based chemical etchant is used. After performing the light etching, a cylinder having a diameter of 2 μm and a height of 5 μm is formed.

After that, so as to contact the side surface of the cylinder,
MOCVD method n ₁ the refractive index of the cavity layer with (in the above case undoped GaAs layer), when the refractive index of the third semiconductors and n _3, the laser oscillation wavelength lambda _0, 0
<2πn ₁ a (2Δ) ^1/2 / λ ₀ ≦ 2.405 (where Δ = (n ₁ ² −n ₃ ² ) / 2 / n ₁ ² ) and the refractive index is satisfied, and 1.7 of p-Al _0.43 Ga _0.57 As is used to form an inverse pn junction of the cylinder with Al _0.43 Ga _0.57 As so as to have a high optical confinement factor.
μm, n-Al _0.43 Ga _0.57 As is buried at 3.3 μm, and then a p ⁺⁺ -GaAs layer (p ~
10 ¹⁹ cm ⁻³ ) is grown to 10 nm. Then, finally, AuZnNi / Au is vapor-deposited on the upper portion and AuGeNi / Au is vapor-deposited on the lower portion as the n-electrode, and after sintering, the process is completed.

A current was injected into the surface-emitting laser configured as described above, and the IL characteristics were examined.
Although the diameter is as small as m, the surrounding area is filled with the above-mentioned third semiconductor, and therefore, at a low threshold value of 0.8 mA, compared with the value reported hitherto, I
It was confirmed that the −L curve rises and laser oscillation occurs. Next, when the current is increased as it is and the far-field image is observed by the silicon vidicon, the mode change is usually observed at 4 to 5 mA in the conventional laser, whereas this is observed in the surface emitting laser according to the present invention. No mode change was observed even if it exceeded 15 mA. The oscillation spectrum is 1 μm determined by the etalon composed of the first and second light reflection layers, and the half width is 0.2 n.
It was less than m and less than the resolution limit of the spectroscope, and was comparable to a normal surface emitting laser. In the above embodiments, the description has been given by taking the case of the surface emitting laser having the oscillation wavelength of 1.0 μm using the InGaAs / GaAs strained superlattice having the well width of 10 nm in the active layer as an example. Even in this case, the same effect can be obtained.

Next, as a second embodiment, an oscillation wavelength of 1.5 using InGaAsP as an active layer on an InP substrate.
FIG. 2 shows the case of a 5 μm surface emitting laser. First, by using the MOCVD method on an n-type InP substrate, 30 pairs of n-InGaAsP (1.45 μm composition) / wherein the optical thickness of each layer is λ / 4 (387.5 nm) of the oscillation wavelength in order.
After forming an InP reflective layer and then an active layer (1.55 μm composition) made of p-InGaAsP as a cavity layer having an optical film thickness of 2λ (λ is the oscillation wavelength), finally p ⁺⁺
-Crystal growth of the InGaAsP contact layer. Then, a highly reflective film composed of 4.5 pairs of dielectric multilayer films made of TiO ₂ and SiO ₂ and having a central wavelength of 1.55 μm is formed by EB vapor deposition. After that, a mask is formed by resist patterning, the outside of the mask is dry-etched by RIE using CF ₄ and H ₂ , and then the dielectric multilayer film is dry-etched.
After dry etching and slight etching using a sulfuric acid system up to the substrate, a cylinder having a diameter of 10 μm and a height of 6.9 μm is formed.

Then, so as to contact the side surface of the cylinder,
Using the MOCVD method, the cavity layer (p-InGaAsP layer which is the active layer in the above case) has a refractive index of n.
₁ , the refractive index of the third semiconductor is n ₃ , the laser oscillation wavelength is λ
_{When 0} is set, 0 <2πn ₁ a (2Δ) ^1/2 / λ ₀ ≦ 2.
405 (where, Δ = (n ₁ ² −n ₃ ² ) / 2 / n ₁ ² ) is satisfied, and a semi-insulating layer iron-doped InGaAsP having a refractive index that enables a high optical confinement coefficient.
(1.28 μm composition), the above-mentioned cylinder is embedded, and finally a p ⁺⁺ -InGaAsP layer is formed as a contact layer to form 10 layers.
nm growth. Finally, Au is used as a p-electrode on the top.
ZnNi / Au is used as an n-electrode on the bottom and AuGeNi /
After Au deposition and sintering, the process is completed.

[0011]

As described above, according to the present invention, a convex first light reflecting surface having a diameter 2a is formed on the main surface of a semiconductor substrate.
After forming the cavity layer and the second light reflection layer, the refractive index of the cavity layer in contact with the side surface of the convex portion is n ₁ , the refractive index of the third semiconductor is n ₃ , and the laser oscillation wavelength is λ ₀ .
0 <2πn ₁ a (2Δ) ^1/2 / λ ₀ ≦ 2.405 (where Δ = (n ₁ ² −n ₃ ² ) / 2 / n ₁ ² ) diameter 2a and refractive index By embedding the convex portion with the third semiconductor having n ₁ , a single lateral mode and low threshold surface emitting laser can be realized. Therefore, it can be used as a light source for optical switching, an optical neural network, and optical information processing, and has great economic effects.

[Brief description of drawings]

FIG. 1 is a structural diagram showing an embodiment of a surface emitting laser according to the present invention.

FIG. 2 is a structural view showing another embodiment of this surface emitting laser.

FIG. 3 is a structural diagram of a conventional surface emitting laser.

[Explanation of symbols]

1 n-type GaAs substrate 2 30 pairs of n-AlAs / GaAS reflection layer 3,5 undoped GaAS reflection layer 4 undoped In _0.2 Ga _0.8 As layer 6 20.5 pairs of p-AlAs / GaAS reflection layer 7 p-Al _0.43 Ga _0.57 As layer 8 n-Al _0.43 Ga _0.57 As layer 9 p ⁺⁺ -GaAs contact layer 10 AuZnNi / Au p electrode 11 AuGeNi / Au n electrode 12 n-type InP substrate 13 30 pairs of n-InGaAsP / InP reflective layers 14 p-InGaAsP active layer 15 p-InP layer 16 p ⁺⁺ -InGaAsP contact layer 17 4.5 paired TiO ₂ / SiO ₂ high reflection layer 18 iron-doped InGaAsP layer

Claims (1)

Claim: What is claimed is: 1. A first light reflecting layer on a main surface of a semiconductor substrate,
By stacking a cavity layer including an active layer and a second light reflecting layer in this order, light emitted from the active layer is emitted by using an optical resonator composed of the first and second light reflecting layers. Laser oscillation is performed, and after the first light reflection layer, the cavity layer, and the second light reflection layer are formed in a convex shape having a diameter 2a on the main surface of the semiconductor, a third light contact layer that contacts the side surface of the projection is formed. In a surface emitting laser in which the convex portion is filled with a semiconductor, a refractive index of the cavity layer is n ₁ , a refractive index of the third semiconductor is n ₃ , a laser oscillation wavelength is λ ₀ and Δ = (n ₁ ² -N
_{When 3} ² ) / 2 / n ₁ ² , 0 <2πn ₁ a (2Δ)
A surface emitting laser having a diameter 2a and a refractive index n ₁ satisfying a condition of ^1/2 / λ ₀ ≦ 2.405.