JPH01108789A - Surface emission semiconductor laser element - Google Patents

Abstract

PURPOSE:To obtain high gain properties by composing a surface emission semiconductor laser element of a GaAs semiconductor substrate having a face azimuth 111 and an active layer having superlattice or quantum well structure formed onto a substrate and consisting of GaAs and AlGaAs. CONSTITUTION:A P-type GaAs buffer layer 2, a P-type Al0.7Ga0.3As clad layer 3, a multiple quantum well active layer 4 in which undoped GaAs quantum well layers and undoped Al0.2Ga0.8As barrier layers are superposed alternately in 200 layers and 199 layers, an N-type Al0.7 Ca0.3As clad layer 5 and an N-type GaAs contact layer 6 are grown continuously on a P-type GaAs substrate 1 having a face orientation 111 by using an MBE method. An SiN film 7 is shaped onto the contact layer 6, and an Zn diffusion layer 8 is formed up to the clad layer 3. The central section of the GaAs substrate is etched until the clad layer 3 is exposed, and a resonator is formed, reflecting mirrors 9, 10 functioning as electrodes in combination are shaped, and the whole is divided into chips. Positive voltage is applied to the electrode 10 for the chip and negative voltage to the electrode 9, and laser beams are extracted from the electrode 10 side. Accordingly, room-temperature continuous oscillation is enabled by low threshold currents.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface-emitting semiconductor laser device, and more particularly to a surface-emitting semiconductor laser device that operates with a low threshold current.

[Prior Art] FIG. 4 is a schematic diagram of a surface-emitting semiconductor laser that performs pulse oscillation at room temperature and has been published by the Institute of Precision Engineering, Tokyo Institute of Technology.

(Nikkei Electronics 1984.6.18 issue) In the figure, 11 is an n-type GaAs substrate, 12 is an n-type GaA substrate.
s buffer layer, 13 is n-type A1004Ga6.6As cladding layer, 14 is p-type GaAs active layer, 15 is p-type A(
1@, 4@g, )4 As cladding layer, 16 is 5i02
Insulating film, 17 is p-type Alo, +50 ao, asAs
a cap layer, 18 an electrode and a reflecting mirror, 19 a reflecting mirror,
20 is an electrode.

Figure 5 is a schematic diagram of a surface-emitting semiconductor laser that pulses at room temperature and was published by the Institute of Precision Engineering, Tokyo Institute of Technology (IEICE Technical Report V).

1.86 No, 8 0QE86-8) 1 in the figure
1 is an n-type GaAs substrate, 13 is an n-type A 6,4 G
ao, s A s cladding layer, 14 is a GaAs active layer,
15 is p-type A (,., 40 ao, g As cladding layer, 18 is electrode, 19 is 2! Reflector of electric multilayer film, 2
0 is an electrode, 21 is p-type A LQ, 4 G ao, sAs
The current confinement layer 22 is n-type A (Lo, < Gao, s
A, S current confinement layer.

Next, the operation will be explained. A surface-emitting semiconductor laser device emits laser light in a direction perpendicular to the semiconductor substrate surface, and a resonator is formed between a reflecting mirror in the direction perpendicular to the substrate surface, and has the following characteristics.

(l) Oscillates in a single longitudinal mode.

(11) Large radiation area 1. Since the output angle is narrow, the coupling with the optical fiber is good.

(111) Since the laser emission surface has a highly reflective mirror,
Strong against return light noise.

(Iv) It is possible to create a two-dimensional array.

(lv) Application to monolithic optical integrated circuits, etc. is possible.

It has the following characteristics and is expected to be a new semiconductor laser device that can replace conventional semiconductor lasers that emit laser light parallel to the substrate surface.

[Problems to be Solved by the Invention] The conventional surface emitting laser element of the type shown in FIG. 4 is a pulse oscillation type, and continuous oscillation of a surface emitting laser at room temperature is not performed. This is because the total gain of the surface emitting laser is about 1/100 of that of a conventional Fabry-Perot semiconductor laser. In other words, a surface emitting laser can normally have a cavity length of only about several μm, which means isometrically a very large mirror loss. As a result, the threshold gain of the laser increases significantly, and it is extremely difficult to obtain continuous oscillation at room temperature in a surface emitting laser that uses a tuple hetero (hereinafter abbreviated as DH) structure grown on a normal (100) substrate. The problem was that it was difficult to

Also, in the case of Figure 5, the total gain of the surface emitting laser is about 1/100 of that of a conventional Fabry-Perot semiconductor laser, and as in Figure 4, continuous oscillation at room temperature could not be achieved with a low threshold current. .

The present invention has been made to solve the above-mentioned problems, and its object is to obtain a surface-emitting semiconductor laser device that can perform continuous oscillation at room temperature with a low threshold current.

[Means for Solving the Problems] The surface-emitting semiconductor laser probe according to the present invention has a plane orientation (1
11), an active layer having a superlattice or multi-ffl quantum well structure is formed on a semiconductor substrate having a superlattice structure or a multi-ffl quantum well structure.

[Effect]

The superlattice or quantum well structure on a semiconductor substrate having a plane orientation (111) in this invention is a conventional DH laser,
It has a higher gain than a superlattice or quantum well structure on a semiconductor substrate with a (100) plane orientation, so it is easy to oscillate.

[Embodiments of the Invention] A surface emitting semiconductor laser device according to the present invention has a surface orientation (1
11) An active layer made of GaAs and AlGaAs having a superlattice or quantum well structure is formed on a GaAs semiconductor substrate having a superlattice or quantum well structure.

A preferred embodiment of the invention is shown in FIG. 1C and is constructed as follows.

In FIG. 1c, 1 is a p-type GaAs semiconductor substrate having a hollow in the center and having a plane orientation of (111), and 2 is a 9u1 GaAs semiconductor substrate formed on the substrate and having a hollow in the center. A buffer layer, 3 is a p-type AlGaAs cladding layer formed on the buffer layer, and 4 is a multi-quantum well active layer made of GaAs and AlGaAs formed on the cladding layer and having a peripheral portion diffused with zinc. 5 is an n-type GaAs cladding layer formed on the multi-quantum well active layer or superlattice layer and whose peripheral portion is diffused with zinc, and 6 is an n-type GaAs cladding layer formed on the multi-quantum well active layer or the superlattice layer, and 6 is an 9 is an n-type GaAs contact layer formed and zinc-diffused in the periphery;
A with a temperature of 200 OA formed on the s contact layer
n of u G e / A u (IQ electrode and reflecting mirror; 10 is the surface and hollow inner surface of the semiconductor substrate, the hollow inner surface of the p-type buffer layer, and the central end face of the p-type Al1GaAs cladding layer); This is a p-side electrode/reflector of A u Z n /A u having a thickness of 2000 A. A reflective layer may be further formed on the light emitting surface of the electrode 10 .

Laser light is oscillated from a hollow portion surrounded by the electrode/reflector.

Next, the reason for configuring the semiconductor laser device in this way will be explained. FIG. 2 is a diagram showing the injection current dependence of the maximum gain in a conventional Fabry-Perot semiconductor laser that emits laser light horizontally to the substrate surface. A single quantum well (hereinafter abbreviated as SQW) laser (L, z-
10 nm (where Lz indicates the quantum well width), the injection current density corresponding to a gain of gmax-5×102 cm-' is about 115, compared to a DH laser. Compared to the (100) SQW laser, the (111) SQW laser can obtain high gain with a lower injection current, and is advantageous for lowering the threshold current of the laser.

Figure 3 shows the conventional Fabry-Perot WGRIN-SCH on (100) and (111) obtained by the inventors' experiments.
(Graded Index 5eparat'e
Confinement Heterostru
ture) SQW (Single Quantum)
3 shows the dependence of the threshold current density (Jth) on the quantum well width (Lz) in a laser (resonator length: 490 μm). For Lz≧70m, (100) and (111)
The difference in J'th above is small, but in the region of Lz < 7 nm, in the (100) SQW laser, J'th increases rapidly, whereas in the (111) SQW laser, J'th almost increases up to Lz 3 nm. Does not increase.

In this laser, the cavity loss, which is the sum of internal loss and mirror loss, is about 30 cm-'. At this level of cavity loss, the quantum well laser on (111) is
0) Above On the other hand, as mentioned above, the cavity length of a surface-emitting laser corresponds to the active layer thickness, so in the SQW structure, as shown in Figure 2, the gain tends to saturate as the injection current increases. It is difficult to obtain sufficient gain for On the other hand, it is effective to increase the gain by multiplexing the quantum wells in the active layer or forming a superlattice, and ideally the saturation gain is 5QWX (the number of quantum wells). (However, the injection current density at the rise of the gain also increases slightly.) At this time, from the characteristics shown in Figure 2, (
111) If the above quantum well is used, the quantum well width can be reduced to 3n.
By making it thin with m<Lz<7nm, (IOC))
It is obvious that it is possible to achieve a lower threshold current than the above quantum well.

Furthermore, in a surface emitting laser, the active layer thickness is in the direction of the cavity, so even if the reflectance of the cavity is 90%, the cavity loss is about 200 to 400 cm-', which is about 10 times larger than that of the conventional Fabry-Perot type.

Therefore, since oscillation occurs in the high current and high gain region shown in FIG. 2, the difference between the (100) and (111) planes becomes larger. Therefore, in a region with such a large loss, even in a region where Lz is even larger than that shown in FIG.
111) provides a lower threshold value than (100).

When Lz≦2 nm, as shown in FIG. 3, a high threshold value is obtained even at low cavity loss, but this is because the wave function seeps out from the quantum well and the confinement effect of the quantum well disappears. The upper limit of Lz is 30 nm below the de Broglie wavelength
You can take the following.

Next, the most preferred embodiment of the method for manufacturing a surface emitting laser device according to the present invention will be described.

1a to 1c are 0.5 degrees (100 degrees) from the plane orientation (111)B as shown in FIG.
) p-type GaAs substrate 1 tilted in the direction (Zn=10”
cm - "This is the Zn impurity concentration of 10 per cm"
This means that there are 18 pieces. (same below) above, MBE
(molecular beam epitaxial growth method) to a thickness of 300 mm.
p-type GaAs buffer layer 2 of layer m (Be=1.0'
8 cm-1> and 3 pm thick p-type A 11°, 7 G
a,), As cladding layer (Be=10" cm-
), 5 nm thick undoped GaAsjl well layer and 5 nm thick undoped A [0,2G a(1,
A multi-quantum well active layer 4 consisting of 200 layers and 199 layers of 6A S barrier layers stacked alternately, and an n-type Ai layer with a thickness of 1 μm.
o, 7Gao, 3AS cladding layer 5 (SL?-10”
cm-3), n with a thickness of 300 layers m! aGaAs contact layer 6 (Si-2X10"cm-') at 720°C
has grown continuously. As already pointed out by the present inventors (Patent Application No. 6O-229382) (111)
For the B-plane, better mirror growth can be obtained by tilting it in the 0.5 degree (100) direction. Next, as shown in FIG. 1b, a 30 μmφ SiN film 7 is formed on the n-type GaAs contact layer 6, and p12A(to) is formed.

7 cao,s Zn diffusion layer 8 is formed up to the As cladding layer 3. The light confinement effect can be obtained by the current confinement due to the Zn diffusion effect and the disordering of the multiple quantum well layer. Using photolithography techniques and a GaAs selective etchant as shown in Figure 1c, p-type All.

, 70a6. @ Ga until As cladding layer 3 is exposed
The central part of the As3 plate is etched to form a resonator, an electrode/reflector 9 (reflectance ~95%) and an electrode/reflector 11 (reflectance ~90%), and then divided into chips. By applying a + voltage to the electrode 10 and a - voltage to the electrode 9 of this chip and flowing a current, laser light can be extracted from the electrode 10 side.

In this example, it was possible to generate a fixed threshold armor type current of 30 mA. For comparison, an element with the same structure was fabricated on a p-type GaAs substrate (Zn-10''cm-'') with (100) plane orientation, and the threshold armor flow was 70m.
A and higher than the examples of the present invention.

Next, as shown in FIG. 1d, the surface orientation (
111) n-type G tilted in 0.5 degree (100) direction from B
On the aAs substrate 1'(n-10" cm-1), M
Using the BE method, a 300 nm thick n-type GaAs buffer layer 2'(Si=1018cm-'') and a 3 μm thick n-type AIO,?Gao,sAs cladding layer 3' (
20 nm thick undoped GaAs quantum well layer 5 nm thick undoped A Lo,
Multi-quantum well active layer 4 consisting of 100 and 99 layers of 2G ao and aA S barrier layers stacked alternately, 1μ thick.
p-type AQ of m. .

7 cao,s As cladding layer 5' (Be=10
A p-type GaAs contact layer 6' (Be-2 x 40"cm-") with a thickness of 300 nm was grown continuously at 720°C.
Lo, t G Jlo, 3 As The central part of the GaAs 1 plate is etched until the cladding layer 3' is exposed to form a resonator. Next, RIB (Reactive
A GaAs contact layer 6' outside the 20 μm diameter area was formed using the ion beam etching method.
and p-type A1g, 70a6. , the As cladding layer 5' is etched. p-type A11O,? Ga6.2
The thickness of the As cladding layer 5' is left at 300 nm to form a ridge type structure. Si in the area other than 20μmφ in the center
N insulating film 7' is formed, and electrode and reflector m8' (reflectance ~
95%), electrode/reflector 9 (reflectance ~90%) is formed, and divided into chips.

In this example, laser oscillation could be obtained with a threshold armor current of 50 mA. For comparison, an element with the same structure was fabricated on an n-type GaAsll1 plate (SimlO''cm-') with (100) plane orientation of 6, and the threshold armor shape was 150.
mA was higher than that of the example of the present invention.

[Effects of the Invention] As described above, according to the present invention, a surface-emitting semiconductor laser probe is formed of a GaAs semiconductor substrate having a plane orientation (111);
G of the superlattice or quantum well structure formed on the substrate
Since the active layer is composed of aAs and AQGaAs, high gain can be obtained, and as a result, a surface-emitting semiconductor laser probe that oscillates in a low threshold armor style can be obtained.

[Brief explanation of the drawing]

1a-c are diagrams showing the manufacturing process of a surface-emitting semiconductor laser device according to one embodiment of the present invention, FIG. 1d is a diagram showing the structure of another embodiment of the present invention, and FIG. FIG. 3 is a diagram showing the injection current dependence of the maximum gain of various conventional Fabry-Perot type lasers, and FIG.
1) Conventional Fabry-Perot GRIN grown on a substrate
FIG. 4 is a diagram showing the quantum well width dependence of the threshold armor current density of a -9CHSQW laser, and FIGS. 4 and 5 are schematic diagrams showing a conventional surface-emitting semiconductor laser device. In the figure, 1 is a p-type aAs substrate, 2 is a p-type GaAs buffer layer, 3 is a p-type A110.7 Ga0.3 AS cladding layer, 4 is a multi-ffi quantum well active layer, and 5 is an n-type Ga
As cositact layer, 6 is n-type GaAs contact layer, 7
is a SiN film, 8 is a Zn diffusion layer, 9 is an electrode/reflector, and 10 is a
is an electrode/reflector, 1' is an n-type GaAs substrate, 2' is an n-type GaAs buffer layer, 3' is an n-type A (1,), 7 ca
o, 3As cladding layer, 5' is p-type Al (1,7Ga
o, a As cladding layer, 6' a p-type GaAs cositact layer, and 8' an electrode/reflector. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] (1) a semiconductor substrate having a plane orientation (111), an active layer having a multi-quantum well structure or a superlattice structure formed on the semiconductor substrate, and a pair of light reflecting layers sandwiching the active layer;
A surface emitting semiconductor laser device comprising the light reflecting layer and a laser radiation path that oscillates laser light in a direction perpendicular to the light reflecting layer.