JPH01298786A - Semiconductor laser device and manufacture thereof - Google Patents

Abstract

PURPOSE:To make it possible to easily obtain stable basic transverse mode oscillation and low threshold currents by forming quantum well structure consisting of a flat well layer and a wall layer on a substrate where a stripe groove is formed. CONSTITUTION:A current checking layer 6 is grown on a substrate 1 by the LPE method. Next, a V-shaped groove 7 is formed by photolithography and chemical etching, and its end is pierced through a current checking layer 6. Next, a clad layer 2 and a protective layer 13 are grown by LPE growth, and its surface is planed. This substrate is heated while being applied with As molecular beam inside an MBE device in ultra-high vacuum so as to vaporize the protective layer 13, and then a clad layer 2', a GRIN layer 11, a well layer 10, a GRIN layer 12, a clad layer 4 and a cap layer 5 are grown by the MBE method. And at the surface of the cap layer 5 is formed an n side electrode 8 of Au-Ge-Ni, and on the reverse of the substrate is formed a (p) side electrode 9 of Au-Zn. This GRIN-SCH SQW-VSIS layer is 820nm in wavelength, and the laser oscillates at low threshold currents of 16mA.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor laser device and a method for manufacturing the same, and particularly to a structure that has an extremely low threshold current and is effective for stable fundamental transverse mode oscillation. The present invention relates to a semiconductor laser device and a manufacturing method thereof.

(Prior Art) Conventional semiconductor laser devices generally have a double heterojunction structure in which an active layer with a thickness of approximately 1000°C is sandwiched between cladding layers having a wider forbidden band width.

The threshold current density of such a semiconductor laser device is at least about 1000 A/cm2. In addition, when a striped structure is applied, the threshold current is generally 30 to 50
It is mA.

Recently, semiconductor laser devices have been developed that have a quantum well structure in which a thin active layer (referred to as a "well layer") with a thickness of 200 Å or less is sandwiched between cladding layers or barrier layers having a wider forbidden band width. The threshold current density of such a laser device is very small, less than 200 A/cm m2, and
When a striped structure is applied, the threshold current is 10m
A and below have been achieved.

Currently, double heterojunction structures are commonly grown by liquid phase epitaxial (LPE) methods.

However, since it is difficult to controllably grow thin films of 200 Å or less using the LPE method, quantum well structures can be grown using the molecular beam epitaxial (MBE) method or metal organic chemical vapor deposition (MOV) method.
PE) method. Incidentally, one of the features of the LPE method is that even if growth is performed on a substrate with grooves or steps formed therein, it has the effect of filling the grooves or steps and forming a flat growth surface. It will be done.

One of the semiconductor laser devices that performs transverse mode control using the effect of the LPE method is called a SIS laser. A schematic cross-sectional configuration of an example of this laser is shown in FIG. 6, and an outline of the manufacturing method of this VSIS laser will be described. p-
Carrier concentration I x 10"c m on GaAs substrate 1
−1 or more n −Ga As current blocking layer 6 is 0.5
It is epitaxially grown to a thickness of ~1 μm, and a V-shaped stripe groove 7 is formed from the surface of the current blocking layer 6 so that its tip reaches the p-GaAs substrate 1.

On this surface, a p-GaAlAs cladding layer 2, a GaAlAs active layer 3, an n-GaAlAs
As cladding layer 4 and n-GaAs cap layer 5
A double heterojunction structure consisting of is grown.

Reference numerals 8 and 9 indicate an n-side electrode and an n-side electrode, respectively.

This VS I S laser uses the inclined side surface G of the V-shaped groove 7.
Until the middle of , the laser oscillation light generated in the active layer 3 becomes n-
The laser light is absorbed by the GaAs current blocking layer 6 and is focused to the center of the V-shaped groove 7 by the effective refractive index distribution formed thereby. Furthermore, since the current is constricted by the current blocking layer 6 so that it flows only within the V-shaped groove 7, the VSIS laser can easily achieve stable fundamental transverse mode oscillation and low threshold current due to the effect of less wasted current. This is an excellent semiconductor laser device that can be obtained.

(Problem to be Solved by the Invention) When trying to perform epitaxial growth on a substrate with grooves or steps as in the above-mentioned VSIS laser manufacturing method using the MBE method or MOVPE method, growth along the grooves or steps on the substrate occurs. occur, and it is impossible to fill them up and make a flat surface as in the LPE method. Therefore, it has been thought that VSIS lasers cannot be manufactured using the MOVPE method or the like. Therefore, conventionally, VSIS lasers have been limited to double hetero-refining.

The present invention uses a quantum well! vsr by applying structure
The purpose of this invention is to provide a novel structure of an S laser and a method for manufacturing the same.

(Means for Solving the Problems) A semiconductor laser device of the present invention includes a semiconductor substrate in which a stripe groove is formed, a semiconductor layer formed on the semiconductor substrate that fills the stripe groove, and a semiconductor layer that is larger than the semiconductor layer. A quantum well structure formed on the semiconductor layer, comprising at least one well layer having a narrow band gap, and a barrier layer sandwiching the well layer and having a band gap wider than the well layer; The striped grooves form an effective index waveguide, thereby achieving the above objective.

In the semiconductor laser device of the present invention, the effective refractive index waveguide is formed by absorbing laser light on the outside of the stripe groove or on the inclined side surface of the stripe groove.

Current blocking layers having a conductivity type opposite to that of the semiconductor substrate may be provided on both sides of the stripe groove to form internal stripes 3 for current confinement.

The quantum well structure on both sides of the stripe is left in a mesa shape with a width narrower than the width of the current distribution spreading on both sides of the stripe groove, and the removed portion is formed into a strip with a forbidden band width smaller than that of the well layer. It may also be configured to be buried with a wide semiconductor layer.

Further, the method for manufacturing a semiconductor laser device of the present invention includes a first epitaxial process in which a semiconductor layer is grown on a semiconductor substrate in which striped grooves are formed so that the striped grooves are completely buried and the surface is flat. and a second epitaxial step of growing on the semiconductor layer a quantum well structure having at least one well layer and a barrier layer sandwiching the well layer and having a bandgap wider than the well layer. This achieves the above objectives.

According to the manufacturing method of the present invention, first, a flat growth surface is formed by filling grooves and steps in a first epitaxial step, and a quantum well structure is grown thereon in a second epitaxial step.

The first epitaxial step can be performed by a liquid phase method, and the second epitaxial step can be performed by a molecular beam method or an organometallic vapor phase method.

(Example) The invention will now be described with reference to examples.

FIG. 1A shows a cross-sectional view of an embodiment of the present invention, and this first embodiment is a VSIS laser to which a quantum well structure is applied. Note that this laser is named QW-VSIS laser. The quantum well structure includes 5QW (single quantum well), MQ
W (multiple quantum well), etc. In addition, in this example, G
RI N-3CH (isolated refractive index isolated confinement hetero)
applied the structure.

Figure 2 shows the manufacturing process of Niko (7) GRIN-3CH5QW-VSIS laser. First, the carrier concentration is I
An n-GaAs current blocking layer 6 with a carrier concentration of 3Xl018c m-3 is formed on a p-GaAs substrate 1 with a thickness of 10"c rrr' to a thickness of about 0.8 μm by LPE method (or MBE method or MOVPE method). (Fig. 2(a)
'), Next, a 4 μm wide Cr) V-shaped PIt7 was formed by photolithography and chemical etching,
The tip was made to penetrate the n-GaAs current blocker N6 (Fig. 2(b)), and then P-
The GaAs cladding layer 2 and the GaAs protective layer 13 are grown so that their surfaces are flat (FIG. 2(C)). The thickness of the p-clad layer 2 was approximately 0.1 μm (1000 μm) outside the V-shaped groove 7, and the thickness of the protective layer 13 was approximately 500 μm. This substrate is placed in an ultra-high vacuum MBE apparatus, and the GaAs protective layer 13 is evaporated by heating the substrate while applying an As molecular beam, and then p-Ga (15A 1
6.5As cladding layer 2' (100 layers thick), Gap
-1A 1 , As (z=0.5~0.25) GRI
N layer 11 layers thickness 11,000 people), Ga2. g5A I
8,65A s well layer 10 (thickness 60 people), Ga+-,
AI, As (z=0.25-0.5) GRIN layer 12
layer thickness 21,000 people), n Ga[1,+, AI6,5
An AS cladding layer 4 (thickness 1 μm) and an n-GaAs cap layer 5 (thickness 0°5 μm) were grown by the MBE method (Fig. 2(d)), and the surface of the cap layer 5 was coated with A.
n of u-Ge-Ni (Fig. 1A) to form the till electrode 8 and the p-side type 8i!9 of Au-Zn on the back surface of the substrate 1, the current blocking layer 6 of this embodiment and the cladding. An energy band (condactylane band) diagram of the portion between the layer 4 and the layer 4 is shown in FIG. 1B.

The GRIN-3CH5QW-VSIS laser of this example oscillated at a wavelength of 820 nm and a low threshold current of 16 mA. This is less than half the threshold current of conventional VSIS lasers. Further, in this example, like the conventional VSIS laser having a double heterostructure, laser oscillation was performed in a stable fundamental transverse mode up to a high output of 40 mW.

The cross-sectional structure of the second embodiment is shown in FIG. 3. This embodiment has the structure of the above-described first embodiment shown in FIG. -GaAs current blocking layer 6
After forming the mesa M by etching until it reaches , a high-resistance n--GaAlAs layer 14 and a p-GaAlAs layer 14 having a larger forbidden band width than the well layer 10 are formed by the LPE method.
．． It is filled with an As layer 15 and an n-GaAs layer 16.

In this example, laser oscillation was performed with a low threshold current of 8 mA.

This causes the current to spread to the outside of the figure-7 groove 7 and the well layer 10.
This is because carriers diffusing to the outside of the figure-7 groove 7 are blocked by the high-resistance buried layer 14, so that the injected current can be used for laser oscillation without waste.

In each of the above embodiments, after evaporating the GaAs protective layer 13 with an MBE device, the p-Ga, 5A I,
A 5A s cladding layer 2' was grown, and the third example shown in FIG. 4A was produced by the MBE method as follows in order to improve the crystallinity and crystal surface flatness of the MBE grown layer. That is, after the GaAs protective layer 13 is evaporated, the thickness is 20
AlAs layer 2a (3 layers) and GaAs2 thickness 20
A multilayer film 2'° was grown in which 2' (2 layers) were alternately laminated.

Then a ag, A I 11. llA si 1
7 (thickness 20 people>, Ga+-, AI, As (z=0
．． 5-0.25) GRIN layer 11 layer thickness 11000 people),
Ga9. ．． 5AI11.85As well layer 10 (thickness 60
Human, ), Ga, -, AI, As (z=0.25~0
．． 5>GRIN layer 12 layers thickness 21000 people), n G
a @, sA 1 (1,5A S cladding layer 4 (thickness 1 μm), and n-GaAs cap layer 5 (thickness 0.
The GR of this third embodiment is shown in FIG. The /lN-3CH5QW-VSrS laser oscillated with a lower threshold current (14 mA) than the first example due to the effect of the multilayer M2°.

Furthermore, as shown in FIG. 5, after forming mesa M, L
A high resistance n--GaAlAs layer 14 and a p-GaAlAs layer 15 having a larger forbidden band width than the well layer 10 are formed by the PE method.
, and a fourth example laser having a configuration in which the well layer 10 was buried with the n-GaAs layer 16 was manufactured. This fourth
The example oscillated laser with a threshold current as low as 7 mA.

Further, the present invention is not limited to the above-mentioned GaAs-GaAlAs semiconductor laser device, but
Electronic devices other than semiconductor laser devices can also be applied as long as they are nGaAsP-based, GaA, 5-AIGaInP-based, etc., and have grooves or steps formed in the substrate.

(Effects of the Invention) As described above, the semiconductor laser device of the present invention has a quantum well structure consisting of a flat well layer and a barrier layer on a substrate in which striped grooves are formed. This is a practically very useful semiconductor laser device that can easily obtain transverse mode oscillation and low threshold current.

In addition, the method for manufacturing the semiconductor laser device of the present invention includes the LPE method, which can flatten the growth surface by filling the stripe grooves and steps formed on the substrate, and the MB method, which can grow a thin film.
This method utilizes the respective features of the E method and the MOVPE method, and allows a transverse mode control type quantum well laser to be easily manufactured.

Figure 1A is a sectional view of the first embodiment of the semiconductor laser device of the present invention, Figure 1B is an energy band diagram of the first embodiment,
Figures 2(a) to (d) are diagrams showing the manufacturing process of the first embodiment, Figure 3 is a sectional view of the second embodiment, Figure 4A is a sectional view of the third embodiment, and Figure 4A is a sectional view of the third embodiment. 4B is an energy band diagram of the third embodiment, FIG. 5 is a sectional view of the fourth embodiment, and FIG. 6 is a sectional view of the conventional example.

DESCRIPTION OF SYMBOLS 1...GaAs substrate, 2.2', 4...Clad layer, 2'°...Multilayer film, 6...Current blocking layer, 7...
・V-shaped groove, 8.9... Electrode, 10... Well layer, 1
1.12...GRIN layer, 13...protective layer, 14-
n--GaAl As layer, 15...p-GaA IA
s layer, 16 = -n -GaAs layer, 17-Ga85
AI+! 1.5AS layer, L-...laser light, M...
Mesa.

that's all

Claims (1)

[Claims] 1. A semiconductor substrate on which stripe grooves are formed, a semiconductor layer formed on the semiconductor substrate that fills the stripe grooves, and at least one semiconductor layer having a bandgap narrower than the semiconductor layer. and a quantum well structure formed on the semiconductor layer, which has a barrier layer sandwiching the well layer and having a bandgap wider than the well layer, and the stripe groove forms an effective refractive index waveguide. A semiconductor laser device being formed. 2. A first epitaxial step of growing a semiconductor layer on the semiconductor substrate in which the stripe grooves are formed so that the stripe grooves are completely buried and the surface is flat;
and a second epitaxial step of growing a quantum well structure having at least one well layer and a barrier layer sandwiching the well layer and having a bandgap wider than the well layer on the semiconductor layer. Method of manufacturing the device.