JP2664794B2 - Method for manufacturing semiconductor laser device - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor laser device, and more particularly, to a method for manufacturing a semiconductor laser device.
The present invention relates to a method for manufacturing a semiconductor laser device which exhibits excellent temperature characteristics and can continuously oscillate visible light even at room temperature.

(Prior Art) In recent years, there has been a demand for the realization of a semiconductor laser device that oscillates in a short wavelength region for the purpose of enhancing the functions of an optical information processing system.

(Al _Y Ga _Y-1 ) _0.5 In _0.5 P crystal (0 ≦ Y ≦ 1) lattice-matched to a GaAs substrate has attracted attention as a material for a visible light semiconductor laser that emits light having a wavelength in the 600 nm band. I have. Hereinafter, in this specification, unless otherwise specified.
(Al _Y Ga _1-Y ) _0.5 In _0.5 P (0 ≦ Y ≦ 1) is referred to as AlGaInP.

As a method for growing an AlGaInP crystal on a GaAs substrate, a molecular beam epitaxy method (MBE method) is expected in addition to a metal organic chemical vapor deposition method (MOCVD method).

It has been reported that an AlGaInP-based visible light semiconductor laser device fabricated using the MBE method continuously emitted visible light at room temperature (Hayakawa, et. Al. Journal of Crystal Growt).
h 95 (1989) pp. 949).

FIG. 2 shows a cross-sectional view of a conventional AlGaInP-based visible light semiconductor laser device manufactured by the MBE method.

On a first conductivity type GaAs substrate 1, a first conductivity type GaAs buffer layer 2, a first conductivity type GaInP buffer layer 3, a first conductivity type AlGaI
An nP cladding layer 4, a GaInP active layer 5, a second conductivity type AlGaInP second cladding layer 6, and a second conductivity type GaInP layer 20 are stacked in this order from the substrate 1 side.

An insulating silicon nitride film 2 is formed on the second conductivity type GaInP layer 20.
1 are formed, and a stripe-shaped groove having a width of 10 μm reaching the second conductivity type GaInP layer 20 is formed in the silicon nitride film 21.

An electrode 1 is provided on the upper surface of the above-described laminated structure and the back surface of the substrate 1.
5 and 14 are formed.

The semiconductor laser device of FIG. 2 is a gain-guided semiconductor laser device in which an insulating silicon nitride film 21 having stripe-shaped grooves narrows the current.

This semiconductor laser device has an oscillation threshold of 93 mA, and can continuously emit visible light at room temperature.

As shown in FIG. 2, many semiconductor laser devices having an AlGaInP crystal grown by the MBE method are gain guided semiconductor laser devices. However, in the gain guided semiconductor laser device, the horizontal and transverse modes of the laser light are not sufficiently controlled. Therefore, there is a need for a semiconductor laser device having an AlGaInP crystal to develop a refractive index guided semiconductor laser device that is excellent in stabilizing the horizontal and transverse modes of laser light.

FIG. 3 shows a sectional view of a conventional example of a refractive index guided semiconductor laser device.

On a first conductivity type GaAs substrate 1, a first conductivity type GaAs buffer layer 2, a first conductivity type AlGaInP cladding layer 4, a GaInP active layer 5, a second conductivity type AlGaInP second cladding layer 6, a second conductivity type G
The aAs layer 8 and the second conductivity type InGaAs layer 30 are stacked in this order from the substrate 1 side. The GaInP active layer 5, the second conductivity type AlGaInP second cladding layer 6, the second conductivity type GaAs layer 8, and the second conductivity type InGaAs layer 30 are etched into a ridge shape having a width of 10 μm, and a ridge portion is formed. ing. Except for the top surface, the silicon oxide layer
Covered by 31. Electrodes 15 and 14 are formed on the upper surface of the silicon oxide layer 31 and the back surface of the substrate 1.

A current flows between the electrodes 15 and 14 via a region on the upper surface of the ridge where the silicon oxide layer 31 is not formed.

Since the semiconductor laser device of FIG. 3 has the narrow active layer 5 having a width of about 10 μm, it can oscillate in a single horizontal and transverse mode.

(Problems to be Solved by the Invention) However, the above-described conventional technology has the following problems.

In the semiconductor laser device shown in FIG. 3, the heat generated in the active layer 5 is not efficiently dissipated due to the air gaps formed on both sides of the ridge portion formed by etching. is there.

In order to manufacture a semiconductor laser device having a structure with excellent heat dissipation and a double heterostructure composed of AlGaInP crystal lattice-matched to a GaAs substrate, a relatively high thermal conductivity is required on the AlGaInP crystal layer. AlGaAs crystal layer, which is large and has excellent heat dissipation properties (thermal conductivity, 0.11 to 1.1 W / cm-deg)
May be formed by the MBE method.

However, when an AlGaAs crystal layer is formed by MBE on a double heterostructure composed of an AlGaInP crystal layer lattice-matched to a GaAs substrate, if the surface of the AlGaInP crystal layer is contaminated with impurities, the AlGaInP crystal layer is formed on the AlGaInP crystal layer. In addition, there is a problem that an AlGaAs crystal layer having excellent crystallinity cannot be grown.

Such contamination is likely to occur when a refractive index guided semiconductor laser device having a layer having a stripe groove is formed on a double hetero structure made of AlGaInP. This is because in order to form a stripe groove, it is necessary to take out the substrate outside the MBE apparatus and perform a process such as an etching process.

Further, this contamination is caused by the AlGaIP crystal layer and the AlGaAs crystal layer being continuously grown in the MBE apparatus.
After the growth of the nP crystal layer, As and P
Also occurs when switching to molecular beam irradiation.

This is because within a few seconds after the above-mentioned primary crystal growth is stopped, impurities such as oxygen and water vapor in the atmosphere in the MBE apparatus are
This is because the surface of the crystal layer where growth has stopped is contaminated.

Further, when an AlGaAs layer is formed on a double hetero structure by the MBE method, it is necessary to raise the substrate temperature to about 620 ° C. At this temperature, however, when the AlGaInP layer constituting the double heterostructure is exposed,
Alternatively, there is a problem that the surface is deteriorated due to the frequent evaporation of P. If an AlGaAs crystal layer is grown on an AlGaInP crystal layer having such surface deterioration, an AlGaAs crystal layer having excellent crystallinity cannot be obtained.

The present invention has been made in order to solve the above-mentioned problems, and has as its basis a semiconductor laser device having a structure excellent in heat radiation and capable of continuously oscillating visible light at room temperature. It is to provide a manufacturing method of.

(Means for Solving the Problems) According to a method for manufacturing a semiconductor laser device of the present invention, a step of forming a double hetero structure made of AlGaInP crystal on a GaAs substrate, and forming an AlGaAs etching stop layer on the double hetero structure Forming a GaAs light absorbing layer on the AlGaAs etching stop layer, and selectively etching a part of the GaAs light absorbing layer to form the AlGaAs etching stop layer.
Forming a stripe groove having a depth not reaching the GaAs etching stop layer in the GaAs light absorbing layer, and irradiating the GaAs light absorbing layer with an As molecular beam in the MBE apparatus, Elevating the temperature above the temperature at which GaAs evaporates, and evaporating the GaAs layer near the surface of the GaAs light absorbing layer, thereby exposing the surface of the AlGaAs etching stop layer in the stripe groove; In the MBE device, the Ga
Forming an AlGaAs layer on the As light absorbing layer, thereby achieving the above object.

(Example) Hereinafter, the present invention will be described with reference to examples.

FIG. 1 is a sectional view showing a method for manufacturing a semiconductor laser device according to an example of the present invention. In the semiconductor laser device manufactured by the method of the present embodiment, as shown in FIG. 1 (d), a first conductivity type GaAs buffer layer 2 and a first conductivity type GaAs buffer layer 2 are formed on a first conductivity type GaAs substrate 1. GaInP buffer layer 3, first conductivity type AlG
aInP first cladding layer 4, GaInP active layer 5, second conductivity type AlG
aInP second cladding layer 6, Al _0.6 Ga _0.4 As etching stop layer 7, and a GaAs light-absorbing layer 8 are stacked from the substrate 1 side in this order.

In the GaAs light absorbing layer 8, a stripe groove (width: 5 μm) reaching the Al _0.6 Ga _0.4 As etching stop layer 7 is formed.

By filling the stripe groove, the second conductivity type Al
_0.6 Ga _0.4 As regrown cladding layer 9 is composed of GaAs layer 8 and Al _0.6 G
a _0.4 As is formed on the etching stop layer 7. Al
The Al composition ratio of the _0.6 Ga _0.4 As etching stop layer 7 and the Al _0.6 Ga _0.4 As regrown cladding layer 9 exhibits a sufficiently low refractive index necessary to confine the light generated in the active layer 5 in the active layer 5. It is designed to be.

On the second conductivity type Al _0.6 Ga _0.4 As regrown cladding layer 9,
A second conductivity type GaAs cap layer 10 is formed. Electrodes 15 and 14 are formed on the upper surface of the second conductivity type GaAs cap layer 10 and the rear surface of the substrate 1, respectively.

Next, a method for manufacturing the above-described semiconductor laser device will be described with reference to FIGS.

First, as shown in FIG. 1A, a first conductivity type GaAs buffer layer 2 and a first conductivity type Ga
InP buffer layer 3, a first conductivity type AlGaInP first cladding layer 4, GaInP active layer 5, a second conductivity type AlGaInP second clad layer 6, Al _0.6 Ga _0.4 As etching stop layer 7, and a GaAs light-absorbing layer 8, In this order, the substrate was grown by MBE from the substrate 1 side. The substrate temperature during this growth ranges from about 510 ° C. to about 570 ° C.
° C (about 700 ° C for the GaAs layer). In order to maintain the cleanliness of the growth layer, the substrate 1 was not taken out of the MBE apparatus during the step of growing each layer.

Here, the second conductivity type AlGaInP second cladding layer 6 and the second
The total thickness of the conductive type Al _0.6 Ga _0.4 As and the etching stop layer 7 was set to about 2500 ° so that light generated in the active layer 5 leaked to the GaAs light absorbing layer 8.

Thereafter, once the substrate 1 is taken out of the MBE apparatus, G
A portion of the aAs light absorbing layer 8 was selectively etched using the photomask 13 to form a stripe groove so as not to reach the Al _0.6 Ga _0.4 As etching stop layer 7 (FIG. 1 ( b)). Stripe groove bottom and Al
_0.6 Ga _0.4 As between the upper surface of the etching stop layer 7
The GaAs layer having a thickness of about 1000 ° was left.

 Thereafter, the substrate 1 was again introduced into the MBE apparatus.

Next, in the MBE apparatus, the substrate temperature is raised to 720 ° C. while irradiating a sufficient amount of As molecular beam to the substrate 1 whose upper surface is covered with the GaAs layer, and the state is maintained for several minutes. Was performed.

By this step, the GaAs layer began to evaporate from its surface, and the GaAs layer remaining at the bottom of the stripe groove was removed. Thus, at the bottom of the stripe groove,
The surface of the Al _0.6 Ga _0.4 As etching stop layer 7 was exposed. (FIG. 1 (c)).

This Al _0.6 Ga _0.4 As etching stop layer 7 is heated at 720 ° C.
It is a layer made of a thermally stable material in which the evaporation of the constituent elements does not significantly occur even to the extent. Due to the presence of the Al _0.6 Ga _0.4 As etching stop layer 7, the second conductivity type AlGaInP second cladding layer 6, which should normally be generated at about 720 ° C.
Evaporation of In or P was prevented.

As described above, when the stripe grooves formed, by leaving GaAs layer in the stripe groove bottom, without exposing In the atmosphere of the surface of the Al _0.6 Ga _0.4 As etching scan shoulder stop layer 7, Al _0.6 Ga _0.4 As etching The contamination of the surface of the stop layer 7 by the air could be prevented.

Further, the surface of the GaAs layer contaminated by contact with the atmosphere could be cleaned by evaporating the layer near the surface of the GaAs layer by the above-described process performed in the MBE apparatus.

Further, without the Al _0.6 Ga _0.4 As etching stop layer 7, the second conductivity type AlG which becomes remarkable at about 580 ° C. or more is used.
The deterioration of the aInP second cladding layer 6 due to evaporation of In or P could be prevented.

Subsequent to the above process, the substrate temperature is set to about 620 ° C., and the second conductivity type Al _0.6 Ga _0.4 As regrown cladding layer 9 and the second conductivity type GaAs cap layer 10 are sequentially absorbed from the substrate 1 side in this order. A step of growing the layer 8 and the Al _0.6 Ga _0.4 As etching stop layer 7 by MBE was performed.

The Al _0.6 Ga _0.4 As regrowth cladding layer 9 was designed to have a band gap energy value larger than the energy value of light generated in the active layer 5 by adjusting the Al mixed crystal ratio. In this way, light generated in the active layer 5 can be sufficiently bound in the double heterostructure.

The GaAs layers 8 located on both sides of the stripe groove have a bandcap energy smaller than the energy of light generated in the active layer 5 and easily absorb light generated in the active layer 5. However, as described above, the Al _0.6 Ga _0.4 As regrowth cladding layer 9 is designed to have a band gap large enough to bind the light generated in the active layer 5 into the double hetero structure. . Therefore, a refractive index difference is effectively generated inside and outside the stripe groove provided above the double hetero structure, and the horizontal and transverse modes of the laser beam are unified.

By forming electrodes 15 and 14 on the upper surface of the laminated structure thus formed and the back surface of the substrate 1, a gain guided semiconductor laser device shown in FIG. 1 (d) was produced.

The semiconductor laser device manufactured by the method of the present embodiment has a double heterostructure of AlGaInP,
Light having a wavelength of 70 nm was continuously oscillated at room temperature.
This is because the AlGaAs layer having excellent crystallinity is formed on the etching stop layer whose surface is not contaminated, so that the light absorption loss is small and the oscillation threshold is reduced. Further, since this semiconductor laser device has the Al _0.6 Ga _0.4 As etching stop layer 7 and the second conductivity type Al _0.6 Ga _0.4 As regrown cladding layer 9 having relatively excellent thermal conductivity, the active layer The heat generated in 5 was efficiently dissipated outside the semiconductor laser device. For this reason, temperature characteristics superior to those of the semiconductor laser device of FIG. 3 could be obtained.

Since this semiconductor laser device is of a refractive index waveguide type having a stripe groove inside the device, the horizontal and transverse modes of the oscillating laser light are unified.

According to the manufacturing method of this embodiment, the GaAs layer was left on the AlGaAs etching stopper layer 7 when the stripe groove was formed, so that the surface of the AlGaAs etching stopper layer 7 could be prevented from being contaminated by the air.

When growing the AlGaAs layer 9 in the MBE apparatus,
By evaporating the surface layer of the aAs layer, the surface of the underlying crystal layer forming the growth layer could be cleaned. In addition, since the thermally stable AlGaAs etching stopper layer 7 is provided on the AlGaInP second cladding layer 6 even at the temperature at which GaAs is evaporated, deterioration of the AlGaInP second cladding layer 6 due to evaporation is prevented. Was. In this way, the AlGaAs layer 9 filling the stripe groove is formed in an AlGaIn with excellent crystallinity.
It could be formed above the double heterostructure consisting of the P layer.

In the above-mentioned semiconductor laser device, the double hetero structure was composed of the first conductivity type AlGaInP first cladding layer 4, the GaInP active layer 5, and the second conductivity type AlGaInP second cladding layer 6, but other compositions were used. May be constituted by the AlGaInP-based semiconductor layer. For example, as the first and second clad layers 4 and 6, layers made of AlInP ternary mixed crystal may be used. Further, a layer made of AlGaInP quaternary mixed crystal may be used as active layer 5. Further, as the active layer 5, a layer having a quantum well structure or a superlattice structure may be used. Further, a SCH structure may be formed by providing a guide having little gain or absorption loss between the cladding layer and the active layer 5.

(Effect of the Invention) As described above, the semiconductor laser device manufactured by the method of the present invention has the AlGaAs etching stop layer having relatively excellent thermal conductivity and the AlGaAs layer filling the stripe groove. The heat generated in the double heterostructure can be efficiently dissipated outside the semiconductor laser device. Therefore, the semiconductor laser device of the present invention exhibits excellent temperature characteristics and can continuously oscillate visible light even at room temperature.

Further, according to the method of the present invention, since the GaAs layer is left on the AlGaAs etching stopper layer when forming the stripe groove, the surface of the AlGaAs etching stop layer is not contaminated by the air. Further, when the AlGaAs layer is grown in the MBE apparatus, the upper surface of the substrate can be cleaned by evaporating the GaAs layer. In addition, even at the temperature at which the GaAs is evaporated, the thermally stable AlGaAs etching stop layer exists on the AlGaInP second cladding layer, so that In and P evaporate from the AlGaInP layer during the manufacturing process. This prevents the AlGaInP second clad layer from deteriorating. Thus, an AlGaAs layer having excellent crystallinity can be formed.

Therefore, according to the method of the present invention, it is possible to provide a semiconductor laser device having a refractive index guided type and excellent in temperature characteristics and having a low oscillation threshold.

[Brief description of the drawings]

1 (a) to 1 (d) are cross-sectional views showing an embodiment of the present invention.
FIG. 2 is a sectional view showing a conventional example, and FIG. 3 is a sectional view showing another conventional example. 1 GaAs substrate of first conductivity type, 2 GaAs buffer layer of first conductivity type, 3 GaInP buffer layer of 1st conductivity type, 4 1st cladding layer of AlGaInP of 1st conductivity type, 5… GaInP activity layer,
6 second conductive type AlGaInP second cladding layer, 7 Al _0.6
Ga _0.4 As etching stop layer, 8 GaAs light absorption layer,
9 ... second conductivity type Al _0.6 Ga _0.4 As regrown cladding layer, 10 ...
... second conductivity type GaAs cap layer, 13 ... photomask, 1
4, 15 ... electrodes, 20 ... second conductivity type GaInP layer, 21 ... insulating silicon nitride layer, 30 ... second conductivity type InGaAs layer, 31 ...
Silicon oxide layer.

Continuing from the front page (72) Inventor Naohiro Suyama 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation 56) References JP-A-2-116187 (JP, A) JP-A-61-42987 (JP, A)

Claims (1)

(57) [Claims] A step of forming an AlGaInP crystal double heterostructure on a GaAs substrate; a step of forming an AlGaAs etching stop layer on the double heterostructure; and a step of forming GaAs light on the AlGaAs etching stop layer. Forming an absorption layer; and selectively etching a part of the GaAs light absorption layer to form a stripe groove in the GaAs light absorption layer having a depth not reaching the AlGaAs etching stop layer. In the MBE apparatus, while irradiating the GaAs light absorbing layer with an As molecular beam, the temperature of the GaAs substrate is raised to a temperature higher than the temperature at which GaAs evaporates, and the GaAs layer near the surface of the GaAs light absorbing layer is removed. By evaporating the AlGaAs in the stripe groove
Exposing a surface of an etching stop layer; and forming an AlGaAs layer on the GaAs light absorbing layer in the MBE device so as to fill the stripe grooves. Method.