JP3078004B2 - Manufacturing method of semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing a semiconductor laser device.

(Prior art) A laser is a light wave of a single frequency, and its straightness and
Due to its features such as good coherence and narrow spectrum width, its use in various fields as a light source for optical information processing and optical measurement has been attracting attention.

In recent years, red semiconductor lasers using indium gallium aluminum phosphide (InGaAlP) based materials having an oscillation wavelength in the 0.6 μm band have been commercialized, and are expected as light sources for high-density optical disc devices, laser beam printers, and bar code readers. ing. For such applications, it is necessary to narrow the laser beam to a minute spot, and it is important that stable transverse mode oscillation can be obtained and that the astigmatic difference of the laser beam is small.

In order to realize such characteristics, it is necessary that the semiconductor laser be a refractive index guided type transverse mode control type semiconductor laser.
As this type of semiconductor laser, there is an embedded semiconductor laser using an InGaAlP-based material as an active layer.

Conventionally, such a semiconductor laser has been formed as follows.

First, as shown in FIG. 5A, for example, an n-type In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P film having a thickness of 1 μm is formed on an n-type GaAs substrate 51.
A cladding layer 52, an In _0.5 Ga _0.5 P active layer 53 having a thickness of 40 nm, a p-type In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P cladding layer 54 having a thickness of 1 μm,
200 nm thick p-type In _0.5 Ga _0.5 P conduction facilitating layer 55, 50 n thick
After sequentially forming the m-type p-type GaAs contact layer 56, a striped silicon oxide film 57 is formed.

Thereafter, as shown in FIG. 5 (b), etching is performed using the striped silicon oxide film 57 as a mask to form a striped double hetero structure having a width W.

Then, as shown in FIG. 5 (c), a high-resistance In _0.5
(Ga _0.3 Al _0.7 ) _0.5 P buried layer 58 is formed.

Further, as shown in FIG. 5 (d), after the silicon oxide film 57 used as a mask is removed by etching,
A p-type GaAs contact layer 59 of μm is formed, an AuZn / Au electrode 61 is formed as an electrode on the side opposite to the substrate, and an AuGe / Au electrode 62 is formed as a substrate-side electrode.

However, in such a method, as shown in FIG. 5 (b), a stripe-shaped double hetero structure is formed by etching, so that a part of the active layer is exposed to the air. The exposed portion may be oxidized or contaminated with impurities to form an interface state. The interface state acts as a non-radiative recombination center to lower the luminous efficiency, and causes a deterioration in characteristics such as an increase in leak current through the interface level.

That is, the oscillation threshold current increases, the temperature rises during operation,
There is a problem that a drive current is increased and a semiconductor laser having high reliability and good transmission characteristics cannot be obtained.

Further, during this etching, there is a problem that side etching occurs and the reproducibility and controllability of the stripe width W are not so good, and therefore, the aspect ratio is low,
There is a problem that stable fundamental transverse mode oscillation with small astigmatism cannot be obtained.

Further, in this method, two etching steps are required in the growth process of each layer, so that there is a problem that the crystal growth step must be performed three times.

(Problems to be Solved by the Invention) As described above, when a buried type semiconductor laser is manufactured by a method using a conventional etching process, the active layer must be exposed to the air after etching. An interface level is formed due to oxidation or impurity contamination of the portion, and this interface level causes a reduction in luminous efficiency and an increase in leak current, which has a problem of adversely affecting laser oscillation characteristics and reliability.

Further, according to this method, since the stripe width of the double hetero structure is determined by etching, the controllability of the stripe width is poor, the aspect ratio becomes unstable, and the fundamental transverse mode oscillation with small astigmatic difference can be obtained with good reproducibility. There was a problem that it was not possible.

Furthermore, there is a problem that productivity is poor because the crystal growth step must be performed a plurality of times.

The present invention has been made in view of the above circumstances, and has an object to provide a buried semiconductor laser having good oscillation characteristics, a small astigmatism, and a low aspect ratio without controlling an etching process with good controllability and productivity. I do.

[Configuration of the invention]

(Means for Solving the Problems) In the present invention, after forming a dielectric thin film pattern having a stripe-shaped opening on the substrate surface, a compound semiconductor is sequentially formed on the substrate surface exposed at the opening of the dielectric thin film pattern. The layer is selectively grown, and a double hetero structure in which the active layer is surrounded by a cladding layer is formed in a stripe shape. Subsequently, the side of the double hetero structure parallel to the stripe direction has a bandgap wider than the active layer. The active layer is buried by growing a high resistance layer made of a semiconductor material having a large refractive index and a small refractive index in the lateral direction.

(Function) The present invention controls the growth temperature and the raw material supply ratio of the group V element to the group III element (hereinafter referred to as the V / III ratio), thereby enabling the growth in the vertical direction and the lateral direction with respect to the substrate. This is based on the point that the speed ratio can be controlled.

That is, in the method of the present invention, first, a dielectric mask is formed on a semiconductor substrate while leaving a stripe-shaped opening having a width W, the growth temperature is increased, and the V / III ratio is set to a lower value. Growth is promoted, and a double hetero structure is formed on the semiconductor substrate exposed at the opening.

Then, the growth temperature is lowered in the apparatus as it is, and V / III
A high ratio is set to promote lateral growth, and a high-resistance buried layer is laterally grown to bury the active layer on the side surface parallel to the stripe direction of the stripe-shaped double heterostructure. Therefore, after the active layer is formed, the buried structure can be formed in the growth apparatus without exposing the side surface of the active layer to the atmosphere, and the interface between the active layer and the buried layer is formed by oxidation or impurity contamination. Level formation can be avoided.

In addition, since the stripe width of the double hetero structure can be controlled by the opening width of the mask, the controllability of the transverse mode characteristics of laser oscillation is improved as compared with the conventional method in which side etching is easily generated and variation is easily generated. Very good.

Thus, a semiconductor laser having a low aspect ratio and a small astigmatic difference can be formed with good reproducibility.

Further, since an etching step is not required during the growth, crystal growth can be performed continuously, and the productivity is extremely high.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Example 1 First, as shown in FIG. 1A, for example, (111) n
A silicon oxide film 12 is formed on a type GaAs substrate 11 with a stripe extending in the [112] direction and leaving a stripe-shaped opening h having an opening width of 2 μm.

Then, an organic compound containing a group III element and a hydrogen compound containing a group V element are supplied at a substrate temperature of 840 ° C. and a gas ratio such that the V / III ratio becomes 50 by metal organic chemical vapor deposition (MOCVD). As shown in FIG. 1 (b), a 1 μm thick n-type
In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P clad layer 13, 40 nm thick In
_0.5 Ga _0.5 P active layer 14, p-type In _0.5 (Ga _0.3 Al
_0.7 ) _0.5 P cladding layer 15 is selectively grown vertically in the opening to form a stripe-shaped double hetero structure having a rectangular cross section.

After that, the substrate temperature was 700 ° C and the V / III ratio was 600
An organic compound containing a group III element and a hydrogen compound containing a group V element are supplied at a gas ratio such that the two side surfaces of the stripe-shaped double heterostructure are formed as shown in FIG.
μm undoped or chromium-doped high-resistance In
_{A 0.5} (Ga _0.3 Al _0.7 ) _0.5 P buried layer 16 is formed.

Subsequently, the substrate temperature was again 840 ° C and the V / III ratio was
An organic compound containing a group III element and a hydrogen compound containing a group V element are supplied at a gas ratio of 50, and FIG. 1 (d)
As shown in FIG. 7, a 50-nm-thick p-type In _0.5 Ga _0.5 P conduction facilitating layer 17 and a 200-nm-thick p-type GaAs contact layer 18 are sequentially laminated.

Finally, as shown in FIG. 1 (e), a Ti / Pt / Au electrode 19 is formed as an electrode on the side opposite to the substrate, and an AuGe / Au electrode 20 is formed as a substrate-side electrode.

The semiconductor laser thus formed has more stable oscillation characteristics and operating current than the semiconductor laser obtained by the conventional etching process shown in FIGS. 5 (a) to 5 (e). Was extremely small.

In addition, there was little deterioration during operation and the reliability was high.

Furthermore, a stable lateral mode control type semiconductor laser having a low aspect ratio and a small astigmatic difference was obtained.

Furthermore, crystal growth can be performed with the substrate installed in the CVD apparatus only by switching between the gas ratio (V / III ratio) and the substrate temperature, and the productivity is greatly improved.

Embodiment 2 Next, a second embodiment of the present invention will be described.

In this example, the surface is flattened to facilitate mounting on a heat sink or the like.

A silicon oxide film 12 is formed on an n-type GaAs substrate 11 while leaving a stripe-shaped opening h exactly in the same manner as in the process of the first embodiment shown in FIGS. 1 (a) to 1 (d). , N-type In
_{A 0.5} (Ga _0.3 Al _0.7 ) _0.5 P cladding layer 13, an In _0.5 Ga _0.5 P active layer 14, and a P-type In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P cladding layer 15 are selectively grown vertically in this opening. At the very least, after forming a striped double heterostructure with a rectangular cross section, the substrate temperature was subsequently set to 700 ° C and the V / III ratio was set to 600, followed by lateral growth, and undoped or chromium-doped on the side of the striped double heterostructure. High resistance In _0.5 (G
a _0.3 Al _0.7 ) _0.5 P buried layer 16 is formed, followed by vertical growth again at a substrate temperature of 840 ° C. and a V / III ratio of 50 to form a p-type In _0.5 Ga _0.5 P conduction facilitating layer 17. , P-type Ga
As contact layers 18 are sequentially laminated.

However, the thickness of the p-type GaAs contact layer 18 during the process was 0.3
μm.

Then, as shown in FIG. 2 (a), a silicon oxide film
12 is removed by etching.

Thereafter, as shown in FIG.
A p-type GaAs contact layer 21 is formed so as to embed the stripe-shaped double hetero structure so that the / III ratio becomes 400, and a silicon oxide film having an opening H in the upper layer.
12, and finally, a Ti / Pt / Au electrode 22 is formed as an electrode on the opposite side to the substrate in the same manner as in Example 1.
An AuGe / Au electrode 23 is formed as a substrate-side electrode.

In the semiconductor laser structure thus formed, the oscillation characteristics are further improved.

In addition, since the surface is flattened and the distance between the electrode, the active layer, and the substrate is sufficiently large, mounting on a heat sink with the surface opposite to the substrate facing down is facilitated.

Embodiment 3 Next, a third embodiment of the present invention will be described. In this example, after all the growth in the vertical direction is performed, the growth in the horizontal direction is performed.

As shown in FIG. 3 (a), in exactly the same manner as in the process of the first embodiment shown in FIGS. 1 (a) and 1 (b), n
A silicon oxide film 12 is formed on a GaAs substrate 11 while leaving a stripe-shaped opening h, and n-type In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P
Cladding layer 13, In _0.5 Ga _0.5 P active layer 14, P-type In _0.5 (Ga
_{A 0.3} Al _0.7 ) _0.5 P cladding layer 15 is selectively vertically grown in the opening to form a stripe-shaped double hetero structure, and subsequently, a p-type In _0.5 Ga _0.5 P conduction facilitating layer 31 is formed. A p-type GaAs contact layer 32 is sequentially formed.

Thereafter, as shown in FIG.
° C., V / III ratio to form the lateral undoped or chromium-doped on the side surfaces of the stripe-shaped double heterostructure perform growth of the high-resistance _{In 0.5 (Ga 0.3 Al 0.7)} 0.5 P buried layer 33 as 600.

Finally, as in the first embodiment, a Ti / Pt / Au electrode 34 is formed as an electrode on the opposite side of the substrate, and an AuGe / Au electrode 35 is formed as a substrate-side electrode.

With the semiconductor laser structure formed in this way, the same oscillation characteristics as in the first embodiment can be obtained.

Further, in this method, the number of times of changing the setting of the growth temperature in the vapor phase growth is only one degree, and the productivity is further improved.

Embodiment 4 Next, a fourth embodiment of the present invention will be described.

In this example, after all growth in the vertical direction is performed in the same manner as in the third embodiment, growth is performed in the horizontal direction, and the surface is flattened in the same manner as in the second embodiment to facilitate mounting on a heat sink or the like. .

3A and 3B, a silicon oxide film 12 is formed on an n-type GaAs substrate 11 while leaving a stripe-shaped opening h in the same manner as in the third embodiment. n-type In
_{A 0.5} (Ga _0.3 Al _0.7 ) _0.5 P cladding layer 13, an In _0.5 Ga _0.5 P active layer 14, and a P-type In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P cladding layer 15 are selectively grown vertically in this opening. After forming a stripe-shaped double hetero structure,
Type In _0.5 Ga _0.5 P conduction facilitating layer 31, p-type GaAs contact layer
32 sequentially laminated form, further, a substrate temperature of 700 ° C., V / III ratio lateral performs growth this striped double hetero In sides of undoped or chromium-doped high resistance structure _0.5 as 600 (Ga _0.3 Al _0.7 A _0.5 P buried layer 33 is formed.

Then, as shown in FIG. 4 (a), a silicon oxide film
12 is removed by etching.

Thereafter, as shown in FIG.
/ III ratio of 400, and p-type GaAs contact layer 21
Is formed, and a silicon oxide film 12 having an opening H is formed thereon. Finally, a Ti / Pt / Au electrode 22 is formed as an electrode on the side opposite to the substrate in the same manner as in Example 1. Then, an AuGe / Au electrode 23 is formed as a substrate-side electrode.

In the semiconductor laser structure formed in this manner, the same oscillation characteristics and reliability as those of the second embodiment can be obtained.

Further, in this method, the number of times of changing the setting of the growth temperature in the vapor phase growth is one less than in the method of Embodiment 2, and the productivity is further improved.

In each of the above embodiments, n-type GaAs was used as the substrate.
Although the substrate is used, it goes without saying that a p-type substrate may be used. In that case, the conductivity type of each layer may be reversed. At this time, it is necessary to form the energization facilitating layer on the substrate side.

The composition ratio, impurity concentration, and thickness of each semiconductor layer are not limited to the examples and can be appropriately changed as needed, and can be applied to a semiconductor laser using a material other than the InGaAlP-based material. It goes without saying that it is possible.
However, In _0.5 (Ga _1-x Al _x ) _0.5 P of the cladding layer and In _0.5 (Ga _1-y Al _y ) _0.5 P of the active layer can be implemented in all cases where x> y.

In addition, the present invention can be variously modified and implemented without departing from the spirit thereof.

〔effect〕

As described above, according to the method of the present invention, a buried type semiconductor laser can be formed without introducing an etching process during growth, and the buried layer and the buried layer can be formed as compared with a method using a conventional etching process. It is possible to greatly suppress the generation of the interface state generated at the interface with the active layer.

Further, since the number of times of growth can be reduced, productivity is improved.

Also, since the stripe width of the double hetero structure is determined by the opening width of the silicon oxide mask, the controllability of the transverse mode characteristics of laser oscillation is improved, and a semiconductor laser with a small aspect ratio and a small astigmatic difference can be obtained with good reproducibility. It becomes possible.

[Brief description of the drawings]

FIGS. 1 (a) to 1 (e) are views showing a manufacturing process of a semiconductor laser according to a first embodiment of the present invention, and FIGS. 2 (a) to 2 (b) are views showing a process of the present invention. FIGS. 3 (a) to 3 (c) are diagrams showing a manufacturing process of the semiconductor laser according to the second embodiment, FIGS. 3 (a) to 3 (c) are diagrams showing a manufacturing process of the semiconductor laser according to the third embodiment of the present invention, and FIGS. 4A to 4B are diagrams showing a manufacturing process of a semiconductor laser according to a fourth embodiment of the present invention, and FIG.
FIG. 5 to FIG. 5 (d) are views showing a manufacturing process of a conventional semiconductor laser. 11 n-type GaAs substrate, 12 silicon oxide film, h stripe-shaped opening, 13 n-type In _0.5 (Ga _0.3 Al _0.7 ) _0.5
P cladding layer, 14 ... In _0.5 Ga _0.5 P active layer, 15 ... P type
In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P clad layer, 16 ...
In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P buried layer, 17 ... p-type In
_0.5 Ga _0.5 P conduction facilitating layer, 18 p-type GaAs contact layer, 19 Ti / Pt / Au electrode, 20 AuGe / Au electrode, 21
p-type GaAs contact layer, 22 ... TiGe / Au electrode, 23 ... AuG
e / Au electrode, 31 ... p-type In _0.5 Ga _0.5 P conduction facilitating layer, 32 ...
... p-type GaAs contact layer, 33 ... High resistance In _0.5 (Ga _0.3
Al _0.7 ) _0.5 P buried layer, 34 ... Ti / Pt / Au electrode, 35 ...
AuGe / Au electrode, 51 n-type GaAs substrate, 52 n-type In
_0.5 (Ga _0.3 Al _0.7 ) _0.5 P clad layer, 53 …… In _0.5 Ga _0.5
P active layer, 54: p-type In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P cladding layer, 55: p-type In _0.5 Ga _0.5 P conduction facilitating layer, 56: p
Type GaAs contact layer, 57: silicon oxide film, 58: high resistance In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P buried layer, 59: p-type
GaAs contact layer, 60 ... AuZn / Au electrode, 61 ... AuGe / A
u.

────────────────────────────────────────────────── ─── Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01S 5/00-5/50 JICST file (JOIS)

Claims (1)

(57) [Claims] 1. A dielectric film forming step of forming a dielectric thin film pattern having a stripe-shaped opening on a substrate surface, and a compound semiconductor layer is sequentially grown on the substrate surface exposed at the opening of the dielectric thin film pattern. A selective growth step of forming a double hetero structure in which the active layer is sandwiched between cladding layers in a stripe shape, and subsequently, on a side surface parallel to the stripe direction of the double hetero structure, the forbidden band width is larger than the active layer and A lateral growth step of laterally growing a high resistance layer made of a semiconductor material having a small refractive index to bury an active layer, and an electrode forming step of forming an electrode on the cladding layer side opposite to the substrate side and the substrate side. A method for manufacturing a semiconductor laser, comprising: