JPH06177483A - Manufacture of semiconductor laser device - Google Patents

Abstract

PURPOSE:To improve even the confining properties of currents in addition to the reduction of loss resulting from optical absorption by utilizing a substrate with a stepped section constituted of an inclined plane. CONSTITUTION:A process, in which an undoped Ga0.5In0.5P active layer 36 forming double-hetero (AlGaInP/GaInP/AlGaInP) structure while being curved in a shape succeeding a striped mesa 31A, is formed on a P-GaAs substrate 31 with the mesa 31A, is carried out, and a P-Al0.5In0.5P second current block layer 38 is shaped and the whole surface is etched in an anisotropic manner. A process, in which an N-(Al0.7Ga0.3) Pn-side clad layer 37 as the foundation of a section oppositely faced to the curved undoped Ga0.5In0.5P active layer 36 is exposed and the P-Al0.5In0.5P second current block layer 38 is left in other sections, is included.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention manufactures a semiconductor laser device capable of lateral mode control and having a structure suitable for generating visible light in the 0.6 [.mu.m] band, for example. Regarding the improvement of the method.

At present, visible light semiconductor lasers are POS (p
Although it is expected as a light source for improving the performance of optical information processing devices such as point of sales), optical disk devices, and laser printers, the ease of manufacture,
Improvements are needed in terms of low threshold and high efficiency.

[0003]

2. Description of the Related Art Generally, GaAs / AlGaInP based semiconductor lasers have problems in current confinement and lateral mode control as compared with GaAs / AlGaAs based semiconductor lasers. The cause is that it is difficult to grow a material containing Al on a semiconductor layer containing Al because AlGaInP is formed by a vapor phase growth method.
(Buried heterostructure) It is difficult to realize a change in refractive index by embedding a material containing Al like a semiconductor laser.

FIG. 10 is a fragmentary front view showing a lateral mode control type GaAs / AlGaInP semiconductor laser which has been put into practical use (if necessary, Japanese Patent Laid-Open No. 62-2007).
See Japanese Patent Publication No. 86).

In the figure, 1 is a substrate, 2 is an n-side cladding layer, 3 is an undoped active layer, 4 is a p-side first cladding layer,
5 is a current blocking layer, 6 is a p-side second cladding layer, and 7 is p
A side spike prevention layer, 8 is a p-side buffer layer, and 9 is a p-side electrode contact layer.

The following is an example of the main data relating to the parts shown in the figure. Substrate 1 Material: n-GaAs Impurity: Si About n-side clad layer 2 Material: n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P Impurity: About Se undoped active layer 3 Material: Ga _0.5 In _0.5 P p-side First Cladding layer 4 Material: p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P Impurity: Mg About current blocking layer 5 Material: n-GaAs Impurity: About Se p-side second cladding layer 6 Material: p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P Impurity: Mg About p-side spike prevention layer 7 Material: p-Ga _0.5 In _0.5 P Impurity: About Zn p-side buffer layer 8 Material: p-GaAs Impurity: About Zn p-side electrode contact layer 9 Material : P-GaAs Impurity: Zn

As is apparent from FIG. 10, the active layer 3 in this semiconductor laser is flat, and p- (Al
_The p-side second cladding layer 6 made of _0.7 Ga _0.3 ) _0.5 In _0.5 P is formed into a mesa stripe, and the current blocking layer 5 made of n-GaAs is embedded to change the refractive index in the lateral direction. However, in this structure, the current blocking layer 5 filling both sides of the p-side second cladding layer 6 forming the mesa stripe is made of GaAs that absorbs light and has a so-called loss guide structure. Therefore, there is a drawback in that it is difficult to obtain a high quantum efficiency.

In addition, current confinement is performed without depending on the diffusion region, and a double heterostructure is formed on a substrate having a step.
There is known a semiconductor laser having a high quantum efficiency that enables lateral mode control by forming a step in the active layer by forming e: DH) (if necessary, Japanese Patent Application No. 2-15999).
(See No. 7).

FIG. 11 shows a lateral mode control type GaAs / AlGaIn using a stepped substrate composed of a gentle slope.
It is a principal part cutting front view showing a P-type semiconductor laser.

In the figure, 21 is a substrate, 22 is a current blocking layer, 23 is a buffer layer, 24 is a p-side spike prevention layer, 25 is a p-side cladding layer, 26 is an undoped active layer,
Reference numeral 27 denotes an n-side cladding layer, and 28 denotes an n-side electrode contact layer.

The following is an example of main data relating to the respective parts shown in the figure. Substrate 21 Material: p-GaAs Impurity: Zn Current block layer 22 Material: n-GaAs Impurity: Se Buffer layer 23 Material: p-GaAs Impurity: Zn p-side spike prevention layer 24 Material: p- (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P Impurity: About Mg p-side clad layer 25 Material: p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P Impurity: About Mg undoped active layer 26 Material: Ga _0.5 In _0.5 P n-side clad layer 27 Regarding: Material: n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P Impurity: Sen Regarding the n-side electrode contact layer 28 Material: n-GaAs Impurity: Se

Since this semiconductor laser does not have the loss guide structure as in the conventional example described with reference to FIG. 10, the absorption loss of light need not be taken into consideration. However, the current confinement is performed by the current blocking layer 22, and since that portion is separated from the active layer 26, there is a problem in the current confinement property.

[0013]

Generally, when an AlGaInP-based crystal is grown using a substrate having a step,
Liquid phase epitaxy
The y: LPE method makes it difficult to grow crystals, and
For example, metalorganic vapor phase growth (metalorganic)
vapor phase epitaxy: MOVP
E) method or molecular beam epitaxial growth (mole)
A crystal having characteristics required for a semiconductor laser can be obtained only by applying a vapor phase epitaxy method such as a circular beam epitaxy (MBE) method.

Therefore, it was considered that a semiconductor laser using a substrate having a step formed of a gentle slope as shown in FIG. 11 is advantageous, but the semiconductor laser shown in FIG. As described above, there is a problem that the current confinement property is not good, and in particular, p-type GaAs is provided between the p-side spike prevention layer 24 and the surface formed of the mesa top surface of the substrate 21 and the surface of the current block layer 22. When the buffer layer 23 is interposed, the current easily spreads in the p-type GaAs buffer layer 23, the current confinement property becomes extremely poor, and desired performance cannot be obtained. In addition, this p-type G
The aAs buffer layer 23 is indispensable for reducing crystal defects.

The present invention intends to improve the current confinement property while reducing the loss caused by light absorption by utilizing a substrate having a step formed of a gentle slope.

[0016]

According to the present invention, current confinement is performed on both upper and lower sides of an active layer, and a synergistic effect of current confinement, that is, an effect that electrons from above and holes from below attract each other is adopted. The basis is that a layer of GaAs or the like having a low resistivity is not sandwiched between the current block layer and the clad layer.

The above can be realized by forming the n-side cladding layer 27 shown in the conventional example shown in FIG. 11 into a mesa as in the conventional example shown in FIG.
It requires precise alignment technology, and thus there is a problem that the manufacturing yield cannot be increased. However, in the present invention, the above is easily realized by the self-alignment method.

FIG. 1 is a fragmentary front view showing a semiconductor laser device for explaining the principle of the present invention. In the figure,
31 is a substrate, 31A is a stripe mesa, 32 is a first current blocking layer, 33 is a p-side buffer layer, 34 is a p-side spike prevention layer, 35 is a p-side cladding layer, 36 is an undoped active layer, and 37 is an n-side. A clad layer, 38 is a second current blocking layer, and 39 is an n-side electrode contact layer.

The following is an example of the main data relating to the parts shown in the figure. Substrate 31 Material: p-GaAs Impurity: Zn First current blocking layer 32 Material: n-GaAs Impurity: Sep p-side buffer layer 33 Material: p-GaAs Impurity: Zn p-side spike prevention layer 34 Material: p -(Al _0.1 Ga _0.9 ) _0.5 In _0.5 P Impurity: Mg About p-side cladding layer 35 Material: p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P Impurity: About Mg undoped active layer 36 Material: Ga _0.5 In _0.5 P n Side cladding layer 37 Material: n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P Impurity: Se Second current blocking layer 38 Material: p-Al _0.5 In _0.5 P Impurity: Mg n Side electrode contact layer 39 Material: n-GaAs Impurity: Se

In the illustrated semiconductor laser device, since the stripe mesa 31A is formed on the substrate 31, the active layer 36 having the double hetero structure is curved in a shape inheriting the mesa 31A. 11 is different from the conventional example shown in FIG. 11 in that the locally embedded second current blocking layer 38 is provided in a portion other than the stripe on the n-side cladding layer 27 (see FIG. 11) which is the n-side cladding layer. I am only doing it. This structure is extremely simple and can be formed by the self-alignment method, which is very useful.

A portion for generating a pn junction to which a reverse electric field is applied,
That is, the second current blocking layer 38 and the n-side cladding layer 37
Since the energy band gap in the active layer 36 is larger than that in the active layer 36, light absorption does not occur, so that no current flows there. Similarly, since there is no light absorption, the breakdown voltage against a reverse electric field is sufficiently high, and since that portion is continuously grown, there is no regrowth interface, and therefore, the occurrence of defects due to regrowth occurs. Since there is no leakage current due to defects, the current block characteristics are ideal.

In order to etch the second current block layer 38, an etching solution having an etching rate different depending on the plane orientation can be used to remove only the mesa top surface and the mesa side surface. Convenient, and also
Since the effect of providing the second current blocking layer 38 is extremely large, the first current blocking layer 32 may be omitted in some cases.

From the above, in the method of manufacturing a semiconductor laser device according to the present invention, (1) stripe mesas (for example, mesas 41 having a side surface index of (111) B) are used.
Semiconductor substrate having A) (for example, p-type GaAs substrate 41)
Double heterostructure (eg AlGaInP / GaI)
nP / AlGaInP) and forming a curved active layer (eg, undoped GaInP active layer 47) in a shape that inherits the mesa of the stripe, and then forms a current blocking layer (eg, p-type AlInP second current blocking layer 50). ) Is formed and then anisotropic etching is applied to the entire surface to expose a base of a portion facing the active layer curved in a shape inheriting the mesa of the stripe and leave the current blocking layer in the other portion. Or including a process, or

(2) A current blocking layer (for example, n) embedded in the side surface of the mesa in a semiconductor substrate having a stripe mesa.
The step of forming a type GaAs first current blocking layer 43) and then forming a double hetero structure and forming an active layer curved in a shape inheriting the mesa of the stripe is included.

[0025]

By adopting the above-mentioned means, it is possible to enjoy the advantage that there is little loss due to light absorption as in the conventional semiconductor laser device using a substrate having a step formed by a gentle slope. In addition, since the poor current confinement property, which is a drawback of the conventional semiconductor laser device, is solved, it is possible to achieve the objects of low threshold current, high efficiency, high output, etc. You can

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 2 to 8 are front sectional views showing a semiconductor laser device in a process key point for explaining a first embodiment of the present invention. Hereinafter, these figures will be referred to. While explaining in detail. See FIG. 2 2- (1) By applying the sputtering method, p-type GaAs
SiO having a thickness of, for example, 200 nm on the substrate 41
_{2 The} film 42 is formed. The p-type GaAs substrate 41 has a surface index of (001) on its main surface and is doped with Zn to a concentration of about 4 × 10 ¹⁸ [cm ⁻³ ]. 2- (2) By applying a resist process in the lithography technology and a wet etching method using an etchant as a (HF + NH ₄ F) mixed etching solution, SiO
_The p-type GaAs substrate 41 is patterned by patterning the ₂ film 42.
A stripe having a width of 4 [μm] extending in the <110> direction is formed.

See FIG. 3. 3- (1) By applying a wet etching method using an etchant of (H ₂ SO ₄ + H ₂ O ₂ + H ₂ O) mixed etching solution, the SiO ₂ film 42 of the stripe is formed. Mesa etching of the p-type GaAs substrate 41 is performed as a mask to form a mesa 41A having a height of, for example, 1.8 [μm]. The surface index on the side surface of the mesa 41A is (111).
It becomes B.

See FIG. 4. 4- (1) With the SiO ₂ film 42 left, the MOVPE method is applied to form an n-type GaAs first current block layer 43 having a thickness of, for example, 1 [μm]. The n-type GaAs first current blocking layer 43 is doped with Se as an n-type impurity to, for example, about 4 × 10 ¹⁸ [cm ⁻³ ], and the surface index of the gentle slope corresponding to the mesa 41A is ( 41
1) It becomes B.

See FIG. 5 5- (1) The stripe SiO ₂ film 42 used as an etching mask and a growth mask is removed by applying a dipping method using hydrofluoric acid as an etchant.

See FIG. 6 6- (1) By applying the MOVPE method, the p-type GaAs buffer layer 44, the p-type GaInP spike prevention layer 45, p
-Type AlGaInP cladding layer 46, non-doped GaIn
P active layer 47, n-type AlGaInP clad layer 48, n
A type GaInP etching stop layer 49 and a p-type AlInP second current blocking layer 50 are grown. The main data of each semiconductor layer grown here is illustrated as follows. About the buffer layer 44 Impurity: Zn Impurity concentration: 5 × 10 ¹⁶ [cm ⁻³ ] Thickness: 50 [nm] About spike prevention layer 45 Impurity: Zn Impurity concentration: 5 × 10 ¹⁷ [cm ⁻³ ] Thickness: 100 [Nm] About the clad layer 46 Impurity: Mg Impurity concentration: 4 × 10 ¹⁷ [cm ⁻³ ] Thickness: 900 [nm] About the active layer 47 Thickness: 80 [nm] About the clad layer 48 Impurity: Se Impurity concentration: 5 × 10 ¹⁷ [cm ⁻³ ] Thickness: 900 [nm] About Etching Stop Layer 49 Impurity: Se Impurity Concentration: 5 × 10 ¹⁷ [cm ⁻³ ] Thickness: 20 [nm] About Second Current Block Layer 50 Impurity: Mg Impurity concentration: 5 × 10 ¹⁷ [cm ⁻³ ] Thickness: 600 [nm] The growth temperature during this crystal growth is 710 [° C.],
Group 5 / Group 3 ratio is 80 for GaAs and 30 for AlGaInP
0 and 600 for GaInP.

See FIG. 7 7- (1) An anisotropic etching of about 500 [nm] is performed on the p-type AlInP second current blocking layer 50 by applying the dipping method using hydrochloric acid as an etchant. Go to
The p-type AlInP second current block layer 50 is left only in the portion other than the stripe. In this case, since the flat surface other than the stripe and the mesa top surface have the same plane orientation, the etching rates are the same, but the p-type AlInP second current block layer 50 has a slight bend at the mesa top surface. The p-type AlInP second current blocking layer 50 on the top surface of the mesa disappears earlier than the flat surface other than the stripe due to the side etching and the side etching from the side surface of the mesa.

See FIG. 8 8- (1) By applying the MOVPE method, the thickness is, for example, 5
[Μm], and the impurity concentration is, for example, 1 × 10 ¹⁸ [c
m ⁻³ ], n-type GaAs contact layer 51 is formed. 8- (2) After that, the insulating film, n
A side electrode and a p-side electrode are formed and completed.

It goes without saying that the semiconductor laser device thus manufactured functions similarly to the semiconductor laser device described with reference to FIG.

FIG. 9 is a fragmentary front view showing a semiconductor laser device at a process step for explaining a second embodiment of the present invention, which will be described below in detail with reference to this figure. However, the basic manufacturing process is the same as the embodiment described with reference to FIGS.

9- (1) The n-type GaAs substrate 6 is manufactured by using the same means as in the first embodiment.
1 mesa etching is performed, and the stripe mesa 61A has a height extending in the <110> direction of, for example, 1.8 μm and a width at the top surface of, for example, 4 μm.
To form. The n-type GaAs substrate 61 has a surface index of (001) on its main surface and has Si of 4 × 10 4.
^The doping is about ¹⁸ [cm ⁻³ ] and the surface index on the side surface of the mesa 61A is (111) B.

9- (2) After removing the etching mask used for the mesa etching to expose the entire surface of the n-type GaAs substrate 61, the n-type GaA is applied by applying the MOVPE method.
s buffer layer 62, n-type (Al _0.1 Ga _0.9 ) _0.5 In
_0.5 P spike prevention layer 63, n-type (Al _0.4 Ga _0.6 )
_0.5 In _0.5 P spike prevention layer 64, n-type (Al _0.7 G
a _0.3 ) _0.5 In _0.5 P cladding layer 65, non-doped G
a _0.5 In _0.5 P active layer 66, p-type (Al _0.7 G
a _0.3 ) _0.5 In _0.5 P clad layer 67, p-type Ga _0.5
In _0.5 P etching stop and spike prevention layer 68, n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P current blocking layer 6
Growing 9.

The main data of each semiconductor layer grown here is illustrated as follows. About buffer layer 62 Impurity: Se Impurity concentration: 5 × 10 ¹⁷ [cm ⁻³ ] Thickness: 2 [μm] About spike prevention layer 63 Impurity: Se Impurity concentration: 2 × 10 ¹⁷ [cm ⁻³ ] Thickness: 100 [Nm] About spike prevention layer 64 Impurity: Se Impurity concentration: 2 × 10 ¹⁷ [cm ⁻³ ] Thickness: 100 [nm] About clad layer 65 Impurity: Se Impurity concentration: 4 × 10 ¹⁷ [cm ⁻³ ] thickness Thickness: 1.5 [μm] About active layer 66 Thickness: 20 [nm] About cladding layer 67 Impurity: Mg Impurity concentration: 4 × 10 ¹⁷ [cm ⁻³ ] Thickness: 1.5 [μm] Etching stop About spike prevention layer 68 Impurity: Zn Impurity concentration: 1 × 10 ¹⁸ [cm ⁻³ ] Thickness: 10 [nm] About current blocking layer 69 Impurity: Se Impurity concentration: 5 × 10 ¹⁷ [cm ⁻³ ] Thickness: 0.5 [μm] The growth temperature during this crystal growth is 710 [° C.],
Group 5 / Group 3 ratio is 100 for GaAs and 2 for AlGaInP
00 and GaInP are 500.

9- (3) About 0.3 [μm] is applied to the n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P current blocking layer 69 by applying the dipping method using hydrochloric acid as the etchant. Anisotropic etching is performed, and n-type (A
l _0.7 Ga _0.3 ) _0.5 In _0.5 P The current blocking layer 69 is left. Here, the n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P current blocking layer 69 remains only on the flat surface other than the stripes, and the n-type (Al
_The reason why the _0.7 Ga _0.3 ) _0.5 In _0.5 P current blocking layer 69 is removed early is the same as in the first embodiment.

9- (4) By applying the MOVPE method, the thickness is, for example, 5
[Μm], and the impurity concentration is, for example, 2 × 10 ¹⁸ [c
m ⁻³ ], p-type GaAs contact layer 70 is formed.
Incidentally, Zn may be used as the impurity in this case.

9- (5) After that, the insulating film, p
A side electrode and an n-side electrode are formed and completed.

The semiconductor laser device manufactured in this way is n-type GaAs in comparison with the semiconductor laser device manufactured according to the first embodiment described with reference to FIGS.
Although the lower current block layer corresponding to the first current block layer 43 does not exist, even with such a current confinement structure only on the upper side, compared with the conventional structure described with reference to FIG. Is improved enough.

That is, as compared with the conventional semiconductor laser shown in FIG. 11, GaAs having a narrow energy band gap and a small resistivity between the n-type current block layer made of GaAs or AlInP and the p-AlGaInP cladding layer. Since there is no buffer layer or the like, the current spreading to the hetero interface can be sufficiently reduced.

[0043]

In the method of manufacturing a semiconductor laser device according to the present invention, a semiconductor substrate having a stripe mesa is formed with an active layer having a double hetero structure and curved in a shape inheriting the stripe mesa. Then, after forming the current blocking layer, anisotropic etching is performed to expose the base of the portion facing the curved active layer and leave the current blocking layer in the other portion.

By adopting the above structure, it is possible to enjoy the advantage that the loss due to light absorption is small as in the case of the conventional semiconductor laser device using the substrate having the step formed by the gentle slope. In addition, since the poor current confinement property, which is a drawback of the conventional semiconductor laser device, is solved, it is possible to achieve the objects of low threshold current, high efficiency, high output, etc. You can

[Brief description of drawings]

FIG. 1 is a fragmentary front view showing a semiconductor laser device for explaining the principle of the present invention.

FIG. 2 is a fragmentary front view showing a semiconductor laser device in a process essential part for explaining a first embodiment of the present invention.

FIG. 3 is a fragmentary front view showing a semiconductor laser device in a process essential part for explaining a first embodiment of the present invention.

FIG. 4 is a fragmentary front view showing a semiconductor laser device in a process essential part for explaining the first embodiment of the present invention.

FIG. 5 is a fragmentary front view showing a semiconductor laser device in a process essential part for explaining the first embodiment of the present invention.

FIG. 6 is a fragmentary front view showing a semiconductor laser device in a process essential part for explaining the first embodiment of the present invention.

FIG. 7 is a fragmentary front view showing a semiconductor laser device in a process essential part for explaining the first embodiment of the present invention.

FIG. 8 is a fragmentary front view showing a semiconductor laser device in a process essential part for explaining the first embodiment of the present invention.

FIG. 9 is a fragmentary front view showing a semiconductor laser device in a process essential part for explaining a second embodiment of the present invention.

FIG. 10 is a lateral mode control type GaA that has been put into practical use.
It is a principal part cutting front view showing a s / AlGaInP type | system | group semiconductor laser.

FIG. 11 is a fragmentary front view showing a lateral mode control type GaAs / AlGaInP based semiconductor laser using a substrate having a step formed by a gentle slope.

[Explanation of symbols]

 31 substrate 31A stripe mesa 32 first current blocking layer 33 p-side buffer layer 34 p-side spike prevention layer 35 p-side cladding layer 36 undoped active layer 37 n-side cladding layer 38 second current blocking layer 39 n-side electrode contact layer

Claims (2)

[Claims] 1. A step of forming a double hetero structure on a semiconductor substrate having a stripe mesa and forming an active layer curved in a shape inheriting the stripe mesa, and thereafter forming a current block layer and then forming an entire surface. A step of exposing the underlayer of a portion facing the active layer curved in a shape inheriting the mesa of the stripe by leaving anisotropic etching on the underlayer and leaving the current blocking layer in the other portion. A method of manufacturing a semiconductor laser device, comprising: 2. A semiconductor substrate having a stripe mesa is formed with a current blocking layer for embedding the side surface of the mesa, and then a double hetero structure is formed and an active layer curved in a shape inheriting the stripe mesa is formed. A method for manufacturing a semiconductor laser device, comprising the steps of: