JPH0423481A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To prevent COD breakage, to restrain temperature of a chip and to enable carrier confinement, etc., with a simple means by forming a first clad layer of a p-type compound semiconductor material whose refraction factor is smaller than that of a second clad layer and whose energy band gap is larger than that of the second clad layer. CONSTITUTION:A material having a small refraction factor (n) and a large energy band gap E9 is used for a clad layer 13 at the side near a substrate 11, and the layer 13 is made thin to allow an active layer 14 to be close to the substrate 11. A material having a large refraction factor (n) and a small energy band gap E9 is used for a guide layer 15, which is made thick. Therefore, light confinement is carried out in the guide layer 15 and a clad layer 16 which are formed thick and the clad layer 13 which is formed thin transmits heat generated in the active layer 14 to the substrate 11 effectively. Thereby, it is possible to prevent COD breakage, to restrain temperature rise of a chip and to ensure carrier confinement, etc., with an extremely simple means.

Description

[Detailed Description of the Invention] [Summary] Regarding the improvement of a semiconductor laser whose constituent material is Aj2GalnP, it is possible to prevent COD destruction, suppress chip temperature rise, ensure carrier confinement, etc. by extremely simple means. For the purpose of this, the method includes an active layer sandwiched between a first cladding layer provided on the side closer to the GaAs substrate and a second cladding layer provided on the side closer to the surface, and the active layer is attached to the GaAs substrate. The first cladding layer is formed thinner than the second cladding layer in order to reduce the leakage of light from the active layer to the first cladding layer, and also to reduce the leakage of light from the active layer to the second cladding layer. In order to increase seepage, the first cladding layer is made of a p-type compound semiconductor material that has a smaller refractive index and a larger energy band gap than the second cladding layer.

[Industrial application field]

The present invention relates to improvements in semiconductor lasers whose constituent materials are AP and Ga1nP.

Generally, AlGaInP semiconductor lasers are, for example,
It oscillates in the short wavelength band of 0.6 [μm] and emits red light,
It is attracting attention as a light source for high-density optical discs, and its high output is expected.

[Prior Art] FIG. 8 shows a cutaway front view of essential parts for explaining a current typical Aj2Ga InP semiconductor laser.

In the figure, 1 is n-type C, aAS substrate, 2 is n-type AnG
alnP cladding layer, 3 is InGaP active layer, 4 is p
A type Aj2GalnP cladding layer, 5 an n-type GaAs buried layer, and 6 a p-type GaAs electrode contact layer, respectively.

This semiconductor laser uses an n-type Af using a quaternary mixed crystal.
fiGalnP cladding layer 2 and p-type A/! The A1 composition in the GaInP cladding layer 4 is the same.

[Problem to be solved by the invention]

AI explained about Figure 8! As mentioned above, higher output power is required for Ga I nP semiconductor lasers, and the obstacles to higher output are:
C0D (catastro) at the end facet of a semiconductor laser.
physically optical damage
) destruction and temperature rise of the semiconductor laser chip.

In a semiconductor laser in which the upper and lower cladding layers have the same composition as shown in FIG. 8, measures are taken to make the InGaP active layer 3 thinner in order to avoid COD destruction. Furthermore, since the light obtained by this InGaP active layer 3 has a wavelength that is absorbed by GaAs, oscillation will be impossible unless the light absorption in the substrate 1 or the electrode contact layer 6 is reduced. Layers 2 and 4 must be formed thickly. However, AnGalnP, which is the constituent material of these cladding layers 2 and 4, has a thermal resistance that is 17 to 20 times higher than that of InP, for example.
If it is formed thickly, the heat generated in the active layer 3 cannot be effectively dissipated.

Therefore, LOC (large optical cavity)
ity) structure, the cladding layer has an asymmetrical structure with respect to the active layer, and is divided into two layers: a thick layer that allows a large amount of light to seep out, and a thin layer that allows a small amount of light to seep out, thereby preventing COD destruction. A configuration has been considered in which the active layer is placed close to a substrate made of GaAs or the like to achieve good heat dissipation.

In this case, it is necessary to lower the Al composition in one of the cladding layers, but in the Aj2Ga I nP semiconductor laser, there is no problem on the valence band side, but the energy band discontinuity value on the conduction band side Since ΔEc is as small as 200 [meV], if the composition of Aff in the p-side cladding layer is reduced to narrow the energy band gap E9, there is a problem in that sufficient electron confinement cannot be ensured.

The present invention attempts to achieve prevention of COD destruction, suppression of chip temperature rise, and ensuring carrier confinement by extremely simple means.

[Means for Solving the Problems] Figure 1 is a diagram showing the field distribution for explaining the present invention in detail, with the vertical axis representing the thickness and the horizontal axis representing the light intensity. It is.

In the figure, 11 is the substrate, 12 is the buffer layer, 13 is the cladding layer, 14 is the active layer, 15 is the guide layer, 16 is the cladding layer, 18 is the electrode contact layer, and 20 is the distribution of light. .

In the illustrated configuration, the substrate 11 is made of a material with good heat dissipation, such as GaAs. Cladding layer 1 on the side closer to the substrate 11
3 has a small refractive index n (and
Using a material with a large energy band gap E9,
Furthermore, the active layer 14 is a thin comb so that it approaches the substrate 11. The active layer 14 uses InGaP. Guide layer 1
5 is made of a material having a large refractive index n and a small energy band gap E9, such as Aj2GalnP, and is thick. The cladding layer 16 is made of, for example, A
I! , the Ga composition of Ga1nP is reduced to 0 or closer to O. Furthermore, as mentioned above, A/2GalnP
The problem with electron confinement in semiconductor lasers is that
The cause is that the energy band discontinuity value ΔEc on the conduction band side is small, so when trying to deal with this problem,
Naturally, the conductivity type of the cladding layer having a large energy band gap and therefore a high AP composition ratio is p-type.

In this way, as is clear from the light distribution 20,
The leakage of light generated in the active layer 14 is transmitted to the cladding layer 13.
It is small for the guide layer 15, and it becomes large for the guide layer 15. Even if the p-side cladding layer is made 0.4 [μm], about half the thickness of a semiconductor laser made using conventional technology,
The total optical loss determined by light absorption to G'a A s is -3
, 2 (cm-'). Therefore, the guide layer 15 and cladding layer 16 formed thickly confine light, and the cladding layer 13 formed thinly functions to efficiently transfer heat generated in the active layer 14 to the substrate 11. becomes possible.

What is important here is that in conventional semiconductor lasers, the thin cladding layer mentioned above for heat dissipation is usually not provided on the side where the heat sink is attached, that is, on the surface side with respect to the active layer. Although it has been thought that A, j
In semiconductor lasers made of 2GaInP-based materials, the thermal resistance of the cladding layer is 17 to 20 times higher than that of InP, so GaAs, which is the substrate and has low thermal resistance, can serve as a sufficient heat sink for heat dissipation. Therefore, even if the cladding layer on the substrate side with respect to the active layer is made thinner, the same effect as that of making the cladding layer on the surface side with respect to the active layer thinner can be obtained.

As described above, in the semiconductor laser of the present invention,
A first cladding layer (for example, p-type AffiTnP) provided on the side closer to the GaAs substrate (for example, the GaAs substrate 11)
cladding layer 13) and a second cladding layer provided on the side closer to the surface (for example, n-type CAI!, o, s Gao,
s) An active layer (
For example, the first cladding layer is formed to be thinner than the second cladding layer in order to bring the active layer closer to the GaAs substrate. The first cladding layer has a smaller refractive index than the second cladding layer, and a lower energy level than the second cladding layer.・P-type compound semiconductor material with a large band gap (for example, the first cladding layer is Affil)
nP, the second cladding layer is (Aj2o, 5Gao, 5
)I nP).

[Effect]

By adopting the above method, even if the active layer is made thinner to prevent COD destruction, the cladding layer provided on the side closer to the substrate is made thinner, so heat dissipation is performed well, and the heat dissipation from the substrate is improved. Since the cladding layer on the near side is made of a compound semiconductor material with a larger energy hand gap and a lower refractive index than the cladding layer on the front side, light generated in the active layer is transmitted through the thick layer on the front side. A large amount seeps out into the cladding layer, and a small amount seeps out into the thin cladding layer on the substrate side. Therefore, a substrate made of GaAs or the same <
The rate at which light is absorbed by the electrode contact layer made of GaAs, that is, the loss of light, can be kept low, and the cladding is made of a compound semiconductor material with a large energy band gap and a small refractive index. Since the conductivity type of the layer is p-type, the confinement of carriers (electrons) is also good.

〔Example〕

FIG. 2 shows a cutaway front view of essential parts of an embodiment of the present invention.

In the figure, 21 is a substrate, 22 is a buffer layer, 23 is a hetero barrier buffer layer, 24 is a cladding layer, 25 is an active layer, 26 is a guide layer, 27 is a cladding layer, 28 is a cap layer, 30 is a Buried layer, 31 is electrode contact layer, 32
3 represents an n-side electrode, and 33 represents a p-side electrode. It goes without saying that the guide layer 26 can be regarded as part of the cladding layer.

Examples of main data regarding each part shown are as follows.

■ About the substrate 2I Material: p-type GaAs Impurity: Zn Impurity concentration: I Type GaAs Impurity: Zn Impurity concentration: 1×1018 [CI[l-3] Thickness: 0.
1 (μm) Refractive index: 3.79 Light absorption coefficient α nee 2X10' [cm publication] ■ About the hetero barrier buffer layer 23 Material: p-type InGa P Impurity: Zn Impurity concentration: I X 1018 (CTI+-3) Thickness: 0.1 (μm) Refractive index n: 3.55 Light absorption coefficient α knee 8 x 10" (published by cm) ■ About cladding layer 24 Material: p-type Aj21nP Impurity: Zn Impurity concentration: 3 x 10" (cr+r3) Thickness: 0.4Cμm] Refractive index n: 3.22 Light absorption coefficient α: O (cm-') ■ About active layer 25 Material: InGaP Thickness: 0.07Cμm] Refractive index n: 3.55 Light absorption coefficient α: O (cm-') (When operating as an active layer) ■ About the guide layer 26 Material: n-type (Aρo, s Gao, s ) InP impurity: Si Impurity concentration: 3 x 10'7 (cm-3) thickness:
0.6 (μm) (Strive portion) Refractive index n: a, as Light absorption coefficient α: 0 (cm-') ■ About the cladding layer 27 Material: n-type AI! , InP Impurity: Si Impurity concentration: 7 x 1017 (cm-3) Thickness: 0
．． 4Cμm] Refractive index n: 3.22 Light absorption coefficient α: O (Cm-') ■ About the cap layer 28 Material: n-type GaAs Impurity: Si Impurity concentration = 1 x 10'8 [cTI+-3] Thickness: 30
0 [In] Refractive index n: 3.79 Light absorption coefficient α knee 2X10'(cm-')■ Regarding the buried layer 30 Material: p-type GaAs Impurity: Zn Impurity concentration: I X 10'9 (cm-3) Thickness difference:
Q, 9 [μm] (flat portion) ■ About the electrode contact layer 31 Material: n-type GaAs Impurity: Si Impurity concentration: I x 10” (cm-”1N) Size: 1.0 (μm) Refractive index n: 3. 79 Light absorption coefficient α knee 2X10'(cm-') ■ Regarding the n-side electrode 32 Material: AuGe/Au Thickness: 500 (people) / 3000 (in) Creation technique: Vacuum evaporation method ■ About the n-side electrode 33 Material: A u / Z n / A u thickness: 300
(Person)/3601:In)/2360 (In)This semiconductor laser had the following: Oscillation wavelength: 670 (nm) Mode: TE Overall optical loss: -3.2 (cm-').

3 to 7 are cutaway front views of main parts of the semiconductor laser at key points in the process to explain the case of manufacturing the embodiment described in FIG. 2, and these figures will be referred to below. I will explain it in detail.

■ See Figure 3. Metalorganic chemical vapor deposition (metalorganic chemical vapor deposition)
chemical vapor deposit
By applying the ion:MOCVD) method, the substrate 2
1, a buffer layer 22, a hetero barrier buffer layer 23, a cladding layer 24, an active layer 25, a guide layer 26, a cladding layer 27, and a cap layer 28 are grown.

In this case, the temperature of the substrate 21 was set to 690 ("C).

Various data regarding each semiconductor layer in this case are as posted earlier (the same applies hereinafter). In the embodiment described with reference to FIG. 2, the constituent material of the guide layer 26 is (AI!,
O, S Gao, s ) InP, which is (AI2x Ga+-x ) o, s I no, s
As P, the X value may be selected in the range of 0.4 to 0.6.

■ See Figure 4 chemical vapor deposition (chemical vapor deposition)

By applying a ur deposition (CVD) method, a thickness of, for example, 2000 nm is deposited on the cap layer 28.
A silicon dioxide film 29 is grown.

This silicon dioxide film 29 is used as a mask for mesa etching the underlying layer and as a mask for selective growth, so it goes without saying that other materials may be used as long as they can fulfill their functions. be.

By applying a resist process in photolithography technology and a wet etching method using buffered hydrofluoric acid as an etchant, the silicon dioxide film 29 is formed with a width of 5.5 [μm] and an axis <110> of the underlying crystal. pattern into stripes extending in the direction.

By applying a wet etching method, the underlying mesa is etched using the striped silicon dioxide film 29 as a mask, and a mesa extending from the cap 28 to a part of the guide layer 26 is formed.

In this case, the guide layer 26 has a thickness of 0.2 at the portion other than the mesa.
Etching is carried out under time control so that approximately [μm] remains.

In addition, as an etchant, NH4O is used for GaAs.
H: H, O,: H20 = 2:1:10 mixture,
Aj2GalnP and AI! , HCl for InP
, : A mixed solution of H and O=1:1 can be used, respectively.

Referring to FIG. 5, by applying the MOCVD method, a buried layer 30 is grown using the striped silicon dioxide film 29 as a mask.

At this time, the temperature of the substrate 21 was set to 650 ("C).

Usually, in the A/jGalnP system, eight! Regrowth on the layer containing a large amount of AI! It is said that it is difficult to achieve good growth due to the oxidation of
As in this embodiment, the bottom of the ridge is placed in the guide layer 26.
That is, since the composition of A1 is made to exist in a layer smaller than that of other cladding layers, it is easy to perform good regrowth from there, and a high-quality buried layer 30 can be obtained.

In this way, when the composition of Affi is asymmetric between the upper and lower layers sandwiching the active layer, A! The side where the composition of
In this case, it is advantageous in manufacturing to form a ridge on the n side.

Referring to FIG. 6, the silicon dioxide film 29 used as a growth and etching mask is removed by applying a dipping method using hydrofluoric acid as the etchant.

Referring to FIG. 7, an electrode contact layer 31 is grown by applying the MOCVD method.

In this case as well, the temperature of the substrate 21 is 650 ('C).

The n-side electrode 32 is formed by applying a vacuum evaporation method, and if necessary, after polishing the back surface of the substrate 21, the same (
The p-side electrode 33 is formed by applying a vacuum evaporation method.

The semiconductor laser of the example described with reference to FIGS. 2 to 7 had the following: Oscillation wavelength: 670 (nm) Mode: TE Overall optical loss: -3.2 (cm-').

〔Effect of the invention〕

The semiconductor laser according to the present invention includes an active layer sandwiched between a first cladding layer provided on the side closer to the substrate and a second cladding layer provided on the side closer to the surface; The cladding layer is formed thinner than the second cladding layer, and the first cladding layer is made of a p-type compound semiconductor material having a smaller refractive index and a larger energy band gap than the second cladding layer. Consisting of

By adopting the above structure, even if the active layer is made thin in order to prevent COD destruction, the cladding layer provided on the side closer to the substrate is made thin, so heat dissipation is performed well, and the substrate The cladding layer on the side closer to the surface is composed of a compound semiconductor material with a larger energy band gap and lower refractive index than the cladding layer on the surface side, so the light generated in the active layer is transmitted to the surface side. There is a large amount of seepage into the thick cladding layer, and a small amount of seepage into the thin cladding layer on the substrate side.
The rate at which light is absorbed by the electrode contact layer made of yaAs, that is, the loss of light, can be kept low, and furthermore, the cladding is made of a compound semiconductor material with a large energy band gap and a small refractive index. Since the conductivity type of the layer is p-type, the confinement of carriers (electrons) is also good.

[Brief explanation of the drawing]

Fig. 1 is a line diagram showing field distribution for explaining the present invention in detail, Fig. 2 is a cutaway front view of essential parts of an embodiment of the present invention, and Figs. 3 to 7 are shown in Fig. 2. FIG. 8 is a cut-away front view of the main part of a semiconductor laser at key points in the process for explaining the case of manufacturing the example.
1 is a front view showing a main part cut away for explaining an nP-based semiconductor laser. In the figure, 11 is the substrate, 12 is the buffer layer, 13 is the cladding layer, 14 is the active layer, 15 is the guide layer, 16 is the cladding layer, 18 is the electrode contact layer, and 20 is the distribution of light. . Patent applicant: Fujitsu Ltd. Representative Patent Attorney Shoji Aitani

Claims (1)

[Scope of Claims] An active layer sandwiched between a first cladding layer provided on the side closer to the GaAs substrate and a second cladding layer provided on the side closer to the surface, the active layer being sandwiched between the GaAs substrate and the second cladding layer provided on the side closer to the surface. The first cladding layer is formed thinner than the second cladding layer in order to approach the active layer. In order to increase light seepage, the first cladding layer is made of a p-type compound semiconductor material that has a smaller refractive index and a larger energy band gap than the second cladding layer. Characteristic AlGaIn lattice matched to GaAs substrate
P-based semiconductor laser.