JPH09326531A - Semiconductor laser and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a GaInP/AlGaInP semiconductor laser with which high output can be obtained. SOLUTION: A hydrogenated amorphous silicon film 40, which is formed by an ECRCVD device, is used for the high reflection coating film of a GaInP/ AlGaInP semiconductor laser. The hydrogenated amorphous silicon film 401 formed by the ECRCVD device has a high refractive index, a high reflection coating film can be formed thereon, and optical breakdown is not generated on the coating film because absorption coefficient is low. Accordingly, a high output semiconductor laser can be accomplished.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser and a manufacturing method.

[0002]

2. Description of the Related Art GaInP / AlGaInP semiconductor lasers have an oscillation wavelength of 630 to 690 nm, which is shorter than the oscillation wavelength of AlGaAs semiconductor lasers, which is 780 nm. However, as a pickup light source for a recording / playback type optical disc system, a high output is required at the time of recording on a disc,
Higher output power of GaInP / AlGaInP based semiconductor lasers is required.

In a high-power semiconductor laser, a high-reflection coating film is formed on one end facet of a cavity and a low-reflection coating film is formed on the other end facet to form an asymmetric coat. The electric field strength distribution inside the resonator at this time is shown in FIG. A high electric field distribution can be obtained on the low reflection side, and high-power laser light can be obtained.

Amorphous silicon is used as the material of the high reflection coating film. This is because amorphous silicon has a high refractive index, and a coating film having a high reflectance can be obtained by combining it with a material having a low refractive index.

Conventionally, the coating film of an AlGaAs semiconductor laser has been deposited using a magnetron sputtering device (see Japanese Patent Laid-Open No. 63-200589). A coating film having a high reflectance is formed by alternately laminating an alumina film and an amorphous silicon film on the cavity end face.

In the case of the magnetron sputtering apparatus, silicon is used as the target and argon is used as the plasma gas. Although the magnetron sputtering apparatus is inexpensive and easy to handle, the amorphous silicon film is deposited between the discharge electrodes of the plasma while the amorphous silicon film 303 is formed on the substrate 304, as shown in FIG.
, The deposited substrate itself is sputtered, resulting in large plasma damage and poor flatness, resulting in low reflectance.

Further, the amorphous silicon film formed by the magnetron sputtering apparatus is amorphous and has many dangling bonds (unbonded hands). Since these are not terminated, many interband levels exist. As shown in 2, the absorption coefficient is large. Therefore, when a coating film is formed using amorphous silicon produced by a magnetron sputtering apparatus, the absorption coefficient is large and the laser beam is absorbed to generate heat.

There is also a method of forming an amorphous silicon film while introducing hydrogen gas into a magnetron sputtering device in order to reduce the absorption coefficient, but since the bond between silicon and hydrogen is weak and hydrogen is easily desorbed from the film, The refractive index changes and the film lacks reliability.

[0009]

As described above, in the deposition of the amorphous silicon film by the conventional magnetron sputtering apparatus, plasma is damaged during the deposition, the laser element is deteriorated, and the deposited amorphous silicon film is also sputtered. The flatness of the film is lacking.

In the case of the asymmetric coating, as shown in FIG. 6, the low reflection coating film side has a high electric field due to the high electric field, so that the optical density is high and optical damage should occur on the low reflection coating film side. If the absorption coefficient of the amorphous silicon film used for is high, optical damage is likely to occur on the high reflection coating film side. GaInP / AlGaInP-based semiconductor lasers have shorter wavelengths than AlGaAs-based semiconductor lasers, and the absorption coefficient tends to increase.If the oscillation wavelength of the semiconductor laser is shortened, the absorption coefficient further increases, limiting the maximum optical output. I will end up.

Further, even if hydrogen is introduced at the time of film deposition in a magnetron sputtering apparatus in order to reduce the absorption coefficient, hydrogen is easily desorbed and the refractive index changes, so that the reflectance of the coating film changes and reliability is improved. There is a problem with sex.

Therefore, in the present invention, GaInP / AlGaIn using a hydrogenated amorphous silicon film having a good flatness, little damage, no hydrogen desorption, and a small absorption coefficient applicable as a coating film of a GaInP / AlGaInP semiconductor laser is used.
An object is to provide a P-based semiconductor laser and a manufacturing method.

[0013]

In order to achieve the above object, the semiconductor laser and manufacturing method of the present invention form hydrogenated amorphous silicon on the end face. Especially EC
Preferably, R plasma is used to form the hydrogenated amorphous silicon. Silane gas (SinH2n
+2) is used to form a film having a high refractive index and a small absorption coefficient. As a result, it is possible to increase the output of the semiconductor laser.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below.

To deposit the coating film, electron cyclotron resonance plasma CVD (Electron Cyclotro) shown in FIG. 1 is used.
n Resonance Plasma CVD) equipment is used.

In the apparatus shown in FIG. 1, a semiconductor laser 103 cut into a bar shape from a wafer is placed on a sample holder 102 so that one end face thereof is irradiated with plasma. First, in order to remove the water adhering to the end face and improve the adhesion of the coating film, the sample holder 102 is heated by, for example, 140 ° C. for 10 minutes by a heating mechanism. When a SiO2 film is formed as the first insulator of the rear surface coating film 403 shown in FIG. 4, for example, monosilane (SiH4) is used.
At a flow rate of 5 sccm and oxygen at a flow rate of 10 sccm, and the SiO2 film 402 is
40Å Accumulate. Next, hydrogenated amorphous silicon 401 which is a second insulator is formed over the first insulator. For example, monosilane (SiH4) is used as the reaction gas, and argon (Ar) is used as the plasma gas. Monosilane is used because the number of H atoms bonded to Si atoms is the largest among silane gases and hydrogenated amorphous silicon 401 is easily deposited. While introducing, for example, monosilane at a flow rate of 2 sccm from the reaction gas inlet 104 and argon at a flow rate of 10 sccm from the plasma gas inlet 107, the waveguide 108
Then, a microwave of 2.45 GHz is introduced, a magnetic field is formed by the exciting coil 106, plasma is generated in the plasma chamber 105 by electron cyclotron resonance, and hydrogenated amorphous silicon 401 is deposited by 550 Å. Highly reflective rear surface coating film 403 due to the combination of the first insulator and the second insulator.
Is formed.

The front coating film 404 is formed on the sample holder 102 so that the other end face is irradiated with plasma. First, in order to remove the water adhering to the end surface and improve the adhesion of the coating film, the sample holder 10
The heating mechanism provided in 2 heats at 140 ° C. for 10 minutes, for example. Next, a SiO 2 film or a SiN film is formed so as to have an optimum reflectance to form a front coating film 404. The laser light 405 is emitted from the front side.

E for the formation of hydrogenated amorphous silicon 401
The reason for using CR plasma is that the ionization rate of argon is high, the deposition rate is high because it accelerates the decomposition of monosilane, and the hydrogenated amorphous silicon film 401 can be efficiently deposited. Therefore, the supply amount of monosilane, which is a reaction gas, is small, particles are hardly generated in the deposition chamber, and the maintenance of the apparatus is also small.

Note that helium (He) may be used as the plasma gas instead of argon. Since argon has a high ionization rate, it has a high decomposition efficiency for silane gas and a high deposition rate, but depending on the plasma conditions, plasma is likely to be generated locally and the deposition rate may have an in-plane distribution. Helium has a lower ionization rate than argon and is slightly inferior in the decomposition efficiency of silane gas, but since the plasma is uniformly generated, the in-plane distribution of the deposition rate is good. Argon and helium may be used properly depending on the application.

Since the coating film acts as a reflection mirror, flatness is important. When the flatness of the hydrogenated amorphous silicon film according to the present invention was examined, as shown in FIG. 3, the hydrogenated amorphous silicon 301 formed on the substrate 302 was extremely flat. Since ECR plasma has a strong directivity and reactive species are supplied vertically to the substrate,
Hydrogenated amorphous silicon is evenly deposited to obtain a flat film. Further, since the ECR plasma does not cause damage and does not sputter the deposited hydrogenated amorphous silicon film, the flatness as deposited can be maintained.

The deposited hydrogenated amorphous silicon film is amorphous because it is deposited at room temperature to about 300 ° C. However, since monosilane is used as a raw material, dangling bonds (unbonded hands) terminate with H (hydrogen). Has been done. Therefore, the level density between bands can be reduced, and the absorption coefficient can be suppressed low.

FIG. 2 shows the wavelength dependence of the absorption coefficient of hydrogenated amorphous silicon used in the present invention and amorphous silicon prepared by a magnetron sputtering apparatus.
For example, the absorption coefficient at a wavelength of 680 nm is 3 × 10 2 cm −1 for hydrogenated amorphous silicon and 5 × 10 4 cm −1 for non-hydrogenated amorphous silicon. Hydrogenated amorphous silicon has an absorption coefficient lower than that of non-hydrogenated amorphous silicon by two digits or more, and when applied to a coating film of a GaInP / AlGaInP-based semiconductor laser, heat generation due to absorption of laser light is small and optical damage does not occur. The maximum light output is improved.

Further, the hatched area in FIG. 2 indicates a range where optical breakdown does not occur in hydrogenated amorphous silicon used for the high reflection coating film. When a hydrogenated amorphous silicon film having a low hydrogen content and an absorption coefficient of 3000 cm-1 or higher is used, optical damage occurs in the hydrogenated amorphous silicon film due to absorption of laser light. Also,
When a hydrogenated amorphous silicon film having a high hydrogen content and an absorption coefficient of 3000 cm-1 or less is used, optical damage does not occur in the hydrogenated amorphous silicon film.

Therefore, when a hydrogenated amorphous silicon film is used as the highly reflective coating film of a GaInP / AlGaInP semiconductor laser, it is necessary that the absorption coefficient be 3000 cm-1 or less.

In the semiconductor laser using the hydrogenated amorphous silicon film having a low absorption coefficient, since the heat generation due to the absorption of the laser light is small, the hydrogenated amorphous silicon film is not damaged and the output can be increased.

FIG. 5 shows the light output characteristics when hydrogenated amorphous silicon is used as a highly reflective coating film of a semiconductor laser. Since the laser light is not absorbed and the coating film is not damaged, the light output is increased.

The high-reflection coating film may be formed by forming a laminated film in two or more cycles. In that case, a coating film with higher reflection can be obtained.

Further, when the ECR plasma is used, the hydrogenated amorphous silicon film can be deposited on the end face of the resonator with low damage, so that the deterioration of the laser device can be reduced and the reliability of the life test and the like is improved.

[0029]

As described above, according to the present invention, when a hydrogenated amorphous silicon film is used as a highly reflective coating film of a GaInP / AlGaInP based semiconductor laser, a coating film having a high reflectance and a low absorption coefficient is formed. Because you can
It is possible to realize a highly reliable semiconductor laser having a large optical output.

[Brief description of drawings]

[Fig. 1] Structural sectional view of ECRCVD system

FIG. 2 is a diagram showing an absorption coefficient of hydrogenated amorphous silicon.

FIG. 3 is a diagram showing flatness of hydrogenated amorphous silicon.

FIG. 4 is a perspective view showing the configuration of a rear coating film.

FIG. 5: Optical output characteristic diagram of GaInP / AlGaInP semiconductor laser

FIG. 6 is a field intensity distribution diagram inside the resonator when an asymmetric coat is formed.

[Explanation of symbols]

 101 deposition chamber 102 sample holder 103 semiconductor laser 104 reaction gas introduction port 105 plasma chamber 106 excitation coil 107 plasma gas introduction port 108 waveguide 301 hydrogenated amorphous silicon film 302 substrate 303 amorphous silicon film 304 substrate 401 hydrogenated amorphous silicon 402 SiO2 403 Rear coating film 404 Front coat film 405 Laser light

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Takamori 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Toshiya Fukuhisa, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. 72) Inventor Masaya Manano 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (6)

[Claims] 1. A semiconductor laser comprising an active layer formed on a substrate and a pair of clad layers sandwiching the active layer, wherein at least one of the cavity end faces of the semiconductor laser has silicon as a constituent element. A semiconductor laser formed by a structure in which a first insulator containing a and a hydrogenated amorphous silicon which is a second insulator are alternately laminated for at least one cycle or more. 2. The absorption coefficient of the second insulator, hydrogenated amorphous silicon, is 3000 cm −1 or less.
The semiconductor laser described in 1. 3. The first insulator is SiO2, SiON, or SiN.
The semiconductor laser according to claim 2, wherein 4. The semiconductor laser according to claim 1, 2 or 3, wherein the semiconductor laser is a GaInP / AlGaInP system. 5. A step of depositing a first insulator containing silicon as a constituent element on at least one of the end faces of the resonator, and hydrogenated amorphous silicon which is a second insulator on the first insulator. And a step of depositing Ga
Manufacturing method of InP / AlGaInP semiconductor laser. 6. The method for manufacturing a GaInP / AlGaInP semiconductor laser according to claim 5, wherein the first insulator and the second insulator are formed by using electron cyclotron resonance plasma.