JPH05315711A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To provide a high power semiconductor laser with reduced deterioration in an end surface processing process of the semiconductor laser by drying the end surface of the laser in a vapor of multiplying sulfated ammonium after a process where the end surface is dipped in a solution of the multiplying sulfated ammonium, and further depositing a protective film on the end surface of the laser. CONSTITUTION:A resonance mirror is formed on an end surface of a semiconductor laser and is then dipped in a solution of (NH4)2S or (NH4)2SX. The end surface is successively dried in a vapor of (NH4)2S or (NH4)2SX at 20 deg.C or higher to deposit a protective film at the temperature of 30 deg.C during deposition or lower.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating an end face for increasing the output of a semiconductor laser.

[0002]

2. Description of the Related Art As an end surface treatment of a semiconductor laser, (N
H4) A method of soaking in 2SX at room temperature for several minutes has been reported (for example, Extented, Abstract, Off, Sent, First, Conference, On, Solid, State, Durable, and Anti-Materials). (Extended Abstract of the 21st Conference on Soli
d State Devices and Materials) 1989, p337).

A resonator mirror of a semiconductor laser is usually formed by cleavage of a crystal as a surface perpendicular to a pn junction surface (this surface is called an end surface). When this end surface is exposed to the air, atoms existing on the surface are present. It is considered that oxygen in the air is mainly bonded to the dangling bonds of the atoms of the group V element. The presence of this bond in the active layer region causes a non-radiative recombination current to flow through the surface levels induced in the forbidden band. Therefore, the carrier density in the active layer region near the end face is smaller than that in other regions, and the population inversion distribution is not formed even during laser oscillation. Therefore, in the region near the end face, it is considered that light absorption is superior to light emission due to the disappearance of electron-hole pairs, and the temperature near the end face rises. Due to this temperature rise, the forbidden band width in the vicinity of the end face is reduced, and the light absorption is further increased.

When the light output increases and the light density near the end face reaches a certain value, the temperature near the end face is changed to the melting temperature of the crystal by positive feedback such as light absorption near the end face, decrease in the forbidden band width, and temperature rise. When it reaches to, the end face is not a resonance mirror surface, and laser oscillation becomes impossible. The COD (Ca
tastrophic Optical Damage: The optical output at that time is called the COD level.

Therefore, sulfur treatment is one of the treatment methods for improving the surface condition of an oxidized semiconductor. What is sulfur treatment?
(NH4) 2SX (ammonium polysulfide) and (NH4) 2S
After immersing the semiconductor surface (including the end face) in a liquid that contains sulfur ions such as (ammonium sulfide) in the solution, immediately dry it or wash it in ultrapure water or an organic solvent such as methanol. The process consists of drying. When this sulfur treatment is applied to the end face of the semiconductor laser,
It is considered that while the end face surface is etched, the oxygen atom bonded to the group V atom on the end face surface is removed, and the bond of the group V atom that has been bonded to oxygen is recombined with the sulfur atom. This will prevent the end faces from being oxidized again and will suppress the increase of surface states. As a result, the COD level of the semiconductor laser is expected to be significantly improved.

[0006]

In the conventional sulfur treatment,
Although air was dried in an atmosphere of inert gas such as nitrogen or under a reduced pressure environment, suspended contaminants in the atmosphere after the semiconductor laser was pulled up from a solution such as ammonium polysulfide and before the drying was completed. Will be absorbed. Then, it is considered that the solution remaining on the end surface during the drying process evaporates while containing the pollutant, so that the concentration of the pollutant in the solution rises and a high-concentration contaminated region is formed on the end surface. Furthermore, since the concentration of sulfur atoms remaining on the end surface during the drying process also gradually changes, the distribution of sulfur atoms bonded to the group V atoms on the end surface becomes uneven, and there are sufficient sulfur atoms to prevent reoxidation. Since a region that does not exist is formed, a semiconductor laser chip whose COD level is not improved will be formed.

Further, even when the excess ammonium polysulfide solution remaining on the semiconductor surface is washed with ultrapure water or an organic solvent such as methanol and then dried in the same manner, the end faces are contaminated by the floating contaminants. It is thought to end.

In these cases, the yield of the semiconductor laser is reduced due to the contaminants as compared with the case where the sulfur treatment is not performed.

Therefore, an object of the present invention is to provide a method of manufacturing a high-power semiconductor laser with less COD level deterioration.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and is obtained by immersing a semiconductor laser having an end face, which is a resonant mirror surface, in an ammonium polysulfide solution or an ammonium sulfide solution. , 20 ℃ continuously
The surface of the semiconductor laser is dried in the vapor from the above ammonium polysulfide solution or ammonium sulfide solution. After that, in the first method, subsequently, the protective film is deposited on the end face at a temperature of 300 ° C. or lower. In the second method, heat treatment is performed in vacuum at a temperature of 150 ° C. or higher and 400 ° C. or lower for 10 minutes or longer, and then a protective film is deposited on the end face at a temperature of 300 ° C. or lower.

[0011]

The present invention prevents contaminants from adhering to the end surface of the semiconductor laser while drying the semiconductor laser dipped in the ammonium sulfide solution or the ammonium polysulfide solution, and at the same time, prevents sulfur contained in the vapor from the solution. It is considered that the atoms are supplied to the end surface to promote the uniform distribution of the sulfur atoms bonded to the end surface. Therefore, CO
The yield of the semiconductor laser chip, in which the characteristics are improved such as the D level is improved, is not lower than the yield of the semiconductor laser that is not subjected to the sulfur treatment.

Further, the release of sulfur atoms from the surface during deposition is suppressed by heat treatment in a vacuum at a temperature of 150 ° C. or higher and 400 ° C. or lower. At this time, the sulfur atom moves from the group V atom having a weak bonding force to the group III atom having a strong bonding force.
Therefore, it is expected that the COD level will be further improved.

Further, by limiting the deposition rate to a low value, destruction of the semiconductor laser surface and release of sulfur atoms can be suppressed, so that the COD level can be further improved.

[0014]

Embodiments will now be described in detail with reference to the drawings.

The sample used here has a stripe width of 4 μm,
It is a lateral mode control type AlGaInP-based visible light semiconductor laser. 1 and 2 show a jig used in this embodiment and a method for carrying it out.

After the end face to be the resonance mirror surface is formed by cleavage from the semiconductor laser wafer, the semiconductor held by the laser holding jig 3 in the ammonium polysulfide solution 2 at a temperature of 20 ° C. or higher placed in the closed container 1. After soaking the end surface of the laser 4 for 5 minutes, the semiconductor laser 4 is immediately pulled up from the ammonium polysulfide 2 by the laser holding jig 3 and dried in the ammonium polysulfide vapor 5. If sulfur is evenly adhered to the end surface of the semiconductor laser, the semiconductor laser 4 is taken out of the closed container 1 and immediately heated to 300 ° C.
Hereinafter, after depositing a protective film on one end face of the semiconductor laser 4, the protective film is subsequently deposited on the other end face.

Here, from the inside of the closed container 1, the semiconductor laser 4
The time that elapses from the time when the protective film is deposited on the end face of the semiconductor laser to the time when it is taken out is 24
Must be less than or equal to time. This is because the sulfur attached to the end surface is sublimated, and the sulfur atoms attached in this way are bonded to the group V atoms on the end surface, and the bonding force is relatively weak. Therefore, in order to obtain the effect of the above-described sulfur treatment, it is necessary to form the protective film before all the sulfur atoms attached to the end surface are released.

FIG. 3 shows the relationship between the injection current and the optical output of the semiconductor laser. The result 11 of the semiconductor laser manufactured according to the method of the present invention, the result 12 of the semiconductor laser manufactured according to the above-described conventional sulfur treatment method, and the case 13 in which the end surface of the semiconductor laser is not treated are compared.

According to the method of the present invention, the COD level is 34
mW, which is the same as the COD level of the semiconductor laser manufactured by the conventional sulfur treatment. On the other hand, the COD level when no end face treatment is performed is 20 mW. Therefore, it can be seen that the COD level of the semiconductor laser manufactured according to the method of the present invention is the same as that in the conventional sulfur treatment, and is 70% higher than that in the case where the end face treatment is not performed. Here, the thickness of the protective film deposited on the end face is optimized so that the reflectance of the end face does not change as compared with that before the protective film is deposited.

Next, after operating the semiconductor laser for 1000 hours at a temperature of 70 ° C. and an optical output of 10 mW, the deterioration rates of the operating current, operating voltage, oscillation wavelength and slope efficiency are compared.

The deterioration rate of the semiconductor laser manufactured according to the present invention was 0.5%. On the other hand, the deterioration rate in the case of being manufactured according to the conventional sulfur treatment was 3%, and the deterioration rate of the semiconductor laser not subjected to the end face treatment was 1%. According to the conventional sulfur treatment, the pollutants in the atmosphere adhere to the end face between the time when it is pulled out of the ammonium polysulfide solution and the time when it is dried, and in the process of drying, there is a large amount of contaminated part, and the sulfur atoms on the end face surface are formed. Is uneven, the characteristics of the semiconductor laser chips differ greatly from each other as compared with the case where no end face treatment is performed.

On the other hand, it is considered that the sulfur atom is uniformly distributed on the end face surface without contaminants adhering to the end face surface during the drying, when manufactured by the method of the present invention.

Further, a semiconductor laser having an end face serving as a resonant mirror surface formed by cleavage is dipped in an ammonium polysulfide solution at a temperature of 20 ° C. for 5 minutes. Then, the semiconductor laser is pulled out from the solution and dried in the vapor of ammonium polysulfide. Immediately above the temperature of 150 ℃ to 400 ℃
After leaving the semiconductor laser in the following vacuum, a protective film is continuously deposited on one end face at 300 ° C. or lower, and then a protective film is deposited on the other end face.

Referring to FIG. 4, regarding the relationship between the injection current and the light output, after drying in ammonium polysulfide vapor as described above, heat treatment was performed in vacuum at 350 ° C. to deposit a protective film on both end faces. Result of fabricated semiconductor laser 21
And the result 22 without heat treatment are compared. 35
When the temperature was raised to 0 ° C, the COD level rose to 51 mW. On the other hand, the COD level without heat treatment is 34 mW, and according to the method of the present invention, the light output is 1.5 times that of the untreated case.

This is because the sulfur atom changes its binding partner from the group V atom having a weak binding force to the group III atom having a strong binding force, so that the sulfur atom is prevented from being released from the surface during the deposition of the protective film. It is thought that it has become possible.
Therefore, the COD level increased because the surface level was reduced by the effect of the sulfur treatment. Further, the formation of a film of sulfur atoms on the surface of the semiconductor laser is considered to suppress the surface destruction due to the deposition of the protective film.

(NH4) 2SX accompanied by this heat treatment
The effect of the end surface treatment is that the temperature rise is 150 ° C or higher, 4
It was found that the same result can be obtained if the temperature is 00 ° C. or lower. When the temperature rises to 150 ° C. or lower, the sulfur atom can hardly move from the group V atom having a weak binding force to the group III atom having a strong binding force, so that the COD level is lowered. Further, when the temperature rises to 400 ° C. or higher, alloying of the metal used in the electrode is promoted to increase contact resistance, and group V atoms such as phosphorus, which is a constituent atom of the laser, are scattered. Since the laser is defective, the light output is significantly reduced. When the group V atom is arsenic, arsenic has a stronger bonding force than phosphorus, and is less likely to be scattered by heat treatment. Therefore, the range of the temperature rising temperature is wider than that when the group V atom is phosphorus.

Although the AlGaInP type semiconductor laser is used in this embodiment, the same effect can be obtained by the end face treatment with (NH4) 2SX accompanied by heat treatment on other semiconductor lasers of the III-V group. Of course.

Further, when the deposition rate is increased, sulfur atoms adhering to the surface of the semiconductor laser are liberated and the surface of the semiconductor laser is destroyed, so that C by sulfur treatment is applied.
There is no improvement in OD level, or CO
This causes a decrease in D level.

[0029]

As described above, according to the present invention, it is possible to efficiently manufacture a semiconductor laser having a high COD level without reducing the yield of the semiconductor laser.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of immersing a semiconductor laser in an ammonium polysulfide solution.

FIG. 2 is a diagram showing an example of drying a semiconductor laser in ammonium polysulfide vapor.

FIG. 3 is a characteristic diagram showing a relationship between an injection current and an optical output of a semiconductor laser manufactured by drying in a vapor of ammonium polysulfide.

[Fig. 4] After drying in vapor of ammonium polysulfide, 3
A characteristic diagram showing the relationship between the injection current and the optical output of a semiconductor laser manufactured by performing heat treatment in a vacuum at 50 ° C.

[Explanation of symbols]

1 Closed container 2 Ammonium polysulfide solution 3 Laser holding jig 4 Semiconductor laser 11 Results when drying in vapor of ammonium polysulfide 12 Results when drying in nitrogen atmosphere 13 When no end surface treatment is performed Results 21 Results of drying in ammonium polysulfide vapor and heat treatment at 350 ° C. in vacuum 22 Results of drying in ammonium polysulfide vapor and without heat treatment

Claims (2)

[Claims] 1. A (NH4) 2S (ammonium sulfide) or (N4) 2S (ammonium sulfide) or (N4)
H4) A method for manufacturing a semiconductor laser comprising a step of immersing in 2SX (ammonium polysulfide), a step of drying in a vapor of an ammonium polysulfide solution, and a step of depositing a protective film on the surface of the resonant mirror. 2. Prior to the step of depositing a protective film on the surface of a resonant mirror made perpendicular to the pn junction surface, at 150 ° C. in vacuum.
The method for manufacturing a semiconductor laser according to claim 1, further comprising a step of performing heat treatment at a temperature of 400 ° C. or lower.