阅读说明：本技术 GaAs基高功率半导体激光器腔面的氮等离子体清洗方法 (Nitrogen plasma cleaning method for cavity surface of GaAs-based high-power semiconductor laser ) 是由 郭林炀 马晓辉 王丽霞 陶涛 李丹 郭胜君 陈琳 许晓东 于 2020-12-10 设计创作，主要内容包括：本发明公开了一种GaAs基高功率半导体激光器腔面等离子体清洗方法,采用氮等离子体作为清洗源,对GaAs基高功率半导体激光器腔面进行干法清洗,并原位蒸镀SiO-2薄膜,用以达到降低表面态,改善发光性能的目的,同时,最大程度去除腔面氧化层又不带来新的损伤。(The invention discloses a GaAs-based high-power semiconductor laser cavity surface plasma cleaning method, which adopts nitrogen plasma as a cleaning source to perform dry cleaning on the GaAs-based high-power semiconductor laser cavity surface and in-situ evaporation of SiO 2 The film is used for achieving the purposes of reducing the surface state and improving the light-emitting performance, and meanwhile, the cavity surface oxide layer is removed to the maximum extent without causing new damage.)

1. A GaAs-based high-power semiconductor laser cavity surface plasma cleaning method is characterized by comprising the following steps: (1) putting the cleaved semiconductor laser into an acetone and ethanol mixed solution for ultrasonic cleaning, after the ultrasonic cleaning is finished, putting the semiconductor laser into a vacuum cavity of a magnetron sputtering system, and drying the laser by using nitrogen;

(2) before plasma cleaning, repeatedly inflating and deflating nitrogen in a vacuum cavity of the magnetron sputtering system for multiple times, taking glow discharge nitrogen plasma in the magnetron sputtering system as a cleaning source, applying negative bias on one side of a substrate, and performing reverse sputtering on the plasma;

(3) after the cleaning is finished, SiO with the thickness of 80nm is immediately evaporated in situ₂A film.

2. The method of claim 1, wherein the volume ratio of acetone to ethanol in the mixed solution is 1: 1.

3. The method of claim 1, wherein the ultrasonic cleaning time is 10min, the ultrasonic frequency is 40KHz, and the power is 0.5W/cm²。

4. The method according to claim 1, wherein a flow rate of nitrogen gas at the time of the plasma reverse sputtering is 40sccm, a cleaning power is 10W, a cleaning gas pressure is 4.7Pa, and a cleaning time is 15 ± 2 min.

Technical Field

The invention relates to a method for cleaning a cavity surface of a GaAs-based high-power semiconductor laser, and belongs to the technical field of cavity surface passivation of high-power semiconductor lasers.

Background

The high-power semiconductor laser has the advantages of small volume, high efficiency, simple modulation and the like, and is widely applied to the fields of communication, medical treatment, high-precision processing, military and the like. High output power and long-term stable reliability are the precondition for the widespread use of high power semiconductor lasers, and Catastrophic Optical lens damage (COD) has always limited the maximum output power and reliability of semiconductor lasers. Since the light emitting region of the semiconductor laser is small, heat generated by absorption is concentrated on the cavity surface and cannot be efficiently transferred. Semiconductor lasers are typically cleaved in air, the facets of which create an oxide layer of a few nanometers thick under the influence of air. Meanwhile, lattice defects may also be generated on the cleaved cavity surface of the semiconductor laser. These can make the cavity surface of the semiconductor laser generate a large number of surface states, and when the laser is in a high-power working state, the surface states capture the carriers around the laser, and form a non-radiative coincidence center and a scattering center, so that the temperature of the cavity surface of the laser rises sharply. Subsequently, due to high temperature, the band gap near the cavity surface is reduced, so that the photon absorption capability of the cavity surface of the laser is enhanced, more injected current is concentrated in a narrow band gap region near the cavity surface, the cycle is repeated, and finally the high-power semiconductor laser is subjected to catastrophic optical mirror surface damage (COD), so that the semiconductor laser fails.

To improve the state of the cavity surface of the semiconductor laser, the density of surface states of the cavity surface of the laser can be reduced. The currently adopted methods mainly include: (1) the facet sulfurization treatment technique is to react the cleaved facet of the semiconductor laser with a sulfur-containing compound to remove the original oxide layer on the facet surface to form a stable sulfurized layer and reduce the density of surface states. Although the performance of the laser can be improved, the technology has poor stability and short effective time, and simultaneously has the defects of easy mixing of impurities in the solution and the existence of volatile toxic gases such as hydrogen sulfide and the like, thereby influencing the passivation effect; (2) the high vacuum cleavage coating technology comprises the steps of cleaving Bar in a high vacuum environment, then coating a passivation film, and coating a high-transmittance and anti-reflection film on a cavity surface. The technology can avoid oxygen and other impurities from polluting the cavity surface, is beneficial to obtaining high output power and high reliability of the laser, but has the disadvantages of complex technical equipment, high process difficulty, high manufacturing cost and difficult popularization; (3) the non-absorption window technology widens the forbidden bandwidth of the material at the cavity surface after special treatment near the cavity surface, forms a transparent area corresponding to the cavity surface with the emission wavelength, and inhibits the light absorption of the cavity surface, but the technology has great technical difficulty and poor repeatability in a secondary epitaxial growth process; (4) the argon plasma cleaning and passivating technology is characterized in that ion beams are utilized to bombard the cavity surface of a semiconductor laser, oxides on the cavity surface and impurities adsorbed on the cavity surface are removed, then a cavity surface passivation film and a cavity surface optical film are plated, the catastrophe optical damage threshold value of a device and the reliability of the device can be improved, Ar ions are most commonly adopted in the technology, but the energy of the Ar ions is difficult to control and remove the cavity surface oxidation layer, and secondary damage to the cavity surface is possibly caused. The conventional method has the defects of low passivation efficiency, high processing cost, complex process and the like, so that the yield of the laser is low, and the practical application of the high-power semiconductor laser technology is severely limited.

Disclosure of Invention

In order to overcome the defects of high processing cost, complex process technology, poor repeatability and the like of the traditional semiconductor laser, the invention aims to provide a nitrogen plasma cleaning method for the cavity surface of the GaAs-based high-power semiconductor laser₂The film is used for achieving the purposes of reducing the surface state and improving the light-emitting performance, and meanwhile, the cavity surface oxide layer is removed to the maximum extent without causing new damage.

The technical scheme for realizing the aim of the invention is as follows: a GaAs-based high-power semiconductor laser cavity surface plasma cleaning method comprises the following steps: (1) putting the cleaved semiconductor laser into an acetone and ethanol mixed solution for ultrasonic cleaning, after the ultrasonic cleaning is finished, putting the semiconductor laser into a vacuum cavity of a magnetron sputtering system, and drying the laser by using nitrogen;

(2) before plasma cleaning, repeatedly inflating and deflating nitrogen in a vacuum cavity of the magnetron sputtering system for multiple times, taking glow discharge nitrogen plasma in the magnetron sputtering system as a cleaning source, applying negative bias on one side of a substrate, and performing reverse sputtering on the plasma;

(3) after the cleaning is finished, SiO with the thickness of 80nm is immediately evaporated in situ₂A film.

Preferably, the volume ratio of acetone to ethanol in the mixed solution is 1:1, the ultrasonic cleaning time is 10min, the ultrasonic frequency is 40KHz, and the power is 0.5W/cm²。

Preferably, the nitrogen flow rate during the plasma reverse sputtering is 40sccm, the cleaning power is 10W, the cleaning pressure is 4.7Pa, and the cleaning time is 15 +/-2 min.

Compared with the prior art, the invention has the advantages that:

(1) the invention adopts nitrogen plasma to clean and plate the SiO2 film, has obvious passivation effect on the cavity surface of the laser, and can effectively remove the GaAs surface oxide layer and obtain more stable passivation effect.

(2) In order to protect the cavity surface of the high-power semiconductor laser cleaned by the nitrogen plasma from secondary pollution, SiO with the thickness of 80nm is immediately evaporated in situ after the cavity surface of the laser is cleaned₂Thin films with PL intensity higher than untreated laser facets and evaporation of SiO only to a thickness of 80nm₂Thin film laser cavity facet, compared with uncleaned laser cavity facet coated with SiO of the same thickness₂The PL intensity of the laser cavity surface of the film is improved by 16.6 times, and the cleaning effect is very obvious.

(3) At the same time, compared with the conventional (NH)₄）₂S+t-C₄H₁₀The treatment process of the O passivation solution and the nitrogen plasma is carried out in a high vacuum environment, so that the possibility of secondary pollution of the cavity surface by impurities is avoided.

Drawings

FIG. 1 is SiO₂Influence of the film anti-reflection effect on the fluorescence spectrum test.

FIG. 2 is a graph of the effect of cleaning power on the intensity of the laser facet PL.

FIG. 3 is a graph of the effect of operating pressure on the intensity of the laser facet PL.

FIG. 4 is a graph of the effect of nitrogen plasma cleaning time on laser facet PL intensity.

FIG. 5 is a graph of the effect of argon plasma cleaning time on laser facet PL intensity.

Detailed Description

The invention is further elucidated with reference to the figures and embodiments.

Example 1

The method comprises the following steps of firstly, putting a cleaved semiconductor laser (the property that a cavity surface is cracked into a smooth plane along a certain direction due to the structure of the semiconductor laser, namely cleavage, and the cracked smooth plane is called a cleavage surface) into acetone and ethanol, mixing, and easily carrying out ultrasonic cleaning, wherein the volume ratio of the acetone to the ethanol in a mixed solution is 1:1, and the time is 10 min;

step two, after ultrasonic cleaning is finished, placing the semiconductor laser in a vacuum cavity of a magnetron sputtering system, and drying the laser by using nitrogen;

thirdly, repeatedly inflating and deflating nitrogen in the vacuum cavity of the magnetron sputtering system for multiple times before formally cleaning the plasma in order to minimize the residual oxygen content in the cavity;

step four, taking glow discharge nitrogen plasma in a magnetron sputtering system as a cleaning source, and applying negative bias on one side of the substrate to realize reverse sputtering of the plasma, wherein the nitrogen flow is 40sccm, the cleaning power is 10W, the cleaning pressure is 4.7Pa, and the cleaning time is 15 +/-2 min;

step five, immediately evaporating SiO with the thickness of 80nm in situ after cleaning₂A film.

The invention evaporates and plates SiO₂The purpose of the film is: because the cavity surface activity of the GaAs-based high-power semiconductor laser cleaned by the nitrogen plasma is increased, if the film is not coated in time, the cavity surface can adsorb a large amount of water vapor, carbon, oxygen and other impurities in the air, the treatment effect is influenced, and meanwhile, the GaAs-based semiconductor laser is coated with SiO with low refractive index₂The film will have some anti-reflection effect on the incident light, as shown in fig. 1.

Through the test of the fluorescence spectrum (PL), the invention is not cleaned but coated with SiO with the same thickness₂Of filmsCompared with the laser cavity surface, the PL intensity of the laser cavity surface is improved by 16.6 times, and the cleaning effect is very obvious; at the same time, compared with the conventional (NH)₄）₂S+t-C₄H₁₀The treatment process of the O passivation solution and the nitrogen plasma is carried out in a high vacuum environment, so that the possibility of secondary pollution of the cavity surface by impurities is avoided.

The invention aims to set the cleaning power to 10W: because the power has great influence on the cleaning effect, if the power is too low, the nitrogen is difficult to glow and can not generate plasma; and if the power is too high, the cavity surface will be damaged, causing the generation of defects, thereby reducing the intensity of the fluorescence spectrum (PL), and selecting a proper radio frequency power to control a proper plasma energy to remove the surface oxide, only introducing acceptable damage defects, as shown in fig. 2.

The purpose of setting the air pressure to 4.7Pa is as follows: the cleaning effect is enhanced as the number of ionized gases increases with the increase of the pressure, the highest photoluminescence intensity is obtained at 4.7Pa, the cleaning effect is the best, but when the pressure is increased, the nitrogen gas is difficult to ionize and the collision probability among gas particles is increased due to excessive gas content, so that the cleaning effect is hindered, as shown in FIG. 3.

The invention sets the cleaning time to be 15 +/-2 min, and aims to: after cleaning for 10min, PL intensity tends to be stable, which means that the oxide layer is basically removed, and meanwhile, due to moderate nitrogen plasma energy, the laser cavity surface is not obviously damaged due to the prolonged time. Although the thickness of the oxide layer can reach a certain stable state within about 10min, the thickness of the oxide layer on the cavity surface of different lasers has a certain difference. Meanwhile, for the cleaved laser tube core, the thickness of the cavity surface oxide layer is different along with the different shelf time of the tube core in the air, and the cleaning time is in direct proportion to the thickness of the oxide layer. The cleaning time of the nitrogen plasma is controlled to be 15 +/-2 min because the cleaning effect reaches a stable level along with the cleaning time, and the PL intensity is obviously reduced even if the nitrogen plasma is cleaned excessively. Compared with the conventional Ar plasma cleaning, the time requirement criteria are much more flexible, as shown in fig. 4 and 5.

In a word, the method adopts nitrogen plasma to clean and plate the SiO2 film, has obvious passivation effect on the cavity surface of the laser, can effectively remove the oxide layer on the GaAs surface, and obtains more stable passivation effect.