CN112813403B - Method for improving reflectivity of high reflective film of semiconductor laser and implementation device thereof - Google Patents

Method for improving reflectivity of high reflective film of semiconductor laser and implementation device thereof Download PDF

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CN112813403B
CN112813403B CN201911118048.1A CN201911118048A CN112813403B CN 112813403 B CN112813403 B CN 112813403B CN 201911118048 A CN201911118048 A CN 201911118048A CN 112813403 B CN112813403 B CN 112813403B
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refractive index
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刘洪武
刘琦
周莉
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Shandong Huaguang Optoelectronics Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/58—After-treatment
    • C23C14/5806—Thermal treatment
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
    • C23C14/08—Oxides
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
    • C23C14/08—Oxides
    • C23C14/081—Oxides of aluminium, magnesium or beryllium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/028—Coatings ; Treatment of the laser facets, e.g. etching, passivation layers or reflecting layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/028—Coatings ; Treatment of the laser facets, e.g. etching, passivation layers or reflecting layers
    • H01S5/0287—Facet reflectivity
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
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Abstract

The invention relates to a method for improving the reflectivity of a high reflective film of a semiconductor laser and a device for realizing the method, the method comprises the steps of preheating a coated bar for 2-5min at the temperature of 140-150 ℃, then carrying out heat preservation treatment for 10-15min at any constant temperature of 200-400 ℃, and finally carrying out cooling treatment for 2-5min at the temperature of 140-150 ℃; and repeating the processes of preheating, heat preservation and temperature reduction for 3-5 times to finish the treatment process of the bars. The invention fills the blank of the processing technology after the laser cavity surface is plated with the high-reflection film in the optical film, and creates a new technological means for improving the reflectivity and the quality of the film layer after film plating. According to the invention, the reflectivity of the high-reflection film is improved, and the stress of the film and the cavity surface in the treatment process is released, so that the performance of the LD chip is improved.

Description

Method for improving reflectivity of high reflective film of semiconductor laser and implementation device thereof
Technical Field
The invention relates to a method for improving the reflectivity of a high reflective film of a semiconductor laser and an implementation device thereof, belonging to the technical field of thin film material processing.
Background
Semiconductor lasers (Semiconductor lasers) were successfully excited in 1962, and continuous output at room temperature was achieved in 1970. With the development of a Laser Diode (LD) having a double hetero junction type Laser and a stripe type structure, the LD has been widely used for optical fiber communication, optical disks, laser printers, laser scanners, and Laser pointers (Laser pens), and is the Laser device that has the largest production capacity at present.
The advantages of the laser diode are: high efficiency, small volume, light weight and low price. Products are also commercialized whose continuous output wavelength covers the infrared to visible range and whose light pulse output is on the order of 50W (pulse width 100 ns), as an example of a laser radar or excitation light source, which is a very easy-to-use laser.
Coating the cavity surface of a side-emitting semiconductor Laser Diode (LD) is an important process; which directly affects the output power and the service life of the LD. Under the condition of keeping the reflectivity of the front cavity surface antireflection film unchanged, the output power of the LD can be effectively improved by improving the reflectivity of the rear cavity surface antireflection film.
In the prior art, the cavity surface of the bar is coated, and then the bar is baked; in the film coating process, the reflectivity of the high-reflection film evaporated on the baked bar cavity surface is low and does not reach the designed refractive index due to the limitation of the equipment, and the refractive index of the baked high-reflection film cannot be changed; in order to further increase the refractive index of the high-reflection film, the number of the coating layers is increased, but the amount of the coating material is increased. The coating thickness is increased, which increases the number of layers of the film, increases the stress between the film and the substrate, and has adverse effect on the performance of the bar.
Chinese patent document CN106300010A reports a method for improving the reliability of a semiconductor laser and provides a method for plating a laser high-reflection film, which adopts the main technical scheme that a plurality of common simple substance film materials with high refractive index are mixed according to a certain proportion, and a laser reflection film is plated by adopting the mixed film materials, so that the damage resistance threshold value and the reflectivity of the laser reflection film are greatly improved; however, this patent has disadvantages that the film material is a mixture, it is not easy to control the ratio and the mixing uniformity, and the reflectance cannot be changed after film formation.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for improving the reflectivity of a high reflective film of a semiconductor laser.
The invention also provides a device for improving the reflectivity of the high-reflection film of the semiconductor laser, which utilizes the moving mechanism to drive the high-reflection film to do reciprocating motion in the quartz furnace tube, so as to realize the preheating, heat preservation and cooling treatment of the high-reflection film, thereby improving the reflectivity of the high-reflection film.
Description of terms:
1. reflectance ratio: the percentage of energy reflected by the object to the total radiated energy;
2. LD: a laser diode;
3. a bar: before the LD chip is not cleaved, the chip bar is formed.
The technical scheme of the invention is as follows:
a method for improving the reflectivity of a high reflective film of a semiconductor laser, wherein a semiconductor laser chip comprises an N-surface electrode, a substrate, an N limiting layer, an active layer, a P limiting layer, an insulating medium layer and a P-surface electrode which are arranged from bottom to top in sequence, and the method comprises the following steps:
(1) Cleaving the semiconductor laser chip into bars;
(2) Placing the bar in a coating device, and evaporating an antireflection film on the front cavity surface of the bar;
(3) And (3) evaporating a high-reflection film on the back cavity surface of the bar: alternately evaporating a low refractive index film and a high refractive index film;
(4) Preheating the coated bar at 140-150 deg.C for 2-5min, maintaining at 200-400 deg.C for 10-15min, and cooling at 140-150 deg.C for 2-5min;
(5) Repeating the step (4) for 3-5 times to complete the treatment process of the bars.
The high-reflection film on the back cavity surface of the bar is composed of multiple films, and the traditional method does not perform other treatment after the coating treatment of the bar, so that stress exists among the film layers due to different materials and different processes. By carrying out annealing treatment of 'heating-heat preservation-cooling' on the coated bars, the method can effectively eliminate partial stress by controlling the change of temperature and improve the performance of the high-reflection film. The annealing treatment after coating can reduce the coating time, reduce the use of coating materials and has no damage to the laser. The invention does not adopt the traditional 'temperature rise-heat preservation-temperature reduction' process, but repeatedly and circularly carries out a plurality of 'temperature rise-heat preservation-temperature reduction' processes, namely, a method for dispersing the heat preservation time is adopted, and the invention has the advantages that the crystallinity of the film can be well controlled; the method can prevent the high-refractive-index film from crystallizing too much and growing too large to increase the surface roughness and influence the optical performance of the film.
According to the invention, in the step (4), the heat preservation treatment is carried out at any constant temperature of 245-255 ℃.
The crystallinity of the high-refractive-index film layer is adjusted by controlling the annealing temperature, so that the refractive index of the high-refractive-index film can be effectively improved, and the overall reflectivity of the high-refractive-index film layer is improved; the purpose of improving the LD light-emitting power and slope efficiency is achieved.
According to the invention, in the step (4), the time of the heat preservation treatment is 15min.
According to the invention, in the step (4), the time of the preheating treatment is 2min. The preheating function is to give a buffer time to the bar and the clamp so as to avoid unnecessary damage caused by expansion with heat and contraction with cold.
According to the present invention, in the step (4), the time of the temperature reduction treatment is preferably 2min. The temperature is lowered to stop crystallization of the high refractive index film so as not to excessively crystallize.
Preferably, according to the invention, said step (4) is repeated 4 times.
According to the present invention, in the step (3), the vacuum degree of the coating equipment is preferably 3 × 10 -6 Torr, and the coating temperature is 100 ℃; the growth rate of the low refractive index film is
Figure BDA0002274624610000031
Growth rate of high refractive index films>
Figure BDA0002274624610000032
Oxygen flow rate is 30sccm; preferably, the growth rate of the low-refractive-index film is +>
Figure BDA0002274624610000033
The growth rate of the high refractive index film is->
Figure BDA0002274624610000034
According to the present invention, preferably, the film material of the low refractive index film is alumina or silica, and the film material of the high refractive index film is any one of titania, zirconia, and silicon; preferably, the film material of the low refractive index film is aluminum oxide, and the film material of the high refractive index film is titanium oxide.
According to the invention, in the step (3), 3-6 pairs of film systems of low refractive index films and high refractive index films are alternately evaporated on the back cavity surface of the bar. Different films are plated according to different product requirements, and different layers are plated.
The device for realizing the method for improving the reflectivity of the high-reflectivity film of the semiconductor laser comprises an annealing furnace, a quartz boat and a moving mechanism, wherein the annealing furnace comprises a furnace wall, a heat insulation layer, a quartz furnace tube, a thermocouple and a lining;
the outer side of the furnace wall is provided with a heat insulation layer, two ends of the furnace wall are provided with bushings, and the furnace wall and the bushings enclose a hearth; the furnace wall is internally provided with a plurality of thermocouples, the quartz furnace tube penetrates through the hearth and comprises a constant temperature area and two transition areas, the transition areas are distributed at two sides of the constant temperature area, the temperature range of the transition areas is 140-150 ℃, and the temperature of the constant temperature area is 200-400 ℃; the quartz boat is placed in the quartz furnace tube, and one end of the quartz boat is connected with the moving mechanism.
The quartz boat is used for placing the bar of treating annealing among the device, drive the quartz boat through moving mechanism and be reciprocating motion in quartzy boiler tube, make the bar at constant temperature district and transition region back and forth movement, the realization is to preheating of the high anti-membrane of semiconductor laser, the circulation of heat preservation and cooling process goes on, thereby reach the annealing to the high anti-membrane, reduce the stress between the membrane material, improve semiconductor laser's performance, the thermocouple is arranged in the temperature distribution of survey quartzy boiler tube, the constant temperature district of constancy of temperature distinguishes with the transition region in the quartzy boiler tube.
According to the optimization of the invention, the moving mechanism comprises a metal rod, a sliding block and a sliding rail, the sliding block is arranged on the sliding rail, a fixing ring is arranged on the sliding block, a quartz boat pull ring is arranged on the quartz boat, one end of the metal rod is connected with the fixing ring, and the other end of the metal rod is connected with the quartz boat pull ring.
According to the invention, the moving mechanism drives the bars to move at a constant speed in the annealing furnace, and the size of the bars moving at a constant speed is 0.8-1.2m/min; further preferably, the size of the uniform movement is 1m/min. The slow movement in the constant temperature area and the transition area can not cause the sample temperature to change too fast to cause unnecessary influence on the performance of the high-reflection film.
The beneficial effects of the invention are as follows:
1. because the stress action exists between the formed coating film and the cavity surface of the LD, the performance of the LD can be influenced by the existence of the stress; the method for improving the reflectivity of the high-reflectivity film of the semiconductor laser can play a role in reducing stress between film materials.
2. Different from the conventional method of increasing the number of the coating layers to increase the reflectivity, the method can reduce the coating time and reduce the use of coating materials by an annealing treatment method after coating, and has no damage to the laser.
3. The method provided by the invention can obviously improve the reflectivity of the high-reflectivity film, the reflectivity is improved from 89.74% to 96.2% at the wavelength of 800nm, the improvement ratio is 7.2%, and the light output power is increased; different film systems and different layer numbers have different influence effects.
4. The processing method is simple, easy to operate and high in repeatability; the defect that the reflectivity of an evaporation coating film system is low is made up; a method for post-treatment of the bar coating is initiated.
5. The method for improving the reflectivity of the high-reflectivity film of the semiconductor laser has strong practicability, is suitable for coating films of various laser cavity surfaces and can be applied to coating films of all LD cavity surfaces.
6. The method provided by the invention has obvious broadening effect on the high-reflectivity area of the high-reflectivity film system.
7. The implementation device of the method for improving the reflectivity of the high reflective film of the semiconductor laser has the advantages of simple structure, easiness in implementation, low input cost and strong applicability.
Drawings
Fig. 1 is a schematic structural view of a cavity surface of an edge emitting semiconductor laser.
FIG. 2 is a schematic diagram showing the variation of refractive index with wavelength of an alumina film layer
FIG. 3 is a schematic diagram of the refractive index of a titanium oxide film varying with wavelength.
Fig. 4 is a schematic structural diagram of an implementation apparatus for improving the reflectivity of a high reflective film of a semiconductor laser according to the present invention.
FIG. 5 is a graph showing the temperature of the coated sliver in an annealing furnace as a function of time.
FIG. 6 is a comparison of reflectivity curves for the rear facets of the LD bars before and after annealing furnace treatment.
1. The device comprises a P-surface gold electrode, 2, an insulating medium layer, 3, a P limiting layer, 4, an active layer, 5, an N limiting layer, 6, a substrate, 7, an N-surface gold electrode, 8, a thermocouple, 9, a heat insulation layer, 10, a lining, 11, a furnace wire, 12, a furnace wall, 13, a quartz furnace tube, 14, a sliding block, 15, a sliding rail, 16, a quartz boat, 17, a quartz boat pull ring, 18, a metal rod, 19 and a fixing ring.
Detailed Description
The invention is further defined in the following, but not limited to, by the figures and examples in the specification.
Example 1
A method for improving the reflectivity of a high reflective film of a semiconductor laser comprises the following steps:
(1) In the embodiment, the semiconductor laser chip is an edge-emitting semiconductor laser chip, the chip of the semiconductor laser is cleaved into bars along the direction vertical to the photoetching ridge, the width of each bar is the cavity length of each laser chip, two newly-cleaved cavity surfaces, one front cavity surface and an evaporation antireflection film are coated on the front cavity surface; the other is a back cavity surface, and a high-reflection film is evaporated.
A schematic structural diagram of a cavity surface of a side-emitting semiconductor laser chip is shown in fig. 1, and the chip is provided with an N-surface gold electrode 7, a substrate 6, an N-limitation layer 5, an active layer 4, a P-limitation layer 3, an insulating medium layer 2 and a P-surface gold electrode 1 from bottom to top in sequence; the cavity surface is the position needing film coating.
(2) The bars are placed on a coating fixture, so that the cavity surfaces of all the bars form a plane.
(3) Mounting the clamp with the bars on a workpiece disc of a coating device, and evaporating an antireflection film on the front cavity surface of the bars;
(4) The anchor clamps of the stick are put in the upset, and the another side is the high anti-membrane of back cavity face coating by vaporization, and low refracting index membrane and high refracting index membrane are rolled over to the coating by vaporization in turn, and the membrane material of low refracting index membrane chooses for use for the aluminium oxide, and the membrane material of high refracting index membrane chooses for use for the titanium oxide. The vacuum degree of the coating equipment is 3 multiplied by 10 -6 Torr, coating temperatureThe degree is 100 ℃; the growth rate of the low refractive index film is
Figure BDA0002274624610000051
Growth rate of high refractive index films>
Figure BDA0002274624610000052
The oxygen flow rate was 30sccm. And 6 pairs of film systems of low refractive index films and high refractive index films are alternately evaporated on the back cavity surface of the bar.
As shown in fig. 2 and 3, the refractive index of alumina changes little in the conventional production and the refractive index of titania does not reach the theoretical value below 2.4 in the conventional production; the higher the refractive index of titanium oxide, the better it is required to obtain a thin film having high reflectance. The refractive index of the titanium oxide film layer is correspondingly increased along with the increase of the crystallinity of the titanium oxide, but the surface roughness of the titanium oxide film layer is increased along with the increase of the crystallinity of the titanium oxide film layer, so that the performance of the optical film is influenced. Therefore, the refractive index is slightly increased accordingly but the titanium oxide thin film cannot be crystallized at once. A compromise process is taken that can both increase the refractive index and not affect the overall performance of the film.
(5) And taking out the coating clamp provided with the bars for later use after coating.
(6) Preheating the coated bar for 2min at 140-150 deg.C, maintaining at 245-255 deg.C for 15min, and cooling at 140-150 deg.C for 2min.
(7) And (4) repeating the step (6), namely performing the four processes of preheating, heat preservation and temperature reduction, wherein the total heat preservation time is 60min, completing heating, and taking the bars out of the annealing device.
Example 2
The method for improving the reflectivity of the high reflective film of the semiconductor laser and the device for realizing the method are provided by embodiment 1, as shown in fig. 4, the method comprises an annealing furnace, a quartz boat 16 and a moving mechanism, wherein the annealing furnace comprises a furnace wall 12, a heat insulating layer 9, a quartz furnace tube 13, a thermocouple 8 and a lining 10;
the outer side of the furnace wall 12 is provided with an insulating layer 9, two ends of the furnace wall 12 are provided with bushings 10, and the furnace wall 12 and the bushings 10 enclose a hearth; a heating furnace wire 11 is arranged in a furnace wall 12, a plurality of thermocouples 8 are arranged in the furnace wall 12, a quartz furnace tube 13 penetrates through a hearth, the quartz furnace tube 13 comprises a constant temperature area and two transition areas, the transition areas are distributed on two sides of the constant temperature area, the average temperature of the transition areas is 145 ℃, and the temperature of the constant temperature area is 245 ℃; the quartz boat 16 is placed in the quartz furnace tube 13, and one end of the quartz boat 16 is connected with the moving mechanism.
Quartz boat 16 is used for placing the high anti-membrane of semiconductor laser among the device, drives quartz boat 16 through moving mechanism and is reciprocating motion in quartzy boiler tube 13 for the high anti-membrane at constant temperature district and transition zone back and forth movement, the circulation that realizes preheating, heat preservation and the cooling process of the high anti-membrane of semiconductor laser goes on, thereby reaches the annealing to the high anti-membrane, reduces the stress between the membrane material, improves semiconductor laser's performance.
The moving mechanism comprises a metal rod 18, a sliding block 14 and a sliding rail 15, the sliding block 14 is arranged on the sliding rail 15, a fixing ring 19 is arranged on the sliding block 14, the fixing ring 19 is used for fixing the metal rod 18, and the lower end of the fixing ring 19 is fixed on the sliding block 14 through a bolt. The quartz boat 16 is provided with a quartz boat pull ring 17, one end of the metal rod 18 is fixedly connected with the fixing ring 19, and the other end of the metal rod 18 is connected with the quartz boat pull ring 17. The moving mechanism drives the bars to move at a constant speed in the device at a speed of 1m/min. The slow movement in the constant temperature area and the transition area can not cause the sample temperature to change too fast to cause unnecessary influence on the performance of the high-reflection film.
When the preheating treatment is measured, the temperature of the annealing furnace is set, the thermocouple 8 is used for measuring the temperature distribution in the quartz furnace tube 13, the middle temperature constant area is a constant temperature area, the two side temperature gradual change areas are transition areas, and the positions of the constant temperature area and the transition areas are recorded.
According to the designed preheating, heat preservation and cooling time and temperature, the positions of a constant temperature area and a transition area in the quartz furnace tube 13 and the moving speed of the quartz boat 16 in the annealing furnace, the movement of the sliding block 14 on the sliding rail 15 is controlled by a control program, and the control program is the prior art.
The processing process of the coated bar in the implementation device is as follows: placing the coated bars on a quartz boat 16, placing the quartz boat 16 in a quartz furnace tube 13 of an annealing furnace, setting a control program, wherein the program corresponds to the treatment process, starting to move leftwards to a transition region for preheating treatment, pushing the quartz boat 16 to a constant temperature region for heat preservation after the treatment is finished, driving the quartz boat 16 to move to the transition region for cooling by a metal rod 18 after the heat preservation is finished, and pushing the constant temperature region … … for four times after the cooling is finished; after the completion, the slide 14 returns to the initial state, and the processing is completed this time, and the apparatus is automatically stopped. The specific process is as follows: preheating in a transition zone with average temperature of 145 deg.C for 2min; then the mixture is moved to a 245 ℃ constant temperature area at a constant speed of 1m/min for constant temperature treatment for 15min. The bars move from the constant temperature area to the transition area with the average temperature of 145 ℃ at a constant speed of 1m/min, and the bars are subjected to cooling treatment in the transition area for 2min. The heating profile of the bars in the annealing apparatus is shown in fig. 5. And pressing a start button to start a control program, starting to perform 'preheating-heat preservation-cooling' circular motion, and after finishing the annealing process, cooling and taking down the sample for testing.
The crystallinity of the film layer is adjusted by controlling the annealing temperature, so that the refractive index of the high-refractive-index film can be effectively improved, and the integral reflectivity of the film layer is improved; the purpose of improving the LD light-emitting power and slope efficiency is achieved.
The high-reflection film on the rear cavity surface of the bar consists of multiple films, and stress exists between the films due to different materials and different processes; by annealing in a tubular alloy furnace, partial stress can be effectively eliminated by controlling the change of temperature, and the performance of the high-reflection film is improved. The annealing treatment after coating can reduce the coating time, reduce the use of coating materials and has no damage to the laser.
The annealed bars were tested in a spectrophotometer, and the test results are shown in table 1, and in order to test the reflectance of the bars, the bars and the silicon wafer were coated together and then tested.
Table 1 shows the change in reflectance between 795 nm and 810nm before and after the process of the device of this example 2,
TABLE 1
Figure BDA0002274624610000071
As can be seen from table 1, the reflectance at the 800nm range before the annealing treatment was 89.74% for the reflectances before and after the device implementation treatment provided in example 2 and in the 795-810nm range; the reflectivity of the treated batten at 800nm is 96.02%, and the highest reflectivity near 800nm can be up to 96.35%. After the preheating-heat preservation-cooling treatment is carried out on the bar high-reflection film by the annealing furnace for multiple cycles, the reflectivity of the bar high-reflection film is greatly increased, and the bar high-reflection film is obviously widened.
Broadening refers to a significant increase in the wavelength region of high reflectivity, such as the wavelength band with reflectivity greater than 90%, as shown in fig. 6, and the curve before and after annealing treatment can be seen to have a significant broadening effect on the high reflectivity region of the high reflectivity film system.
The reflection spectrum is broadened, so that the reflection spectrum can be applied to multi-dynamic wavelength use; the application range is widened, and the method is suitable for the condition that the wavelength reflectivity is more than 95 percent, like the condition that the wavelength can not be used before treatment in the table, and the wavelength can be used after treatment, and can be used from 795 nm to 810 nm.
Example 3
According to embodiment 2, a method for improving the reflectivity of a high reflective film of a semiconductor laser and a device for implementing the method are provided, which are characterized in that:
in the step (6), carrying out preheating treatment on the bars for 5min, wherein the preheating temperature is within the range of 140-150 ℃; then moving the substrate to a constant temperature area at a constant speed of 1m/min for heat preservation treatment for 10min; moving the strips at a constant speed of 1m/min to a temperature of 140-150 ℃ for cooling for 5min.
The bars prepared in this example were tested, and the highest reflectance of the bars around 800nm wavelength was 90% before and after annealing by this method.
Example 4
According to embodiment 2, a method for improving the reflectivity of a high reflective film of a semiconductor laser and a device for implementing the method are provided, which are characterized in that:
in the step (6), the temperature of the heat preservation treatment is set to be 200 ℃ under the constant temperature condition, and the time of the heat preservation treatment is 10min.
The bar prepared in this example was tested and had a maximum reflectance of 89% at a wavelength around 800nm before annealing and 91% at a wavelength around 800nm after annealing.
Example 5
According to embodiment 2, a method for improving the reflectivity of a high reflective film of a semiconductor laser and a device for implementing the method are provided, which are characterized in that:
repeating the step (6) for 3 times, and keeping the temperature for 45min.
The bar prepared in this example was tested, and the bar had a maximum reflectance around 800nm of 90% before annealing treatment, and the bar treated by this method had a maximum reflectance around 800nm of 94.4%.
Comparative example 1
(1) In this example, the semiconductor laser chip is an edge-emitting semiconductor laser chip, a schematic cross-sectional structure diagram is shown in fig. 1, and the semiconductor laser chip is provided with an N-plane gold electrode 7, a substrate 6, an N-limit layer 5, an active layer 4, a P-limit layer 3, an insulating dielectric layer 2, and a P-plane gold electrode 1 in sequence from bottom to top; the section is the position needing coating.
Cleaving a wafer of the semiconductor laser to cleave the chip into bars along a direction perpendicular to the photoetching ridge, wherein the width of each bar is the cavity length of each laser chip, and two newly cleaved cavity surfaces, one front cavity surface, are coated with an antireflection film by evaporation; the other is a back cavity surface, and a high-reflection film is evaporated.
(2) The bars are placed on a coating fixture, so that the cavity surfaces of all the bars form a plane.
(3) Mounting the clamp with the bars on a workpiece disc of a coating device, and evaporating an antireflection film on the front cavity surface of the bars;
(4) The fixture of the stick is put in the upset, and at another side back cavity face coating by vaporization high anti-membrane, low refracting index membrane and high refracting index membrane are evaporated in turn to the coating material of low refracting index membrane chooseed for use to be aluminium oxide, and the coating material of high refracting index membrane chooseed for use to be titanium oxide. Film coating equipmentDegree of vacuum of 3X 10 -6 Torr, and the coating temperature is 100 ℃; the growth rate of the low refractive index film is
Figure BDA0002274624610000081
The growth rate of the high refractive index film is->
Figure BDA0002274624610000082
The oxygen flow rate was 30sccm. And 6 pairs of low-refractive-index films and high-refractive-index film layers are alternately evaporated on the back cavity surface of the bar.
After the bar is coated with the high-reflection film by vapor on the back cavity surface, the bar is taken out from the film coating equipment after the film coating is finished.
The test results of the coated wafers (silicon wafers coated with the bars for testing the reflectivity after coating) are shown in fig. 6, and it can be seen from the test results that the reflectivity of the bars treated by the method at the wavelength of 800nm is 89.74%.
Comparative example 2
According to embodiment 2, a method for improving the reflectivity of a high reflective film of a semiconductor laser and a device for implementing the method are provided, which are characterized in that:
after the high-reflection film is evaporated on the back cavity surface of the bar, the bar is taken out of the film coating equipment after the film coating is finished, the bar is preheated for 2min at the temperature of 140-150 ℃, then the bar is subjected to heat preservation treatment for 60min at any constant temperature of 245-255 ℃, and finally the temperature is reduced for 2min at the temperature of 140-150 ℃, and the annealing treatment of the bar is finished.
The test was conducted on the coupons prepared in comparative example 2, and the reflectance of the bars at 800nm before annealing was 89.74%, and the reflectance of the bars after annealing at 808nm was 96.02%. Compared with the test data of example 2, the effect of treating the bars in multiple cycles of preheating-heat preservation-cooling provided by example 2 is better than the effect of treating bars in one-time completion of preheating-heat preservation-cooling provided by comparative example 2.

Claims (4)

1. A method for improving the reflectivity of a high reflective film of a semiconductor laser, wherein a semiconductor laser chip comprises an N-surface electrode, a substrate, an N limiting layer, an active layer, a P limiting layer, an insulating medium layer and a P-surface electrode which are arranged from bottom to top in sequence, and is characterized by comprising the following steps of:
(1) Cleaving the semiconductor laser chip into bars;
(2) Placing the bar in a coating device, and evaporating an antireflection film on the front cavity surface of the bar;
(3) And (3) evaporating a high-reflection film on the rear cavity surface of the bar: alternately evaporating a low refractive index film and a high refractive index film;
(4) Preheating the coated bars for 2min at the temperature of 140-150 ℃, then carrying out heat preservation treatment for 15min at any constant temperature of 245-255 ℃, and finally carrying out cooling treatment for 2min at the temperature of 140-150 ℃;
(5) Repeating the step (4) for 4 times to complete the processing process of the bars;
the device for realizing the method comprises an annealing furnace, a quartz boat and a moving mechanism, wherein the annealing furnace comprises a furnace wall, a heat insulation layer, a quartz furnace tube, a thermocouple and a lining;
the outer side of the furnace wall is provided with a heat insulation layer, two ends of the furnace wall are provided with bushings, and the furnace wall and the bushings enclose a hearth; the furnace wall is internally provided with a plurality of thermocouples, the quartz furnace tube penetrates through the hearth and comprises a constant temperature area and two transition areas, the transition areas are distributed on two sides of the constant temperature area, the temperature range of the transition areas is 140-150 ℃, and the temperature of the constant temperature area is 200-400 ℃; the quartz boat is placed in the quartz furnace tube, and one end of the quartz boat is connected with the moving mechanism;
the moving mechanism comprises a metal rod, a sliding block and a sliding rail, the sliding block is arranged on the sliding rail, a fixing ring is arranged on the sliding block, a quartz boat pull ring is arranged on the quartz boat, one end of the metal rod is connected with the fixing ring, and the other end of the metal rod is connected with the quartz boat pull ring;
when the preheating treatment is measured, the temperature of the annealing furnace is set firstly, then the temperature distribution in the quartz furnace tube is measured by using a thermocouple, the middle temperature constant area is a constant temperature area, the two side temperature gradual change areas are transition areas, and the positions of the constant temperature area and the transition areas are recorded;
controlling the movement of the sliding block on the sliding rail by a control program according to the designed time and temperature for preheating, heat preservation and cooling, the positions of a constant temperature area and a transition area in the quartz furnace tube and the moving speed of the quartz boat in the annealing furnace;
the processing process of the coated bar in the implementation device is as follows: placing the coated bars on a quartz boat, placing the quartz boat in a quartz furnace tube of an annealing furnace, setting a control program, wherein the program corresponds to a treatment process, starting to move leftwards to a transition region for preheating treatment, pushing to a constant temperature region for heat preservation after treatment, driving the quartz boat to move to the transition region for cooling by a metal rod after heat preservation is finished, pushing to the constant temperature region after cooling is finished, and returning to the initial state after the temperature reduction is finished for four times, wherein the treatment finishing equipment automatically stops;
the film material of the low refractive index film is alumina, and the film material of the high refractive index film is titanium oxide.
2. The method according to claim 1, wherein in the step (3), the vacuum degree of the coating equipment is 3 x 10 -6 Torr, and the coating temperature is 100 ℃; the growth rate of the low-refractive-index film is 4-6A/s; the growth rate of the high refractive index film was 4-6A/s with an oxygen flow of 30sccm.
3. A method as claimed in claim 1 for increasing the reflectivity of a high reflective film of a semiconductor laser wherein the low refractive index film has a growth rate of 6 a/s and the high refractive index film has a growth rate of 6 a/s.
4. A method for improving the reflectivity of high reflective films of a semiconductor laser as claimed in claim 1, wherein in step (3), the back cavity surfaces of the bars are alternately evaporated with 3-6 pairs of films of low refractive index films and high refractive index films.
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