TWI804424B - Design and manufacturing of 1550 nm distributed bragg reflector multiple optical layers for vertical cavity surface emitting laser - Google Patents

Abstract

A method for manufacturing a distributed bragg reflector is provided. The distributed bragg reflector is applied in a vertical-cavity surface emitting laser for 1550 nm. The vertical-cavity surface emitting laser includes a top distributed bragg reflector, a bottom distributed bragg reflector, and a vertical resonant cavity (containing a p-type electrode and a n-type electrode) and a multiple quantum well light-emitting layer between the top distributed bragg reflector and the bottom distributed bragg reflector. The method for manufacturing the distributed bragg reflector includes: sputtering to form an optical multiple layer that contains silicon layers and silicon dioxide layers which are alternatively stacked. The silicon dioxide layers are formed through a nano-sputtering process and a plasma micro oxidized process. In order to strengthen basic physical optical requirements of the resonant laser, a reflectivity of the bottom distributed bragg reflector is necessary more than 99.9%, and a reflectivity of the bottom distributed bragg reflector is necessary ranging from 95% to 99%.

Description

Manufacturing method of Bragg reflector for 1550nm vertical surface-emitting semiconductor laser

The invention relates to a method for manufacturing a Bragg reflector, in particular to a method for manufacturing an upper Bragg reflector or a lower Bragg reflector in a 1550nm vertical resonant cavity surface-emitting laser.

Compared with traditional edge-emitting lasers, vertical-cavity surface emitting lasers (Vertical-cavity surface emitting lasers, VCSELs) have (1) lower power consumption, (2) easy to match with fiber coupling and ( 3) The advantage of being easy to fabricate a laser array has become one of the light-emitting elements currently attracting attention.

The existing vertical resonant cavity surface-emitting laser device at least includes a P-type electrode, an N-type electrode, a multiple quantum well active layer for generating photons, and upper Bragg reflectors (Distributed bragg reflector, respectively) located on both sides of the active layer. DBR) and the lower Bragg reflector. The P-type electrode and the N-type electrode inject current into the active layer of the multiple quantum well to excite photons, and use the upper and lower Bragg mirrors to form a vertical resonant cavity, which can be generated by the surface of the component (that is, the vertical active layer) direction) of the outgoing laser beam.

In the prior art, Bragg reflectors are made by Metal-organic chemical vapor deposition (MOCVD), and will have different refractive indices The semiconductor materials are alternately stacked on the substrate to form semiconductor thin films. Moreover, through the selection of materials and the design of thickness, the effect of reflecting light of a specific wavelength can be achieved.

In the vertical resonant cavity surface-emitting laser, in order to strengthen the basic physical optics requirements for forming a resonant laser, the Bragg mirror needs to have extremely high reflectivity. Specifically, the upper Bragg mirror needs to have a reflectivity of at least 96%, and the lower Bragg mirror needs to have a reflectivity of 99.9%. In order to achieve the effect of high reflectivity, semiconductor materials in the prior art need to be provided with about 60 layers of semiconductor thin films. Therefore, the Bragg reflector in the prior art has the disadvantages of complex structure and complicated manufacturing process.

The technical problem to be solved by the present invention is to provide a method for manufacturing a Bragg reflector aiming at the deficiencies of the prior art.

In order to solve the above-mentioned technical problems, one of the technical solutions adopted by the present invention is to provide a method for manufacturing a Bragg reflector, which is used in a 1550-nanometer vertical cavity surface-emitting laser and acts as an upper Bragg reflector. Mirror or lower Bragg reflector, the manufacturing method of Bragg reflector includes: forming an optical multilayer film on a substrate, the substrate is a silicon wafer, a gallium arsenide wafer, a silicon carbide wafer or a glass substrate . When applied to a 1550nm vertical common-cavity surface-emitting laser as a lower Bragg reflector, the steps of forming an optical multilayer film include: forming a molybdenum layer on the substrate, forming a silver layer on the molybdenum layer, and forming a silver layer on the silver layer. Alternately stacked silicon layers and silicon dioxide layers are formed on the layer, and the silicon dioxide layer is formed by nano-sputtering and plasma micro-oxidation procedures.

One of the beneficial effects of the present invention is that the manufacturing method of the Bragg reflector provided by the present invention can be achieved by "forming alternately stacked silicon layers and silicon dioxide layers on the silver layer" and "the silicon dioxide layer is The technical solution formed by rice sputtering and plasma micro-oxidation process can improve the reflectivity of the lower Bragg reflector to 99.9%, thereby achieving the effect of improving the luminous efficiency of the laser device.

For enabling a further understanding of the features and technical content of the present invention, please refer to the following The detailed description and drawings related to the present invention, however, the provided drawings are only for reference and illustration, and are not intended to limit the present invention.

Z1: laser device

10: Substrate

20: Lower Bragg reflector

21: Silicon layer

22: Silicon dioxide layer

23: reflective metal layer

24: Thermal diffusion barrier layer

30:Multiple quantum well active light-emitting structure layer

31: first conductivity type semiconductor layer

33: Second conductivity type semiconductor layer

40: Upper Bragg reflector

41: Silicon layer

42: Silicon dioxide layer

50: Electrode structure

51: The first metal electrode

52: Second metal electrode

80: Pre-pumping chamber

90: Sputtering chamber

91: Radio Frequency Triggered Inductively Coupled Plasma Equipment

92: target

93: RF stage self-bias device

L: laser beam

Fig. 1 is a side view of the vertical resonant cavity surface-emitting laser of the present invention.

2 is a schematic diagram of the vacuum pre-evacuation chamber, the sputtering chamber and the micro-oxidation chamber used when forming an optical multilayer film in the present invention.

3 is a schematic diagram of the relative positional relationship between the substrate and the target during sputtering.

Figure 4A is a schematic diagram of an inductively coupled plasmonic device.

FIG. 4B is a schematic diagram of a self-biasing device for a radio frequency carrier.

5A is an AFM image of the surface of a silicon dioxide layer with a thickness of 209.4 nm formed by the nano-sputtering and plasma micro-oxidation procedures of the present invention.

5B is an AFM image of the surface of a silicon dioxide layer with a thickness of 200 nm formed by activated sputtering in the prior art.

FIG. 6A is a side view of the lower Bragg reflector in the 1550nm vertical cavity surface-emitting laser of the present invention.

FIG. 6B is a transmission electron microscope image of a Bragg reflector fabricated by the nano-sputtering and plasma micro-oxidation procedures of the present invention.

FIG. 7 is a curve of spectral reflectance in the light wavelength range from 1450 nm to 1650 nm of the 1550 nm vertical resonant cavity surface-emitting laser middle-lower Bragg reflector of the present invention.

Fig. 8 is a side view of the upper Bragg reflector in the 1550nm vertical cavity surface-emitting laser of the present invention.

9 is a side view of the lower Bragg reflector with a diffusion barrier layer in a 1550nm vertical resonator surface-emitting laser according to the present invention.

10 is the spectral reflectance curve of the lower Bragg reflector with a diffusion barrier layer in the 1550 nm vertical resonator surface-emitting laser of the present invention in the range of light wavelengths from 1450 nm to 1650 nm.

The following is a description of the implementation of the "method for manufacturing a Bragg mirror" disclosed in the present invention through specific specific examples. Those skilled in the art can understand the advantages and effects of the present invention from the content disclosed in this specification. The present invention can be implemented or applied through other different specific embodiments, and various modifications and changes can be made to the details in this specification based on different viewpoints and applications without departing from the concept of the present invention. In addition, the drawings of the present invention are only for simple illustration, and are not drawn according to the actual size, which is stated in advance. The following embodiments will further describe the relevant technical content of the present invention in detail, but the disclosed content is not intended to limit the protection scope of the present invention. In addition, the term "or" used herein may include any one or a combination of more of the associated listed items depending on the actual situation.

Please refer to FIG. 1, the present invention provides a laser device Z1, which is especially suitable for use as a laser device with an infrared wavelength (wavelength is 1550 nm), and can emit sufficient light intensity under the premise of meeting safety regulations. Beam L.

In the embodiment of the present invention, the laser device Z1 is a vertical cavity surface emitting laser device (vertical cavity surface emitting laser, VCSEL), using two distributed Bragg reflectors (Distributed Bragg Reflector, DBR) as mirror layers , so that the initial light beam generated by the laser device Z1 can reflect and resonate back and forth between the two mirror layers to amplify the gain, and finally emit the laser light beam L.

It is worth noting that the reflector layer of the present invention is formed by nano-sputtering and plasma micro-oxidation procedures rather than by chemical vapor deposition, so the reflector layer of the present invention can be formed on a film In the case of a small number of layers, the lower Bragg reflector has a high reflectivity effect of 99.9%. In this way, the laser device Z1 of the present invention can be applied to vehicle radar and LiDAR (light detection and ranging, LiDAR).

Please refer to FIG. 1 , the laser device Z1 includes a lower Bragg reflector 20 , a multiple quantum well active light-emitting structure layer 30 , and an upper Bragg reflector 40 . In detail, in this embodiment, the laser device Z1 further includes a substrate 10 . The lower Bragg reflector 20, the multiple quantum well active light-emitting structure layer 30 and the upper Bragg reflector 40 are all arranged on the substrate 10, and the multiple quantum well active light-emitting structure layer 30 is located between the lower Bragg reflector 20 and the upper Bragg reflector 40 between.

The substrate 10 can be an insulating substrate or a semiconductor substrate. The insulating substrate is, for example, a glass substrate, and the semiconductor substrate is, for example, silicon, germanium, silicon carbide or III-V semiconductors. Group III-V semiconductors are, for example, gallium arsenide (Gallium Arsenide, GaAs), arsenic phosphide (Indium Phosphide, InP), aluminum nitride (Aluminum Nitride, AIN), indium nitride (Indium Nitride, InN) or nitride Gallium (Gallium Nitride, GaN).

Each of the lower Bragg reflector 20 and the upper Bragg reflector 40 includes alternately stacked first film layers (silicon layer 21) and second film layers (silicon dioxide layer 22), and the refractive index of the first film layer is higher than that of the second film layer. The refractive index of the coating. Due to the difference in refractive index, when light enters the second film layer from the first film layer, total reflection will occur once the incident angle is greater than the critical angle. The materials of the first film layer and the second film layer will affect the refractive index, and the refractive index and thickness of the first film layer and the second film layer will produce different reflection effects on light of different wavelengths. In order to achieve a reflection effect that meets the requirements (the reflectivity is more than 99.5%, or even more than 99.9%), the present invention has very strict requirements on the thickness of the first film layer and the second film layer, specifically, the first film layer and the second film layer The allowable thickness error of the second film layer is less than ±1%. When using different materials, the corresponding thickness specification requirements will be completely different.

In order to improve the reflectivity of the lower Bragg reflector 20 (please refer to FIG. 6A), the lower Bragg reflector 20 can also include a reflective metal layer 23. By setting the reflective metal layer 23, the first The total number of layers of the film layer 21 and the second film layer 22 . In detail, the reflective metal layer 23 can be a single metal layer or composed of multiple metal layers. The thickness of the reflective metal layer 23 may be 20 nm to 100 nm, and the total thickness of the reflective metal layer 23 is preferably 50 nm to 100 nm. The material of the reflective metal layer 23 is selected from the group consisting of aluminum, silver and molybdenum. However, the present invention is not limited thereto.

In some embodiments, the lower Bragg reflector 20 (please refer to FIG. 9 ) may further include a thermal diffusion barrier layer 24, and the thermal diffusion barrier layer 24 is disposed on the first film layer and the second film layer, especially the silicon layer. 21 and above. The thermal diffusion barrier layer 24 can prevent silicon atoms in the silicon layer 21 from diffusing into the first conductive type semiconductor layer 31 (n-type electrode). In this embodiment, the material of the thermal diffusion barrier layer 24 can be niobium pentoxide, tantalum pentoxide or titanium dioxide, and the thickness of the thermal diffusion barrier layer 24 is from 10 nanometers to 80 nanometers, preferably from 30 nanometers to 80 nanometers. 50 nm, more preferably 40 nm.

The multiple quantum well active light emitting structure layer is used to generate the laser beam L, and the laser beam L can reflect and resonate back and forth between the two reflector layers to amplify the gain. The vertical resonant cavity structure includes a first conductivity type semiconductor layer 31 (N-type gallium arsenide), a multiple quantum well active light-emitting structure layer 30, a second conductivity type semiconductor layer 33 (P-type gallium arsenide), multiple quantum wells The well active light emitting structure layer 30 is located between the first conductive type semiconductor layer 31 and the second conductive type semiconductor layer 33 , and the current confinement layer is located between the multiple quantum well active light emitting structure layer 30 and the second conductive type semiconductor layer 33 .

The first conductivity type semiconductor layer 31 and the second conductivity type semiconductor layer 33 have opposite conductivity types. When the first conductive type semiconductor layer 31 is a P-type semiconductor, the second conductive type semiconductor layer 33 is an N-type semiconductor. When the first conductive type semiconductor layer 31 is an N-type semiconductor, the second conductive type semiconductor layer 33 is a P-type semiconductor. In detail, the material of the first conductive type semiconductor layer 31 and the second conductive type semiconductor layer 33 may be gallium arsenide, but the present invention is not limited thereto.

In some embodiments, after the lower Bragg reflector 20 is formed, the lower Bragg reflector 20 can be modified first, and then the first conductivity type semiconductor layer 31 is provided, so that the lower Bragg reflector 20 and the first conductivity type semiconductor A lattice matching layer is formed between layers 31 .

The electrode structure includes a first conductivity type semiconductor layer n-type electrode 31 and a second electrode layer p-type electrode 33, through the setting of the first conductivity type semiconductor layer 31 and the second electrode layer 33, the laser device Z1 and The external circuit is electrically connected. The first metal electrode 51 is disposed on the first conductive type semiconductor layer 31 (n-type electrode), and is electrically connected to the first conductive type semiconductor layer 31 . The second metal electrode 52 is disposed on the second conductive type semiconductor layer 33 (p-type electrode), and is electrically connected with the second conductive type semiconductor layer 33 . The second metal electrode 52 is disposed on the second conductive type semiconductor layer 33 and surrounds the upper Bragg reflector 40 .

The invention provides a design and manufacturing method of a Bragg reflector. The Bragg reflector is formed by sputtering and applied to a vertical resonant cavity surface-emitting laser. In the vertical cavity surface-emitting laser, the reflectivity of the upper Bragg mirror can be as high as 98%, and the reflectivity of the lower Bragg mirror can be as high as 99.9%.

The method provided by the invention is suitable for forming optical multilayer films on silicon wafers, silicon carbide wafers, gallium arsenide wafers or glass substrates, and is applied to vertical resonant cavity surface-emitting lasers as Bragg reflectors.

[Formation of aluminum layer, molybdenum layer and silver layer]

2 and 3, the method for forming the reflective metal layer 23 includes: (1) placing the substrate 10 on a self-bias device (wafer holder) 93 on a radio frequency stage, and sending the substrate 10 to the pre-extraction The chamber (load lock chamber) 80 is evacuated so that the pressure in the pre-evacuation chamber 80 is lower than 1×10 ⁻³ Torr. (2) The substrate 10 is transferred into the sputtering chamber 90, and the pressure in the sputtering chamber 90 is maintained at 5×10 ⁻⁶ Torr. (3) Under an argon atmosphere of 3×10 ⁻³ Torr, the wafer carrying the substrate 10 is moved to the front of the sputtering cathode (target 92 ), and is sputtered by direct current sputtering (DC) or RF sputtering. In a radiofrequency sputtering (RF) manner, a molybdenum layer, silver layer or aluminum layer (reflective metal layer 23 ) is deposited on the substrate 10 by sputtering. The process parameters include: wafer holder moving rate from 50 mm/min to 3000 mm/min, and RF sputtering input power from 0.5 kW to 3.0 kW. The thicknesses of the molybdenum layer, the silver layer and the aluminum layer can be adjusted according to the structural design of the Bragg reflector.

[Formation of silicon layer and silicon dioxide layer]

Please refer to FIG. 3 , which is a schematic diagram of transferring the substrate to the front of the target to form a silicon layer or a silicon dioxide layer. In the plasma sputtering system, the sputtering plasma is generated by a DC sputtering power generator or an RF sputtering power generator with a frequency of 13.56MHz, and the target material 92 used is an intrinsic single crystal with a purity of 99.9999%. Silicon (Intrinsic crystal silicon) target. During the sputtering process, the radio frequency stage carrying the substrate 10 moves from the bias device 93 to the front of the target ⁹² , and performs sputtering under an argon atmosphere of 3×10 A silicon layer of a specified thickness is deposited. The process parameters include: the moving speed of the RF stage from the bias device 93 is 50 mm/min to 3000 mm/min, and the input power of the RF sputtering is 0.5 kW to 3.0 kW. The thickness of the silicon layer and the silicon dioxide layer can be adjusted according to the design of the Bragg reflector.

In the present invention, a radio frequency triggered inductively coupled plasma (RF triggered inductively couple plasma) device (as shown in Figure 4A) or a radio frequency carrier self-bias device (RF substrate bias device) (as shown in Figure 4B) is used to generate electric current slurry to oxidize the silicon film to form a silicon dioxide film.

[Formation of silicon layer]

Please refer to Fig. 2, shown in 3, the forming method of silicon layer comprises: (1) base material 10 is placed on the wafer holder stage, is transported in the pre-pumping chamber 80, and vacuumizes pre-pumping chamber The pressure in 80 is lower than 1×10 ^-3 Torr. (2) The substrate 10 is transferred from the pre-extraction chamber 80 to the sputtering chamber 90, and the pressure in the sputtering chamber 90 is maintained at 5×10 ⁻⁶ Torr. (3) Under an argon atmosphere of 3×10 ^-3 Torr, the radio frequency stage carrying the substrate 10 moves from the bias device 93 to the front of the sputtering cathode (target 92 ), and performs DC sputtering or radio frequency sputtering A silicon layer with a thickness of 100 nm to 300 nm is deposited on the substrate 10 by sputtering. Process parameters include: wafer holder movement rate from 50 mm/min to 3000 mm/min, RF sputtering input power from 1.0 kW to 2.0 kW.

[Formation of silicon dioxide layer]

In the present invention, the silicon dioxide layer is formed by nano-sputtering and plasma micro-oxidation. Please refer to Fig. 2, shown in 3, (1) base material 10 is placed on the radio frequency carrier self-biasing device 93, is sent in the pre-pumping chamber 80, and vacuumizes and makes the pressure in the pre-pumping chamber 80 low at 1×10 ^-3 torr. (2) The substrate 10 is transferred from the pre-extraction chamber 80 to the sputtering chamber 90, and the pressure in the sputtering chamber 90 is maintained at 5×10 ⁻⁶ Torr. (3) Under an argon atmosphere of 3×10 ^-3 Torr, the wafer holder carrying the substrate 10 is moved to the front of the sputtering cathode (target 92 ), and is sputtered by DC sputtering or RF sputtering. A silicon thin film with a thickness of 2 nm is deposited on the substrate 10 . Process parameters include: wafer holder movement rate from 50 mm/min to 3000 mm/min, RF sputtering input power from 0.5 kW to 2.0 kW.

In the first operating condition, after sputtering a silicon thin film with a thickness of 2 nm, the substrate 10 was moved to the RF-TICP device 91, and the base pressure in the RF-TICP device 91 was maintained at 8 ×10 ^-6 torr. The input power of RF-triggered inductively coupled plasma equipment is 300W to 1000W, and the plasma is generated by RF coil at a frequency of 13.56MHz. The plasma gas is a mixed gas containing argon and oxygen, and the working pressure is controlled at 0.001 Torr to 0.1 Torr. In order to oxidize the silicon film into a silicon dioxide film, the processing time of the substrate 10 in the radio frequency triggered inductively coupled plasma device is 2 minutes to 5 minutes.

In the second operating condition, after sputtering a silicon thin film with a thickness of 2 nanometers, the substrate 10 is moved to the RF stage self-bias device 93, and the base pressure in the frequency stage self-bias device 93 is maintained at 8 x 10 ^-6 torr. The input power of the radio frequency plasma is 500 watts to 1500 watts, and the plasma is generated by the radio frequency power supply at a frequency of 13.56 MHz. The plasma gas is a mixed gas containing argon and oxygen, and the working pressure is controlled at 0.005 Torr to 0.1 Torr. In order to oxidize the silicon film into a silicon dioxide film, the processing time of the substrate 10 in the RF stage self-biasing device 93 is 2 minutes to 5 minutes.

Regardless of the first operating condition or the second operating condition, after the plasma micro-oxidation process, a silicon film with a thickness of 2 nm can be oxidized into a silicon dioxide film with a thickness of about 4 nm. via heavy By repeating the above steps, multiple layers of silicon dioxide films can be stacked to form a silicon dioxide layer with a specific thickness. For example, if a silicon dioxide layer with a thickness of 100 nanometers is to be formed, the above-mentioned first operating condition or second operating condition can be used to repeat the above-mentioned formation of a silicon film with a thickness of 2 nanometers, and then oxidation to form a 4-nanometer silicon dioxide layer. Step 25 of the SiO2 thin film. If the expected thickness of the silicon dioxide layer is not an integral multiple of 4 nanometers, for example: 102 nanometers (the above steps need to be repeated 25.5 times), the input power can be adjusted according to the linear relationship. In one of the specific steps, a layer with a thickness of A 1 nm silicon film is oxidized to form a 2 nm thick silicon dioxide film, so that the silicon dioxide layer has a specific expected thickness. Often a specific step is considered the last step in the overall procedure.

As mentioned above, forming a silicon dioxide layer with a thickness of 100 nm is equivalent to repeating the above steps 25 times. Forming a silicon dioxide layer with a thickness of 102 nm is equivalent to repeating the above steps 25 times, and then performing a specific step.

In the present invention, the thickness of each silicon dioxide film and the surface roughness of the silicon dioxide film on the c-axis can be finely controlled through the micro-oxidation procedure of nanometer sputtering. In an exemplary embodiment, the thickness variability of the silicon dioxide layer with a thickness of 200 nm and the surface roughness on the c-axis are both less than 2 nm, even less than 1.5 nm (as shown in FIG. 5A ). In contrast, if a silicon dioxide layer with a thickness of 200 nm is formed by sputtering in a single step under a mixed atmosphere of argon and oxygen in the traditional reactive sputtering method, the silicon dioxide layer The surface roughness on the c-axis can be as high as 15 nm to 20 nm (as shown in FIG. 5B ).

Please refer to Table 1. In order to prove that the manufacturing method of the present invention can precisely control the thickness of the silicon dioxide layer, the silicon dioxide layers of sample 1 and sample 2 were formed according to the above steps (second operating conditions). Specifically, a 2-nanometer amorphous silicon film was first deposited by sputtering, and then oxidized with a 600-watt oxygen plasma to form a silicon dioxide film. After repeated stacking, the silicon dioxide layers of samples 1 and 2 were obtained. . The thickness of the silicon dioxide layer is listed in Table 1, and the surface roughness of the silicon dioxide layer is measured using a surface atomic force microscope (AFM).

As can be seen from the results in Table 1, the arithmetic mean roughness (Ra) of the silicon dioxide layer surface is less than 0.2 nanometers (preferably less than 0.12 nanometers), and the root mean square roughness (Rq) of the silicon dioxide layer surface less than 0.2 nm (preferably less than 0.15 nm), and the average peak-to-valley depth (Z) of the surface of the silicon dioxide layer is less than 1.5 nm (preferably less than 1.3 nm).

[Formation of lower Bragg mirror in 1550nm vertical cavity surface-emitting laser]

Please refer to FIG. 2, (1) place the substrate on the wafer holder stage, transfer it to the pre-pumping chamber 80, and evacuate the pressure in the pre-pumping chamber 80 to be lower than 1×10 ^{− 3} pallets. (2) The substrate is transferred from the pre-extraction chamber 80 to the sputtering chamber 90, and the pressure in the sputtering chamber 90 is maintained at 5×10 ⁻⁶ Torr. (3) Sputtering and depositing an aluminum layer with a thickness of 80 nm on the substrate by DC sputtering or radio frequency sputtering under an argon atmosphere of 3×10 ⁻³ Torr.

Referring to FIG. 6A , the lower Bragg reflector 20 of the present invention may have a structural design as shown in FIG. 6A . According to the sequence formed on the aluminum layer (reflective metal layer 23), the thicknesses of the first silicon layer 21 and silicon dioxide layer 22 are 173.3 nm and 270 nm respectively, and the second group of silicon layer 21 and silicon dioxide The thicknesses of the silicon layer 22 are 98.2 nm and 270.4 nm respectively, the thicknesses of the third group of silicon layer 21 and silicon dioxide layer 22 are respectively 295.2 nm and 269.8 nm, the fourth group of silicon layer 21 and silicon dioxide layer The thicknesses of 22 are respectively 98.4 nm and 269.9 nm. Finally, a silicon layer with a thickness of 98.4 nm is formed on the uppermost silicon dioxide layer 22 . The surface of each layer body in the present invention is smooth and has good quality. Please refer to FIG. 6B , which is a cross sectional electron microscope image of the lower Bragg reflector. The dark-colored layer in Figure 6B corresponds to the silicon layer 21, the light-colored layer corresponds to the silicon dioxide layer 22, and the patterned layer corresponds to on the aluminum layer (reflective metal layer 23).

Please refer to FIG. 7 . FIG. 7 is a spectral reflectance curve of the lower Bragg reflector measured by a reflectance measuring instrument (Hitachi, model U4100). According to the above-mentioned structural design, the lower Bragg reflector 20 of the present invention has an average reflectance of 100.06% of light in the wavelength range from 1450 nm to 1650 nm, and can be applied to a vertical resonant cavity surface-emitting type with a wavelength of 1550 nm. laser.

The total thickness of the aforementioned Bragg mirrors is about 2000 nm. Through nano-sputtering and plasma micro-oxidation procedures, the present invention can precisely control the surface roughness of the silicon dioxide layer on the c-axis. The arithmetic average roughness (Ra) of the Bragg reflector under the atomic force microscope is 0.25 nm, the root mean square roughness (Rq) is 0.32 nm, and the average peak-to-valley depth (Z) is 3.10 nm.

The present invention provides a method for manufacturing a Bragg reflector, which can be applied to the lower Bragg reflector 20 or the upper Bragg reflector 40 in a 1550nm vertical resonant cavity surface-emitting laser. The optical multilayer film in the lower Bragg reflector 20 is made by nano-sputtering and plasma micro-oxidation, and the reflectivity of the lower Bragg reflector 20 can be as high as 99.9% to 100%. In the present invention, the applicable substrate 10 is a silicon wafer, a gallium arsenide wafer, a silicon carbide wafer or a glass substrate. Please refer to FIG. 6A , the manufacturing method for forming the lower Bragg reflector 20 includes: forming a reflective metal layer 23 (aluminum layer) on the substrate 10, forming an amorphous silicon layer 21 on the reflective metal layer 23, and The silicon dioxide layer 22 is formed by sputtering and plasma micro-oxidation, and the above steps are repeated to form alternately stacked amorphous silicon layers 21 (high refractive index) and silicon dioxide layers 22 (low refractive index) to achieve the desired reflectivity.

[Formation of upper Bragg mirror in 1550nm vertical common cavity surface-emitting laser]

The Bragg reflector of the present invention can be applied to the lower Bragg reflector 20 or the upper Bragg reflector 40 in a 1550nm vertical resonant cavity surface-emitting laser. The optical multilayer film in the upper Bragg reflector 40 is formed by nano-sputtering and plasma micro-oxidation. The reflectivity of the upper Bragg reflector 40 can be as high as 98.0% to 99.0%. Referring to FIG. 8 , the upper Bragg reflector 40 of the present invention is suitable to be formed on the second conductive type semiconductor layer (P-type GaAs) 33 . Manufacture of the upper Bragg reflector 40 The method includes (see FIG. 8 ): forming a silicon layer 41 on the second conductive type semiconductor layer (P-type gallium arsenide) 33, and forming a silicon dioxide layer 42 through nano-sputtering and plasma micro-oxidation procedures, and repeating In the above steps, alternately stacked amorphous silicon layers 41 (high refractive index) and silicon dioxide layers 42 (low refractive index) are formed to achieve desired reflectivity.

Please refer to FIGS. 2 and 4B. The method for manufacturing the upper Bragg reflector includes: (1) placing the P-type gallium arsenide layer on a self-biasing device 93 of a radio frequency carrier, and transferring it to the pre-pumping chamber 80, And evacuate to make the pressure in the pre-pumping chamber 80 lower than 1×10 ⁻³ Torr. (2) The P-type GaAs layer is delivered to the sputtering chamber 90, and the pressure in the sputtering chamber 90 is maintained at 5×10 ⁻⁶ Torr. (3) In an argon atmosphere of 3×10 ^-3 Torr, according to the first operating condition or the second operating condition, the silicon dioxide layer is formed by sputtering with nano-sputtering and plasma micro-oxidation procedures. The specific operating conditions of the first operating condition and the second operating condition are as described above, and will not be repeated here.

Please refer to FIG. 8 , the upper Bragg reflector 40 of the present invention may have a structural design as shown in FIG. 8 . According to the sequence formed on the second conductivity type semiconductor layer 33 (P-type gallium arsenide layer), the thicknesses of the first group of silicon dioxide layer 42 and silicon layer 41 are 543.9 nm and 100.3 nm respectively, and the thicknesses of the second group The thicknesses of the silicon dioxide layer 42 and the silicon layer 41 in the first group are 271.7 nanometers and 100.3 nanometers respectively, the thicknesses of the silicon dioxide layer 42 and the silicon layer 41 in the third group are 272.2 nanometers and 100.1 nanometers respectively, and finally, at the last A silicon dioxide layer 42 with a thickness of 272 nm is formed on the upper silicon layer 41 .

According to the above-mentioned structural design, the upper Bragg reflector 40 of the present invention has an average reflectance of 98.8% in the wavelength range of 1450 nm to 1650 nm, and can be applied to the vertical common cavity surface emission of 1550 nm. type laser.

[A thin layer of refractory metal oxide (e.g. niobium pentoxide) is formed on the lower Bragg mirror in a 1550nm vertical common cavity surface-emitting laser as a thermal diffusion barrier]

The Bragg reflector of the present invention can be applied to the lower Bragg reflector 20 or the upper Bragg reflector 40 in a 1550nm vertical resonant cavity surface-emitting laser. Optics in the lower Bragg mirror 20 The multilayer film is formed by nano-sputtering and plasma micro-oxidation. The optical reflectivity of the lower Bragg reflector 20 can be as high as 99.9% to 100%. Next, an N-type gallium arsenide layer (first conductive type semiconductor layer 31 ), multiple quantum wells (Multiple Quantum Well, MQW) (multiple quantum well active light-emitting structure layer 30) and P-type gallium arsenide layer (second conductivity type semiconductor layer 33). On the other hand, the process temperature of the traditional metalorganic chemical vapor deposition method is as high as 800°C. At high temperature, the silicon atoms in the lower Bragg mirror 20 may diffuse into the N-type gallium arsenide layer (the first conductive type semiconductor layer 31). In order to avoid the diffusion of silicon atoms, a refractory metal oxide thin layer (for example: niobium pentoxide layer) can be set on the uppermost silicon layer 21 in the lower Bragg reflector 20 as a thermal diffusion barrier layer 24, such as Figure 9 shows. The thickness design of the thermal diffusion barrier layer 24 must conform to the principle of light interference and maintain the high reflectivity (99.9% to 100%) of the lower Bragg reflector 20 .

Please refer to shown in Fig. 2, the manufacturing method of lower Bragg reflector comprises: (1) base material is placed on the radio frequency stage self-biasing device 93, is sent in the pre-pumping chamber 80, and vacuumizes pre-pumping chamber The pressure in chamber 80 is less than 1 x 10 ^-3 Torr. (2) The substrate 10 is transferred from the pre-extraction chamber 80 to the sputtering chamber 90, and the pressure in the sputtering chamber 90 is maintained at 5×10 ⁻⁶ Torr. (3) Under an argon atmosphere of 3× ^10-3 Torr, sputter-deposit a molybdenum layer with a thickness of 60 nm on the substrate by means of DC sputtering or radio-frequency sputtering, and then sputter on the molybdenum layer Plating deposits a silver layer with a thickness of 20 nm. And, according to the aforementioned steps, alternately stacked silicon layers 21 and silicon dioxide layers 22 are formed on the silver layer (the reflective metal layer 23 ).

Please refer to FIG. 9 , the lower Bragg reflector 20 of the present invention may have a structural design as shown in FIG. 9 . According to the order formed on the silver layer (reflective metal layer 23), the thicknesses of the first group of silicon layer 21 and silicon dioxide layer 22 are 173.3 nm and 270 nm respectively, and the thicknesses of the second group of silicon layer 21 and silicon dioxide The thicknesses of the silicon layer 22 are 98.4 nm and 269.9 nm respectively, the thicknesses of the third group of silicon layer 21 and silicon dioxide layer 22 are respectively 295.2 nm and 269.9 nm, and the thicknesses of the fourth group of silicon layer 21 and silicon dioxide layer 22 have a thickness of 98.5 nanometers and 269.3 nanometers respectively. Finally, on the uppermost silicon dioxide layer 22, a thickness of 89.4 nm silicon layer 21 and 20 nm thick niobium pentoxide layer.

Please refer to shown in Fig. 10, according to the above-mentioned structural design, the lower Bragg reflector 20 of the present invention has an average reflectance of 100.06% in the light in the wavelength range of 1450 nm to 1650 nm, and can be applied to 1550 nm vertical common-cavity surface-emitting laser.

The total thickness of the aforementioned lower Bragg reflector 20 is about 2000 nm. The present invention can precisely control the surface roughness of the silicon dioxide layer on the c-axis through nano-sputtering and plasma micro-oxidation procedures. The arithmetic mean roughness (Ra) of the lower Bragg reflector 20 with the thermal diffusion barrier layer 24 under the atomic force microscope is 0.18 nanometers, the root mean square roughness (Rq) is 0.23 nanometers, and the average peak-to-valley depth (Z) is 2.00 nm.

[Advantageous Effects of Embodiment]

One of the beneficial effects of the present invention is that the manufacturing method of the Bragg reflector provided by the present invention can be achieved by "forming a silicon layer and a silicon dioxide layer that are alternately stacked repeatedly on the silver layer" and "the silicon dioxide layer is Nano-sputtering and plasma micro-oxidation procedures” to improve the reflectivity of the Bragg mirror, thereby achieving the effect of improving the luminous efficiency of the laser device.

Further, the present invention forms a silicon dioxide layer or silicon layer through sputtering, nano-sputtering and plasma micro-oxidation procedures, which can precisely control the thickness of the silicon dioxide layer or silicon layer, and make the silicon dioxide layer or The surface of the silicon layer has the characteristic of high flatness. In this way, the reflectivity of the Bragg mirror can be increased up to 99.9%.

The content disclosed above is only a preferred feasible embodiment of the present invention, and does not therefore limit the scope of the patent application of the present invention. Therefore, all equivalent technical changes made by using the description and drawings of the present invention are included in the application of the present invention. within the scope of the patent.

10: Substrate

20: Lower Bragg reflector

21: Silicon layer

22: Silicon dioxide layer

23: reflective metal layer

Claims (8)

A method for manufacturing a Bragg reflector, the Bragg reflector is applied to a 1550-nanometer vertical resonant cavity surface-emitting laser and used as an upper Bragg reflector or a lower Bragg reflector, and the method for manufacturing the Bragg reflector includes : forming an optical multilayer film on a substrate, the substrate being a silicon wafer, a gallium arsenide wafer, a silicon carbide wafer or a glass substrate; wherein, it is applied to a vertical resonant cavity of 1550 nm When the surface-emitting laser is used as the lower Bragg reflector, the step of forming the optical multilayer film includes: forming a reflective metal layer on the substrate, and forming alternately stacked silicon layers on the reflective metal layer and a silicon dioxide layer, the silicon dioxide layer is formed by a nano-sputtering and plasma micro-oxidation process; When the lower Bragg reflector is described, a thermal diffusion barrier layer is formed on the optical multilayer film, and the diffusion barrier layer is formed through a one-stage sputtering micro-oxidation process, and the reflectivity of the lower Bragg reflector is 99.9% to 100%. The manufacturing method as described in Claim 1, wherein, when applied to the vertical resonant cavity surface-emitting laser of 1550 nm as the lower Bragg reflector, according to the order formed on the substrate , the optical multilayer film comprises: a molybdenum layer with a thickness of 60 nm, a silver layer with a thickness of 20 nm, a silicon layer with a thickness of 173.3 nm, and a silicon dioxide layer with a thickness of 270 nm. layer, said silicon layer with a thickness of 98.2 nm, said silicon dioxide layer with a thickness of 270.4 nm, said silicon layer with a thickness of 295.2 nm, said silicon dioxide layer with a thickness of 269.8 nm, The silicon layer with a thickness of 98.4 nm, the silicon dioxide layer with a thickness of 269.9 nm, and the silicon layer with a thickness of 98.4 nm, the allowable thickness error of each layer in the optical multilayer film is less than ±1 %. The manufacturing method according to claim 1, wherein, when applied to the vertical resonant cavity surface-emitting laser of 1550 nm as the upper Bragg reflector, the cloth The reflectivity of the lager mirror is 96% to 99%. The manufacturing method as described in Claim 1, wherein, when applied to the 1550nm vertical cavity surface-emitting laser as the upper Bragg reflector, the substrate is a gallium arsenide wafer, according to In terms of the order formed on the substrate, the optical multilayer film includes: the silicon dioxide layer with a thickness of 543.9 nm, the silicon layer with a thickness of 100.3 nm, and the silicon dioxide layer with a thickness of 271.7 nm. The silicon dioxide layer, the silicon layer with a thickness of 100.3 nm, the silicon dioxide layer with a thickness of 272.2 nm, the silicon layer with a thickness of 100.1 nm, and the two layers with a thickness of 272 nm For the silicon oxide layer, the allowable thickness error of each layer in the optical multilayer film is less than ±1%. The manufacturing method as described in Claim 1, wherein, when applied to the vertical resonant cavity surface-emitting laser of 1550 nm as the lower Bragg reflector, according to the order formed on the substrate , the optical multilayer film comprises: a molybdenum layer with a thickness of 60 nm, a silver layer with a thickness of 20 nm, a silicon layer with a thickness of 173.3 nm, and a silicon dioxide layer with a thickness of 270 nm. layer, said silicon layer with a thickness of 98.4 nm, said silicon dioxide layer with a thickness of 269.9 nm, said silicon layer with a thickness of 295.2 nm, said silicon dioxide layer with a thickness of 269.9 nm, The silicon layer with a thickness of 98.5 nm, the silicon dioxide layer with a thickness of 269.3 nm, the silicon layer with a thickness of 89.4 nm, and the niobium pentoxide layer with a thickness of 20 nm, the The allowable thickness error of each layer in the optical multilayer film is less than ±1%. The manufacturing method according to claim 1, wherein the reflective metal layer is composed of a single-layer metal layer or a multi-layer metal layer, and the material of the reflective metal layer is selected from the group consisting of: aluminum , silver and molybdenum. The manufacturing method according to claim 1, wherein the reflective metal layer includes an aluminum layer, and the thickness of the aluminum layer is 70 nm to 90 nm. The manufacturing method according to claim 1, wherein the reflective metal layer comprises a molybdenum layer and a silver layer, the molybdenum layer has a thickness of 50 nm to 70 nm, and the silver layer has a thickness of 10 nm to 30 nm.

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