Patent Publication Number: US-2022224080-A1

Title: Vertical cavity surface emitting laser device and manufacturing method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 110100815 filed in Taiwan, R.O.C. on Jan. 8, 2021, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a vertical cavity surface emitting laser (VCSEL) device and its manufacturing method, and more particularly to the VCSEL device and its manufacturing method using a P-type distributed Bragg reflector (DBR) with less stacked layers to achieve low series resistance. 
     Description of Related Art 
     Semiconductor light emitting device can be divided into Light-Emitting Diode (LED) device and Laser Diode (LD) device. The LED device is a divergent light source with weak luminous energy and too-large beam angle, so that its functionality is insufficient and can only be applied for general lighting or used in 2D sensing systems. On the other hand, the laser beam generated by the LD device has large beam angle and better shape than those of the LED device and the advantages of low power consumption, high efficiency and high speed, so that the LD device is applicable for the fields of 3D sensing and optical communication. As to the structural aspect, the structure of the LD device is more complicated, the material requirement is higher, and the design is more difficult, and the epitaxy technology with a high level of difficulty is required for the mass production of the LD device. Although both the LD device and the LED device are light emitting devices, their uses, effects, structures and technical fields are different. 
     As the name suggests, the vertical cavity surface emitting laser (VCSEL) device emits a laser beam vertically from the surface of a grain surface, and the LD device is one of the VCSEL devices. For example, Gallium Arsenide (GaAs) is used as a substrate of the VCSEL device, a first mirror layer is formed at the top of the substrate, an active layer is formed at the top of the first mirror layer, an oxide layer is formed at the top of the active layer, and a second mirror layer is formed at the top of the oxide layer. As an example, wet oxidation is used to manufacture the VCSEL device, the substrate is an N-type (n+GaAs or N−GaAs) substrate, the first mirror layer is an N-type distributed Bragg reflector (N-DBR), and the second mirror layer is a P-type distributed Bragg reflector P-DBR). The VCSEL device uses the second mirror layer and the first mirror layer disposed at the top and bottom of the active layer respectively as reflective mirror surfaces to generate a laser beam emitted from a resonant cavity. 
     For example, the N-DBR is generally formed by repeatedly stacking a stacked pair composed of a lower layer Al 0.12 Ga 0.88 As and an upper layer Al 0.9 Ga 0.1 As, and the N-DBR can be obtained by doping silicon with an undoped DBR, and the N-DBR has approximately 35 silicon-doped stacked pairs. The P-DBR is also formed by repeatedly stacking a stacked pair composed of a lower layer Al 0.12 Ga 0.88 As and an upper layer A l0.9 Ga 0.1 As, and the P-DBR can be obtained by doping carbon with an undoped DBR, and the P-DBR has approximately 25 carbon-doped stacked pairs. The N-DBR and the P-DBR adopt a total of approximately 60 stacked pairs (or approximately 120 layers) to achieve high reflectivity of approximately 99.9% for the N-DBR and approximately 99.0% for the P-DBR. However, the large quantity of layers (up to 120 layers) also leads to high series resistance. 
     In one of the methods, the high series resistance is overcome by performing a high-concentration silicon and carbon doping for the N-DBR and the P-DBR respectively, but actually the carbon doping concentration of P-DBR (which is a P-type semiconductor) has an upper limit of approximately 0.30×10 19 ˜1.0×10 19  atoms/cm 3 , so that the resistance value of the P-DBR cannot be lower than the required resistance value. Even though the carbon doping concentration of the P-DBR can be 1.0×10 19  atoms/cm 3  or above, it will be difficult to control the reproducibility and uniformity of the P-DBR with the same thickness during the epitaxial process, and the traditional VCSEL device has an issue of unable to overcome the high series resistance of the P-DBR effectively. 
     SUMMARY 
     Therefore, it is a primary objective of the present disclosure to overcome the problems of the prior art by providing a VCSEL device and its manufacturing method in accordance with the present disclosure. 
     To achieve the foregoing and other objectives, the present disclosure discloses a VCSEL device and its manufacturing method based on the N-DBR can achieve a doping concentration higher than that of the P-DBR to effectively reduce the series resistance, and the effective mass of electron is smaller than that of the electron hole, and the resistance of the N-DBR will not be affected by the oxide apertures disposed at the center of the oxide layer, so that the resistance of the P-DBR is much greater than that of the N-DBR. In this way, a majority of the series resistance of the VCSEL device comes from the P-DBR, so that the present disclosure can reduce the series resistance of the VCSEL device by converting a part of the P-DBR into N-DBR. 
     The present disclosure discloses a VCSEL device and its manufacturing method, and the VCSEL device includes: a substrate; a first mirror layer which is a first N-type distributed Bragg reflector layer disposed at the top of the substrate; a tunnel junction layer disposed at the top of the first mirror layer; a second mirror layer which is a P-type distributed Bragg reflector layer disposed at the top of the tunnel junction layer, and the first mirror layer and the second mirror layer include a plurality of stacked pairs respectively, and stacked pair includes a first layer and a second layer; the tunnel junction layer includes a heavily doped N-type layer and a heavily doped P-type layer, wherein an N-type filling layer is disposed between the heavily doped N-type layer and the first mirror layer, and a P-type filling layer is disposed between the heavily doped P-type layer and the second mirror layer; an active layer, disposed at the top of the second mirror layer; and an oxide layer, disposed at the top of the active layer; and a third mirror layer, disposed at the top of the oxide layer, and the third mirror layer is a second N-type distributed Bragg reflector layer. 
     In another embodiment, the tunnel junction layer has an area equal to the area of the first mirror layer and/or the area of the second mirror layer. 
     In another embodiment, the oxide layer includes an oxide aperture disposed at a central area of the oxide layer and an oxide area disposed around the oxide aperture, and the oxide aperture has an area smaller than the area of the tunnel junction layer. 
     In another embodiment, the tunnel junction layer has an area equal to the area of the first mirror layer and/or the area of the second mirror layer; and the oxide layer includes an oxide aperture disposed at a central area of the oxide layer and an oxide area disposed around the oxide aperture, and the oxide aperture has an area smaller than the area of the tunnel junction layer. 
     In another embodiment, the sum of the thickness of the heavily doped N-type layer and the thickness of the N-type filling layer is equal to the thickness of the first layer, and the sum of the thickness of the heavily doped P-type layer and the thickness of the P-type filling layer is equal to the thickness of the second layer; or the sum of the thickness of the N-type filling layer, the thickness of the heavily doped N-type layer, the thickness of the heavily doped P-type layer and the thickness of the P-type filling layer is equal to the thickness of the first layer, or the thickness of the second layer. 
     The present disclosure further provides a VCSEL device manufacturing method using an in-situ one-time epitaxy to avoid the risk of process variation, and the VCSEL device manufacturing method of this disclosure includes the following epitaxy steps: In a step of providing a substrate, the substrate is provided in a cavity. In the step of forming a first mirror layer: The first mirror layer is formed in-situ at the cavity on the substrate, and the first mirror layer is a first N-type distributed Bragg reflector layer. In the step of forming a tunnel junction layer, the tunnel junction layer is formed in-situ at the cavity on the first mirror layer. In the step of forming a second mirror layer, the second mirror layer is formed in-situ at the cavity on the tunnel junction layer, and the second mirror layer is a P-type distributed Bragg reflector layer. In the step of forming an oxide layer and a third mirror layer, an active layer, the oxide layer and the third mirror layer are formed on the second mirror layer, and the step of forming the oxide layer and the third mirror layer is carried out in-situ at the cavity. 
     In another embodiment, the tunnel junction layer has an area equal to the area of the first mirror layer and/or the area of the second mirror layer; and the oxide layer includes an oxide aperture at a central area of the oxide layer and an oxide area around the oxide aperture, and the oxide aperture has an area smaller than the area of the tunnel junction layer. 
     In another embodiment, the first mirror layer and the second mirror layer include a plurality of stacked pairs, and each stacked pair includes a first layer and a second layer; the tunnel junction layer includes a heavily doped N-type layer and a heavily doped P-type layer, and an N-type filling layer is disposed between the heavily doped N-type layer and the first mirror layer, and a P-type filling layer is disposed between the heavily doped P-type layer and the second mirror layer; and the sum of the thickness of the heavily doped N-type layer and the thickness of the N-type filling layer is equal to the thickness of the first layer, and the sum of the thickness of the heavily doped P-type layer and the thickness of the P-type filling layer is equal to the thickness of the second layer; or the sum of the thickness of the N-type filling layer and the thickness of the heavily doped N-type layer, the thickness of the heavily doped P-type layer and the thickness of the P-type filling layer is equal to the thickness of the first layer or the thickness of the second layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view showing the structure of a VCSEL device in accordance with this disclosure; 
         FIG. 2  is a cross-sectional view showing the structure of a VCSEL device having a stacked pair in accordance with this disclosure; 
         FIG. 3  is a cross-sectional view showing the structure of a tunnel junction layer and a filling layer in accordance with this disclosure; 
         FIG. 4  is a flow chart showing the epitaxy steps of a VCSEL device manufacturing method in accordance with this disclosure; and 
         FIG. 5  shows an electric field amplitude versus distance graph to compare a VCSEL device of the present disclosure with a traditional VCSEL device. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     This disclosure will now be described in more detail with reference to the accompanying drawings that show various embodiments of the invention. 
     With reference to  FIG. 1  for a VCSEL device of the present disclosure, the VCSEL device  100  includes: a first electrode  10 ; a substrate  11 , which can be contacted with the first electrode  10  and disposed at the top or bottom of the substrate  11 ; a first mirror layer  12 , which is disposed at the top of the substrate  11 , and can be a first N-type distributed Bragg reflector (first N-DBR) and contacted with an upper surface of the substrate  11 ; a tunnel junction (TJ) layer  13 , which is disposed at the top of the first mirror layer  12  and can be contacted with an upper surface of the first mirror layer  12 ; a second mirror layer  14 , which is disposed at the top of the tunnel junction layer  13 , and can be a P-type distributed Bragg reflector (P-DBR), and contacted with an upper surface of the tunnel junction layer  13 ; an active layer  15 , which is disposed at the top of the second mirror layer  14 , and can be contacted with an upper layer of the second mirror layer  1 ; an oxide layer  16 , disposed at the top of the active layer  15 ; a third mirror layer  17 , disposed at the top of the oxide layer  16 , and can be a second N-type distributed Bragg reflector (second N-DBR); and a second electrode  18 , which is disposed at the top of the third mirror layer  17  and can be contacted with the third mirror layer  17 . In other words, the VCSEL device  100  includes the substrate  11 , the first mirror layer  12 , the tunnel junction layer  13 , the second mirror layer  14 , the active layer  15 , the oxide layer  16  and the third mirror layer  17  sequentially arranged from bottom to top. 
     The first electrode  10  and the second electrode  18  can be made of gold, silver, copper, iron, cobalt, nickel, titanium or their analogues or alloys, wherein the alloy can be zinc alloy or germanium alloy, and the first electrode  10  and the second electrode  18  can be made of the same material or different materials. Basically, the first electrode  10  and the second electrode  18  can be both N-type (ohmic) electrodes or can be both P-type (ohmic) electrodes. For example, the first electrode  10  is an N-type electrode and the second electrode  18  is also N-type electrode. The second electrode  18  is in a ring shape, with its central area acting as a light exit aperture  181 , and the VCSEL device  100  can emit a laser beam through the light exit aperture  181 . 
     The substrate  11  can be made of a common monocrystalline semiconductor material such as the gallium arsenide (GaAs), gallium nitride (GaN), aluminium gallium arsenide (AlGaAs) or gallium phosphide (GaP) substrate. Preferably, the substrate  11  is a GaAs substrate. The substrate  11  includes a buffer layer  111  made of the same material, and the buffer layer  111  is an N-type semiconductor layer and can be a part of the substrate  11 . The substrate  11  must have a smooth crystal surface provided for the subsequent epitaxy growth process of forming the first mirror layer  12  on the upper surface of the buffer layer  111 . In other words, the first mirror layer  12  is grown on the upper surface of the substrate  11 . 
     Each of the first mirror layer  12 , second mirror layer  14  and third mirror layer  17  is a multilayer structure, in which each adjacent layer is made of alternately stacked semiconductor materials with different refractive indexes. The first mirror layer  12  (or first N-DBR) is an N-type semiconductor layer such as a doped silicon (Si) and/or tellurium (Te) AlGaAs layer. The second mirror layer  14  (P-DBR) is a P-type semiconductor layer such as a doped carbon (C) and/or zinc (Zn) AlGaAs layer. Each of the first mirror layer  12  and the second mirror layer  14  is an AlGaAs multilayer structure with different aluminium mole percentages to change the refractive index. The third mirror layer  17  (or second N-DBR) is also an N-type semiconductor layer such as a doped silicon (Si) and/or tellurium (Te) AlGaAs layer. The first mirror layer  12  and the third mirror layer  17  can be the same N-type semiconductor layer or different N-type semiconductor layers. Each of the first mirror layer  12  and the third mirror layer  17  has a reflectivity greater than 99.9%, and the overall reflectivity of the combined first mirror layer  12 , tunnel junction layer  13  and second mirror layer  14  is also greater than 99.9%. 
     The tunnel junction layer  13  can be a multilayer structure including a heavily doped N-type layer  131  and a heavily doped P-type layer  132 . In the tunnel junction layer  13 , the heavily doped P-type layer  132  is disposed adjacent to the second mirror layer  14 , and the heavily doped N-type layer  131  is disposed adjacent to the first mirror layer  12 . The tunnel junction layer  13  is made of a material such as GaAs, AlGaAs, InGaP, AlInP, AlGaInP or InGaAsP. For example, the heavily doped N-type layer  131  is a doped silicon (Si) and/or tellurium (Te) AlGaAs layer or a Group III phosphide semiconductor layer such as an indium gallium phosphide (InGaP) layer; and the heavily doped P-type layer  132  is a doped carbon (C) AlGaAs layer or a Group III phosphide semiconductor layer (such as an InGaP layer). 
     The active layer  15  can include one or more quantum well layers with spectral gap wavelength, and each quantum well layer emits laser beams under an operating wavelength. For example, the active layer  15  can include an AlGaAs layer, a GaAs layer, a gallium arsenic phosphide (GaAsP) layer or an indium gallium arsenide (InGaAs) layer. The active layer  15  can also include quantum holes or other device structures with an appropriate light emitting property such as quantum dots or similar device structures. The quantum well layers, quantum holes or quantum dots are disposed in the active layer  15  and separated to generate the required laser beams. 
     The oxide layer  16  can be an optically and electrically limited oxide layer formed by oxidizing one or more epitaxial layers. For example, the oxide layer  16  can be an oxide area  161  of aluminium oxide (A 1203 ) formed by a lateral oxidation of the epitaxial layer (such as an AlGaAs layer) and an oxide aperture  162  including a metal (such as unoxidized aluminium) and disposed at a central area. Therefore, the oxide area  161  is an insulated area disposed around the conductive oxide aperture  162 , and the oxide aperture  162  is passed through the oxide area  161  to form a conductive path with a limited area, and electricity and light (laser beam) are passed from the oxide aperture  162 , and the oxide aperture  162  is a current-limiting aperture. The smaller the oxide aperture  162 , the larger the resistance value. The oxide aperture  162  can be formed at the bottom of the light exit aperture  181 , and the oxide aperture  162  is slightly smaller than the light exit aperture  181 . 
     It is noteworthy that the tunnel junction layer  13  is disposed between the first mirror layer  12  and the second mirror layer  14 , so that the first N-DBR of the first mirror layer  12 , the tunnel junction layer  13 , and the P-DBR of the second mirror layer  14  can be formed with the same or substantially similar valence band, and the combination of the first mirror layer  12 , the tunnel junction layer  13  and the second mirror layer  14  can be formed into a P-type distributed Bragg reflector structure  20 . In other words, the tunnel junction layer  13  is allowed to switch from the N-type semiconductor layer to the P-type semiconductor layer. For example, the tunnel junction layer  13  is switched from the first N-DBR of the first mirror layer  12  to the P-DBR of the second mirror layer  14 . Therefore, the dimensions (including area and shape) of the tunnel junction layer  13  can be the same as those of the first mirror layer  12  and/or the second mirror layer  14 . 
     In addition, the tunnel junction layer  13  can be formed at the bottom of the oxide aperture  162 , and the oxide aperture  162  has an area smaller than the area of the tunnel junction layer  13 , so that the VCSEL device  100  of the present disclosure uses the oxide aperture  162  with a smaller area as an electrically and optically limited channel, and the tunnel junction layer  13  with a larger area is not used as the electrically and optically limited channel. In other words, the tunnel junction layer  13  is not used for the effect of the current-limiting aperture. Further, the VCSEL device  100  of the present disclosure has the oxide aperture  162  and the tunnel junction layer  13  at the same time, and the effects and purposes of the oxide aperture  162  and the tunnel junction layer  13  are different. The oxide aperture  162  is a current-limiting aperture and the tunnel junction layer  13  is used to switch the first N-DBR of the first mirror layer  12  to the P-DBR of the second mirror layer  14 . 
     As described above, each of the first mirror layer  12 , the second mirror layer  14  and the third mirror layer  17  is a multilayer structure with each adjacent layer made of alternately stacked semiconductor materials of different refractive indexes. In  FIG. 2 , each of the first mirror layer  12 , the second mirror layer  14  and the third mirror layer  17  includes a plurality of stacked pairs  30 . Each stacked pair  30  includes a first layer  301  and a second layer  302 . The first layer  301  and the second layer  302  of the stacked pair  30  are formed by different materials of different concentrations, and the first layer  301  includes aluminium gallium arsenide (Al 0.12 Ga 0.88 As) having an aluminium concentration of 12% and a refractive index of 3.55; the second layer  302  includes aluminium gallium arsenide (Al 0.9 Ga 0.1 As) having an aluminium concentration of 90% and a refractive index of 2.93. In the calculation of thickness, each adjacent layer (including the first layer  301  and the second layer  302 ) has a thickness approximately equal to a quarter of the wavelength multiplied by the refractive index of each layer. The aforementioned wavelength refers to the wavelength (such as 850 nm) of the laser beam emitted by the VCSEL device. In an embodiment, the first mirror layer  12  has W stacked pairs  30 , and the second mirror layer  14  has Z stacked pairs  30 , and the sum of W and Z is approximately equal to 35, and Z is preferably an integer between 1 and 10 such as Z=1, 3, 5 or 10. Please refer to Table 1 below. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Constituent  
                   
                   
                   
                   
                 Dopant  
                 No. of  
               
               
                   
                 of Stacked  
                   
                 X  
                 Thickness  
                   
                 Content  
                 Stacked  
               
               
                 DBR Type  
                 Pair  
                 Material  
                 value  
                 (nm)  
                 Dopant  
                 (atoms/cm 3 )  
                 Pairs 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Second mirror  
                 Second  
                 AlxGa1-  
                 0.9  
                 72  
                 C  
                 3.0 × 10 18    
                 Z  
               
               
                 layer  
                 layer  
                 xAs  
                   
                   
                   
                   
                   
               
               
                 (P-DBR)  
                 First layer  
                 AlxGa1-  
                 0.12  
                 60  
                 C  
                 3.0 × 10 18    
                   
               
               
                   
                   
                 xAs  
                   
                   
                   
                   
                   
               
               
                 First mirror  
                 Second  
                 AlxGa1-  
                 0.9  
                 72  
                 Si  
                 Greater than  
                 W  
               
               
                 layer  
                 layer  
                 xAs  
                   
                   
                   
                 3.0 × 10 18    
                   
               
               
                 (First N-DBR)  
                 First layer  
                 AlxGa1-  
                 0.12  
                 60  
                 Si  
                 Greater than  
                   
               
               
                   
                   
                 xAs  
                   
                   
                   
                 3.0 × 10 18   
               
               
                   
               
            
           
         
       
     
     Wherein, W+Z=35, and Z is an integer between 1 and 10. 
     Since the resistance of the P-DBR is much greater than the resistance of the N-DBR, most of the series resistance of the VCSEL device comes from the P-DBR, and the first mirror layer  12  and the third mirror layer  17  of the VCSEL device  100  of the present disclosure are N-DBRs, and only the second mirror layer  14  is a P-DBR. Compared with the traditional VCSEL device that requires  25  stacked pairs of the P-DBR the VCSEL device  100  of the present disclosure only has at most  10  stacked pairs  30  of the P-DBR. Obviously, the VCSEL device  100  of the present disclosure can reduce the series resistance of the VCSEL device. 
     Based on the description above, the three-layer combination of the first mirror layer  12 , the tunnel junction layer  13  and the second mirror layer  14  constitutes the P-type distributed Bragg reflector structure  20 , so that the thickness of the heavily doped N-type layer  131  and the thickness of the heavily doped P-type layer  132  can be equal to the thickness of the first layer  301  (such as 60 nm as shown in Table 1) and the thickness of the second layer  302  (such as 72 nm as shown in Table 1) to comply with the design of reflectivity for the each stacked layer of the DBR (the P-type distributed Bragg reflector structure  20 ). Embodiments of various tunnel junction layers  13  will be described below. 
     Basically, in order to achieve the tunnelling function, the thickness of the heavily doped N-type layer  131  of the tunnel junction layer  13  and the thickness of the heavily doped P-type layer  132  of the tunnel junction layer  13  must be at least 10 nm (preferably 10 nm˜15 nm), and its doping concentration must be greater than 1.0×10 20  atoms/cm 3  (preferably greater than 3.0×10 20  atoms/cm 3 ). Therefore, based on the configuration of the heavily doped N-type layer  131  and the heavily doped P-type layer  132  with a minimum thickness, another embodiment as shown in  FIG. 3  is implemented, wherein an N-type filling layer  1310  is disposed between the heavily doped N-type layer  131  and the first mirror layer  12 , and a P-type filling layer  1320  is disposed between the heavily doped P-type layer  132  and the second mirror layer  14 . The sum of the thickness of the heavily doped N-type layer  131  and the thickness of the N-type filling layer  1310  is equal to the thickness of the first layer  301 , and the sum of the thickness of the heavily doped P-type layer  132  and the thickness of the P-type filling layer  1320  is equal to the thickness of the second layer  302 , thereby complying with the design of reflectivity of each stacked layer of the DBR (the P-type distributed Bragg reflector structure  20 ). 
     In another embodiment, the tunnel junction layer  13 , the N-type filling layer  1310  and the P-type filling layer  1320  are AlGaAs layers, and the VCSEL device  100  is sequentially and adjacently stacked with the first mirror layer  12 , the N-type filling layer  1310 , the heavily doped N-type layer  131 , the heavily doped P-type layer  132 , the P-type filling layer  1320  and the second mirror layer  14 . Please refer to Table 2 below. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                   
                   
                   
                 Dopant  
                 No. of  
               
               
                   
                   
                   
                 X  
                 Thickness  
                   
                 Content  
                 Stacked  
               
               
                 Type  
                 Constituent  
                 Material  
                 value  
                 (nm)  
                 Dopant  
                 (atoms/cm 3 )  
                 Pairs 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Second mirror  
                 Second layer  
                 AlxGa1-  
                 0.9  
                 72  
                 C  
                 About  
                 Z  
               
               
                 layer  
                   
                 xAs  
                   
                   
                   
                 3.0 × 10 18    
                   
               
               
                 (P-DBR)  
                 First layer  
                 AlxGa1-  
                 0.12  
                 60  
                 C  
                   
                   
               
               
                   
                   
                 xAs  
                   
                   
                   
                   
                   
               
               
                 Filling layer  
                 P-type filling  
                 AlxGa1-  
                 0.9  
                 57  
                 C  
                 3.0 × 10 18    
                 — 
               
               
                   
                 layer  
                 xAs  
                   
                   
                   
                   
                   
               
               
                 Tunnel junction  
                 Heavily doped  
                 AlxGa1-  
                 0.9  
                 15  
                 C  
                 Greater than  
                 — 
               
               
                 layer (TJ)  
                 P-type layer  
                 xAs  
                   
                   
                   
                 3.0 × 10 20    
                   
               
               
                   
                 Heavily doped  
                 AlxGa1-  
                 0.12  
                 15  
                 Te  
                 Greater than  
                 — 
               
               
                   
                 N-type layer  
                 xAs  
                   
                   
                   
                 3.0 × 10 20    
                   
               
               
                 Filling layer  
                 N-type filling  
                 AlxGa1-  
                 0.12  
                 45  
                 Si  
                 Greater than  
                 — 
               
               
                   
                 layer  
                 xAs  
                   
                   
                   
                 3.0 × 10 18    
                   
               
               
                 First mirror  
                 Second layer  
                 AlxGa1-  
                 0.9  
                 72  
                 Si  
                 Greater than  
                 W  
               
               
                 layer  
                   
                 xAs  
                   
                   
                   
                 3.0 × 10 18    
                   
               
               
                 (First N-DBR)  
                 First layer  
                 AlxGa1-  
                 0.12  
                 60  
                 Si  
                 Greater than  
                   
               
               
                   
                   
                 xAs  
                   
                   
                   
                 3.0 × 10 18   
               
               
                   
               
            
           
         
       
     
     The sum (60 nm) of the thickness of the heavily doped N-type layer  131  (15 nm) and the thickness of the N-type filling layer  1310  (45 nm) is equal to the thickness of the first layer  301  (60 nm), and the sum (72 nm) of the thickness of the heavily doped P-type layer  132  (15 nm) and the thickness of the P-type filling layer  1320  (57 nm) is equal to the thickness of the second layer  302  (72 nm). Wherein, W+Z=35, and Z is an integer between 1 and 10. 
     In another embodiment, the tunnel junction layer  13  is a combination of an AlGaAs layer and an InGaP layer, and the N-type filling layer  1310  and the heavily doped N-type layer  131  are InGaP layers (with a refractive index of 3.27), and the heavily doped P-type layer  132  and the P-type filling layer  1320  are AlGaAs layers. Please refer to Table 3 below. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                   
                   
                   
                   
                 Dopant  
                 No. of  
               
               
                   
                   
                   
                 X  
                 Thickness  
                   
                 Content  
                 Stacked  
               
               
                 Type  
                 Constituent  
                 Material  
                 value  
                 (nm)  
                 Dopant  
                 (atoms/cm 3 )  
                 Pairs 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Second mirror  
                 Second layer  
                 AlxGa1-  
                 0.9  
                 72  
                 C  
                 About  
                 Z  
               
               
                 layer  
                   
                 xAs  
                   
                   
                   
                 3.0 × 10 18    
                   
               
               
                 (P-DBR)  
                 First layer  
                 AlxGa1-  
                 0.12  
                 60  
                 C  
                   
                   
               
               
                   
                   
                 xAs  
                   
                   
                   
                   
                   
               
               
                 Filling layer  
                 P-type filling  
                 AlxGa1-  
                 0.9  
                 57  
                 C  
                 3.0 × 10 18    
                 — 
               
               
                   
                 layer  
                 xAs  
                   
                   
                   
                   
                   
               
               
                 Tunnel  
                 Heavily doped  
                 AlxGa1-  
                 0.9  
                 15  
                 C  
                 Greater than  
                 — 
               
               
                 junction layer  
                 P-type layer  
                 xAs  
                   
                   
                   
                 3.0 × 10 20    
                   
               
               
                 (TJ)  
                 Heavily doped  
                 InxGa1-  
                 0.5  
                 15  
                 Te  
                 Greater than  
                 — 
               
               
                   
                 N-type layer  
                 xP  
                   
                   
                   
                 3.0 × 10 20    
                   
               
               
                 Filling layer  
                 N-type filling  
                 InxGa1-  
                 0.5  
                 45  
                 Si  
                 Greater than  
                 — 
               
               
                   
                 layer  
                 xP  
                   
                   
                   
                 3.0 × 10 18    
                   
               
               
                 First mirror  
                 Second layer  
                 AlxGa1-  
                 0.9  
                 72  
                 Si  
                 Greater than  
                 W  
               
               
                 layer  
                   
                 xAs  
                   
                   
                   
                 3.0 × 10 18    
                   
               
               
                 (first N-DBR)  
                 First layer  
                 AlxGa1-  
                 0.12  
                 60  
                 Si  
                 Greater than  
                   
               
               
                   
                   
                 xAs  
                   
                   
                   
                 3.0 × 10 18   
               
               
                   
               
            
           
         
       
     
     In Table 3, which is similar to Table 2, the sum (60 nm) of the thickness of the heavily doped N-type layer  131  and the thickness (15 nm) and the thickness of the N-type filling layer  1310  (45 nm) is equal to the thickness of the first layer  301  (60 nm), and the sum (72 nm) of the thickness of the heavily doped P-type layer  132  (15 nm) and the thickness of the P-type filling layer  1320  (57 nm) is equal to the thickness of the second layer  302  (72 nm). Wherein, W+Z=35, and Z is an integer between 1 and 10. 
     In another embodiment, the tunnel junction layer  13  is a combination of an AlGaAs layer and an InGaP layer, and the N-type filling layer  1310  and the heavily doped N-type layer  131  are AlGaAs layers, and the heavily doped P-type layer  132  and the P-type filling layer  1320  are InGaP layers. Please refer to Table 4 below. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
                   
                   
                   
                   
                   
                 Dopant  
                 No. of  
               
               
                   
                   
                   
                 X  
                 Thickness  
                   
                 Content  
                 Stacked  
               
               
                 Type  
                 Constituent  
                 Material  
                 value  
                 (nm)  
                 Dopant  
                 (atoms/cm 3 )  
                 Pairs 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Second mirror  
                 Second layer  
                 AlxGa1-  
                 0.9  
                 72  
                 C  
                 About  
                 Z  
               
               
                 layer  
                   
                 xAs  
                   
                   
                   
                 3.0 × 10 18    
                   
               
               
                 (P-DBR)  
                 First layer  
                 AlxGa1-  
                 0.12  
                 60  
                 C  
                   
                   
               
               
                   
                   
                 xAs  
                   
                   
                   
                   
                   
               
               
                 Filling layer  
                 P-type filling  
                 InxGa1-  
                 0.5  
                 57  
                 C  
                 3.0 × 10 18    
                 — 
               
               
                   
                 layer  
                 xP  
                   
                   
                   
                   
                   
               
               
                 Tunnel  
                 Heavily doped  
                 InxGa1-  
                 0.5  
                 15  
                 C  
                 Greater than  
                 — 
               
               
                 junction layer  
                 P-type layer  
                 xP  
                   
                   
                   
                 3.0 × 10 20    
                   
               
               
                 (TJ)  
                 Heavily doped  
                 AlxGa1-  
                 0.12  
                 15  
                 Te  
                 Greater than  
                 — 
               
               
                   
                 N-type layer  
                 xAs  
                   
                   
                   
                 3.0 × 10 20    
                   
               
               
                 Filling layer  
                 N-type filling  
                 AlxGa1-  
                 0.12  
                 45  
                 Si  
                 Greater than  
                 — 
               
               
                   
                 layer  
                 xAs  
                   
                   
                   
                 3.0 × 10 18    
                   
               
               
                 First mirror  
                 second layer  
                 AlxGa1-  
                 0.9  
                 72  
                 Si  
                 Greater than  
                 W  
               
               
                 layer  
                   
                 xAs  
                   
                   
                   
                 3.0 × 10 18    
                   
               
               
                 (first N-DBR)  
                 first layer  
                 AlxGa1-  
                 0.12  
                 60  
                 Si  
                 Greater than  
                   
               
               
                   
                   
                 xAs  
                   
                   
                   
                 3.0 × 10 18   
               
               
                   
               
            
           
         
       
     
     In Table 4, which is similar to Table 2, the sum (60 nm) of the thickness of the heavily doped N-type layer  131  (15 nm) and the thickness of the N-type filling layer  1310  (45 nm) is equal to the thickness of the first layer  301  (60 nm), and the sum (72 nm) of the thickness of the heavily doped P-type layer  132  (15nm) and the thickness of the P-type filling layer  1320  (57 nm) is equal to the thickness of the second layer  302  (72 nm). 
     Wherein, W+Z=35, and Z is an integer between 1 and 10. 
     In another embodiment, the tunnel junction layer  13  is an AlGaAs layer. Unlike the previous embodiments, the sum of the thickness of the N-type filling layer  1310  and the thickness of the heavily doped N-type layer  131 , the thickness of the heavily doped P-type layer  132 , and the thickness of the P-type filling layer  1320  is equal to the thickness of the first layer  301 . Please refer to Table 5 below. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                   
                   
                   
                   
                   
                   
                 Dopant  
                 No. of  
               
               
                   
                   
                   
                 X  
                 Thickness  
                   
                 Content  
                 Stacked  
               
               
                 Type  
                 Constituent  
                 Material  
                 value  
                 (nm)  
                 Dopant  
                 (atoms/cm 3 )  
                 Pairs 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Second mirror  
                 Second layer  
                 AlxGa1-  
                 0.9  
                 72  
                 C  
                 About  
                 Z  
               
               
                 layer  
                   
                 xAs  
                   
                   
                   
                 3.0 × 10 18    
                   
               
               
                 (P-DBR)  
                 First layer  
                 AlxGa1-  
                 0.12  
                 60  
                 C  
                   
                   
               
               
                   
                   
                 xAs  
                   
                   
                   
                   
                   
               
               
                   
                 Second layer  
                 AlxGa1-  
                 0.9  
                 72  
                 C  
                   
                   
               
               
                   
                   
                 xAs  
                   
                   
                   
                   
                   
               
               
                 Filling layer  
                 P-type filling  
                 AlxGa1-  
                 0.12  
                 15  
                 C  
                 Greater than  
                 — 
               
               
                   
                 layer  
                 xAs  
                   
                   
                   
                 3.0 × 10 18    
                   
               
               
                 Tunnel  
                 Heavily doped  
                 AlxGa1-  
                 0.12  
                 15  
                 C  
                 Greater than  
                 — 
               
               
                 junction layer  
                 P-type layer  
                 xAs  
                   
                   
                   
                 3.0 × 10 20    
                   
               
               
                 (TJ)  
                 Heavily doped  
                 AlxGa1-  
                 0.12  
                 15  
                 Te  
                 Greater than  
                 — 
               
               
                   
                 re-type layer  
                 xAs  
                   
                   
                   
                 3.0 × 10 20    
                   
               
               
                 Filling layer  
                 N-type filling  
                 AlxGa1-  
                 0.12  
                 15  
                 Si  
                 Greater than  
                 — 
               
               
                   
                 layer  
                 xAs  
                   
                   
                   
                 3.0 × 10 18    
                   
               
               
                 First mirror  
                 Second layer  
                 AlxGa1-  
                 0.9  
                 72  
                 Si  
                 Greater than  
                 W  
               
               
                 layer  
                   
                 xAs  
                   
                   
                   
                 3.0 × 10 18    
                   
               
               
                 (first N-DBR)  
                 First layer  
                 AlxGa1-  
                 0.12  
                 60  
                 Si  
                 Greater than  
                   
               
               
                   
                   
                 xAs  
                   
                   
                   
                 3.0 × 10 18   
               
               
                   
               
            
           
         
       
     
     In Table 5, the sum (60 nm) of the thickness of the N-type filling layer  1310  (15 nm), the thickness of the heavily doped N-type layer  131  (15 nm), the thickness of the heavily doped P-type layer  132  (15 nm) and the thickness of the P-type filling layer  1320  (15 nm) is equal to the thickness of the first layer  301  (60 nm). Wherein, W+Z=35, and Z is an integer between 1 and 10. 
     In another embodiment, the tunnel junction layer  13  is an AlGaAs layer. The sum of the thickness of the N-type filling layer  1310 , the thickness of the heavily doped N-type layer  131 , the thickness of the heavily doped P-type layer  132 , and the thickness of the P-type filling layer  1320  is equal to the thickness of the second layer  302 . Please refer to Table  6  below. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 6 
               
               
                   
               
               
                   
                   
                   
                   
                   
                   
                 Dopant  
                 No. of  
               
               
                   
                   
                   
                 X  
                 Thickness  
                   
                 Content  
                 Stacked  
               
               
                 Type  
                 Constituent  
                 Material  
                 value  
                 (nm)  
                 Dopant  
                 (atoms/cm 3 )  
                 Pairs 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Second mirror  
                 Second layer  
                 AlxGa1-  
                 0.9  
                 72  
                 C  
                 About  
                 Z  
               
               
                 layer  
                   
                 xAs  
                   
                   
                   
                 3.0 × 10 18    
                   
               
               
                 (P-DBR)  
                 First layer  
                 AlxGa1-  
                 0.12  
                 60  
                 C  
                   
                   
               
               
                   
                   
                 xAs  
                   
                   
                   
                   
                   
               
               
                 Filling layer  
                 P-type filling  
                 AlxGa1-  
                 0.9  
                 21  
                 C  
                   
                 — 
               
               
                   
                 layer  
                 xAs  
                   
                   
                   
                   
                   
               
               
                 Tunnel  
                 Heavily doped  
                 AlxGa1-  
                 0.9  
                 15  
                 C  
                 Greater than  
                 — 
               
               
                 junction layer  
                 P-type layer  
                 xAs  
                   
                   
                   
                 3.0 × 10 20    
                   
               
               
                 (TJ)  
                 Heavily doped  
                 AlxGa1-  
                 0.9  
                 15  
                 Te  
                 Greater than  
                 — 
               
               
                   
                 N-type layer  
                 xAs  
                   
                   
                   
                 3.0 × 10 20    
                   
               
               
                 Filling layer  
                 N-type filling  
                 AlxGa1-  
                 0.9  
                 21  
                 Si  
                 3.0 × 10 18    
                 — 
               
               
                   
                 layer  
                 xAs  
                   
                   
                   
                   
                   
               
               
                 First mirror  
                 First layer  
                 AlxGa1-  
                 0.12  
                 60  
                 Si  
                 About  
                 — 
               
               
                 layer  
                   
                 xAs  
                   
                   
                   
                 3.0 × 10 18    
                   
               
               
                 (First N-DBR)  
                 Second layer  
                 AlxGa1-  
                 0.9  
                 72  
                 Si  
                 Greater than  
                 W  
               
               
                   
                   
                 xAs  
                   
                   
                   
                 3.0 × 10 18    
                   
               
               
                   
                 First layer  
                 AlxGa1-  
                 0.12  
                 60  
                 Si  
                 Greater than  
                   
               
               
                   
                   
                 xAs  
                   
                   
                   
                 3.0 × 10 18   
               
               
                   
               
            
           
         
       
     
     In Table 6, the sum (72 nm) of the thickness of the N-type filling layer  1310  (21 nm), the thickness of the heavily doped N-type layer  131  (15 nm), the thickness of the heavily doped P-type layer  132  (15 nm) and the thickness of the P-type filling layer  1320  (21nm) is equal to the thickness of the second layer  302 . Wherein, W+Z=35, and Z is an integer between 1 and 10. 
     It is noteworthy that the configuration of the N-type filling layer  1310  and the P-type filling layer  1320  can make the sum of the thickness of the N-type filling layer  1310 , the thickness of the tunnel junction layer  13 , and the thickness of the P-type filling layer  1320  to be equal to the thickness of the first layer  301  or the thickness of the second layer  302  to comply with the thickness of each adjacent layer which is equal to a quarter of the emitting wavelength multiplied by the refractive index of each layer. Therefore, the configuration of the N-type filling layer  1310  and the P-type filling layer  1320  can reduce the thickness of the heavily doped N-type layer  131  and the thickness of the heavily doped P-type layer  132 . For example, the thickness can be reduced to 15 nm, in order to further overcome the difficulty of controlling the reproducibility and uniformity of a traditional P-type semiconductor in a doping process with high carbon doping concentration due to the thickness of the first layer  301  or the thickness of the second layer  302 . 
     In  FIG. 4 , the VCSEL device  100  of the present disclosure is manufactured by a VCSEL device manufacturing method comprising the following epitaxy steps. 
     S 1 : Provide a substrate  11  in a cavity, wherein the substrate  11  is a GaAs substrate. 
     S 2 : Form a first mirror layer  12  (or first N-DBR) in-situ at the cavity on the substrate  11  by Molecular Beam Epitaxy (MBE) or Metal Organic Chemical Vapor Deposition (MOCVD), wherein the first mirror layer  12  is a doped silicon (Si) and/or tellurium (Te) AlGaAs layer. 
     S 3 : Form a tunnel junction layer  13  in-situ at a cavity on the first mirror layer  12  by MBE or MOCVD, wherein both the heavily doped N-type layer  131  and the heavily doped P-type layer  132  of the tunnel junction layer  13  have a thickness equal to 10 nm˜15 nm and a doping concentration greater than 1.0×10 20  atoms/cm 3 . 
     S 4 : Form a second mirror layer  14  (P-DBR) in-situ at a cavity on the tunnel junction layer  13  by MBE or MOCVD. 
     S 5 : Sequentially form an active layer  15 , an oxide layer  16  and a third mirror layer  17  (or second N-DBR) in-situ at a cavity on the second mirror layer  14  by MBE or MOCVD, wherein the oxide layer  16  is manufactured in-situ or ex-situ or manufactured at different cavities by wet oxidation. Preferably the oxide layer  16  is manufactured in-situ by wet oxidation, and the aluminium mole percentage of the oxide layer  16  is Al 0.95 Ga 0.05 As or above to facilitate the formation of an insulating oxide area  161  (or aluminium oxide area) during the oxidation process. 
     It is noteworthy that the epitaxy steps of the VCSEL device manufacturing method including the step S 1  of providing a substrate, the step S 2  of forming a first mirror layer, the step S 3  of forming a tunnel junction layer, and the step S 4  of forming a second mirror layer are performed in-situ in the same cavity and completed in a “first-time epitaxy” manner, and even the step S 5  of forming an active layer, an oxide layer and a third mirror layer is also performed in-situ in the same cavity and completed in the same “one-time epitaxy” manner as mentioned above. In this way, the tunnel junction layer  13  has dimensions (including area and shape) same as those of the first mirror layer  12  and/or the second mirror layer  14 . In other words, if the tunnel junction layer  13  has an area smaller than the area of the first mirror layer  12  or the area of the second mirror layer  14 , then it will be necessary to remove the tunnel junction layer  13  from the epitaxial chamber after its formation, and reduce the tunnel junction layer  13  in other chambers by dry or wet etching, and then transfer them back to the epitaxial cavity for a “second-time epitaxy” of the second mirror layer  14 . Obviously, moving the tunnel junction layer into and out from the epitaxial cavity twice will cause a risk of process variation, so that the VCSEL device manufacturing method of the present disclosure performs an in-situ one-time epitaxy to avoid the risk of process variation. 
     In Table 2, the VCSEL device of an embodiment (with Z=10) has an internal electric field intensity distributed in the vertical direction as follows: The structure of a traditional VCSEL device includes a first electrode, a substrate, an N-DBR, an active layer, an oxide layer, a P-DBR and a second electrode sequentially arranged from bottom to top. In an embodiment of the present disclosure, the first electrode, substrate, active layer, oxide layer and second electrode of the VCSEL device  100  have the same composition, structure and thickness of the traditional VCSEL device. The differences between the VCSEL device  100  of the present disclosure and the traditional VCSEL device different are: (1) The VCSEL device  100  of the present disclosure has the tunnel junction layer  13 ; (2) The third mirror layer  17  (or the second N-DBR) of the VCSEL device  100  of the present disclosure has  25  stacked pairs  30 , and the corresponding P-DBR of the traditional VCSEL device also has  25  stacked pairs; (3) The P-type distributed Bragg reflector structure  20  of the VCSEL device  100  of the present disclosure includes the second mirror layer  14  (P-DBR) with 10 (Z=10) stacked pairs  30  and the first mirror layer  12  (first N-DBR) with 25 (W=25) stacked pairs  30 , and the first mirror layer  12  and the second mirror layer  14  have a total of  35  stacked pairs  30 , and the corresponding N-DBR of the traditional VCSEL device also has  35  stacked pairs. Obviously, the VCSEL device  100  of the present disclosure has the P-DBR  10  with only 10 stacked pairs, which is less than the P-DBR with  25  stacked pairs in the traditional VCSEL device, so that the VCSEL device  100  of the present disclosure can reduce the series resistance of the VCSEL device significantly. In  FIG. 5 , the series resistance is reduced, so that the VCSEL device  100  of the present disclosure improves the vertical distribution of electric field intensity by 32.7% over the traditional VCSEL device. The vertically distributed electric field intensity can be used with a commercially available VCSEL simulator (such as LASERMOD) to execute numerical analysis. 
     The present disclosure uses the tunnel junction layer to switch a part of the P-DBR of the VCSEL device to N-DBR in order to reduce the series resistance of the VCSEL device, and the tunnel junction layer is not used for the effect of a current-limiting aperture. In the present disclosure, the configuration of the N-type filling layer and the P-type filling layer can reduce the thickness of the heavily doped N-type layer and the thickness of the heavily doped P-type layer to comply with the design of reflectively of each stacked layer of the DBR. The VCSEL device manufacturing method of the present disclosure adopts an in-situ and one-time epitaxy to avoid the risk of process variation.