Abstract:
A semiconductor device used for conversion between light and electricity, comprising a semiconductor stack comprising an upper surface; and an upper electrode formed on the semiconductor stack and comprising a first linear electrode and second electrodes, wherein the first linear electrode is closer to a center of the upper surface than the second electrodes, wherein the first linear electrode has a width varying along a first direction thereof, and each of the second electrodes has a uniform width along a second direction thereof.

Description:
REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/894,980, entitled “Concentrated Photovoltaic Cell”, filed May 15, 2013, (Attorney Docket No. EPIS/0036), which claims the right of priority based on TW application Serial No. 101119652, filed on May 30, 2012, and the content of which are hereby incorporated by reference in their entireties. 
     
    
     TECHNICAL FIELD 
       [0002]    The application relates to a semiconductor device, and more particularly, to a semiconductor device comprising a semiconductor stack comprising an upper surface; and an upper electrode comprising an electrode pattern. 
       DESCRIPTION OF BACKGROUND ART 
       [0003]    Due to the shortage of fossil energy, countries around the world are aware of the importance of the environmental protection. In recent years, alternative energy and renewable energy technologies are developed, wherein the photovoltaic cell gets much attention. The photovoltaic cell directly converts solar energy into electrical energy. When the amount of the sunlight is greater and the concentration magnification of the concentrator module is higher, the electricity per unit area of the photovoltaic cell is higher and the cost of power generation of the photovoltaic cell is cheaper. 
         [0004]    The conversion efficiency of the photovoltaic cells differs when that material of the photovoltaic cells changes. For example, the conversion efficiency of a silicon-based photovoltaic cell is about 12%˜20%, and the conversion efficiency of a group III-V based photovoltaic cell is about 31%˜41%. The silicon material absorbs energy having wavelength between 400 nm and 1100 nm, and the group III-V material absorbs energy having wavelength between 300 nm and 1900 nm. The conversion efficiency of the group III-V based photoelectric cell is higher compared with the silicon-based photovoltaic cell. 
         [0005]    The concentrated photovoltaic cell generates power by focusing the sunlight on the group III-V based photovoltaic cell through optical concentrator so the power generation efficiency of the photovoltaic cell is increased and the cost of the power generation is reduced. Taking a photovoltaic cell having a size of 4 inches wafer and comprising group III-V based material for example, it can produce 2.4 W power under one sun without the optical concentrator and 650 W power under 500 suns with the optical concentrator. In this case, the concentration magnification of the optical concentrator is expressed with multiples of sun. For example, 500 suns expressed that the light intensity received by the photovoltaic cell with the optical concentrator is 500 times of that without the optical concentrator under the same unit area. 
         [0006]      FIG. 1  illustrates a diagram of a conventional concentrator module  1 . The concentrator module  1  comprises a first optical concentrator  13 , a second optical concentrator  11  and a photovoltaic cell  10 .  FIG. 2  illustrates a top-viewed diagram of the photovoltaic cell  10 . The photovoltaic cell  10  comprises a plurality of collector electrodes  102  and a plurality of grid electrodes  103  formed on an upper surface  101 .  FIG. 2A  illustrates a partial enlargement of a top-viewed diagram of the plurality of grid electrodes  103 . Each of the plurality of grid electrodes  103  comprises a same width w, and a spacing s between adjacent grid electrodes  103  is the same. A pitch d between the first grid electrode  103   a  and the second grid electrode  103   b  is the sum of the width w and the spacing s. As shown in  FIG. 2A , the pitch d between the plurality of grid electrodes  103  is the same. 
         [0007]    The first optical concentrator  13  and the second optical concentrator  11  focuses a sunlight  12  on the upper surface  101  of the photovoltaic cell  10  with high concentration magnification, which achieves higher photoelectric conversion efficiency, provides higher power generation and reduces the costs of power generation. However, the light concentration of the conventional concentrator module  1  is uneven. When the sunlight  12  is incident on the upper surface  101  of the photovoltaic cell  10 , the light intensity distribution of the sunlight  12  is uneven on the upper surface  101 , which leads to higher resistance of the photovoltaic cell  10  and reduces the power generation efficiency of the photovoltaic cell  10  as a whole.  FIG. 3  illustrates an example of the conventional photovoltaic cell  10  with the conventional concentrator module  1 .  FIG. 3  shows an example of the photovoltaic cell  10  having a size 5 mm×5 mm. The photovoltaic cell  10  receives the sunlight  12  from the concentrator module  1 . Within a radius of 1 mm from the center of the upper surface  101  of the photovoltaic cell  10 , the concentration magnification of the sunlight  12  incident on the photovoltaic cell  10  by the first optical concentrator  13  and the second optical concentrator  11  is more than 1000 suns. Beyond a radius of 1 mm from the center of the upper surface  101  of the photovoltaic cell  10 , the concentration magnification of the sunlight  12  incident on the photovoltaic cell  10  by the first optical concentrator  13  and the second optical concentrator  11  is less than 200 suns. 
       SUMMARY OF THE APPLICATION 
       [0008]    A semiconductor device used for conversion between light and electricity, comprising a semiconductor stack comprising an upper surface; and an upper electrode formed on the semiconductor stack and comprising a first linear electrode and second electrodes, wherein the first linear electrode is closer to a center of the upper surface than the second electrodes, wherein the first linear electrode has a width varying along a first direction thereof, and each of the second electrodes has a uniform width along a second direction thereof. 
         [0009]    A semiconductor device used for conversion between light and electricity, comprising a semiconductor stack comprising an upper surface; and an upper electrode comprising a first linear electrode and second electrodes, wherein the first linear electrode is closer to a center of the upper surface than the second electrodes, wherein the first linear electrode has a various width, and the second electrodes have a uniform pitch there between. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  illustrates a diagram of a conventional concentrator module; 
           [0011]      FIG. 2  illustrates a top-viewed diagram of a conventional photovoltaic cell; 
           [0012]      FIG. 2A  illustrates a partial enlargement of a top-viewed diagram of a conventional photovoltaic cell; 
           [0013]      FIG. 3  illustrates an example of a conventional photovoltaic cell with a conventional concentrator module; 
           [0014]      FIG. 4  illustrates a cross-sectional diagram of a concentrated photovoltaic cell in accordance with a first embodiment of the present application; 
           [0015]      FIG. 5  illustrates a top-viewed diagram of a concentrated photovoltaic cell in accordance with a first embodiment of the present application; 
           [0016]      FIG. 6  illustrates a partial enlargement of a top-viewed diagram of a concentrated photovoltaic cell in accordance with a first embodiment of the present application; 
           [0017]      FIG. 7  illustrates a top-viewed diagram of a concentrated photovoltaic cell in accordance with a second embodiment of the present application; 
           [0018]      FIG. 8  illustrates a partial enlargement of a top-viewed diagram of a concentrated photovoltaic cell in accordance with a second embodiment of the present application; 
           [0019]      FIG. 9  illustrates a top-viewed diagram of a concentrated photovoltaic cell in accordance with a third embodiment of the present application; 
           [0020]      FIG. 10  illustrates a partial enlargement of a top-viewed diagram of a concentrated photovoltaic cell in accordance with a third embodiment of the present application; 
           [0021]      FIG. 11  illustrates a top-viewed diagram of a concentrated photovoltaic cell in accordance with a fourth embodiment of the present application; 
           [0022]      FIG. 12  illustrates a partial enlargement of a top-viewed diagram of a concentrated photovoltaic cell in accordance with a fourth embodiment of the present application; 
           [0023]      FIG. 13  illustrates a top-viewed diagram of a concentrated photovoltaic cell in accordance with a fifth embodiment of the present application; and 
           [0024]      FIG. 14  illustrates a partial enlargement of a top-viewed diagram of a concentrated photovoltaic cell in accordance with a fifth embodiment of the present application. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0025]    The embodiment of the application is illustrated in detail, and is plotted in the drawings. The same or the similar part is illustrated in the drawings and the specification with the same number. 
         [0026]      FIG. 4  illustrates a cross-sectional diagram of a concentrated photovoltaic cell  20  in accordance with a first embodiment of the present application.  FIG. 5  illustrates a top-viewed diagram of the concentrated photovoltaic cell  20  in accordance with the first embodiment of the present application.  FIG. 4  illustrates the cross-sectional diagram alone line X-X′ of  FIG. 5 . As shown in  FIG. 4 , the concentrated photovoltaic cell  20  is operable to absorb a light, such as sunlight. The concentrated photovoltaic cell  20  comprises a semiconductor stack  210  comprising an upper surface S 1  and a lower surface S 2  opposite to the upper surface S 1 , wherein the upper surface S 1  is formed near a side where the light incident thereon and operable to absorb the light, and the light incident on the upper surface S 1  comprises a light intensity distribution; an upper electrode  200  formed on the upper surface S 1  of the semiconductor stack  210 ; a lower electrode  209  formed on the lower surface S 2  of the semiconductor stack  210 ; and an anti-reflective layer  201  formed on the upper surface S 1  of the semiconductor stack  210 . The anti-reflective layer  201  comprises dielectric materials, such as silicon nitride (SiN x ), silicon oxide (SiO 2 ), aluminum oxide (Al 2 O 3 ), or titanium oxide (TiO x ). The anti-reflective layer  201  reduces reflection of the light on the upper surface S 1 . The material of the upper electrode  200  and the lower electrode  209  comprises metal, such as titanium, platinum, nickel, gold, or silver, which can be formed on the semiconductor stack  210  by electroplating, vapor deposition, or sputter. 
         [0027]    The semiconductor stack  210  comprises one junction or multiple junctions. As shown in  FIG. 4 , the semiconductor stack  210  comprises a window layer  205  formed on a side near the anti-reflective layer  201 , a top subcell  206 , a middle subcell  207 , and a bottom subcell  208  formed on a side near the lower electrode  209 . The material of the semiconductor stack  210  comprises group III or group V element, such as arsenic (As), gallium (Ga), aluminum (Al), indium(In), phosphorus (P), or nitrogen (N). The semiconductor stack  210  may be formed by a known epitaxy method such as metallic-organic chemical vapor deposition (MOCVD) method, a molecular beam epitaxy (MBE) method, a hydride vapor phase epitaxy (HVPE) method, sputtering, or electrical plating. 
         [0028]    The window layer  205  directs the light incident on the upper surface S 1  of the semiconductor stack  210  towards the top subcell  206 , the middle subcell  207 , and the bottom subcell  208 . The top subcell  206 , the middle subcell  207 , and the bottom subcell  208  absorb the light and convert that into an electrical current. The upper electrode  200  and the lower electrode  209  collect and export the electrical current provided from the top subcell  206 , the middle subcell  207 , and the bottom subcell  208 . 
         [0029]    As shown in  FIG. 5 , the upper electrode  200  comprises a plurality of collector electrodes  202  and a plurality of grid electrodes  203 . An electrode pattern of the upper electrode  200  is related with resistance, fill factor (FF), or short-circuit current (I sc ) of the concentrated photovoltaic cell  20 . A width or a pitch of the plurality of grid electrodes  203  can be adjusted to change the light shielding area of the upper electrode  200 .  FIG. 5  illustrates the top-viewed diagram of the concentrated photovoltaic cell  20  in accordance with the first embodiment of the present application. The upper electrode  200  comprises an electrode pattern approximately corresponding to an intensity distribution of the light absorbed by the upper surface S 1 , wherein the light intensity distribution comprises a high light-concentrated area I having a first light intensity and a low light-concentrated area II having a second light intensity, wherein the second light intensity is lower than the first light intensity. The electrode pattern comprises a first electrode area  204  and a second electrode area  201  different from the first electrode area  204 . The first electrode area  204  and the second electrode area  201  are approximately corresponding to the high light-concentrated area I and the low light-concentrated area II respectively. The first electrode area  204  comprises an area disposed on a center area of the upper surface S 1 . The plurality of grid electrodes  203  and the plurality of collector electrodes  202  are formed by lithography, wherein the plurality of collector electrodes  202  comprises a width larger than 50 μm, preferably larger than 100 μm. 
         [0030]    As shown in  FIG. 5 , a ratio of the first electrode area  204  and the upper surface S 1  is not larger than 80%. An optical concentrator (not shown) having a concentration magnification, such as at least 200 suns above, is disposed on the semiconductor stack  210  near a side where the sunlight incident thereon. The high light-concentrated area I comprises a concentration magnification larger than that of the optical concentrator, such as 200 suns above; and the low light-concentrated area II comprises a concentration magnification lower than that of the optical concentrator, such as 200 suns below. The plurality of grid electrodes  203  and the plurality of collector electrodes  202  are perpendicular to each other, and the grid electrodes  203  are parallel to each other. The width of the plurality of grid electrodes  203  in the first electrode area  204  is smaller than that in the second electrode area  201 . The pitch of the plurality of grid electrodes  203  in the first electrode area  204  is equal to that in the second electrode area  201 . 
         [0031]      FIG. 6  illustrates a partial enlargement of a top-viewed diagram of the plurality of grid electrodes  203  shown in  FIG. 5 . As shown in  FIG. 6 , the pitch of a plurality of grid electrodes  203   a  in the first electrode area  204  (the high light-concentrated area I) is d 1 , the pitch of a plurality of grid electrodes  203   b  in the second electrode area  201  (the low light-concentrated area II) is d 2 . In the embodiment, the width w 1  of the plurality of grid electrodes  203   a  in the first electrode area  204  is smaller than the width w 2  in the second electrode area  201 , and the pitch d 1  of the plurality of grid electrodes  203   a  is equal to the pitch d 2  of the plurality of grid electrodes  203   b . The pitch d 1  of the plurality of grid electrodes  203   a  in the first electrode area  204  or the pitch d 2  of the plurality of grid electrodes  203   b  in the second electrode area  201  is between 50 μm˜300 μm, preferably between 90 μm˜200 μm. In the embodiment, the width w 1  of the plurality of grid electrodes  203  in the first electrode area  204  is smaller than the width w 2  of the plurality of grid electrodes  203  in the second electrode area  201 , which reduces light shielding area of the plurality of grid electrodes  203  in the high light-concentrated area I and increases short-circuit current (I sc ) of the concentrated photovoltaic cell  20 . 
         [0032]      FIG. 7  illustrates a top-viewed diagram of a concentrated photovoltaic cell  20  in accordance with a second embodiment of the present application.  FIG. 8  illustrates a partial enlargement of a top-viewed diagram of a plurality of grid electrodes  203  shown in  FIG. 7 . As shown in  FIG. 8 , the pitch d 1  of a plurality of grid electrodes  203   a  in the first electrode area  204  (the high light-concentrated area I) is smaller than the pitch d 2  of a plurality of grid electrodes  203   b  in the second electrode area  201  (the low light-concentrated area II). The pitch d 1  of the plurality of grid electrodes  203   a  in the first electrode area  204  (the high light-concentrated area I) is larger than 50 μm, preferably larger than 90 μm. The pitch d 2  of the plurality of grid electrodes  203   b  in the second electrode area  201  (the low light-concentrated area II) is smaller than 300 μm, preferably smaller than 200 μm. In the embodiment, the width w 1  of the plurality of grid electrodes  203   a  in the first electrode area  204  is smaller than the width w 2  of the plurality of grid electrodes  203   b  in the second electrode area  201 , which reduces light shielding area of the plurality of grid electrodes  203   a  in the high light-concentrated area I. The pitch d 2  of the plurality of grid electrodes  203  in the second electrode area  201  is larger than the pitch d 1  of the plurality of grid electrodes  203  in the first electrode area  204 , which reduces light shielding area of the plurality of grid electrodes  203  in the low light-concentrated area II, and increases short-circuit current (I sc ) of the concentrated photovoltaic cell  20 . 
         [0033]      FIG. 9  illustrates a top-viewed diagram of a concentrated photovoltaic cell  20  in accordance with a third embodiment of the present application.  FIG. 10  illustrates a partial enlargement of a top-viewed diagram of a plurality of grid electrodes  203  shown in  FIG. 9 . As shown in  FIG. 10 , the pitch d 1  of a plurality of grid electrodes  203   a  in the first electrode area  204  (the high light-concentrated area I) is smaller than the pitch d 2  of a plurality of grid electrodes  203   b  in the second electrode area  201  (the low light-concentrated area II). The pitch d 1  of the plurality of grid electrodes  203   a  in the first electrode area  204  (the high light-concentrated area I) is larger than 50 μm, preferably larger than 90 μm. The pitch d 2  of the plurality of grid electrodes  203   b  in the second electrode area  201  (the low light-concentrated area II) is smaller than 300 μm, preferably smaller than 200 μm. In the embodiment, the width w 1  of the plurality of grid electrodes  203   a  in the first electrode area  204  is equal to the width w 2  of the plurality of grid electrodes  203   b  in the second electrode area  201 . In the embodiment, the pitch d 2  of the plurality of grid electrodes  203  in the second electrode area  201  is larger than the pitch d 1  of the plurality of grid electrodes  203  in the first electrode area  204 , which reduces light shielding area of the plurality of grid electrodes  203  in the low light-concentrated area II, and increases short-circuit current (I sc ) of the concentrated photovoltaic cell  20 . 
         [0034]      FIG. 11  illustrates a top-viewed diagram of a concentrated photovoltaic cell  20  in accordance with a fourth embodiment of the present application.  FIG. 12  illustrates a partial enlargement of a top-viewed diagram of a plurality of grid electrodes  203  shown in  FIG. 11 . As shown in  FIG. 12 , the pitch d 1  of a plurality of grid electrodes  203   a  in the first electrode area  204  (the high light-concentrated area I) is equal to the pitch d 2  of a plurality of grid electrodes  203   b  in the second electrode area  201  (the low light-concentrated area II). The pitch d 1  of the plurality of grid electrodes  203   a  in the first electrode area  204  or the pitch d 2  of the plurality of grid electrodes  203   b  in the second electrode area  201  is between 50 μm˜300 μm, preferably between 90 μm˜200 μm. The width w 1  of the plurality of grid electrodes  203   a  in the first electrode area  204  is smaller than the width w 2  of the plurality of grid electrodes  203   b  in the second electrode area  201 . In the embodiment, the plurality of grid electrodes  203   b ′ in the second electrode area  201  is connected to the collector electrode  202  and extends towards a direction away from the collector electrode  202 , and the plurality of grid electrodes  203   b ′ is connected to the grid electrode  203   a  in the first electrode area  204 . In other words, one side of the grid electrode  203   b ′ in the second electrode area  201  is connected to the collector electrode  202 , and another side of the grid electrode  203   b ′ is connected to the grid electrode  203   a  in the first electrode area  204 . The width w 2  of the grid electrode  203   b ′ is larger than the width w 1  of the grid electrode  203   a , which reduces resistance loss when the photo-induced current flows from the high light-concentrated area I to the low light-concentrated area II. 
         [0035]      FIG. 13  illustrates a top-viewed diagram of a concentrated photovoltaic cell  20  in accordance with a fifth embodiment of the present application.  FIG. 14  illustrates a partial enlargement of a top-viewed diagram of a plurality of grid electrodes  203  shown in  FIG. 13 . As shown in  FIG. 14 , the pitch d 1  of a plurality of grid electrodes  203   a  in the first electrode area  204  (the high light-concentrated area I) is smaller than the pitch d 2  of a plurality of grid electrodes  203   b  in the second electrode area  201  (the low light-concentrated area II). The pitch d 1  of the plurality of grid electrodes  203   a  in the first electrode area  204  (the high light-concentrated area I) is larger than 50 μm, preferably larger than 90 μm. The pitch d 2  of the plurality of grid electrodes  203   b  in the second electrode area  201  (the low light-concentrated area II) is smaller than 300 μm, preferably smaller than 200 μm. The width w 1  of the plurality of grid electrodes  203   a  in the first electrode area  204  is smaller than the width w 2  of the plurality of grid electrodes  203   b  in the second electrode area  201 . In the embodiment, the plurality of grid electrodes  203   b ′ in the second electrode area  201  is connected to the collector electrode  202  and extends towards a direction away from the collector electrode  202 , and the grid electrodes  203   b ′ are respectively connected to the grid electrodes  203   a  in the first electrode area  204 . In other words, one side of the grid electrode  203   b ′ in the second electrode area  201  is connected to the collector electrode  202 , and another side of the grid electrode  203   b ′ is connected to the grid electrode  203   a  in the first electrode area  204 . The width w 2  of the grid electrode  203   b ′ is larger than the width w 1  of the grid electrode  203   a , which reduces resistance loss when the photo-induced current flows from the high light-concentrated area I to the low light-concentrated area II. 
         [0036]    The principle and the efficiency of the present application illustrated by the embodiments above are not the limitation of the application. Any person having ordinary skill in the art can modify or change the aforementioned embodiments. Therefore, the protection range of the rights in the application will be listed as the following claims.