Nitride semiconductor device

Abstract

A nitride semiconductor device has a nitride semiconductor layer structure. The structure includes an active layer of a quantum well structure containing an indium-containing nitride semiconductor. A first nitride semiconductor layer having a band gap energy larger than that of the active layer is provided in contact with the active layer. A second nitride semiconductor layer having a band gap energy smaller than that of the first layer is provided over the first layer. Further, a third nitride semiconductor layer having a band gap energy larger than that of the second layer is provided over the second layer.

What is claimed is:  
     
         1 . A nitride semiconductor device having a nitride semiconductor layer structure comprising: 
 an active layer of a quantum well structure which has a first surface and a second surface and which comprises an indium-containing nitride semiconductor;    a first nitride semiconductor layer which is formed to adjoin the first surface of the active layer and has a band gap energy larger than that of the active layer;    a second nitride semiconductor layer which is formed on the first surface side of the active layer at a location more distant from the active layer relative to the first nitride semiconductor layer and which has a band gap energy smaller than that of the first nitride semiconductor layer; and    a third nitride semiconductor layer which is formed on the first surface side of the active layer at a location more distant from the active layer relative to the second nitride semiconductor layer and which has a band gap energy larger than that of the second nitride semiconductor layer.    
     
     
         2 . The device according to  claim 1 , wherein said first nitride semiconductor layer has a thickness sufficiently thin such that carriers may tunnel therethrough.  
     
     
         3 . The device according to  claim 1 , wherein said first nitride semiconductor layer has a thickness of 0.1 μm or less.  
     
     
         4 . The device according to  claim 3 , wherein said first nitride semiconductor layer has a thickness of 10 angstroms or more.  
     
     
         5 . The device according to  claim 1 , wherein said active layer is doped with an impurity.  
     
     
         6 . The device according to  claim 5 , wherein said impurity comprises silicon or germanium.  
     
     
         7 . The device according to  claim 5 , wherein said impurity is doped in said at least one well layer.  
     
     
         8 . The device according to  claim 1 , wherein said layer structure is provided on a p-side of the active layer.  
     
     
         9 . The device according to  claim 8 , wherein said second nitride semiconductor layer adjoin said first nitride semiconductor layer.  
     
     
         10 . The device according to  claim 9 , wherein said third nitride semiconductor layer adjoins said second nitride semiconductor layer.  
     
     
         11 . The device according to  claim 1 , wherein said layer structure is provided on an n-side of the active layer.  
     
     
         12 . The device according to  claim 11 , wherein said second nitride semiconductor layer adjoins said first nitride semiconductor layer.  
     
     
         13 . The device according to  claim 12 , wherein said third nitride semiconductor layer adjoins said second nitride semiconductor layer.  
     
     
         14 . A nitride semiconductor device comprising: 
 an active layer of a quantum well structure which has a first surface and a second surface and which comprises an indium-containing nitride semiconductor;    a first layer which adjoins the first surface of the active layer and has a band gap energy larger than that of the active layer;    a second layer which is formed on the first surface side of the active layer at a location more distant from the active layer relative to the first layer and which comprises a nitride semiconductor containing an acceptor impurity and which has a band gap energy smaller than that of the first layer; and    a third layer which is formed on the first surface side of the active layer at a location more distant from the active layer relative to the second layer and which comprises a nitride semiconductor containing an acceptor impurity and which has a band gap energy larger than that of the second layer.    
     
     
         15 . The device according to  claim 14 , wherein said first layer has a thickness sufficiently thin such that carriers may tunnel therethrough.  
     
     
         16 . The device according to  claim 14 , wherein said first layer has a thickness of 0.1 μm or less.  
     
     
         17 . The device according to  claim 16 , wherein said first layer has a thickness of 10 angstroms or more.  
     
     
         18 . The device according to  claim 14 , wherein said active layer is doped with an impurity.  
     
     
         19 . The device according to  claim 18 , wherein said impurity comprises silicon or germanium.  
     
     
         20 . The device according to  claim 18 , wherein said impurity is doped in said at least one well layer.  
     
     
         21 . The device according to  claim 14 , wherein said second layer adjoins said first layer.  
     
     
         22 . The device according to  claim 21 , wherein said third layer adjoins said second layer.  
     
     
         23 . A nitride semiconductor device comprising: 
 an active layer of a quantum well structure which has a first surface and a second surface and which comprises an indium-containing nitride semiconductor,    a first layer which is formed to adjoin the second surface of the active layer and which comprises a nitride semiconductor and which has a band gap energy larger than that of the active layer;    a second layer which is formed on the second surface side of the active layer at a location more distant from the active layer relative to the first layer, which comprises an n-type nitride semiconductor, and which has a band gap energy smaller than that of the first layer,    a third layer which is formed on the second surface side of the active layer at a location more distant from the active layer relative to the second layer, which comprises an n-type nitride semiconductor, and which has a band gap energy larger than that of the second layer.    
     
     
         24 . The device according to  claim 23 , wherein said first layer has a thickness sufficiently thin such that carriers may tunnel therethrough.  
     
     
         25 . The device according to  claim 23 , wherein said first layer has a thickness of 0.1 μm or less.  
     
     
         26 . The device according to  claim 25 , wherein said first layer has a thickness of 10 angstroms or more.  
     
     
         27 . The device according to  claim 23 , wherein said active layer is doped with an impurity.  
     
     
         28 . The device according to  claim 27 , wherein said impurity comprises silicon or germanium.  
     
     
         29 . The device according to  claim 27 , wherein said impurity is doped in said at least one well layer.  
     
     
         30 . The device according to  claim 23 , wherein said second layer adjoins said first layer.  
     
     
         31 . The device according to  claim 30 , wherein said third layer adjoins said second layer.  
     
     
         32 . A nitride semiconductor device comprising: 
 an active layer of a quantum well structure which has a first surface and a second surface and which comprises an indium-containing nitride semiconductor;    a first nitride semiconductor layer structure comprising a first p-side nitride semiconductor layer which is formed to adjoin the first surface of the active layer and has a band gap energy larger than that of the active layer, a second p-side nitride semiconductor layer which is formed on the first surface side of the active layer at a location more distant from the active layer relative to the first p-side nitride semiconductor layer and which has a band gap energy smaller than that of the first p-side nitride semiconductor layer, and a third p-side nitride semiconductor layer which is formed on the first surface side of the active layer at a location more distant from the active layer relative to the second p-side nitride semiconductor layer and which has a band gap energy larger than that of the second p-side nitride semiconductor layer; and    a second nitride semiconductor layer structure comprising a first n-side nitride semiconductor layer which is formed to adjoin the second surface of the active layer and has a band gap energy larger than that of the active layer, a second n-side nitride semiconductor layer which is formed on the second surface side of the active layer at a location more distant from the active layer relative to the first n-side nitride semiconductor layer and which has a band gap energy smaller than that of the first n-side nitride semiconductor layer, and a third n-side nitride semiconductor layer which is formed on the second surface side of the active layer at a location more distant from the active layer relative to the second n-side nitride semiconductor layer and which has a band gap energy larger than that of the second n-side nitride semiconductor layer.    
     
     
         33 . The device according to  claim 32 , wherein said first p-side nitride semiconductor layer has a thickness sufficiently thin such that carriers may tunnel therethrough.  
     
     
         34 . The device according to  claim 32 , wherein said first p-side nitride semiconductor layer has a thickness of 0.1 μm or less.  
     
     
         35 . The device according to  claim 25 , wherein said first p-side nitride semiconductor layer has a thickness of 10 angstroms or more.  
     
     
         36 . The device according to  claim 32 , wherein said active layer is doped with an impurity.  
     
     
         37 . The device according to  claim 36 , wherein said impurity comprises silicon or germanium.  
     
     
         38 . The device according to  claim 36 , wherein said impurity is doped in said at least one well layer.  
     
     
         39 . The device according to  claim 32 , wherein said first n-side nitride semiconductor layer has a thickness sufficiently thin such that carriers may tunnel therethrough.  
     
     
         40 . The device according to  claim 32 , wherein said first n-side nitride semiconductor layer has a thickness of 0.1 μm or less.  
     
     
         41 . The device according to  claim 40 , wherein said first n-side nitride semiconductor layer has a thickness of 10 angstroms or more.  
     
     
         42 . The device according to  claim 32 , wherein said second p-side nitride semiconductor layer adjoins said first p-side nitride semiconductor layer, and said third p-side nitride semiconductor layer adjoins said second p-side nitride semiconductor layer.  
     
     
         43 . The device according to  claim 42 , wherein said second n-side nitride semiconductor layer adjoins said first n-side nitride semiconductor layer, and said third n-side nitride semiconductor layer adjoins said second n-side nitride semiconductor layer.  
     
     
         44 . A nitride semiconductor device having, on a substrate, a layer structure comprising an n-type contact layer, a first n-type clad layer which comprises an aluminum-containing nitride semiconductor, a second n-type clad layer which comprises an indium-containing nitride semiconductor or GaN, an active layer of a quantum well structure which comprises an indium-containing nitride semiconductor, a first p-type clad layer which comprises an aluminum-containing nitride semiconductor, a second p-type clad layer which comprises an indium-containing nitride or GaN, a third p-type clad layer which comprises an aluminum-containing nitride semiconductor, and a p-type contact layer.  
     
     
         45 . The device according to  claim 44 , wherein said active layer is doped with an impurity.  
     
     
         46 . The device according to  claim 45 , wherein said impurity comprises silicon or germanium.  
     
     
         47 . The device according to  claim 45 , wherein said impurity is doped in a well layer.  
     
     
         48 . A nitride semiconductor device comprising: 
 a first clad layer comprising an n-type nitride semiconductor;    an active layer of a quantum well structure provided on the first clad layer, said active layer comprising a nitride semiconductor containing indium and gallium and having at least one well layer having a thickness not greater than 70 angstroms, wherein said well layer is placed on an underlying layer in a state lattice-mismatched with the underlying layer and includes a plurality of indium-rich regions and indium-poor regions; and    a second clad layer which is provided on the active layer and comprises a nitride semiconductor doped with an acceptor impurity.    
     
     
         49 . The device according to  claim 48 , wherein said active layer is doped with an impurity.  
     
     
         50 . The device according to  claim 49 , wherein said impurity comprises silicon or germanium.  
     
     
         51 . The device according to  claim 49 , wherein said impurity is doped in said well layer.  
     
     
         52 . A nitride semiconductor device including a first n-type layer which comprises an n-type, aluminum-containing nitride semiconductor or n-type gallium nitride; and a second n-type layer which comprises an n-type, aluminum-containing nitride semiconductor, wherein the device has a third n-type layer which comprises an n-type, indium-containing nitride semiconductor between the first n-type layer and the second n-type layer.