Semiconductor device

Abstract

A semiconductor device having small leakage current and high breakdown voltage during reverse blocking, small on-state resistance and large output current at forward conduction, short reverse recovery time at shutoff, and high peak surge current value is provided. An n-type layer is made of a group-III nitride, and a p-type layer is made of a group-IV semiconductor material having a smaller band gap than the group-III nitride. The energy level at the top of the valence band of the n-type layer is lower than the energy level at the top of the valence band of the p-type layer, so that a P—N junction semiconductor device satisfying the above requirements is obtained. Further, a combined structure of P—N junction and Schottky junction by additionally providing an anode electrode to be in Schottky contact with the n-type layer also achieves the effect of decreasing voltage at the rising edge of current resulting from the Schottky junction.

1 . A semiconductor device comprising:
 a first semiconductor layer having a first conductivity type;   a second semiconductor layer joined to said first semiconductor layer at a first junction, said semiconductor layer having a second conductivity type different from said first conductivity type;   a first electrode joined to said first semiconductor layer; and   a second electrode joined to said second semiconductor layer, wherein   said first semiconductor layer is made of a group-III nitride having a composition of Al 1-x-y Ga x In y N (x≧0, y≧0, 0≦x+y≦1), and   said second semiconductor layer is made of a group-IV semiconductor material having a smaller band gap than said group-III nitride.   
   
   
       2 . The semiconductor device according to  claim 1 , wherein
 said first conductivity type is an n-type,   said second conductivity type is a p-type,   said first electrode is a cathode electrode,   said second electrode is an anode electrode, and   an energy level at a top of a valence band of said first semiconductor layer is lower than an energy level at a top of a valence band of said second semiconductor layer in the vicinity of said first junction.   
   
   
       3 . The semiconductor device according to  claim 2 , further comprising:
 a third electrode joined to said first semiconductor layer at a second junction, said third electrode having a Schottky contact property to said first semiconductor layer, wherein   said second electrode and said third electrode are connected in parallel, and said third electrode serves as an anode electrode.   
   
   
       4 . The semiconductor device according to  claim 3 , wherein
 said second semiconductor layer is deposited on a partial region of a main surface of said first semiconductor layer to create said first junction, and   said third electrode is formed on surfaces of said first semiconductor layer and said second electrode to create said second junction adjacent to said first junction.   
   
   
       5 . The semiconductor device according to  claim 2 , wherein
 said group-III nitride has a composition of Al 1-x Ga x N (0≦x≦1) at least in the vicinity of said first junction of said first semiconductor layer.   
   
   
       6 . The semiconductor device according to  claim 2 , wherein
 a hole density is 1×10 19 /cm 3  or higher at least in the vicinity of said first junction of said second semiconductor layer.   
   
   
       7 . The semiconductor device according to  claim 2 , wherein
 an acceptor density is 1×10 20 /cm 3  or higher at least in the vicinity of said first junction of said second semiconductor layer.   
   
   
       8 . The semiconductor device according to  claim 7 , wherein
 said group-IV semiconductor material is Si 1-z Ge z  (0≦z≦1) at least in the vicinity of said first junction of said second semiconductor layer.   
   
   
       9 . The semiconductor device according to  claim 8 , wherein
 said group-IV semiconductor material is Si at least in the vicinity of said first junction of said second semiconductor layer.