Semiconductor device having doped seed layer and method of manufacturing the same

Abstract

A semiconductor device includes a substrate and a seed layer over the substrate. The seed layer includes a first seed sublayer having a first lattice structure, wherein the first seed sublayer includes AlN, and the first seed sublayer is doped with carbon, and a second seed sublayer over the first seed layer, wherein the second seed layer has a second lattice structure different from the first lattice structure, and a thickness of the second seed sublayer ranges from about 50 nanometers (nm) to about 200 nm. The semiconductor device further includes a graded layer over the seed layer. The graded layer includes a first graded sublayer including AlGaN, having a first Al:Ga ratio; and a second graded sublayer over the first graded sublayer, wherein the second graded sublayer includes AlGaN having a second Al:Ga ratio. The semiconductor device further includes a two-dimensional electron gas (2-DEG) over the graded layer.

What is claimed is: 
     
         1 . A semiconductor device comprising:
 a substrate;   a seed layer in direct contact with the substrate, wherein the seed layer comprises:
 a first seed sublayer having a first lattice structure, wherein the first seed sublayer comprises AlN, and the first seed sublayer is doped with carbon, and 
 a second seed sublayer over the first seed sublayer, wherein the second seed sublayer has a second lattice structure different from the first lattice structure, and a thickness of the second seed sublayer ranges from about 50 nanometers (nm) to about 200 nm; 
   a graded layer in direct contact with the seed layer, wherein the graded layer comprises:
 a first graded sublayer including AlGaN, wherein the first graded sublayer has a first Al:Ga ratio; and 
 a second graded sublayer over the first graded sublayer, wherein the second graded sublayer includes AlGaN, and the second graded sublayer has a second Al:Ga ratio different from the first Al:Ga ratio; and 
   a two-dimensional electron gas (2-DEG) over the graded layer.   
     
     
         2 . The semiconductor device of  claim 1 , further comprising:
 a source electrode;   a drain electrode; and   a gate, wherein the source electrode is closer to the 2-DEG than the gate.   
     
     
         3 . The semiconductor device of  claim 2 , further comprising a semiconductor layer between the gate and the 2-DEG. 
     
     
         4 . The semiconductor device of  claim 2 , further comprising a dielectric layer between the gate and the 2-DEG. 
     
     
         5 . The semiconductor device of  claim 4 , wherein the dielectric layer contacts a sidewall of the gate. 
     
     
         6 . The semiconductor device of  claim 1 , wherein the 2-DEG is a normally conductive 2-DEG. 
     
     
         7 . The semiconductor device of  claim 1 , wherein the 2-DEG is a normally non-conductive 2-DEG. 
     
     
         8 . A method of making a semiconductor device, the method comprising:
 growing a first seed sublayer over a substrate, wherein the first seed sublayer comprises AlN;   doping the first seed sublayer with carbon;   growing a second seed sublayer over the doped first seed sublayer, wherein the second seed sublayer comprises AlN, and a thickness of the second seed sublayer ranges from about 50 nanometers (nm) to about 200 nm;   growing a first graded sublayer over the second seed sublayer, wherein the first graded sublayer comprises AlGaN, and the first graded sublayer has a first Al:Ga ratio;   growing a second graded sublayer over the first graded sublayer, wherein the second graded sublayer comprises AlGaN, and the second graded sublayer has a second Al:Ga ratio different from the first Al:Ga ratio; and   forming a two-dimensional electron gas (2-DEG) over the second graded sublayer.   
     
     
         9 . The method of  claim 8 , further comprising forming a gate over the 2-DEG. 
     
     
         10 . The method of  claim 9 , wherein forming the gate comprises causing the 2-DEG to be a normally conductive 2-DEG. 
     
     
         11 . The method of  claim 9 , wherein forming the gate comprises causing the 2-DEG to be a normally non-conductive 2-DEG. 
     
     
         12 . The method of  claim 9 , further comprising forming a semiconductor layer over the 2-DEG, wherein forming the gate comprises forming the gate over the semiconductor layer. 
     
     
         13 . The method of  claim 9 , further comprising forming a dielectric layer over the 2-DEG, wherein forming the gate comprises forming the gate over the dielectric layer. 
     
     
         14 . The method of  claim 13 , wherein forming the gate comprises forming the gate having a sidewall in contact with the dielectric layer. 
     
     
         15 . The method of  claim 8 , wherein doping the first seed sublayer with carbon comprises doping the first seed sublayer using a carbon source selected from the group consisting of at least one of CH 4 , C 7 H 7 , C 16 H 10 , CBr 4 , and CC l4 . 
     
     
         16 . The method of  claim 8 , wherein doping the first seed sublayer with carbon comprises performing an in-situ doping during the growing of the first seed sublayer. 
     
     
         17 . A semiconductor device comprising:
 a substrate;   a seed layer in direct contact with the substrate, wherein the seed layer comprises:
 a first seed sublayer having a first lattice structure, wherein the first seed sublayer comprises AlN, and the first seed sublayer is doped with carbon, and 
 a second seed sublayer over the first seed sublayer, wherein the second seed sublayer has a second lattice structure different from the first lattice structure, and a thickness of the second seed sublayer ranges from about 50 nanometers (nm) to about 200 nm; 
   a graded layer in direct contact with the seed layer, wherein the graded layer comprises a plurality of layers of AlGaN, wherein each of the plurality of layers of AlGaN has a different Al:Ga ratio for each other of the plurality of layer of AlGaN; and   a selectively conductive two-dimensional electron gas (2-DEG) over the graded layer.   
     
     
         18 . The semiconductor device of  claim 17 , wherein a dopant concentration of the carbon ranges from 2×10 17  atoms/cm 3  to about 1×10 20  atoms/cm 3 . 
     
     
         19 . The semiconductor device of  claim 17 , further comprising:
 a semiconductor layer over the selectively conductive 2-DEG; and   a gate over the semiconductor layer.   
     
     
         20 . The semiconductor device of  claim 17 , further comprising:
 a dielectric layer over the selectively conductive 2-DEG; and   a gate over the dielectric layer.