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

A transistor comprising:

• a single layer silicon substrate, wherein the silicon substrate comprises p-type dopants;
• a seed layer above and in direct contact with the silicon substrate, wherein the seed layer consists of carbon-doped AlN having a substantially constant carbon dopant concentration ranging from about 2×1017 atoms/cm3 to about 1×1020 atoms/cm3, wherein the seed layer comprises a first seed sublayer having a first lattice structure and a first carbon dopant concentration and a second seed sublayer having a second lattice structure having a second carbon dopant concentration, the second lattice structure being different than the first lattice structure, the first carbon dopant concentration and the second carbon dopant concentration are substantially equal, the first seed sublayer having a thickness ranging from about 20 nm to about 80 nm, and the second seed sublayer having a thickness ranging from about 50 nm to about 200 nm;
• a graded layer above and in direct contact with the seed layer, wherein the graded layer is doped with p-type dopants and comprises;
• a first graded sublayer including AlxGa1-xN, where x ranges from 0.7 to 0.9,
• a second graded sublayer on the first graded sublayer, the second graded sublayer including AlyGa1-yN, where y ranges from 0.4 to 0.6, and
• a third graded sublayer on the second graded sublayer, the third graded sublayer including AlzGa1-zN, where z ranges from 0.15 to 0.3;
• a channel layer directly over the graded layer;
• and
• an active layer in direct contact with the channel layer, wherein the active layer has a band gap discontinuity with the channel layer.

A method of making a transistor, the method comprising:

• providing a silicon substrate comprising p-type dopants;
• forming an AlN seed layer above and in direct contact with the silicon substrate, wherein a first sublayer is formed on the silicon substrate at a first temperature and a second sublayer formed on the first sublayer at a second temperature, the second temperature being higher than the first temperature, wherein the second temperature ranges from about 1000° C. to about 1300° C.;
• doping the AlN seed layer, wherein doping the AlN seed layer comprises introducing carbon dopants into a portion of the AlN seed layer closest to the silicon substrate;
• forming a channel layer over the AlN seed layer;
• forming an active layer in direct contact with the channel layer, wherein the active layer has a band gap discontinuity with the channel layer;
• and
• forming a graded layer in direct contact with the AlN seed layer with the channel layer comprising a single material layer in direct contact with the graded layer, wherein the graded layer comprises:
• a first graded sublayer including AlxGa1-xN, where x ranges from 0.7 to 0.9;
• a second graded sublayer on the first graded sublayer, the second graded sublayer including AlyGa1-yN, where y ranges from 0.4 to 0.6;
• and
• a third graded sublayer on the second graded sublayer, the third graded sublayer including AlzGa1-zN, where z ranges from 0.15 to 0.3.