Ohmic electrode for two-dimensional carrier gas (2DCG) semiconductor device

A semiconductor device, comprising:

• a semiconductor film comprising a first two-dimensional carrier gas (2DCG) and a second 2DCG overlying the first 2DCG;
• a first source/drain electrode and a second source/drain electrode laterally spaced from each other and overlying and ohmically coupled to the first and second 2DCGs;
• and
• a gate electrode overlying the first and second 2DCGs and laterally between the first and second source/drain electrodes;
• wherein the semiconductor film forms a fin structure, wherein the first source/drain electrode has a plurality of protrusions protruding downward into the fin structure, wherein the gate electrode has a pair of leg portions, which extend downward along opposite sidewalls of the fin structure and which have individual bottom surfaces elevated relative to the first 2DCG and recessed relative to the second 2DCG.

A method for forming a semiconductor device, the method comprising:

• forming a semiconductor film comprising a first channel layer, a first barrier layer, a second channel layer, and a second barrier layer that are vertically stacked, wherein the first channel layer and the first barrier layer contact at a first heterojunction and the second channel layer and the second barrier layer contact at a second heterojunction overlying the first heterojunction, and wherein a first two-dimensional carrier gas (2DCG) and a second 2DCG are respectively in the first and second channel layers;
• performing a first etch into the semiconductor film to form a fin structure;
• after the first etch, performing a second etch into the fin structure to form a plurality of recesses, which expose individual sidewalls of the second channel layer and the second barrier layer;
• forming a first source/drain electrode and a second source/drain electrode, wherein the first source/drain electrode is formed filling the plurality of recesses;
• and
• forming a gate electrode overlying the fin structure, laterally between the first and second source/drain electrodes, wherein the gate electrode straddles the fin structure with a pair of leg portions between which the fin structure is laterally and directly arranged, and wherein the pair of leg portions have individual bottom surfaces recessed relative to the second 2DCG and elevated relative to the first 2DCG.