Germanium-Based Sensor with Junction-Gate Field Effect Transistor and Method of Fabricating Thereof

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

• forming an oxide layer over a silicon substrate;
• forming a sensor cavity in the oxide layer that exposes the silicon substrate;
• forming a doped silicon layer and a germanium layer in the sensor cavity, wherein the doped silicon layer is disposed between the silicon substrate and the germanium layer and between the oxide layer and the germanium layer;
• forming a first doped region, a second doped region, a third doped region, and a fourth doped region in the germanium layer, wherein the first doped region is between the second doped region and the third doped region, the fourth doped region is over the first doped region, the first doped region includes a first type dopant, and the second doped region, the third doped region, and the fourth doped region include a second type dopant;
• forming a gate over the germanium layer, wherein the gate is over the fourth doped region and the gate includes the second type dopant;
• and
• forming a fifth doped region, a sixth doped region, and a seventh doped region in the germanium layer, wherein the fifth doped region overlaps the first doped region and the second doped region, the sixth doped region overlaps the first doped region and the third doped region, the fourth doped region is between the fifth doped region and the sixth doped region, the seventh doped region is under the gate, the fifth doped region and the sixth doped region include the first type dopant, and the seventh doped region includes the second type dopant.

A photosensitive device comprising:

• a semiconductor substrate;
• and
• a germanium-based sensor having:
• a germanium layer wrapped by a doped silicon layer, wherein the doped silicon layer is between and separates a bottom of the germanium layer and the semiconductor substrate,
• a laterally-diffused photodiode having a first p-n junction and a second p-n junction disposed in the germanium layer,
• a double-gate junction field effect transistor having a first doped gate structure, a second doped gate structure, a first source/drain region disposed in the germanium layer, a second source/drain region disposed in the germanium layer, and a channel region that extends between the first source/drain region and the second source/drain region, wherein:
• the channel region extends under the first doped gate structure and the second doped gate structure;
• the first source/drain region is disposed over and connected to the first p-n junction and the second source/drain region is disposed over and connected to the second p-n junction;
• and
• the first doped gate structure and the second doped gate structure each include a doped conductive layer disposed over a doped region in the germanium layer.