A Phototransistor Based on GaN-A1xGa1-xN Heterostructure

We propose to demonstrate the feasibility of fabricating a phototransistor using the A1xGa1-xN material system. The proposed phototransitor is based on a GaN-A1xGa1-xN heterojunction which exhibits a 2-D electron gas conduction when a bias is applied on the source-drain terminals. The device is maintained in a nominally OFF state by applying a reverse bias voltage on the gate terminal. With optical radiation (ultraviolet) incident on the device from the transparent (sapphire) substrate side, electronhole pairs are generated and the device is switched to the ON state due to the reduction in the reverse bias depletion voltage. High electron currents are expected due to the 2-D electron gas conduction implying a large current transfer ratio for the device. Because of the large bandgap of the A1xGa1-xN material system such a phototransistor in principle should be usable in high temperature applications. In Phase I we will prove the feasibility of our technical approach by fabaricating large area devices. In Phase II the devices will be optimized to obtain high speeds and performance levels.