Demonstration and analysis of reduced reverse-bias leakage current via design of nitride semiconductor heterostructures grown by molecular-beam epitaxy

An approach for reducing reverse-bias leakage currents in Schottky contacts formed to nitride semiconductor heterostructures grown by molecular-beam epitaxy is described, demonstrated, and analyzed. By incorporation of a GaN cap layer atop a conventional AlxGa1−xN/GaN heterostructure field-effect transistor epitaxial layer structure, the direction of the electric field at the metal-semiconductor interface of a Schottky contact is reversed, resulting in a suppression of electron flow into conductive screw dislocations that are known to dominate reverse-bias leakage currents in nitride semiconductors grown by molecular-beam epitaxy. Analysis of temperature-dependent current-voltage characteristics indicates that, in structures incorporating a GaN cap layer, reverse-bias leakage currents are reduced by one to three orders of magnitude, with the mechanism for leakage current flow differing from that established previously for the more conventional structure due to the alteration in the electric field at the metal-semiconductor interface. Scanned probe measurements of local, nanoscale current distributions confirm directly that current flow via conductive dislocations is suppressed in structures incorporating the GaN cap layer. © 2006 American Institute of Physics. DOI: 10.1063/1.2150591