Investigation of Gate Current in Neutron irradiated Al_xGa_1-xN/GaN Heterogeneous Field Effect Transistors Using Voltage and Temperature Dependence

Author

Thomas E. Gray

Date of Award

3-7-2007

Document Type

Thesis

Degree Name

Master of Science in Nuclear Engineering

Department

Department of Engineering Physics

First Advisor

James C. Petrosky, PhD

Abstract

The gate current of Al₂₇Ga₇₃N/GaN heterogeneous field effect transistors (HFETs) is investigated using current-voltage (IV) and current-temperature (IT) measurement demonstrating that trap assisted tunneling (TAT) is the primary current mechanism. A thermionic trap assisted tunneling (TTT) model is used with variables of Schottky barrier height, trap energy, donor density and trap density. This results in a sigma of 1.38x10^-8 A for IT data measured between 85K and 290K and for IV data measured between 0.0 V and -4.0 V. High energy (>0.5 MeV) neutron irradiation confirms an increase of gate current with fluence. An increase in magnitude of threshold voltage is also observed. The TTT model suggests that increased trap density is responsible for increased gate current at a fluence of 1.2x10¹². An increase in trap density from the unirradiated fit value of 4.593x10²¹ to 5.737x10²¹ traps/m³ and an increase in the position of traps in the energy band from 0.896 to 0.9028 V results in a fit with σ of 1.77x10^-9 A. An increase in donor defect density is modeled resulting in a sigma of 5.00x10-9 A and an increase in threshold voltage magnitude consistent with the observed change in measured IV behavior.

AFIT Designator

AFIT-GNE-ENP-07-02

DTIC Accession Number

ADA464330

Recommended Citation

Gray, Thomas E., "Investigation of Gate Current in Neutron irradiated Al_xGa_1-xN/GaN Heterogeneous Field Effect Transistors Using Voltage and Temperature Dependence" (2007). Theses and Dissertations. 2923.
https://scholar.afit.edu/etd/2923