A Closed-Form Charge Control Model for the Threshold Voltage of Depletion- and Enhancement-Mode AlGaN/GaN Devices

A closed-form charge control model (CCM) for threshold voltage (Vth) of single-heterojunction (AlGaN/GaN) devices is developed. The CCM reveals the mechanisms of how the space charges across the barrier of a heterojunction deplete or enhance 2-D electron gas. The Vthof both depletion- and enhancement-mode heterostructure field-effect transistors may be calculated through this model. Considering the strained and relaxed states, and surface states, the calculated results for Vthare in good agreement with simulation results. The generalized form for CCM may have wide applications for theoretical-based design for Vthof AlGaN/GaN devices.