Examination Committee

Prof Xiangrong WANG, PHYS/HKUST (Chairperson)
Prof Kevin J CHEN, ECE/HKUST (Thesis Supervisor)
Prof Anthony H W CHOI, Department of Electrical and Electronic Engineering, The University of Hong Kong (External Examiner)
Prof Jianan QU, ECE/HKUST
Prof Zhiyong FAN, ECE/HKUST
Prof Jiannong WANG, PHYS/HKUST
 

Abstract

GaN-based heterojunction transistors are being developed with intensive efforts for high-efficiency power converters, owing to their capabilities of delivering lower conduction/switching losses, higher switching frequency, and higher operating temperatures compared to conventional Si power devices. However, the development of GaN-based power devices is still challenged by deep electron traps that are inevitable in state-of-the-art GaN-on-Si epitaxial heterostructures, which would increase the dynamic ON-resistance (RON) and result in additional power losses during switching operations. In this work, we proposed and developed a new way of suppressing the adverse effects of electron traps and thus enhancing the GaN power devices’ dynamic performance by on-chip photon pumping.

First, a Schottky-on-heterojunction light-emitting diode (SoH-LED) was demonstrated on a p-doping-free AlGaN/GaN heterostructure, from which electroluminescence (EL) could be generated. The EL spectra included a yellow band, a blue band and a narrow GaN-bandedge UV emission at 3.4 eV. A model based on hot-electron induced surface states impact ionization was proposed to explain the underlying mechanisms of the hole generation and injection processes. The SoH-LED provided a unique on-chip photon source fully compatible with GaN-on-Si power devices. A SoH-LED was seamlessly integrated onto the AlGaN/GaN high-electron-mobility transistor (HEMT) platform. Experimental results revealed that the photons from SoH-LED could effectively accelerate the electron de-trapping processes from both the surface and buffer traps, demonstrating the feasibility of using on-chip photon pumping to improve the dynamic performances of power HEMTs.

Finally, a compact photonic-ohmic-drain field-effect transistor, i.e. PODFET, was designed and demonstrated on a conventional GaN-on-Si power HEMT platform. The PODFET exhibited a simple yet effective approach to driving the compact photon source with intrinsic channel current. During each switching event, the photon generation was switched ON in synchronization with the channel current, pumping electrons from the deep traps with ease and effectively suppressing dynamic RON degradation which was reduced from 50% in conventional device to 6% in PODFET under 600-V 5-µs high-voltage switching.