GaN based High Electron Mobility Transistors (HEMTs) and Metal-Oxide-Semiconductor High Electron Mobility Transistors (MOSHEMTs) are well established in high-power applications such as switches, power amplifiers and transceivers. Recently, there has been a tremendous advancement in the domain of wireless/mobile communication technology, with the recent introduction of 5G and RF standards for IoT and near field communication in the frequency range of 30 – 300 GHz and higher. The requirement of high scalability and low-power consumption is driving the research focus towards the use of advanced GaN based MOSHEMT devices.
Scaling down the dimensions of GaN-based HEMTs and MOSHEMTs is, however, associated with multiple technological challenges, such as process optimization (thermal budgets, buffer development among others), device design (field plates, device parasitics, etc.) and device reliability (buffer and device breakdown, current dispersion, gate-stack reliability, etc.). Charge trapping in the defects of the gate-stack, channel, at the channel/barrier interface responsible for the 2D-Electron-Gas (2DEG), and barrier/gate-stack interface play a role in the electrical characteristics of devices, and impact figures-of-merit such as ON/OFF current and mobility in DC characteristics. More importantly, AC characteristics such as threshold and maximum oscillation frequency (ft/fmax), parasitic losses and dynamic on-Resistance (RON) are also affected. Temperature dependence of mobility and oxide charge trapping can modulate the dominant reliability mechanisms.
This PhD will focus on the device reliability characterization and (semi-)empirical modeling of device reliability. Impact of defects in the bulk of the device (GaN/Barrier interface, access regions etc.) as well as the gate-stack could be studied in detail. Different characterization techniques, such as Bias-Temperature-Instability (BTI), Hot-Carrier Degradation (HCD) and TDDB (Time-Dependent Dielectric Breakdown) characterization, and device RON dispersion measurements will be employed. A fundamental understanding of the degradation mechanisms will help in formulating technological solutions to improve the device reliability and lifetime.
Candidates are expected to have a Master's degree in Engineering Science with a strong interest in semiconductor physics and good quantitative/analytical skills. Prior experience in semiconductor material characterization, device physics and reliability is an advantage.
Literature study: 20% Characterization: 40% Modelling: 40%
Required background: A Master’s degree in Engineering Science with a strong interest in semiconductor physics and good quantitative/analytical skills. Prior experience in semiconductor material characterization, device physics and reliability is an advantage.
Type of work: Literature study: 20%, Characterization: 40%, Modelling: 40%
Supervisor: Guido Groeseneken
Daily advisor: Vamsi Putcha
The reference code for this position is 2020-047. Mention this reference code on your application form.