(Invited) Radiation Effects on the Self-Heating of AlGaN/GaN High Electron Mobility Transistors

Abstract

Gallium nitride (GaN) has emerged as one of the most attractive wide bandgap materials for near-future electronics technology, specifically for applications that require high-power and high-frequency devices. The spontaneous and piezoelectric polarization of GaN utilized in AlGaN/GaN high electron mobility transistors (HEMT), provides significantly low ON-resistance due to the formation of a two-dimensional electron gas (2-DEG) channel at the AlGaN/GaN heterointerface without any intentional doping. The fact that these devices do not rely upon dopants to carry the current, in conjunction with superior material property of GaN, makes AlGaN/GaN HEMTs perfect candidates for deep space applications. However, the high voltage operation and the inherently low ON-resistance in AlGaN/GaN HEMTs result in extremely high power densities. Consequently, intense self-heating deteriorates device performance and more importantly, reliability.In order to counter the potential thermal problems associated with these device technologies for deep space applications, it is necessary to advance the knowledge of device irradiation and its effect on self-heating, material interfaces, and properties of constituent materials. To achieve this goal, a set of AlGaN/GaN HEMTs were irradiated with a proton flux at an energy level of 1 MeV at a fluence of 2x1015/cm2. Diverse optical thermography techniques including infrared thermography, thermoreflectance thermal imaging, and micro-Raman spectroscopy were used to quantify the effect of radiation on the device temperature distribution. It was observed that, as compared to pre-irradiated devices, irradiated devices show a 40% higher device peak temperature under identical power dissipation (5 W/mm). To understand the contributing factors behind the observations (and the resulting deterioration of device mean-time-to-failure), the device material stack and transmission line measurement (TLM) structures were analyzed further. Steady-state thermoreflectance (SSTR) measurement, standard electrical characterization, and 3D coupled electro-thermal modeling were performed to capture changes in the thermal conductivity, interfacial thermal boundary resistance, ohmic contact resistance, and sheet resistivity of the devices. This comprehensive study will support the exploitation of the full potential of GaN electronics for deep space and other applications that require radiation hardness.