Observations and Physical Insights Into Time-Dependent Hot Electron Current Confinement in AlGaN/GaN HEMTs on C-Doped GaN Buffer

Abstract

In this work, we report a unique time-dependent evolution of drain current and hot electron distribution along the width of AlGaN/GaN HEMTs on C-doped GaN buffer during semi- ON state stressing. The drain current evolution with stress time exhibited two distinct phases, i.e., first, drain current reduction at lower stress times, which, second, is followed by an increase in the magnitude for longer stress times. Electroluminescence (EL) measurements revealed this to be accompanied by a transition in the hot electron distribution along the device width, from being uniform (during the current reduction phase) to being confined near the center of the device (during current increase phase). Detailed experiments involving measure-stress-measure (M-S-M) routine showed a gate-stack-dependent threshold voltage shift in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\text {SiN}}_{x}$ </tex-math></inline-formula> -gated MISHEMTs to be responsible for the reduction in the drain current. On the other hand, increase in the drain current and hot electron confinement were observed in Schottky as well as MIS-gated devices. Furthermore, in situ thermoreflectance-based temperature monitoring showed a nonuniform temperature distribution along the device width. Detailed computations, taking into account the nonuniform temperature distribution, established heating induced nonuniform hole emission along the device width and their subsequent lateral redistribution to be responsible for the experimentally observed current increase and hot electron confinement.