(Invited) Simulation of the Effects of As-Grown Defects on GaN-Based Power HEMTs

Abstract

With the wide band-gap of Gallium Nitride (GaN) and high mobility of 2 dimensional electron gas(2DEG), AlGaN/GaN high electron mobility transistors (HEMTs) are considered ideal candidates for high speed and power applications ranging from hybrid vehicles to space communication. Developments in the fabrication of GaN-based blue LEDs have been incorporated into the processing of AlGaN/GaN HEMT structures leading to improvements in amount of defects and dislocations resulting from heteroepitaxial growth. But evident degradation of dynamic performance of such devices due to the presence of as-grown defects still remains a subject of major concern. Using FLorida Object Oriented Device Simulator (FLOODS) TCAD, this work looks to analyze the impact of variation of defect properties as well as their spatial distribution and concentration on the steady-state and dynamic behavior of AlGaN/GaN HEMTs. FLOODS TCAD’s defect modeling capability will be applied to examine how multiple defect levels, of both donor and acceptor-like nature, can influence device performance. Particular emphasis will be on transient switching, such as gate-lag and drain-lag experiments, in consideration of the slow nature observed frequently in literature. While comprehensive investigation of the role of charged defects at the AlGaN/passivation layer interface on performance degradation has already been performed, contribution by as-grown defects, expected to be in significant quantity in the GaN buffer layer, is yet to be investigated. Building on experimental results, which suggest the presence of multiple acceptor-like defects, impact on steady-state current-voltage characteristics will be observed followed by an examination of how such defects will affect dynamic performance by isolating their contribution to transient and switching behavior. Figure: (a) Drain current against gate voltage at VDS=0.5V for HEMT A with 1 acceptor-like level (nT=1014 cm-3, Et=Ec-0.7eV) and HEMT B with 2 acceptor levels(Level 1: nT=1014 cm-3, Et=Ec-0.7eV; Level 2: nT=1015 cm-3, Et=Ec-0.5eV) (b) Optical pumping like detrapping of electrons, biasing at VDS=1V and VGS=0V. HEMT A(Level 1: nT=1013 cm-3, Ec-0.2eV, τ=1s; Level 2: nT=4x1013 cm-3, Ec-0.5eV, τ=1ms), HEMT B(Level 1: nT=1013 cm-3, Ec-0.2eV, τ=1s; Level 2: nT=1013 cm-3, Ec-0.5eV, τ=1ms) Figure 1