“Kink” in AlGaN/GaN-HEMTs: Floating Buffer Model

Abstract

We report on a floating buffer model to explain "kink," a hysteresis in the output characteristics of Fe-doped AlGaN/GaN HEMTs observed at low drain bias. Unintentionally doped background carbon can make the GaN buffer p-type allowing it to electrically float. We further note that reverse bias trap-assisted leakage across the junction between the 2DEG and the p-type buffer can provide a mechanism for hole injection and buffer discharging at just a few volts above the knee, explaining the "kink" bias dependence and hysteresis. We show that HEMTs with a different background carbon have dramatically different kink behaviors consistent with the model. Positive and negative magnitude drain current transient signals with 0.9-eV activation energy are seen, corresponding to changes in the occupation of carbon acceptors located in different regions of the GaN buffer. The observation of such signals from a single trap calls into question conventional interpretations of these transients based on the bulk 1-D deep-level transient spectroscopy (DLTS) models for GaN devices with floating regions.

The Role of Carbon Doping on Breakdown, Current Collapse, and Dynamic On‐Resistance Recovery in AlGaN/GaN High Electron Mobility Transistors on Semi‐Insulating SiC Substrates

“…In this work, we calibrated the carbon-related trap concentration in order to match results in terms of DC characteristics and off-state breakdown, as C-V measurements were absent for the fabricated devices [2]. The choice of the C-doping model adopted in this work is justified by the fact that by adjusting the donor-acceptor auto-compensation ratio it is possible to accurately reproduce dynamic effects in different AlGaN/GaN power HEMTs [9]- [13]. Moreover, a higher donor concentration in C-doped GaN compared to the donor density measured in unintentionally doped samples was experimentally confirmed in [14], and attributed to the auto-compensation between C related donors and acceptors, as assumed here.…”

Evaluation of Pulsed I–V Analysis as Validation Tool of Nonlinear RF Models of GaN-Based HFETs

“…The entire experiment was repeated using a second pair of wafers with the same epitaxy and fabrication process resulting in the same measurement results reported here. More details on the epitaxy, drain current transient measurements, and on the kink effect mechanism are given in [24]. The higher background carbon profile of wafer A results in it having a floating p-type buffer leading to the kink and long-time constant recovery while wafer B has a n-type buffer which shows recovery in a few milliseconds.…”

AlInGaN/GaN HEMTs With High Johnson’s Figure-of-Merit on Low Resistivity Silicon Substrate

“…One of the features of our devices in this study is the TEG grown GaN channel in N2 ambient, which shows more than 85 % reduction in residual carbon concentration in the GaN channel than the GaN buffer. Substitutional C (CN) at N-site with an energy level of 0.9 eV above the valence band maxima has been identified as one of the common sources of both DC and RF performance degradation in GaN HEMTs [16]. Therefore, an improvement in dynamic behavior and RF performance is expected due to the reduction in the acceptorlike CN in the vicinity of the heterointerface and the channel, as indicated by several reports [17].…”