Evidence‐Based Understanding of Lateral Hole Transport During OFF‐State Stress Completing Dynamic GaN‐on‐Si Buffer Charging Model

Abstract

Gallium nitride (GaN)‐on‐Si high electron mobility transistors require insulating GaN buffers, which are prone to charge trapping and result in dynamic ON‐state resistance (dR DS,on) that negatively impacts performance and reliability. Herein, simultaneous measurements of threshold voltage shift (dV TH) and dR DS,on during OFF‐state stress with microsecond time resolution are employed. Ohmic p‐GaN gate contacts enable the use of dV TH to probe charge accumulation under the gate, while dR DS,on probes charge accumulation in the gate‐drain access region. Comparison of dV TH and dR DS,on provides direct evidence of lateral hole transport in the GaN buffer when exposed to a lateral electric field in OFF‐state. This lateral hole transport causes positive charge accumulation in the buffer under the gate and triggers a newly proposed electron injection mechanism into the same region. Only by considering the combination of lateral hole transport and electron injection under the gate the observed up to fivefold dR DS,on increase in OFF‐state stress compared to back‐gating at low biases can be explained. Furthermore, another electron spillover mechanism is introduced that occurs for large positive charge accumulation under the gate and limits the maximum negative dV TH. All known and newly introduced processes during OFF‐state are summarized in a concise dynamic buffer charging model.