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

Hassan Hirshy,Martin Kuball,Michael A. Casbon,Trevor Martin,Richard M. Perks,Michael J. Uren,Manikant Singh,Paul J. Tasker

doi:10.1109/ted.2018.2872513

Abstract

This paper evaluates the applicability of pulsed I – V measurements as a tool for accurately extracting nonlinear gallium nitride (GaN)-based heterojunction field-effect transistor (HFET) models. Two wafers with the identical layer structure but different growth conditions have been investigated. A series of I – V measurements was performed under dc and pulsed conditions demonstrating a dramatic difference in the kink effect and current collapse (knee walkout) suggesting different trapping behaviors. However, when radio frequency (RF) I – V waveform measurements, utilizing active harmonic load–pull, were used to study the impact of these traps on the RF performance, both wafers gave good overall RF performance with no significant difference observed. This absence of correlation between pulsed I – V measurement results and RF performance raises a question about the applicability of pulsed I – V measurements alone as a tool for extracting nonlinear device models in the case of GaN HFETs.

Highlights

D UE to the unique material properties of gallium nitride (GaN), high-electron mobility, high break-Manuscript received July 23, 2018; revised August 27, 2018 and September 14, 2018; accepted September 26, 2018
We investigate the impact of traps in AlGaN/GaN heterojunction fieldeffect transistor (HFET) with and without the “kink effect” [22]–[23] and having differing “knee walkout” in pulsed I –V measurement method (P-I –V) measurements. (“Kink effect” is a hysteresis very commonly observed in the knee region, but which is normally assumed to have no impact on the radio frequency (RF) performance)
Two HFET wafers with different growth characteristics resulted in quite distinct dc and pulsed I –V behavior

Summary

INTRODUCTION

D UE to the unique material properties of gallium nitride (GaN), high-electron mobility, high break-. Many empirical and compact physical models have been reported, aimed at predicting the performance of the GaN HFET devices [12]–[21]. Most of these models again rely on P-I –V measurements as a model extraction and validation tool when including the trapping effects. They used P-I –V measurements to acquire the fitting parameters of the trap controlling voltage in the modified nonlinear device model. We investigate the impact of traps in AlGaN/GaN HFETs with and without the “kink effect” [22]–[23] and having differing “knee walkout” in P-I –V measurements. It is found that the measured “kink effect” in dc-I –V , and “knee walkout” in P-I –V , does not necessarily provide a valid prediction of the “knee walkout” observed under RF excitation

EXPERIMENTAL DETAILS

Pulsed I–V

Large-Signal RF

CONCLUSION