A discussion on various experimental methods of impact ionization coefficient measurement in GaN

Dong Ji,Zhengliang Bian,Ke Zeng,Robert J Kaplar,Jeramy R Dickerson,Andrew Binder,Travis J Anderson,Srabanti Chowdhury,Ozgur Aktas,Brendan P Gunning,Bhawani Shankar

doi:10.1063/5.0083111

Abstract

Impact ionization coefficients play a critical role in semiconductors. In addition to silicon, silicon carbide and gallium nitride are important semiconductors that are being seen more as mainstream semiconductor technologies. As a reflection of the maturity of these semiconductors, predictive modeling has become essential to device and circuit designers, and impact ionization coefficients play a key role here. Recently, several studies have measured impact ionization coefficients. We dedicated the first part of our study to comparing three experimental methods to estimate impact ionization coefficients in GaN, which are all based on photomultiplication but feature characteristic differences. The first method inserts an InGaN hole-injection layer, the accuracy of which is challenged by the dominance of ionization in InGaN, leading to possible overestimation of the coefficients. The second method utilizes the Franz–Keldysh effect for hole injection but not for electrons, where the mixed injection of induced carriers would require a margin of error. The third method uses complementary p–n and n–p structures that have been at the basis of this estimation in Si and SiC and leans on the assumption of a constant electric field, and any deviation would require a margin of error. In the second part of our study, we evaluated the models using recent experimental data from diodes demonstrating avalanche breakdown.

Highlights

Electron and hole impact ionization coefficients are critical parameters in the design of high field applications of semiconductors, such as impact ionization avalanche transit-time (IMPATT) diodes, avalanche photodiodes (APDs), and power switches.1 Impact ionization in gallium nitride (GaN) is a topic of obvious interest because the material is a forerunner of that used in many high-power applications
Avalanche breakdown in GaN power diodes was first reported in 2013 on a p–n junction fabricated on free-standing substrates
We investigated different experimental methods of estimating the impact ionization coefficients that have been recently used in GaN

Summary

INTRODUCTION

Electron and hole impact ionization coefficients are critical parameters in the design of high field applications of semiconductors, such as impact ionization avalanche transit-time (IMPATT) diodes, avalanche photodiodes (APDs), and power switches. Impact ionization in gallium nitride (GaN) is a topic of obvious interest because the material is a forerunner of that used in many high-power applications. Avalanche breakdown in GaN power diodes was first reported in 2013 on a p–n junction fabricated on free-standing substrates.. One of the methods examined is based on photomultiplication, a standard technique that is used in Si, GaAs, and SiC for impact ionization measurements and that has been implemented in GaN as well.. The two key criteria for impact ionization studies conducted using photomultiplication methods in Si and SiC are as follows: (1) the device should exhibit a robust avalanche breakdown and (2) the electrons and holes should be separately injected so that the electron and hole impact ionization coefficients can be extracted separately. The substrate removal technique suffers from various mechanical stress issues, and p-GaN substrates are not readily available

DISCUSSION

Findings

CONCLUSION