Modeling of a Breakdown Voltage in GaN Rectifiers and SiC Rectifiers
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Modeling of a Breakdown Voltage in GaN Rectifiers and SiC Rectifiers You- Sang Lee, Min-Koo Han and Yearn-Ik Choi* School of Electrical Eng., Seoul Nat’l Univ., Shinlim-Dong Kwanak-Ku, Seoul 151-742, Korea Tel : +82-2-880-7254, Fax : +82-2-873-9953, E-mail : [email protected] *Dep. of Molecular Science and Technology, Ajou Univ., Wonchun-Dong, Suwon 442-749, Korea, E-mail : [email protected] ABSTRACT The breakdown voltage of wurtzite and zinc-blende GaN rectifiers as function of a doping concentration and the width of epitaxial layer were successfully modeled in the reach-through case. The breakdown voltage was derived by the impact ionization integral employing the effective impact ionization coefficient and an accurate approximation. Our model shows that the breakdown voltage of wurtzite GaN rectifier was larger than those of zinc-blende GaN rectifier and SiC rectifiers including 4H-SiC and 6H-SiC in the condition that both the thickness and doping concentration of epitaxial layer are identical.
INTRODUCTION GaN may be a promising wide band-gap semiconductor material for power devices due to its high electric fields strength and large carrier mobility1. The breakdown voltage may be one of the most important characteristics in these power device applications. However, an accurate evaluation of the breakdown voltage is rather difficult and an analytic model of breakdown voltage in GaN has been scarcely reported. The purpose of our work is to report an analytic model of the breakdown voltage in the GaN reach-through rectifier. We also compare the breakdown voltage of GaN rectifiers with those of SiC reach-through rectifier2. In this work, we successfully derive the breakdown voltage of GaN reachthrough rectifier from the impact ionization integral by an effective impact ionization coefficient3,4. The impact ionization coefficients of GaN in wurtzite and zinc-blende are extracted from ensemble Monte-Carlo simulation using scattering rates which were reported in the literatures5,6. It has reported from the ensemble Monte-Carlo simulation that an impact ionization coefficient of zincblende structure is larger than the impact ionization coefficient of wurtzite structure by more than one order over the wide electric field range. We employ an effective impact ionization coefficient αeff and m-th order approximation in the impact ionization integral without a loss of generality. MODELING OF THE BREAKDOWN VOLTAGE IN GaN RECTIFIERS The mesa structure of GaN retifier has been reported in the literatures. We model the breakdown voltage of one-dimensional GaN rectifier in the mesa structure. The mesa structure GaN rectifier and cross-sectional view and the electric field distribution of reach-through rectifier are shown in fig.1.
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(a) The mesa structure of GaN rectifier (b) cross-sectional and the electric field distribution of reach-through rectifier Figure1. The mesa structure of GaN rectifier, cross-sectional view and the electric field distribution of reach-through rectifier When GaN rectifier is reverse
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