About measurements of electrons and holes impact ionization coefficients in 4H-SiC

TL;DR

This paper analyzes existing data on impact ionization coefficients in 4H-SiC at 300K, proposing a conventional exponential model, calculating breakdown parameters, and presenting new formulas for deriving ionization coefficients from experimental measurements.

Contribution

It provides a unified exponential approximation of impact ionization coefficients and introduces formulas to calculate these coefficients from avalanche and noise measurements.

Findings

Exponential model parameters for electrons and holes in 4H-SiC are established.

Maximum field strength and space charge region thickness at breakdown are calculated.

New formulas enable deriving impact ionization coefficients from experimental data.

Abstract

The analysis of all published results on electrons and holes impact ionization coefficients in 4H-SiC at 300K have been performed. It is shown that the most plausible approximation of dependencies $\alpha_{n,p}$ on the electric field strength $E$ have a conventional kind $\alpha_{n,p}=a_{n,p}\exp(-E_{n,p}/E)$ with the values of the fitting parameters $a_n=38.6\cdot 10^6$ 1/cm, $E_n=25.6$ MV/cm, $a_p=5.31\cdot 10^6$ 1/cm, $E_p=13.1$ MV/cm. These dependencies $\alpha_{n,p}(E)$ have been used to calculate the maximum field strength $E_b$ and the thickness of the space charge region $w_b$ at the breakdown voltage $U_b$. A set of new formulas are presented for calculation of $\alpha_{n,p}(E)$ from results of avalanche multiplication coefficients and excess noise factor measurements at one-side lighting of photodiodes with stepped doping.