Theoretical analysis of band structure effects on impact ionization coefficients in wide-bandgap semiconductors

Abstract

This study theoretically investigates the effects of band structure parameters, such as the bandgap, effective mass, and Brillouin zone (BZ) width, on impact ionization coefficients. A Monte-Carlo simulation considering analytical and tunable band structures reveals that the smaller BZ width significantly reduces impact ionization coefficients, and its impacts can outperform those of the bandgap. The smaller BZ width also leads to positive temperature dependence of impact ionization coefficients, which is discussed focusing on the occurrence of the Bloch oscillation. Our results show the importance of the BZ width in discussing the behavior of impact ionization coefficients.

Tight-binding analysis of the effect of strain on the band structure of GaN

“…According to previous studies, smaller group velocity leads to a reduction in the impact ionization and the effect of which is suggested to be more dominant than the effect of the bandgap. 37,38) Thus, we conclude that tensile uniaxial strain or compressive biaxial strain may be beneficial for achieving higher breakdown voltage in vertical GaN power devices, where the electric field is mainly applied along the 〈0001〉 direction. In addition, as shown in Fig.…”

Defect engineering in SiC technology for high-voltage power devices

“…44,45) Due to this effect, the critical electric field strength along SiC 〈0001〉 becomes much higher than that expected based on the bandgap. 46) In fact, the critical electric field strength along SiC 〈1120〉 is 21%-25% lower than that along SiC〈0001〉. [47][48][49] Figure 3 shows the doping density dependence of the critical electric field strength for SiC〈0001〉, SiC〈1120〉 and Si pn junctions with nonpunch-through structures.…”

Full-band Monte Carlo analysis of strain effects on carrier transport in GaN

“…The energy of the final state after the impact ionization events is assumed to be one-third of the surplus energy as (E − E g )/3. 43,44) The impact ionization coefficient α is calculated by dividing the number of impact ionization events N ii by the displacement L as α = N ii /L.…”

“…This can be attributed to the change not only in the bandgap but also in the group velocity. 19,43,44) For example, when 2% compressive uniaxial strain is applied, the bandgap increases and the conduction band group velocity decreases. Both suppress impact ionization, resulting in a decrease in α n by about 24%.…”