Characteristics of impact ionization rates in direct and indirect gap semiconductors

Abstract

Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Impact ionization rates for electrons and holes in three semiconductors with particular band structure characteristics are examined to determine underlying factors influencing their qualitative behavior. The applicability of the constant matrix element approximation is investigated, and found to be good for the indirect gap material studied, but overestimates threshold softness in the direct gap materials. The effect that final states in the ⌫ valley have in influencing characteristics of the rate in the direct gap materials is investigated, and it is found that they play a significantly greater role than the low density of ⌫ valley states would suggest. The role of threshold anisotropy in affecting threshold softness is examined, and it is concluded that it plays only a small part, and that softness is controlled mainly by the slow increase in available phase space as the threshold energy is exceeded.

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