Monte Carlo simulation of noncubic symmetry semiconducting materials and devices

In this paper, we discuss the complexities that arise in Monte Carlo based modeling of noncubic symmetry semiconductors and their related devices. We have identified three general issues, band structure, scattering mechanisms, and band intersections that require some modification of the Monte Carlo simulator from that for cubic symmetry. Owing to the increased size and number of atoms per unit cell, the band structure is far more complex in noncubic than in zincblende phase semiconductors. This added complexity is reflected by the greater number of bands, smaller Brillouin zone and concomitant increase in the number of band intersections. We present strategies for modeling the effects of band intersections on the carrier dynamics using the Monte Carlo method. It is found that the band intersection points greatly affect the carrier transport, most dramatically in the determination of the impact ionization and breakdown properties of devices and bulk material. Excellent agreement with experimental measurements of the impact ionization coefficients is obtained only when treatment of the band intersections is included within the model.