Gallium nitride & Levinshtein mobility
Add Gallium Nitride as sensor material, based on code by @asantra.
Charge creation energy and Fano factor are taken from https://etd.ohiolink.edu/apexprod/rws_etd/send_file/send?accession=osu1448405475 .
This also adds a new mobility model suitable for Gallium Nitride, the Levinshtein model. See publication: https://doi.org/10.1016/S0038-1101(02)00256-3
Not added so far: Recombination and trapping models.
Edited by Paul Jean Schutze