Velocity enhancement in APDs with sub-100-nm multiplication region

We present an analytic approach to model the velocity enhancement in high field devices with sub-100-nm multiplication regions. In doing so, we consider the energy loss caused by collision between carriers and optical phonons. By inclusion of such effects, we modify carriers' path distance probability density functions (PDFs) for both time and space domain. Using our modified PDFs, we extract a more accurate set of impact ionization coefficients and ionization threshold energies for ultra-thin GaAs-, AlGaAs- and InAlAs-APDs with multiplication regions as narrow as 25 nm.