Monte Carlo modeling of carrier transport and impact ionization in GaSb

An analytical band Monte Carlo (AMC) model has been developed to study the high field electron transport and the impact ionization in bulk gallium antimonide (GaSb). The AMC model uses three non-parabolic spherical valleys; in which Γ valley and L valley represent the first conduction band, while X valley represents the second conduction band. The scattering mechanisms included in this model are polar optical phonon, acoustic phonon, non-polar optical phonon (equivalent and non-equivalent intervalley), ionized impurity and impact ionization. The peak drift velocity occurs at 10 kV/cm and the saturation velocity is 8 × 10
⁴
m/s. Since the intervalley energy separation between the Γ valley and L valley is only 0.0847 eV, most electrons have already populated the higher valleys under small electric field. Thus, electrons in GaSb do not have sufficient time to acquire larger energy and lead to lower velocity before transfer to higher valley. This also leads to lower average electron energy for GaSb. The weak field dependence of GaSb at low field is attributed to majority of electrons impact ionising within the first conduction band. The impact ionization coefficient for GaSb is higher than that of InGaAs as GaSb has higher ionization rates. Besides that, GaSb has lower intervalley energy separation between the first and the second conductions, which leads to shorter average impact ionization path length and time. In addition, electrons in GaSb are able to impact ionise with higher average impact ionization energy as compare to InGaAs.