Advanced simulation of wide band gap semiconductor devices

Electron transport in III-Nitride materials and their related alloys have been studied. Low-field mobility models were extracted and a new high-field mobility model was proposed. It was found that the low- and high-field mobility models fit the Monte Carlo calculations over a practical range of temperature, doping density and electric field. Effect of alloy scattering on electron transport in III-Nitride alloys was bracketed using two different models based on affinity differences or the Philips electronegativity theory. It was found that alloy scattering can potentially have a dominating effect on transport in III-nitride alloys. Zincblende and wurtzite phase GaN MESFETs were studied with a full band self consistent Monte Carlo simulator. It was found that the wurtzite phase MESFET has a higher breakdown voltage, however the zincblende phase MESFET has higher transconductance and cut-off frequency. Differences between the performances of wurtzite and zincblende phase GaN MESFETs were explained to be related to differences between conduction band density of states and the electron effective masses in the two phases. A comparison between GaN and GaAs MESFETs was performed. It was found that a zincblende phase GaN MESFET has a breakdown voltage of at least four times higher than an otherwise equivalent GaAs device. It was also found that contrary to GaAs MESFETs which have a sharp breakdown, GaN MESFETs have a gradual breakdown behavior. RF-breakdown in bulk GaN and in GaN MESFET devices was studied. It was found that in bulk material the effective RF impact ionization coefficient decreases with increasing the frequency of the applied RF field. It was also discovered that the RF-breakdown voltage in devices increases with increase in the frequency of the applied large signal RF excitation. The difference between RF-breakdown and DC-breakdown and the frequency dependence of RF-breakdown was explained to be related to the energy relaxation time of the electrons and the nonlinear dependence of impact ionization generation rate on the initiating particle energy.