Experimental evaluation of impact ionization coefficients in GaN

The impact ionization coefficient of electrons (/spl alpha//sub n/) in GaN is determined as a function of the electric field strength from gate-current analysis in the prebreakdown regime of AlGaN/GaN heterojunction field effect transistors (HJFETs). The experimentally obtained /spl alpha//sub n/, where the assumed effective length of the high electric field is precisely defined since its upper bound is closely limited due to the small gate-drain separation, agrees with that extrapolated from Monte Carlo simulation. It is experimentally confirmed that the breakdown field of GaN is higher than that of GaAs by a factor of about eight.