Velocity-field characteristics of electrons in doped GaAs

Abstract

We report the first comprehensive measurements of the velocity-electric field charac-teristics of electrons in doped GaAs with carrier concentrations between 1 × 1015 and 1.5 × 1018 cms-3 at both 77 and 300 K. These measurements from 0 to 9000 V/cm make use of a 35 GHz technique in order to avoid charge domain formation which would render a DC measurement impossible in regions of negative differential resistance. We observe peak velocities at 300 K of between 0.9 × 107 and 2.2 × 107 cm/s in this doping range. Higher doping results in lower peak velocities which occur at higher electric fields. At 77 K, the trend is the same as at 300 K with peak velocities of between 1.1 × 107 and 3.5 × 107 cm/s. In addition, these measurements demonstrate an increase in electron differential mobility in GaAs with increasing electric field. This effect occurs in moderately doped GaAs because the warm electrons which have been heated by the electric field scatter less efficiently with the ionized impurities than do the colder elec-trons. The increasing differential mobility occurs at electric fields well below the critical field for the onset of negative differential mobility and is more pronounced at 77 K than at 300 K. These results are significant both for the understanding of hot carrier trans-port in doped semiconductors as well as for understanding and modelling GaAs MESFETs. © 1989 AIME.