EXCESS DARK CURRENT DUE TO SAW DAMAGE IN SEMIINSULATING GAAS

Logarithmic plots of current or carrier concentration vs inverse tempe rature in semi-insulating GaAs samples are nearly always well characte rized by straight lines with a donor activation energy of 0.76 +/- 0.0 2 eV, as long as the surfaces are well polished or etched and the edge s are cleaved. However, edges cut with common dicing saws produce an e xcess conductance which can dominate the bulk conductance at room temp erature and below. This excess conductance is due to carrier hopping b etween defects in a surface layer of approximately 2000angstrom thickn ess, which can be easily removed by etching. Some polished surfaces al so exhibit this same effect.