SURFACE PROPERTIES OF N-TYPE GALLUIM ARSENIDE

This paper describes an investigation of GaAs surfaces by means of field effect, surface photovoltage and photoconductance measurements. A wide variety of different etch treatments and also the effect of depositing SiO2 on the surface have been investigated. It is found that the surface barrier always bends towards depletion or inversion. On some etched surfaces the total effective surface trap density is at least 1012 cm-2 but some treatments were found to reduce this to about 3 × 1011 cm-2. The effective surface trap density of SiO2 covered surfaces was 7 × 1011 cm-2 and was not sensitive to the etch treatment of the underlying surface. Under ac fields the mean surface barrier height becomes biased in the direction of further depletion due to an increase in the mean occupancy of the traps. The ac field effect mobility is of the order of 2000 cm2 V-1 sec-1 despite the large surface trap densities. It is also deduced from the ac field effect that fast bulk traps with densities of about 1015 cm-3 are active in the surface space charge layer. A model of the surface is given which explains the observed phenomena. © 1968.