LOW-FREQUENCY NOISE PROPERTIES OF SELECTIVELY DRY-ETCHED INP HEMTS

The low-frequency noise of lattice-matched InAlAs/InGaAs/InP high elec tron mobility transistors (HEMT's) gate recess etched with a highly se lective dry etching process and with conventional wet etching were stu died at different gate and drain biases for the temperature range of 7 7-340 K, The measurements showed a significantly lower normalized drai n current 1/f noise for the dry etched HEMT's under ail bias condition s. No difference in the normalized gate current 1/f noise could be obs erved for the two device types. By varying the temperature, four elect ron traps could be identified in the drain current noise spectra for b oth dry and wet etched devices. No additional traps were introduced by the dry etching step. The concentration of the main trap in the Schot tky layer is one order of magnitude lower for the dry etched HEMT's, N o hydrogen passivation of the shallow donors was observed in these dev ices. We presume hydrogen passivation of the deep levels as the cause for the trap density reduction. The kink effect in the dry etched HEMT 's was observed to be reduced significantly compared with wet etched d evices which gives further evidence of trap passivation during dry etc hing. These results show that dry etched InP HEMT's have suitable char acteristics for the fabrication of devices for noise sensitive applica tions.