Transmission line measurement of gold contact on the arsenic-ion-implanted GaAs after rapid thermal annealing

We study the current-voltage characteristic of AuGeNi contacts made on arsenic-ion-implanted GaAs by using the transmission line measurement. The GaAs:As+ samples were rapid-thermal annealed at 600 degrees C for ranged from 30 to 300 seconds. The mechanism responsible for the large dark current in the as-implanted GaAs:As+ is attributed to the hopping conduction of trapped carriers among the dense deep-level defects. After annealing, the defect density gradually reduces and the perfection of crystal lattice recovers. This results in the evanescence of the hopping conduction and the increasing resistance for GaAs:As+. A turning point at contact spacing between 10 micrometers and 15 micrometers on the curve of resistance as a function of contact spacing is discussed. The change in the contact resistance measured at larger spacing is dominated by bulk GaAs substrate since that the electric field may distribute deeper into the substrate as the contact spacing become larger. The measured resistance at below the turning point is primarily dominated by the implanted GaAs:As+ layer. The contact resistances are estimated to be ranged from 7.8 X 104 to 8 X 109 (Omega) as the annealing time increases from 0 to 300 seconds, respectively. The sheet resistances are increased from 2.4 X 104 to 2 X 1010 (Omega) /$DAL, and the specific contact resistances are increased form 13.8 to 1.6 X 105 (Omega) -cm2 as the annealing time increases. In comparison, the characteristic parameters of the GaAs:As+ annealed for 5 minutes is already better than that of a semi-insulating GaAs substrate. These observations facilitate us to obtain the optimized process condition of an ultra-high resistive GaAs:As+ material for fabrication of ultrafast optoelectronic switches.