Transport properties of p-type doped hydrogenated amorphous germanium thin films

F. FAJARDO; D. COMEDI; I. CHAMBOULEYRON; M. TABACNIKS

Cancun

Congreso; Latin American Congress on Surface Science, Vacuum and their Applications; 1994

SLACS

Doped a-Ge:H samples were prepared by co-sputtering minute amounts of the dopant species In, Ga or Al with a c-Ge target. For all three dopants the activation energy (Ea) of the dark conductivity is found to increase from ~ 0.43 to ~ 0.55 eV at small dopants concentrations. A concomitant decrease of the room-temperature dark conductivity sRT [from ~ 7x10-5 to 3x10-7 (W.cm)-1] is measured. These data indicate a Fermi level shift towards mid-gap, the impurities compensating the non-intentionally doped as-grown n-type material. Higher concentrations of In, Ga or Al produce a decrease of Ea and an increase of sRT, indicating that the Fermi energy is further shifting towards the valence band edge. Thermopower measurements indicate a concomitant change from n- to p-type conduction. The above results show that In, Ga or Al atoms produce, in the a-Ge:H network, an active p-type doping effect.