Band tails and defect density in p-type doped hydrogenated amorphous germanium

D. COMEDI; F. FAJARDO; I. CHAMBOULEYRON

JOURNAL OF NON-CRYSTALLINE SOLIDS

Año: 1996 vol. 200 p. 399 - 403

0022-3093

The correlations between the defect density, N-D, Fermi energy, E(F), and Urbach tail, E(0), are examined for rf-sputtered a-Ge:H films p-type doped by aluminum, gallium and indium. Photothermal deflection spectroscopy was used for the determination of N-D and E(0), while E(F) was deduced from conductivity measurements. The present data show different dependence of N-D on E(F) for samples doped by different dopants, but a similar behavior when N-D is plotted as a function of E(0) or the solid-state dopant impurity concentration. The simple equilibrium model of doping alone is unable to explain the present results. The data suggest that the doping-induced defects observed are related to the large fraction of neutral dopant impurities expected to be present in the material.