Ion-Assisted Doping of II-VI Compounds During Physical Vapor Deposition: Final Subcontract Report, 1 September 1985 - 30 August 1989

This report describes a research program to (1) investigate ion-assisted doping during chemical vapor deposition of CdTe and (2) determine the influence of co-depositing ionized dopant atoms on the growth and structural and photoelectronic properties of the deposited films. In p-CdTe homo-epitaxial films, we controlled doping up to about 6 x 1016 cm3 and 2 x 1017 cm3 for ion-assisted depositionswith As and P ions, respectively. At a growth rate of approximately 0.1 um/min, a substrate temperature of 400 degrees C, and an ion energy of 60 eV, a maximum doping density was found near an ion current of 0.6 uA/cm2. Related studies included elucidating the role of low-energy ion damage in the ion-assisted doping process, and investigating the decrease in carrier density near the surface ofp-CdTe upon heating in vacuum, H2 or Ar. We demonstrate the ability to make carrier density profiles and to grade junctions, and we present preliminary results from polycrystalline p-CdTe films grown on graphite and alumina substrates. We also present solar cells prepared using the p-CdTe as the collector area and n-CdS as the window layer; and we examine their photovoltaic parameters fordifferent carrier densities and configurations in p-CdTe.