Pulsed laser deposition of CdTe thin films for heterojunctions on silicon

Thin films of CdTe were deposited on Si substrates by pulsed laser evaporation (PLE) at substrate temperatures T_s of 25 and 200 degrees C. Films were also deposited by thermal evaporation (TE) for comparison. X-ray diffraction studies showed that while both films were polycrystalline with a zincblende structure, the PLE films showed a preferred (111) orientation. The composition of the films was checked by energy dispersive X-ray analysis (EDAX) and Cd:Te ratios of 1:1.03 (PLE) and 1:1.04 (TE) were obtained. The band gap of the former films was 1.5 eV but no sharp band edge was found for TE films. The resistivity values of PLE and TE films deposited on glass substrates at T_s=200 degrees C were 6-7*10⁴ Omega cm and 3-4*10⁵ Omega cm, respectively. The best ideality factor of the Si-CdTe heterojunction was found to be 1.56 with a barrier height of 0.5 eV from C-V analysis for laser-deposited films at T_s=200 degrees C. These films and heterojunctions were thus found to be superior to thermally evaporated films. Possible reasons for this are discussed.