a Cdlts Study of the Deep Levels in n- and P - Cadmium Telluride Thin Films Deposited by Hot Wall Evaporation

CdTe thin films, both undoped and with different dopants, have been deposited unto graphite and Corning 7059 glass substrates using a Three-Stage Hot Wall Vacuum Evaporator (TSHWVE) system. The dopants were incorporated into the CdTe thin films using a "delta doping" technique. The conductivity type of the doped CdTe thin films was determined using the hot probe method, and the film stoichiometry was determined using X-ray and Auger electron spectroscopy measurements. Schottky diodes fabricated on the CdTe thin films that were deposited on graphite substrates have been studied using Current-Voltage (I-V), Capacitance-Voltage (C-V), and Capacitance Deep Level Transient Spectroscopy (CDLTS). The conductivity type of CdTe films that were undoped and doped with Antimony (Sb), Phosphorus (P), Gold (Au), Silver (Ag), and Copper (Cu) were found to be p-type, while Indium (In) doped CdTe thin films were found to be n-type. The highest carrier concentration of the CdTe films are 1 times 10^ {16} cm^{-3} , 1 times 10^ {17} cm^{-3} , and 7.5 times 10 ^{15} cm^{ -3} for In-, Sb-, and P-doped CdTe, respectively. For the In-doped CdTe films three majority carrier trap are found with activation energies measured from the conduction band of 0.23 +/- 0.05 eV, 0.46 +/- 0.06 eV, and 0.78 +/- 0.05 eV. For the Sb-doped CdTe films three majority carrier traps are found with activation energies measured from the valence band of 0.27 +/- 0.06 eV, 0.50 +/- 0.06 eV, and 0.80 +/- 0.06 eV. For the P-doped CdTe films three majority carrier traps are found with activation energies measured from the valence band of 0.28 +/- 0.05 eV, 0.50 +/- 0.06 eV and 0.75 +/- 0.05 eV. Our capture measurements on In-, Sb-, and P-doped CdTe showed non-exponential transients, however they could be fitted very well by Pons theory, and allowed us to determine values for the trap concentration (N_{ rm T}), the trap capture rate (c _{rm n,p}) and the trap capture cross-section (sigma_{rm n,p}). However, the capture cross-sections so derived are approximately two orders of magnitude smaller than estimates given in the literature earlier. (Abstract shortened by UMI.).