NEW METHOD FOR THE DETERMINATION OF VCD CONCENTRATIONS IN P-CDTE

If p-CdTe crystals are dipped in an AgNO3 solution followed by storage of the crystals at 300 K, one can observe a strong decrease in the hole concentration after some days. This is obviously due to fast diffusion of silver, which takes place most probably via interstitial sites (Ag(i)), and is consistent with the increase in the degree of compensation detected by photoluminescence (PL) analysis. Deep-level transient spectroscopy investigations have shown the appearance of a new hole trap at 0.47 eV after the silver diffusion procedure, which is tentatively assigned to the Ag(i) deep donors. If the silver treatment is applied to p-CdTe crystals annealed in a tellurium atmosphere, the concentration of Ag(Cd) impurities grows owing to the defect reaction V(Cd) + Ag(I) --> Ag(Cd) as can be seen from the enhancement of the corresponding (A0, X) line in the PL spectra. Positron annihilation measurements with the same crystals have confirmed this reaction by the observation of a decrease in the average positron lifetime before the silver treatment (about 295 ps) to a value of about 285 ps which occurs after some hundred hours. By means of a quantitative PL analysis we are able to estimate the concentration of isolated V(Cd) in p-CdTe from the increased Ag(Cd) concentration. Other possible defect reactions are discussed on the basis of our PL investigations.