Photoconductivity Analysis in High Resistivity p Type Zinc Compensated Silicon

The decay of photoconductivity following band gap radiation has been measured in the temperature range 180–300 K on p type zinc compensated silicon samples containing approximately 1016 cm−3 of As and having room temperature resistivities between 0.7 and 50 K Ω cm. A strong correlation was found between the concentration of the neutral zinc atoms Nz0, deduced from resistivity vs. temperature measurements, and the measured decay time, suggesting that the recombination traffic was predominantly via the lower zinc level E1 and without the interference of any other traps. This enabled us to estimate the capture cross section for electrons on neutral zinc atoms, Szn0, to be approximately 1.2 × 10−16 cm2 and to be temperature independent in the measurement range. The resistivity measurements confirmed that E1 is located 0.31 eV above the top of the valence band and indicated that the concentration of any 'unwanted' traps that may be present in our samples was appreciably less than 2 × 1013 cm−3 in the range 0.07–0.15 eV below the center of the band gap. Correlation of the above results with our previously published data on n type zinc doped samples indicates that the electron trap influencing the photodecay times in n samples is a single acceptor center having a capture cross section of approximately 10−16 cm2. The results of measurements on more than seven zinc compensated samples with room temperature resistivities covering the range of 70 Ω cm n type, through near intrinsic, to 500 Ω cm p type results in a unified model capable of consistently explaining all our observations.