Recombination in high-resistivity n-type Zn-compensated silicon

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Abstract
The photocurrent decay following pulsed band‐gap excitation has been measured in the temperature range 230–300°K on n‐type zinc‐compensated silicon samples containing approximately 1016 cm−3 of arsenic and having room‐temperature resistivities between 3 and 150 kΩ cm. Sensitization of photoconductivity due to the addition of zinc was observed, and the decay time increased by several orders of magnitude over its value before compensation. From an analysis of the possible recombination mechanisms in such high‐resistivity samples, we conclude, in light of our measurements, that in the specified temperature range and under low‐level excitation conditions (i) the lower zinc level has a negligible effect on recombination time, (ii) thermal quenching of photoconductivity is an unlikely process, (iii) unipolar conductivity prevails due to the giant hole‐capture cross section of the zinc ions, and (iv) the photodecay is largely influenced by a deep‐lying αtype electron trap. The density and location of this trap are estimated to be, respectively, 1.3×1013 cm−3 and 0.4 eV below the conduction band edge. Resistivity measurements in the range 180–300°K yield a value of 0.49 eV for the location of the zinc‐sensitizing level E2 with respect to the conduction band edge. This tends to support other recent independent studies over earlier ones which placed E2 at 0.55 eV. No differences were observed in any of our measurements between Czochralski and float‐zone silicon.