Reconfirmation with Discussion of Anomalies in Photoconductivity of Cu_2O at Low Temperatures

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We reported previously a series of unexpected emergences with anomalies of transient photoconductivity Q(T, λ) of Cu_2O below 100 K with decreasing temperature in contrast to the submergences of Q(T, λ) observed in most of normal photoconductor such as AgCl, AgBr, CdS at low temperatures. Here, we have reexamined the temperature variation of effective electric fields applied on the specimens of Cu_2O, both experimentally and numerically in detail. By estimating an influence of the effective electric fields on the magnitude of Q(T, λ), we obtained further corrected results of Q(T, λ) qualitatively common to various Cu_2O specimens below 100 K. These corrections established the overall behaviours of the "anomalous temperature dependence" of Q(T, λ) of Cu_2O previously reported especially below 100 K to be not influenced by a spurious effect. We give further discussion on the phenomena in terms of the mobility μ(T) and/or of the life time τ(T) due to usual trapping processes of photocarriers based on the one-electron approximation, but without success. Here, we note a finite value of photocarrier density n_0, sustained even down to T=1.6 K. We eventually have to invoke a many-body aspect in elucidating these anomalous phenomena of Q(T, λ) and n_0(T) observed in Cu_2O.
1995-07-15