TEMPERATURE-DEPENDENCE OF PHOTOCONDUCTIVITY SPECTRA AND PHASE LAG OF P-TYPE CUGAS2 BY POLARIZED-LIGHT EXCITATION

Photoconductivity spectra and phase lag of the photocurrent for the modulated excitation light are studied between 80 and 340 K on undoped p-type CuGaS2. For the low-resistivity samples, both the intrinsic peak and the extrinsic peak via shallow donor arc clearly observed in the polarization-dependent spectra, indicating the selection rule of the uppermost valence bands. For the high-resistivity samples, however, the polarization-dependent behavior of the spectra is greatly reduced due to the mergence of the broadened shallow donor band into the conduction bandtails. On the other hand, a broad peak via deep donor is observed for both types of samples, where almost trap-free hole current with a small phase lag is dominant below 250 K. Above 250 K, there appears a rapid increase in the phase lag, showing the enhancement of the thermal release of trapped holes on a shallow acceptor state.