Residual-photoconductivity spectra in HgTe/CdHgTe quantum-well heterostructures

Residual-photoconductivity spectra (RPS) are studied for HgTe/CdHgTe quantum-well heterostructures of $n$- and $p$-type conduction at $T$ = 4.2 K. RPS is shown to be both positive (an increase in the carrier concentration in the quantum well) and negative depending on the illumination wavelength. The RPS maxima in the sample with $n$-type conduction in general correspond to the RPS minima in the $p$-type samples and vice versa. It is found for $p$-type samples that illumination at specific wavelengths leads to the “freezing” of free carriers in the quantum well (QW) but not to a change in the conduction type. This fact indicates the important role of the built-in electric field in the RPS mechanism; this field is “switched-off” upon QW neutralization.