Fast photoresponse and high parallel transport in n-type PbTe/PbEuTe quantum wells

We investigated the photoconductivity effect in n-type PbTe/Pb_0.88Eu_0.12Te quantum wells for a temperature range of 300-10 K using infrared light. The measurements revealed that at high temperatures, the photoresponse has small amplitude. As temperature decreases to T ∼ 75 K, however, the photoconductivity amplitude increases reaching a maximum value 10 times higher than the original value before illumination. From Hall measurements performed under dark and light conditions, we show that this effect is a result of the carrier concentration increase under illumination. Unexpectedly, for further reduction of temperature, the amplitude starts to decrease again. The electrical resistance profiles indicate that the transport occurs through barriers and the well that behave as two parallel channels. For temperatures below 75 K, transport is more effective in the quantum well, where the signal reduction can be associated with the electron-electron scattering due to the increase in the carrier concentration that occurs under illumination. We also used the random potential model to explain the origin of the persistent effect observed in the photoconductivity curves.