Defect induced shortening of excess carrier lifetime in single period nipi structures

Abstract

High sensitivity for detecting optically generated excess carriers in the mid infrared spectrum is offered by nipi structures of PbTe. The built in nipi potential separates the electron–hole pairs in real space which leads to a high excess carrier lifetime τ. The temperature dependence of τ in PbTe single period nipi structures grown on BaF₂ substrates under repeated thermal cycling ranging from 300 to 12 K was studied in the present paper. The typical behaviour of the lifetime τ deviates from theory. This was attributed to the fact that the lattice mismatch and the different thermal expansion of BaF₂ and PbTe generate a temperature dependent strain which causes strain induced lattice defects. Besides misfit dislocations at the interface, threading dislocations are generated, which form channels for enhanced recombination of the excess carriers. A special temperature cycling technique is presented which can change the number and the arrangement of the strain induced defects and leads to higher excess carrier lifetimes τ at low temperatures.