Conduction-band offsets in pseudomorphic In_xGa_1-xAs/Al_0.2Ga_0.8As quantum wells (0.07≤x≤0.18) measured by deep-level transient spectroscopy

The variation of the potential of a quantum well is similar to that of a deep trap. In that respect a quantum well can capture and emit carriers in much the same way as a trap. The thermal emission energy from a quantum well is closely related to the appropriate band offset. With that in mind, we have carried out deep-level transient spectroscopy measurements on Schottky-barrier diodes containing one or more pseudomorphic In_xGa_1-xAs/Al_0.2Ga_0.8As (0<x≤0.18) quantum wells. The objective was to estimate the conduction-band offset, ΔE_c, as a function of x and the resulting strain. From detailed balance between emission and capture, an Arrhenius-type expression was derived to analyze the transient emission data. It is seen that the percentage band offset ΔE_c/ΔE_g varies from 62% for x=0.07 to 70% at x=0.18. Furthermore, a linear interpolation of the data leads to ΔE_c/ΔE_g=58% at x=0, which is close to the widely accepted value. Our results support recent theoretical calculations from which a monotonic increase in ΔE_c with strain in this heterostructure system is predicted.