Electron beam induced current studies of strain balanced InGaAs/InGaAs multiquantum wells

Abstract

Strain balanced InGaAs/InGaAs multiquantum well photovoltaic cells have been shown to be of great interest for thermophotovoltaic applications, where the absorption needs to extend well into the near infrar ed region to intercept most of the radiation emitted by heat sources operating in the range 1200-1700 ° C. The present work has investigated In_yGa_{1 - y}As/In_xGa_{1 - x}As multiquantum well devices grown by metalorganic vapour phase epitaxy (MOVPE)on InP,and designed to have the absorption edge between 1800 and 2000 nm. Although strain balancing prevents misfit dislocations developing in the quantumwells, plastic relaxation may occur through the generation of conical defects when the difference between the compressive strain of the wells and the tensile strain of the barriers exceeds a critical value. Despite that they appear to be electrically active, these defects turn out to have a limited effecton the dark current of these cells, which is comparable to that of the best control cells (same structure but with no quantum wells). On the other hand, the conical defects appear to be correlated with the dramatic drop in the photocurrent even at a very low forward bias voltage. In the present study, electron beam induced current (EBIC) has been used to study the electrical properties ofthe defects on a microscopic scale, and made it possible to explain their influence on the electrical characteristics of the photovoltaic devices.