Deep level transient spectroscopy study of indium gallium arsenic nitride grown by MBE and MOCVD for multijunction solar cells

The III-V compound semiconductor alloy InGaAsN, which may be used as a part of a electricity generating solar cell, has a potential up to 40% efficiency when put into a multilayer cell consisting of InGaP, GaAs and Ge. Although minority carrier electrons are not intentionally injected into the depletion region of the measured samples, electron traps are detected in both Schottky barrier and p-n junction InGaAsN and GaAsN samples and these have adversely affected the performance of such devices. Deep Level Transient Spectroscopy (DLTS)---a high frequency transient capacitance technique---has been used to detect traps in p-type GaAs, GaAsN, InGaAs and InGaAsN grown by Molecular Beam Epitaxy (MBE) and Metal Organic Chemical Vapor Deposition (MOCVD). Thermal annealing of minority carrier traps in p-type InGaAsN and GaAsN is investigated by using DLTS. Upon annealing, an apparent recovery of the photovoltaic properties is observed for InGaAsN and GaAsN diodes and solar cells correlating with changes in the DLTS data. This recovery reveals that nitrogen related E1 center has an important role in governing the solar cell performance.