Effects of substrate miscut on the properties of InGaP solar cells grown on GaAs(001) by solid-source molecular beam epitaxy

Abstract

The growth of ternary InGaP alloys is often susceptible to atomic ordering, which leads to an anomalous bandgap reduction as well as the formation of antiphase boundaries (APBs). The effect of substrate miscut on the performance of lattice-matched In0.52Ga0.48P solar cells grown on GaAs(001) substrates by solid-source molecular beam epitaxy (SS-MBE) is investigated. A B-type miscut enhanced single-variant atomic ordering even with SS-MBE, resulting in a bandgap (Eg) reduction from 1.87 eV for an alloy grown on an exact substrate to 1.85 eV for that grown on the substrate miscut 6° toward (111)B. Conversely, an A-type miscut suppressed the formation of atomic ordering, resulting in the Eg widening of the alloy grown on the substrate miscut 6° toward (111)A to 1.89 eV. With regard to solar cell performance, InGaP solar cells grown on A-type miscut substrates enhanced the open-circuit voltage (VOC) and WOC (= Eg/q − VOC) because of the low degree of atomic ordering. Large improvements in WOC and efficiency to 0.58 V and 10.93%, respectively, were obtained for the cell grown on the substrate miscut 2° toward (111)B. A reduction in the number of APBs due to single-variant atomic ordering was related to this latter result.