Growth temperature optimization of interfacial misfit technique for growth of GaSb subcells on GaAs substrates

Abstract

Access to lattice matched narrow bandgap semiconductors is a challenge for improved efficiency of GaAs based multi-junction solar cells (MJSCs). GaSb has a bandgap of 0.72 eV and is ideally suited to be used as a Near-Infrared subcell for MJSCs. However, when used as a replacement for Germanium in GaAs based MJSCs, the large lattice mismatch between GaSb and GaAs results in significant threading dislocation density in the GaSb subcell. The threading dislocation density in the GaSb epilayer can be reduced to a certain extent by the realization of 90° interfacial misfit dislocation arrays (IMF) between the GaSb and GaAs layers. The substrate temperature during the growth of the GaSb epi-layer on GaAs has a strong impact on the threading dislocation density while making use of the IMF technique. In this study, several substrate temperatures (ranging from 350°C to 540°C) are explored to achieve reduced threading dislocation density which is measured using both plan-view Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD) rocking curve analysis. A low growth temperature (of 420°C) shows the reduction of threading dislocation to the level of ~1.3×108 cm–2.