Characterization of GaP / InGaP and GaP / GaAsP strained-layer quantum wells grown by metalorganic chemical vapor deposition

Abstract

GaP/InGaP and GaP/GaAsP strained-layer quantum well (QW) structures with 3.0–5.0 nm thick well layers in the direct gap region were grown on GaP substrates by metalorganic chemical vapor deposition (MOCVD) using triethylgallium (TEGa) and ethyldimethylindium (EDMIn) for the column III sources and 100% AsH 3 and PH 3 for the column V sources. The strained QW structures were characterized using TEM and 4.2 K photoluminescence (PL). Transmission electron microscope (TEM) images indicate that the structures are uniform with sharp, defect-free interfaces. The QW layers are clearly resolved and appear to be free of misfit dislocations or other defects. The InGaP QW structures exhibit improved 4.2 K PL linewidths and a shift of the peak energies to shorter wavelengths compared to InGaP bulk layers of the same compositions. The GaAsP QW structures also exhibit sharp PL emission linewidths. The band alignments for the GaP/InGaP and GaP/GaAsP strained heterojunctions were calculated using local-density-functional pseudopotential formalism and the model-solid approach. Optical transition energies between the conduction band and valence subbands at the Γ point were calculated for the InGaP and GaAsP strained QWs, taking into account both the strain-modified band structures and quantum confinement effects. By employing the results derived from the theoretical predictions, we show that the 4.2 K PL spectra of the InGaP strained wells exhibit both the n = 1 heavy-hole and light-hole related transitions. We also show that the degree of removal of valence band degeneracy can be determined from the PL spectra.