Photoluminescent and electrical properties of InGaPAs mixed crystals liquid phase epitaxially grown on (100) GaAs

Abstract

The liquid phase epitaxial growth of InGaPAs layers on (100) GaAs is described for growth temperatures of 785 and 815 °C. Photoluminescence (PL) spectra and electron Hall mobility of the layers are investigated as a function of crystal composition. The width of PL spectra measured at 300 K is 40 meV, approximately the same value as that of GaAs, when the energy gap Eg of the layers is 1.9 eV or lower than 1.6 eV. The spectral width is around 80 meV when the energy gap of the layers is around 1.75 eV. The increase in the spectral width is attributed to variation of the local energy gap from analysis of dependence of the PL spectra on temperature and on excitation intensity. The indication that local energy gap varies in layers with Eg around 1.75 eV is consistent with the composition dependence of electron mobility. The mobility shows a sharp dip down to 1000 cm2/Vs around this composition, while it depends on composition only slightly for layers with Eg lower than 1.6 eV. The dip in composition dependence is attributed to space-charge scattering from analysis of temperature dependence of mobility. X-ray diffraction spectrum and surface morphology are also reported. The width of x-ray diffraction spectra is large for layers with Eg around 1.75 eV. This indicates that the local lattice constant varies significantly. Thick and uniform layers are particularly difficult to grow for such composition. These composition dependences of PL spectra, x-ray diffraction, and surface morphology are more significant in layers grown at 785 °C than in layers grown at 815 °C. The local variation of energy gap and lattice constant is attributed to variation of local composition caused by immiscibility of InGaPAs.