Optical studies of GaInP/AIGaInP quantum wells: device-related materials parameters and substrate orientation effects

Abstract

Ga0.5In0.5P/ AI0.35Ga0.15In0.5P, lattice-matched to GaAs, has been used to fabricate laser diodes with room temperature emission in the 630-670 nm range. Growth, by MOCVD, on misoriented substrates has been shown1 to minimize band-gap variations and other anomalous behavior associated with spontaneous ordering in these alloys. Here, we use a variety of optical techniques to compare bulk and quantum well epilayers of this material grown on normal and misoriented substrates and to extract fundamental materials information. The normal substrates are (100) 2° off towards (110), and misoriented substrates are (100) 10° off towards (110); importantly, equivalent structures were grown on half wafers of these orientations in the same reactor at the same time for direct comparison. At 5 K the 10°-off bulk sample shows single-peaked photoluminescence (PL) at 1.995 eV, with a linewidth of 6.8meV. No anomalous behavior with temperature or fluence was observed, consistent with minimal effects of ordering. The PL linewidths of the 10°-off quantum wells (7.0 meV at 2.021 eV for 120 Å, 9.6 meV at 2.045 eV for 75 Å, and 11.4 meV at 2.072 eV for 50 Å wells) are, to our knowledge, the narrowest yet reported in this material system. The 2°-off quantum wells show linewidths ~1.5 to 2 times these values in each case, shifted to longer wavelengths by ~20 meV. The 2° bulk PL is double-peaked, with a tail to lower energy, and is strongly fluence and temperature dependent, consistent with known effects of ordering. Longitudinal optical phonon energies for Ga0.5In0.5P have been determined by resonant Raman spectroscopy. Photoluminescence excitation measurements are also reported. The results have been incorporated into envelope function calculations in an attempt to determine a consistent set of materials parameters (band gaps, excitonic binding energies, band offsets, effective masses, etc.) for device design purposes.