CHARACTERIZATION OF ZN-(1-Y)MGYSXSE(1-X) EPILAYERS GROWN BY LOW-PRESSURE METALORGANIC VAPOR-PHASE EPITAXY

Optical properties of Zn1-yMgySxSe1-x epilayers grown on GaAs substrat es by low-pressure metalorganic vapour phase epitaxy (LP-MOVPE) were i nvestigated with photoluminescence spectroscopy, reflection spectrosco py and X-ray diffraction. The sulphur (x) and magnesium (y) content in the samples measured by EPMA (electron probe micro analysis) was vari ed in the range 0 less than or equal to x, y less than or equal to 0.2 5, respectively. The photoluminescence study of these quaternary epila yers was performed in the temperature range between 14 and 300 K. Low and negligible concentration of deep levels was achieved. Comparison o f the measured halfwidths of the band edge emissions with calculated m inimum alloy broadening values allowed the estimation of the compositi on fluctuation of the majority of the epilayers to be less than 1%. Ho wever, at large x or large y (x, y greater than or equal to 0.15) broa dening in the band edge emission indicates an increased composition de viation from randomness. Bandgap reduction up to 75 meV with respect t o the theoretically expected bandgap in the case of total randomness w as observed. Enhanced phase separation and ordering effects especially at large x or large y seem to be the reason for the emission broadeni ng as well as for the bandgap reduction.