POLARIZED PHOTOMODULATED REFLECTIVITY AND PHOTOLUMINESCENCE STUDIES OF ORDERED INGAP2 UNDER PRESSURE

Spontaneous ordering of ternary alloys grown on misoriented substrates has been of recent interest. Ordering induced band gap reduction, and valence band splittings exhibiting novel polarization properties have been investigated by theory and experiment. In this paper, we discuss polarized photomodulated reflectivity (PR) and photoluminescence stud ies of MOCVD grown InGaP2 epilayers lattice-matched to a GaAs substrat e. These structures were grown on a (001) face with a misorientation o f two degrees along [110]. The high degree of ordering has enabled us to measure accurately the crystal field splitting and additional struc ture not reported in the PR spectra. For the electric field E parallel to [110] two features in the PR spectra are seen; for E parallel to[( 1) over bar 10], however, additional features are observed. A comparis on with the spectra of disordered samples of the same alloy compositio n has enabled a determination of the band gap reduction due to orderin g. The linewidths of the PR peaks are approximately 5-10 meV which has enabled us to study them in detail as a function of hydrostatic press ure at cryogenic temperatures. The pressure dependence is slightly sub linear with the first order term of 8-9 meV/kbar for pressures well be low the Gamma-X crossover. Also observed is the indirect level crossin g which occurs under pressure at about 40 kbar. A comparison of PR lin eshapes at 1 bar is also presented at several commonly used experiment al temperatures. The data indicate a substantial change in PR lineshap es, showing that interpretation of reflectivity data for these samples must be carried out carefully.