THE EFFECT OF PRESSURE ON THE BAND-GAP ENERGY IN ORDERED GAINP AND ALGAINP GROWN BY MOVPE

Photoluminescence (PL) measurements on Ga0.52In0.48P and Al0.18Ga0.34I n0.48P alloys, grown by metalorganic vapor phase epitaxy (MOVPE) on Ga As, have been made as a function of pressure up to about 4.5 GPa at 77 K. The substrates are oriented on the (100) and off the (100) plane t oward [011] and [01(1) over bar] by up to 25 degrees. The band-gap ene rgy anomaly in the CuPt-type ordered structure has been systematically investigated at high pressures. With increasing pressure the E(0) ban d gap shows a sublinear shift toward higher energies. For some samples , this shift tends to saturate, of the PL peak shows a decrease in ene rgy with pressure. The pressures needed for these observations are fou nd to be significantly smaller in AlGaInP than in GaInP. The observed behaviors strongly depend on substrate misorientation, and hence refle ct the degree of ordering in these alloys. These results clearly demon strate the importance of the effects of repulsion between the Gamma-fo lded energy states on the optical spectra in the CuPt-type ordered str ucture. Possible explanations for some of the trends in high-pressure behavior of the E(0) direct band gap in GaInP and AlGaInP samples havi ng different degrees of ordering are discussed, including the modifica tion of the ordinary Gamma-X crossover upon ordering.