An optical study of the properties of (Al xGa 1− x) 0.51In 0.49P epitaxial layers with varying composition, hydrostatic pressure and GaAs substrate orientation

Abstract

Optical studies were performed using photoluminescence (PL) at 300 and 4.2 K, and photoluminescence excitation spectroscopy (PLE) at 4.2 K, to evaluate the optical properties of (Al x Ga 1− x ) 0.51In 0.49P, grown on (001) GaAs misorientated 10° towards <111>A substrate type, as a function of x, the Al mole-fraction in the solid, from x=0 to 0.46. An estimate of the room temperature band-gap dependence on x was determined from PL and PLE to be Eg=1.9+0.7 x eV. The 300 K PL intensity was measured as a function of x for the above samples and two other substrate orientations which were also included in each growth run. A factor of ∼25 decrease in PL intensity was observed for samples grown on 10 and 15° misorientated substrates as the emission wavelength changed from ∼650 ( x=0) to 570 nm ( x=0.46). In comparison, material grown on the 2° misorientated substrate showed a much larger decrease in PL intensity of ∼120 over the same compositional range. The PL emission energy of the material grown on the 2° misorientation substrates was ∼40 meV lower than the PL emission energy of the material grown on the 10 and 15° misorientated substrates. This shift of ∼40 meV is consistent over the whole compositional range studied and is explained by differences in the degree of ordering of the AlGaInP alloy as a function of substrate orientation. Hydrostatic pressure measurements have revealed that the variation of PL efficiency with Al compositions can be explained by a combination of the increasing concentration of non-radiative centres associated with increasing Al in (Al x Ga 1− x ) 0.51In 0.49P (extrinsic effects) and the decreasing Γ- X separation energy in these materials (intrinsic effects).