Surface morphology and lattice distortion of heteroepitaxial GaInP on InP

We examine the relation between surface morphology and lattice distortions of a number of Ga_xIn_1-xP epilayers (x ≈ 0.04) grown on InP (001) substrates using atomic force microscopy (AFM) and high resolution X-ray diffractometry (HRXRD). The heteroepitaxial layers (thickness ≈ μm) were grown by low pressure metalorganic vapour phase epitaxy (MOVPE) at temperatures from 600 to 660°C. AFM images over a scale of 75 μm by 75 μm show no surface corrugations for samples grown at 640°C. For other growth temperatures between 600 and 660°C, unidirectional corrugations aligned along the [10] direction or a cross-hatched pattern can be seen on the sample surfaces with a typical interline separation of 10 μm. Another feature revealed by AFM is the presence, for some samples, of weak parallel corrugations along the direction making a 54° angle with the [10] direction. HRXRD spectra recorded first with the [110] and then with the [10] direction in the plane of incidence reveal an asymmetric relaxation in the sample plane accompanied by a broadening of the epilayer X-ray peak for diffraction with the [110] direction in the plane of incidence. The lattice distortion changes from tetragonal to orthorhombic as the surface corrugations appear along the [10] direction. Proton microprobe scans indicate that these samples are compositionally uniform so that the asymmetry is not the result of lateral variations of the alloy composition. Finally, low temperature photoluminescence from these samples shows good agreement between observed and calculated peak positions on the basis of the strains obtained from HRXRD measurements.