Structural and optical properties of Al_0.48In_0.52As layers grown on InP by molecular beam epitaxy: Influence of the substrate temperature and of a buffer layer

We have studied the crystalline and optical properties of Al _yIn_1-yAs ternary alloys grown by molecular beam epitaxy on InP substrates. We obtain Al_0.48In_0.52As layers with both high structural quality and excellent optical performance by growing (i) at high substrate temperature (600°C), (ii) on a high-quality Ga _xIn_1-xAs/Al_yIn_1-yAs short-period superlattice buffer, (iii) or on a high-quality Ga_xIn_1-xAs buffer layer, as attested by double-crystal x-ray diffraction and photoluminescence measurements. In addition the experimental results indicate a significant reduction of the clustering level in these samples which is interpreted in terms of a smoothing of the growth front, a thermodynamically controlled growth mode, and the interplay between In segregation and In desorption. Our investigations further show that the improvement of the structural quality and of the optical performance are strongly correlated. Finally, we report the first evidence of excitonic features in photoluminescence excitation spectra of the Al_yIn_1-yAs ternary alloy.