Accurate control of As and Sb incorporation ratio during solid-source molecular-beam epitaxy

This paper reports an accurate method for controlling the As/Sb ratio in group-V alloys such as AlAs_xSb_1−x by modulating As₂ and Sb₂ beams during molecular beam epitaxy (MMBE). Experimental results show that the AlAs mole fraction is linearly proportional to the As-shutter duty-cycle, which is easy to control and extremely reproducible. Compared with conventional MBE the MMBE technique dramatically reduces the degree of dependence of AlAs mole fraction on the As₂ flux about an order of magnitude, providing a very straightforward means to obtain group-V alloys with required composition without changing group-V effusion-cell temperatures. X-ray diffraction measurements reveal that the typical lattice mismatch for thick AlAs_xSb_1−x cladding layers in laser structures grown on InAs is less than 6.5 × 10⁻⁴. In addition, MMBE dramatically improves the surface morphology and crystalline quality. Based on these improvements, room temperature photoluminescence from GaAs_0.08Sb_0.92/AlAs_0.16Sb_0.84 single quantum well structures and cw operation of InAs/AlAs_0.16Sb_0.84 lasers up to 95 K are also observed for the first time. It is expected that this method can also be applied to the MBE growth of other group-V alloys.