Limits in growing TlGaAs/GaAs quantum-well structures by low-temperature molecular-beam epitaxy

TlGaAs/GaAs multiple-quantum-well (MQW) structures were grown on GaAs substrates at a substrate temperature of 190 °C by molecular-beam epitaxy. The MQW structures were intended to consist of four identical TlGaAs wells, each of which is sandwiched by GaAs barrier layers. X-ray diffraction was used to investigate the limits to Tl content and thickness of the TlGaAs well layer for forming the MQW structures. Successful growth of TlGaAs/GaAs MQW structures having nominal Tl contents of 6, 8, and 9% was confirmed for the three different well thicknesses of about 15, 10, and 5 nm, respectively, while further increase in Tl content resulted in failure in forming MQW structures. The bounds for forming the MQW structures are discussed in terms of the epitaxial thickness of TlGaAs. The effect of the MQW structures on retarding the formation of Tl droplets is pointed out.