Structural characterization of ZnSe/ZnMgSe MQWs grown on (1 0 0)GaAs by low pressure MOVPE

Abstract

A detailed structural characterization of ZnSe/ZnMgSe multiple quantum wells (MQWs) grown on GaAs by low pressure metalorganic vapour phase epitaxy is presented. ZnSe/Zn 0.83Mg 0.17Se MQWs having between 6 and 12 periods were deposited at 330°C and 304 mbar reactor pressure on (1 0 0)GaAs after a 4.2 nm ZnSe buffer layer. The MQWs had nominal 4.4 nm thick ZnSe wells and 5.3 nm thick Zn 0.83Mg 0.17Se barriers. The MQW structural properties were investigated by high-resolution X-ray diffraction (HRXRD) and X-ray specular reflectivity (XSR) measurements. Besides the MQWs-substrate mismatch, simulation of the HRXRD and XSR patterns allowed to determine the MQW period, individual layer thickness and barrier composition. Between 8 and 10 periods the MQW structure begins to relax, its critical thickness on GaAs being between 92 and 113 nm. Furthermore, HRXRD showed broader zeroth and first-order satellite peaks with increasing MQW periods, a result ascribed to strain fluctuations induced by either inhomogeneous Mg incorporation in the ZnSe lattice and/or interface roughening. Comparison of experimental and simulated XSR patterns allowed to determine the rms roughness at each multilayer interface, which linearly increases along the growth direction due to a cumulative intrinsic roughening.