Microstructural characterization of InGaAs/GaAs quantum wells grown at low substrate temperatures

Abstract

The composition and thickness of InxGa1-xAs/GaAs quantum wells play an important role in the determination of their optical and electronic properties. InxGa1-xAs/GaAs single quantum wells (SQWs) grown at low substrate temperatures with various In compositions (x) and well thicknesses were investigated by reflected high energy electron diffraction (RHEED) and photoluminescence (PL) techniques to determine when the critical thickness for pseudomorphic growth was exceeded. Cross-sectional TEM methods were employed to directly determine the critical layer thickness of InGaAs on GaAs and the presence of the dislocations generated in these layers.The samples were grown by MBE on semi-insulating (100) GaAs substrates at substrate temperatures of 410°C and 460°C. They consisted of undoped SQWs and barriers in which the well width was varied from 1 nm to 22 nm. The In composition in the well layers was varied from 0.3 to 0.5. The growth rates and In compositions were deduced from RHEED intensity oscillation measurements . Cross-sectional specimens for TEM studies were prepared in the usual manner, by mechanical thinning followed by Ar+ ion milling. A Philips EM400T operated at 120 keV was used to observe the specimens.