INDIUM SEGGEGATION IN MBE GROWN GAAS/INGAAS/GAAS QUANTUM WELLS

Abstract

Solid state III-V semiconductor device technologies are well established for high speed microwave and optoelectronic devices. Many approaches have been taken to detect indium surface segregation at InGaAs/GaAs interfaces with the purpose of improving interface abruptness. Such studies are not straight-forward and the experimental approaches of many of them misinterpreted indium profiles at the monolayer scale, producing unlikely surface segregation models. The present study employed molecular beam epitaxy (MBE) for layer growth and a novel sample preparation technique was devised which translated vertical chemical depth profiles into horizontal profiles. The use of Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) then allowed vertical indium segregation to be observed and measured. Measured indium segregation profiles are found to depend on the primary growth conditions, substrate temperature, the As₄ to group III flux ratio and the group III growth rate. A rate equation model was developed that incorporates the primary growth parameters, As₄ flux rate, group III growth rate and substrate temperature, to model the growth process kinetically. This fits the experimental data, but only if As₄ molecules are assumed to play a site-blocking role that inhibits the chemical incorporation of the group III elements and indium. This model successfully explains the interaction of the group III and V species on gallium and arsenic terminated surfaces in the MBE growth process.