PHOTOLUMINESCENCE STUDY OF SURFACE SEGREGATION OF IN IN INGAAS-BASED STRUCTURES GROWN BY MBE AND ATOMIC LAYER MBE

A study on In segregation and its minimization in structures prepared by molecular beam epitaxy (MBE) and atomic layer MBE (ALMBE) is described. The segregation was studied in InGaAs/GaAs multi-quantum wells (MQWs) by means of the energy shift of excitonic transitions, which is induced by segregation, through the distorsion of composition profiles and, hence, of electronic band edge profiles. Detailed attention was paid to the design of the MQW structures, in order to minimize spurious effects which may affect the recombinant energies. The structures consist of a number of uncoupled quantum wells with In molar fraction; of 0.15 and ca. 0.30 and with well thicknesses of ten monolayers. They were grown by MBE and by ALMBE at temperatures in the ranges 300-495 degrees C and 215-515 degrees C, respectively. The results show that by reducing the growth temperature the In segregation is significantly reduced and that it is minimized for temperatures lower than ca. 340 degrees C (MBE) and ca. 260 degrees C (ALMBE). The accurate design of the structures and the careful choice of the growth conditions allow efficient excitonic emissions to be obtained from QWs prepared by means of MBE and ALMBE at temperatures as low as 300 and 215 degrees C, respectively.