INVESTIGATION OF NEAR INTERFACE PROPERTIES IN SEMIINSULATING INP SUBSTRATES WITH EPITAXIAL GROWN INGAAS AND INALAS BY PHOTOREFLECTANCE

An extensive photoreflectance (PR) study has been done on a series of undoped and n-type, InGaAs and InAlAs molecular beam epitaxy (MBE) grown layers with different In mole fractions, and epilayer thicknesses on Fe-doped semi-insulating (SI)-InP substrates. Three substrate features were observed in the spectra. From investigations of the temperature dependence, time constant dependence, and an additional cw light beam intensity dependence, they were identified as an excitonic transition from the substrate, a free electron transition near the interface which gives a Franz-Keldysh oscillation, and a transition from the spin-orbit split-off valence band. The Franz-Keldysh effect indicates that a temperature dependent built-in electric field is formed near the interface. The dependence of the field on doping concentration, strain, or epilayer composition (band gap) was insignificant. The PR signal from a SI-InP wafer after a pre-MBE-growth heating was found to be strongly enhanced over that from an untreated wafer. This signal was even more enhanced after an epilayer was grown on top, indicating the formation of a built-in field. These results are indicative of a redistribution of charge near the interface/surface in the process of MBE growth; the associated PR signal (phase) could be used for in situ monitoring of epilayer growth on SI-InP wafers.