Optical Studies of Low Dimensional Magnetic and Non-Magnetic Semiconductor Structures

The focus of this thesis is on optical studies of the properties of semiconductor heterostructures fabricated by the molecular beam epitaxy.ZnCdSe quantum wells were grown on the cleaved (110) edge ofZnCdSe/ZnSe multiple quantum well structures with the intent ofcreating T-shaped quantum wires at intersections of the quantumwells. Extensive polarization-dependent micro-photoluminescencestudies were carried out on all the samples. We report theobservation of the photoluminescence emission from the quantumwire in one of the samples. The absence of the quantum wirephotoluminescence lines in other samples may be caused by theroughness of the interfaces formed by ZnCdSe deposition on thecleaved (110) surface which can affect the quality of theT-junctions formed by the intersection of the quantum wells. Inaddition to preliminary success in fabricating ZnCdSe quantumwires in the ZnSe matrix, this work has also resulted in theobservation of zero-dimensional ZnSe/ZnCdSe quantum structures (natural quantum dots). The natural quantum dots result from thecarrier localization on the fluctuations of the thickness of theZnCdSe quantum wells grown on (110) cleaved surface due to (110)interface roughness.We also describe the properties of self-assembled CdSe quantumdots grown on Mn-passivated ZnSe buffers. We show that the Mndeposited on the ZnSe surface acts as a nucleating seed forself-assembled QD formation. At certain optimal growth conditions,the presence of Mn on ZnSe surface results in a significantimprovement in size uniformity compared to CdSe dots grown on ZnSewithout Mn passivation as evidenced by photoluminescence as wellas transmission electron microscopy experiments. We also show thatthe dots exhibit large Zeeman splitting observed in thephotoluminescence emission, indicating that this growth method issuitable for fabricating magnetic quantum dots that exhibit strongspin polarization effects.In addition to our studies of the II-VI semiconductorheterostructures, we have investigated the magnetic properties offerromagnetic GaMnAs, GaMnSb, and InMnSb grown on hybridGaAs/II-VI substrates by the magneto-optical Kerr effect andmagnetic circular dichroism measurements. The results of themagneto-optical experiments were compared with those obtained bydirect magnetization measurements and electrical transport.