Investigation of optoelectronic properties of low dimensional ferromagnetic semiconductor alloys with different crystal orientation

In these thesis optical properties of diluted magnetic semiconductor Ga0.999Mn0.001As/AlAs quantum well and Mn-free GaAs&AlAs quantum well structures grown by molecular beam epitaxy (MBE) on semi-insulating GaAs substrates with orientations (100 ), (110), (311)B and (411)B are investigated. Optical transition energies were theoretically calculated and compared with the results obtained from photoreflectance (PR) and photoconductivity (PC) experimental techniques. Mn-free and Mn-containing samples, grown on (100 ), (110), (311)B and (411)B orientations, were fabricated in Hall Bar and simple bar geometry in order to make photoconductivity measurements. From the Hall measurements, it was concluded that the carrier concentration is not large enough to affect the optical transition energy. Therefore, it has been determined that solving the Schrödinger equation will be sufficient for the calculation of the optical transition. The experimental results were analyzed by comparing them with theoretically calculated optical transition energies. Optical transitions below the bandgap of GaAs are observed due to the low-temperature growth of the AlAs/GaAs quantum well structures. It is found that the optical bandgap is almost dependent of the crystal orientation. Introducing Mn into GaAs causes redshift of the bandgap. The optical bandgap energy of the GaMnAs is more sensitive than Mn-free GaAs samples. The effect of the localized state on the optical transition is more random than the Mn-free samples. We do not detect the ferromangetic effect due to the compensation phenomena. Analyzing of experimental results with the theoretical calculation give i) high energy quantized states contribute optical transitions, and ii) forbidden or indirect transtion may contribute optical transitions. The fabrication process was carried out at Advanced Lithography Laboratory/Istanbul University Science Faculty Physics Department. All measurements during this thesis, were carried out by using facilities of Nano- and Optoelectronics Research Laboratories/Istanbul University Science Faculty.