Characterization of Bismuth Containing Compounds
Examensarbete för masterexamen
Roy, Ivy Saha
New semiconductor materials with more beneficial properties are continuously demanding for device applications. The heaviest group V and least studied bismuth containing compounds have potential applications in electronics, optoelectronics, thermoelectric field and also in fundamental physics. Dilute bismides offer large bandgap bowing in valence band by shifting up the valence band edge. This property offers a grand freedom to engineer band structure of semiconductors for potential high-speed electronic and infrared optoelectronic applications. Also it provides a large spin orbit coupling effect which is useful to suppress inter-valence band Auger recombination processes in 1.55 μm lasers. The potential applications for dilute bismides alloys are expected in heterostructure bipolar transistors, light emitting devices, laser diodes and solar cells. Another Bi-containing material Bi2Te3 has great thermoelectric property; this property can be used for the applications of cooling different types of devices and for power generation from waste heat. In this research project, different features have been found and studied for different Bi containing compounds. The samples were grown by a Riber Compact21 MBE system with varying growth temperatures and Bi flux. MBE grown Bismuth containing compounds GaSbBi, GaAsBi, InGaAsBi QW, InSbBi and also Bi2Te3 are investigated by atomic force microscopy (AFM), X-ray diffraction (XRD) and Photoluminescence (PL) techniques and then surface morphologies, structural and optical properties are explored from these characterizations, respectively. The MBE grown GaSb1-xBix thin films are established for the first time. Strategies have been taken care of to avoid the formation of Bi droplets and enhance Bi incorporation. From XRD and AFM, maximum Bi incorporation with smooth surface has been obtained for growth temperature of 370 ºC and then saturation occurs. InGaAsBi QW samples are characterized by PL at room temperature (RTPL) and also at low temperature (LTPL) for different sample positions and temperatures, respectively. When Bi is incorporated, 10 times higher PL intensity has been achieved comparing with the reference InGaAs QW sample. For Bi2Te3 samples grown on Si substrates, growth temperature of 240°C showed the best feature both in AFM and XRD characterizations. Since this project on Bi-containing compounds is still under experimental demonstration, there is a lot to do for improving the material quality. One important future goal of this project is to establish the relation between the fundamental physical parameters such as lattice constant, bandgap and effective mass etc and the Bi composition. Getting hold of improved quality Bi containing QWs at 1.55 μm is another goal of this research in future. The future Bi containing compounds research is expected to be accelerated at a much fast pace.
Elektroteknik och elektronik , Electrical Engineering, Electronic Engineering, Information Engineering