Fabrication and Characterization of GaInAs-InP Nanostructures

[摘要] This thesis is concerned with the fabrication and characterization of semiconductor nanostructures. In particular, the semiconductor material used in this research consisted of InGaAs, as a quantum well layer, sandwiched between layers of InP, which acts as a barrier layer. The driving force behind this research was twofold. Firstly, it included a desire to understand the physics governing the behaviour of these devices. As the lateral sizes of these devices decrease, theories predict that the structures will give strong atom-like resonances, so a study of these structures is similar to studying large quasi-atoms. Secondly, besides the fundamental physics involved, there was also a practical application stimulating this research. Already, quantum well lasers are used in the consumer electronics market, and it was speculated that by using quantum wire or dot systems the laser threshold currents would be reduced still further, yielding improved laser efficiency. The fabrication process involved electron beam lithography to pattern structures as small as 1 Onm in diameter, reactive ion etching (RIE) to transfer these patterns to the semiconductor, and various other post-RIE fabrication steps including wet chemical etching and annealing, as required. No evidence of an optically inactive "dead layer" was found because luminescence was observed from even the smallest structures. If an optically inactive region did exist its thickness could only be of the order of a few nanometres. The characterization of the nanostructures included techniques such as photoluminescence spectroscopy and absorption measurements. The photoluminescence measurements revealed the participation of a number of different energy levels in the emission spectra when the lateral dimensions of the nanostructures were reduced to 100nm or less. This high energy level participation became more pronounced when the lateral dimensions were reduced below 50nm. Quantum confinement was clearly observed in the low temperature emission spectra of 10nm and 20nm diameter dots. This quantum confinement was manifested by an energy upshift of the PL peak energy. It was found that exciton transport plays a crucial role in the emission strength of wires. This was attributed to localization effects resulting from variations in the layer thickness at the InGaAs/InP interface, as well as alloy potential fluctuations. Annealing of a sample after RIE and wet chemical etching reduced the absolute PL intensity of the quantum structures and also caused narrowing of the PL emission. Wet chemical etching of a sample after RIE narrowed the PL spectrum of quantum structures compared with structures of similar lateral dimensions which were only subjected to RIE. In particular, the samples which were wet etched did not exhibit the broadening to high energies characteristic of the RIE only samples.

[发布机构] University:University of Glasgow

[关键词] Electrical engineering, Condensed matter physics, Nanotechnology