Investigation of structural characteristics of III-V semiconductor nanowires grown by molecular beam epitaxy

Abstract

One-dimensional nanowires made of III-V semiconductors have attracted significant research interest in the recent decades due to their distinct physical and chemical properties that can potentially lead to a wide range of applications in nanoelectronics and optoelectronics. As a key class of III-V semiconductor nanowires, InAs nanowires have attracted special attention due to their narrow bandgap, relatively high electron mobility, and small electron effective mass, which made them a promising candidate for the applications in future optical and highfrequency electronic devices.One of the challenges in realizing these unique III-V nanowire properties in nanowire-based devices is to integrate nanowires on the nano-devices or chips with well-organized arrangement. To solve this issue, the epitaxial nanowire growth provides the uniqueness that well aligned nanowires can be grown on the chosen substrates, and by selecting substrates with particular orientations, specifically orientated nanowires can be grown. Au-assisted nanowire growth is one of the most common methods to grow epitaxial III-V nanowires via the vapor-liquid-solid (VLS) mechanism or vapor-solid-solid (VSS) mechanism.For III-V nanowires, one of the coherent problems is that the stacking faults and/or twin defects can easily be introduced in both wurtzite or zinc-blende structured nanowires due to the small energy differences between wurtzite and zinc-blende stacking sequences of their dense planes. For III-V nanowires to be practically useful, it is of significant importance to minimize the lattice defects in nanowires, and to control their crystal phase and structural quality. In this regard, in this thesis, we investigated the growth parameters on the growth behaviour, crystal phase and structural quality of III-V nanowires, particularly InAs and GaAs nanowires. By carefully tuning the growth parameters, we have successfully achieved the controlled growth of InAs and GaAs nanowires with defect-free wurtzite structure and/or zincblende structure. I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the policy and procedures of The University of Queensland, the thesis be made available for research and study in accordance with the Copyright Act 1968 unless a period of embargo has been approved by the Dean of the Graduate School.I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis. In the meantime, I am very grateful for the staff of Centre for Microscopy and Microanalysis (CMM) at UQ, who helped me in so many ways. They are Richard IV Publications during candidature

Er-doped AlGaAs native oxides: photoluminescence characterization and process optimization

“…By in situ doping with Er during crystal growth, the doping profile can be easily tailored as needed, with a doping depth as deep as the thickness of the AlGaAs layer. However, the highest Er concentration is limited by its solubility in the AlGaAs semiconductor, about 5 10 cm and 4 10 cm for Al Ga As grown at 580 C and 400 C, respectively [28]. In contrast, ion implantation can achieve an Er concentration well above the solubility limit because the Er is not distributed in a thermal equilibrium phase with its host.…”

“…1) Er Incorporation in situ During Molecular Beam Epitaxial Growth: Several AlGaAs and AlInAs samples, grown by MBE for a previous study [28], [29] of Er-doped semiconductors at North Carolina State University, Raleigh, were subsequently provided to the University of Notre Dame, IN, for additional oxidation and photoluminescence studies to further explore the suitability of the native oxides as rare earth hosts. The Al In As:Er sample used in this work was grown as a mismatched film on a GaAs substrate, originally for doping calibration, and chosen for this study due to its higher Er effusion cell temperature of 900 C, yielding an Er concentration of 0.03 at.%.…”

“…The Al Ga As:Er layers are also 1.4 m thick, and are capped with a 60 GaAs layer. The Er concentrations versus Er cell temperature for all samples are based upon a calibration study performed with secondary ion mass spectrometry on several Al Ga As:Er samples grown at 540 C [28]. Er incorporation during the MBE growth of GaAs:Er [30] and AlGaAs:Er [28] has been shown to be independent of substrate temperature.…”

“…The wet oxide of Fig. 6(b) was prepared through wet oxidation at 500 C for 81 min, with a post-oxidation anneal in Ar at 725 C for 1 h. Since the PL intensity from the unoxidized semiconductor has previously been shown to drop after annealing at temperatures higher than 600 C due to the diffusion and segregation of Er atoms [28], the semiconductor sample of Fig. 6(c) was not annealed.…”