Defects and their properties in InP and InGaAs: An ab initio study

Vedel, Christian Dam (2024) Defects and their properties in InP and InGaAs: An ab initio study. PhD thesis, University of Glasgow.

Abstract

Defects in III-V optoelectronic semiconductor devices are one the main bottlenecks for further device improvements and can in extreme cases even cause complete loss of function of the device. Some defects have very low formation energies, which makes avoiding them during device fabrication particularly hard and sometimes impossible.

One such case of defects are polytypic defects in indium phosphide, such as rotational twin planes, which besides their detrimental effects, also have unique properties that can possibly be utilised beneficially. One such possibility is crystal-phase quantum wells, which is a quantum well created by the crystal structure of a single material. Through ab initio studies in the state-of-the-art simulation software suite QuantumATK, it is in this thesis found that such crystal-phase quantum wells must have a minimal width of 10 nm. Another property which can potentially be utilised, is the dielectric constant anisotropy, which is discovered to be induced in Zincblende InP by the breaking of the A-direction symmetry by polytypic defects. One semiconductor property usually affected by defects, which is especially important in electronic devices like transistors, but which is also important in optoelectronic devices, is the current transport in the semiconductor. In the case of polytypic defects in InP, it is in this thesis discovered that for current transport along the [1 1 1]/[0 0 0 1]-direction, it is more beneficial to have more defects, rather than fewer of them, if they cannot be completely avoided, due to the Wurtzite structure having better transport properties. For transport in the defect plane, it is found that the defects increase the current conducting capabilities of InP, with a well-defined optimal fraction of polytypic defects.

A defect-related property which is especially important in optical devices such as PIN photodiodes, due to its detrimental effect on the photocurrent, is trap-assisted recombination. This recombination is studied in 23 different experimentally feasible point defects in In0.53Ga0.47As in this thesis, and it is found that only 7 of them can host a notable carrier recombination. Out of those 7 defects, the most detrimental defects are found to be the antisites, and in particular the double antisites. This discovery is unfortunate for semiconductor devices, as the defect levels of the antisites also aligns well with the experimentally measured levels, suggesting that they are regularly occurring in device fabrication. In order to do this study, two different atomistic ab initio methods for simulating random alloys are also evaluated and compared, and it is found that the Special Quasi-random Structure (SQS) method performs better than the Virtual Crystal Approximation (VCA) for these types of studies, based on their implementation in QuantumATK U-2022.12 by Synopsys.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: T Technology > TK Electrical engineering. Electronics Nuclear engineering
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Funder's Name: European Commission (EC)
• Supervisor's Name: Georgiev, Professor Vihar
• Date of Award: 2024
• Depositing User: Theses Team
• Unique ID: glathesis:2024-84425
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 02 Jul 2024 12:50
• Last Modified: 02 Jul 2024 13:45
• Thesis DOI: 10.5525/gla.thesis.84425
• URI: https://theses.gla.ac.uk/id/eprint/84425