Predictive simulation and design of III-V heterostructures for light emission and detection

Semiconductor heterostructures have been long established for a variety of applications, particularly in photonic devices such as light-emitting diodes (LEDs) and lasers, in addition to photodetectors and optical amplifiers. Predictive simulations are key to support the development of these technologies. In this Thesis we employ both first-principles and continuum empirical - based respectively on density functional theory (DFT) and the k·p method – calculations to analyse and optimise III-V semiconductor heterostructures for light emission and detection. III-V superlattices (SLs) have attracted significant interest for emission and detection at mid-infrared (mid-IR) wavelengths, for applications relevant to the environmental, industrial, medical, agricultural and defence sectors. We develop a robust framework to rigorously analyse the electronic and optical properties of III-V SLs. We employ a semi-analytical plane wave expansion method in conjunction with an 8-band k·p Hamiltonian to compute SL electronic structure, paying careful attention to the identification and mitigation of spurious solutions. The calculated SL eigenstates are then used directly to compute optical emission and absorption spectra, which are in turn used to define figures of merit that allow for in silico optimisation of SL structures for applications as mid-IR emitters and photodetectors. Firstly, we present a theoretical analysis of mid-IR radiative recombination in InAs/GaSb SLs. The calculated SL eigenstates are used directly to compute spontaneous emission spectra and the radiative recombination coefficient B. We elucidate the origin of the relatively large B coefficients in InAs/GaSb SLs which, despite the presence of spatially indirect (type-II-like) carrier confinement, are close to that of bulk InAs and compare favourably to those calculated for mid-IR type-I pseudomorphic and metamorphic quantum well structures having comparable emission wavelengths. Our analysis explicitly quantifies the roles played by carrier localisation (specifically, partial delocalisation of bound electron states) and miniband formation (specifically, miniband occupation and optical selection rules) in determining the magnitude of B and its temperature dependence. Across the 3.5 - 7 µm wavelength range we use the room temperature B coefficient as a figure of merit. We identify that B is governed by the relative thickness of the electron-confining InAs and hole-confining GaSb layers, with our analysis of B vs. relative thickness providing guidance for the growth of optimised SLs for mid-IR light emitters. These results, combined with the expected low non-radiative Auger recombination rates in structures having spatially indirect electron and hole confinement, corroborate recently observed high output power in prototype InAs/GaSb SL inter-band cascade LEDs. Secondly, we perform a systematic optimisation of 3 - 5 µm photodetection in strain-balanced InAs/InAs(1−x)Sb(x) SLs, which constitute an emerging platform for the development of efficient mid-IR photodetectors. Growing strain-balanced SLs allows to realise high material quality in structures containing up to several hundred SL periods, by mitigating defect formation associated with lattice relaxation. For a given target detector cut-off wavelength we employ continuum elasticity theory to identify a strain-balanced SL at each Sb composition x. We then utilise the calculated SL electronic structure to compute the optical absorption spectrum. The SL absorption spectra are used in a model calculation of the internal quantum efficiency (IQE) for photocurrent generation which is employed as a figure of merit to quantify photodetector performance. We demonstrate that increasing the Sb composition to x ≈ 30% can increase the (relative) IQE at fixed cut-off wavelength by ≈ 15%, with minimal additional improvement in performance expected at higher Sb compositions. Thirdly, we then develop an improved set of band parameters for the III-P semiconductors, which we extract from a comprehensive suite of DFT calculations. Despite their relevance to the development of quantum-confined heterostructures for classical and quantum applications, there remains significant uncertainty regarding several key band parameters for the III-P semiconductors AlP, GaP and InP. In literature reports, there is significant uncertainty regarding: (i) the direct band gap in AlP, the magnitude of which varies by approximately 1 eV, and (ii) the reported band edge deformation potentials for III-P compounds. Using hybrid-functional first-principles calculations we demonstrate that the Γ(6c)-Γ(8v) band gap of AlP is approximately 1 eV larger than the widely assumed value of 3.63 eV. This prediction is validated by using the predicted inter-band transition energies to reevaluate literature spectroscopic ellipsometry data. Having validated our calculated band structures vs. experimental and theoretical literature data, we compute a comprehensive and consistent set of band parameters for III-P semiconductors, including: direct and indirect band gaps, band edge effective masses, inter-band momentum (Kane) matrix elements, band edge deformation potentials, direct and indirect band gap pressure coefficients, and valence band offsets. Our revised parameter sets reconcile the large spread in reported values for the direct band gap of AlP, and the energy ordering of the AlP conduction band valleys, in addition to providing a consistent set of band edge deformation potentials for GaP and InP. Overall, our DFT calculations enable us to extract a complete and consistent set of 8-band k·p parameters for III-P semiconductors, providing an improved basis upon which to develop predictive calculations of the electronic and optical properties of pseudomorphic and metamorphic III-P heterostructures.

Grantor dc:publisher

University College Cork

Year dc:date.issued

2025

Author dc:creator

• Murphy, Cónal

Advisors dc:contributor.advisor

• O'Reilly, Eoin P.
• Broderick, Christopher
• Schulz, Stefan

• Semiconductor
• Simulations
• Condensed matter physics
• Mid-infrared (mid-IR)
• III-V heterostructures
• III-P alloys
• In silico optimisation
• Visible wavelength
• Density functional theory (DFT)
• k.p method
• Radiative recombination
• Optical absorption
• Photodetectors
• Light emitting diode
• Continuum
• First-principles
• Optoelectronic

Statement dc:rights

• © 2025, Cónal Murphy.

Licence dc:rights.uri

• https://creativecommons.org/licenses/by/4.0/

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/10468/17947

OAI identifier oai:identifier

oai:cora.ucc.ie:10468/17947