Engineering Optical Phonon Lifetime by Vibrational Doping
Abstract
The proposed research aims to design and create novel semiconducting materials with significantly improved thermal performance through the control of hot phonon effects. While most Ôphonon engineeringÕ approaches focus on controlling the propagation of acoustic phonons, i.e. heat flow, this fundamentally new and transformative approach seeks to suppress the accumulation of heat in stationary hot optical phonons, and so to facilitate the flow of energy from the hot carrier plasma to mobile acoustic phonons. In the proposed approach, the hot optical phonon generation will be suppressed by phonon engineering of the material using vibrational doping to reduce the longitudinal optical (LO) phonon lifetime. This will suppress the generation of hot phonons that heat the carriers and degrade the performance of devices operating at high power density. The objectives of the proposed research are: 1) To develop GaAs materials with reduced LO phonon lifetime and good optical material quality for the suppression of carrier heating and other hot phonon effects. 2) To study the LO phonon decay pathways caused by doping with vibrational defects using temperature dependent Raman scattering and phonon spectroscopy. 3) To validate KlemensÕ theoretical model for dopant-induced anharmonicity and reach a fundamental understanding of LO phonon decay processes, which opens the route to engineer a wider range of materials for controlling hot phonon effects. Bulk GaAs samples will be grown by molecular beam epitaxy, and their Raman room-temperature linewidths used to assess lattice anharmonicity and phonon lifetime. To ensure that changes in the intrinsic LO phonon lifetime are observed, doping compensation and/or surface depletion will be used to suppress parasitic lifetime reduction due to LO phonon-plasma coupling losses. QW samples will be grown using the most promising dopants identified in the bulk materials to confirm photoluminescence (PL) efficiency and electronic device suitability. Standard techniques will be used to assess the material quality: Hall effect measurements will be used to characterize the carrier plasma density and mobility. Temperature dependent and time-resolved PL measurements will be used to assess the material optical quality. Lattice disruption will be assessed by PL microscopy and symmetry-forbidden 1-LO phonon resonant Raman scattering. Non equilibrium phonon spectroscopy will be used to to directly observe carrier relaxation and phonon scattering, specifically the LO phonon decay paths and the onset of hot-phonon processes. Carrying out a systematic study of the effects of different dopants and doping densities on LO phonon decay in GaAs using these techniques will lead to a more complete understanding of the effects of vibrational defects on LO phonon lifetime and decay processes. Thus experimentally validating KlemensÕ theoretical model of impurity-induced anharmonicity in the case of LO phonons, and developing a phenomenological model which can be used for the design of phonon engineered semiconductor materials to control hot phonon effects in high power and high frequency electronic and optoelectronic devices. By seeking to determine unique designs for optimizing semiconductor materials with uncharacteristic compositions, this multidisciplinary project, involving groups from Physics and Engineering aligns with the ARO International Programs the Innovations in Materials Program as described in the BAA. The project aims to reach a scientific understanding and engineering control of vibrational defect (dopant) states in semiconductors leading to Òunprecedented property developmentÓ with the prospects of significantly improving the efficiency, thermal management and speed of devices.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jun 25, 2021
- Source ID
- W911NF2110307
Entities
People
- Anthony Kent
Organizations
- Army Contracting Command
- United States Army
- University of Nottingham