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Title: Ultrafast acoustic modulation of transport in semiconductor devices
Author: Moss , Daniel Max
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2013
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This thesis investigates the fast strain response of electrical transport in GaAs-based semiconductor device structures (~ GHz). The transport was either across a semiconductor junction, or parallel or perpendicular to the plane of a quantum well (QW). Picosecond strain pulses were generated by thermalisation of femtosecond optical pump pulses in a metal transducer film adhered to the device's back surface. The QW-based device experiments employed picosecond strain pulses to modulate the photocurrent generated in a QW, excited by femtosecond optical pulses. Two devices were investigated: a p-i-n diode containing a QW in the intrinsic region (Q-p-i-n), and a device based on planar-transport across two QWs. The modelled photocurrent response of the Q-p-i-n diode was based on strain-induced changes in the QW's optical absorption. The predicted and the observed responses had the same order of magnitude. These experiments show that the photo carrier populations in a QW, which may be probed with picosecond resolution, are highly sensitive (fractional change in photocurrent/strain ~ 600) to sub-terahertz acoustic wave packets - several orders of magnitude greater than achievable with conventional pump probe techniques (reflectivity change/strain ~ 30). The junction-based experiments employed picosecond strain pulses to control device current on fast timescales. These devices were probed electrically using high-speed detection electronics (rise time ~ 30 ps). Three device structures were examined: p-n and Schottky diodes and a metal-semiconductor field effect transistor. The models attributed the changes in current to strain-induced, localised shifts in the semiconductor band structure. For the p-n and Schottky diodes, the predicted current response was within an order of magnitude of experimental values. These junction-based devices, operable at room temperature, also respond highly sensitively and on fast timescales (~ GHz) to sub-terahertz acoustic wave packets. Further development could potentially extend this to ultrafast timescales (~ THz). ·
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available