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Near-field photocurrent characterisation of semiconductor devices. / Mathew Paul Ackland

Swansea University Author: Mathew Paul, Ackland

Abstract

A near-field scanning optical microscope (NSOM) has been modified to perform near-field photocurrent imaging via the development and implementation of a two- stage amplification/detection scheme. The near-field photocurrent imaging capability has been employed along with simultaneous topographic ima...

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Published: 2005
Institution: Swansea University
Degree level: Doctoral
Degree name: Ph.D
URI: https://cronfa.swan.ac.uk/Record/cronfa42382
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Abstract: A near-field scanning optical microscope (NSOM) has been modified to perform near-field photocurrent imaging via the development and implementation of a two- stage amplification/detection scheme. The near-field photocurrent imaging capability has been employed along with simultaneous topographic image acquisition in the analysis of the buried Schottky interface of nickel-silicon carbide (Ni-SiC) Schottky contacts. Silicon carbide is stable at high temperatures and operating powers and thus could fulfil a wide range of potential applications, however in order to implement SiC devices in such applications stable metal contacts are a necessity and remain a field requiring optimisation. Near-field photocurrent imaging has directly imaged the buried interface properties and lateral variations in the Schottky barrier energy on the nanoscale, which have been related to the macroscopic electrical characteristics of the Schottky contact. The Schottky barrier energy has been increased by 0.155eV via annealing at 500°C, this resulted in an increase in the lateral variation in barrier properties, as reflected in the ideality factor increase of 0.3, and similarly recorded by near-field photocurrent imaging. Near-field photocurrent imaging has also been applied in the characterisation of quantum well laser devices, and powerfully combined with the complementary optical collection and topographic imaging modes. The photocurrent imaging mode probes the electronic device characteristics, whilst near-field collection imaging characterises the optical output of operating laser devices, the two independent imaging modes are correlated by the simultaneous surface topographies. GaInP/AlGaInP based quantum well lasers have been used in the study of the effectiveness of multi-quantum barrier (MQB) reflectors in enhancing the electronic carrier confinement of the quantum well active region, and thus in increasing the operational efficiency of such devices. Collection imaging has proved that the incorporation of MQB's does not impair the devices optical characteristics, whilst near-field photocurrents have sensed the location of the MQB's and detected improvements in the electronic carrier confinement. The NSOM has also been employed in the characterisation of InGaAsP/InP buried heterostructure multiquantum well lasers, imaging the active region and surrounding current blocking structure at high resolution. Photocurrent imaging has mapped the location and extent of the pn-junctions that form the current blocking structure, and aided the identification of probable current leakage paths through the structure. Collection imaging has characterised the highly confined optical output of such devices and located electroluminescence external to the active region, again aiding the identification of current leakage pathways. These imaging modes are complemented by simultaneous topographic images displaying unprecedented sensitivity to the active region and sample structure.
Keywords: Condensed matter physics.;Electromagnetics.
College: College of Science