Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636273
Title: Cross-sectional scanning tunnelling microscopy of biased laser structures
Author: Cobley, R. J.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2006
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Abstract:
This work investigates Cross-Sectional Scanning Tunnelling Microscopy applied to semiconductor laser structures which are biased whilst they are being scanned. Images are presented as a function of sample bias. Increasing the sample bias removes the built-in band bending across the device and causes the horizontal topographic gradient of the scan to change. The p-type side of the sample is held at ground whilst the n-type side is biased. When tunnelling out of a double quantum well structure the topographic height of the n-type side increases by around 0.2nm at 1V. Tunnelling in to the structure, the height decreases by 0.02nm under low tunnelling current conditions. A tunnelling current model is developed which confirms these changes. Tunnelling in to a buried heterostructure device the apparent topographic height of the n-type side is again found to decrease, by over 2nm. Biased-dependent spectroscopic shifts are also observed with this device which are again confirmed by modelling. In both devices the apparent height of the quantum wells is found to increase by a factor of 2.5 to 4 times, at 1V sample bias. This is caused by the effects of tip-induced band bending being altered by the applied bias. An experimental and modelled example of a superlattice structure which displays contrast enhancement through tip-induced band bending is given. Several other device-specific physical and irreversible changes occur as a result of sample bias. These are well-suited to give characterisation information not available from other techniques.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.636273  DOI: Not available
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