Magneto-transport in cdte/cdmnte dilute magnetic semiconductor single barrier structures
Magneto-transport in cdte/cdmnte dilute magnetic semiconductor single barrier structures
This thesis presents work done on electrical transport through dilute magnetic semiconductor (DMS) single barriers in both zero and non-zero magnetic fields. The fields are applied either perpendicular or parallel to the DMS layers. The main samples under investigation consist of 100Å and 200Å CdTe/Cd0.8Mn0.2Te/CdTe single barrier heterostructures. In addition electrical characterisation of the non-magnetic layers is performed.
Current through the barrier is measured as a function of voltage, magnetic field and temperature. A theoretical model is derived in order to calculate the current as a function of barrier height, barrier width, emitting layer carrier concentration, applied bias and temperature. These variables are then treated as fitting parameters and comparisons are made between the calculated and the experimental currents.
The barriers are shown to produce non-Ohmic transport. The roles of quantum mechanical tunnelling and thermal activation across the barrier are investigated and shown to be highly mixed. An unexpectedly high degree of tunnelling is found to occur at high temperatures, within the region previously assumed to be dominated by thermal activation. Moreover the barrier height is found to be lower and the width greater than expected. These observations suggest that a high level of Mn diffusion occurs, possibly due to In dopant related effects. This suggestion is validated by the high emitting layer carrier concentration suggested by the fitting. At low temperatures and voltages the thicker barrier sample is shown to contain a parasitic leak path which short-circuits the barrier. This leak may exist in both samples but only becomes dominant where the barriers are sufficiently opaque to the incident carriers.
Changes in a magnetic field are expected to be due to sp-d exchange induced giant Zeeman splitting in the barrier and either normal spin splitting or sp-d exchange effects in the emitter regions. The application of a magnetic field is shown to produce either an enhancement or suppression of the barrier dominated current, dependent on the field orientation and the level of transmission. Current enhancement is seen when the transmission through the barrier is low, i.e. at low fields and voltages, whereas suppression is seen in the high transmission barrier current and in the leak dominated conduction. Comparisons of the experimental and calculated results suggest that the low voltage current through the barrier is dominated by emission from three dimensional states in the CdTe layers.
University of Southampton
1999
Lyons, Vivienne Ruth
(1999)
Magneto-transport in cdte/cdmnte dilute magnetic semiconductor single barrier structures.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
This thesis presents work done on electrical transport through dilute magnetic semiconductor (DMS) single barriers in both zero and non-zero magnetic fields. The fields are applied either perpendicular or parallel to the DMS layers. The main samples under investigation consist of 100Å and 200Å CdTe/Cd0.8Mn0.2Te/CdTe single barrier heterostructures. In addition electrical characterisation of the non-magnetic layers is performed.
Current through the barrier is measured as a function of voltage, magnetic field and temperature. A theoretical model is derived in order to calculate the current as a function of barrier height, barrier width, emitting layer carrier concentration, applied bias and temperature. These variables are then treated as fitting parameters and comparisons are made between the calculated and the experimental currents.
The barriers are shown to produce non-Ohmic transport. The roles of quantum mechanical tunnelling and thermal activation across the barrier are investigated and shown to be highly mixed. An unexpectedly high degree of tunnelling is found to occur at high temperatures, within the region previously assumed to be dominated by thermal activation. Moreover the barrier height is found to be lower and the width greater than expected. These observations suggest that a high level of Mn diffusion occurs, possibly due to In dopant related effects. This suggestion is validated by the high emitting layer carrier concentration suggested by the fitting. At low temperatures and voltages the thicker barrier sample is shown to contain a parasitic leak path which short-circuits the barrier. This leak may exist in both samples but only becomes dominant where the barriers are sufficiently opaque to the incident carriers.
Changes in a magnetic field are expected to be due to sp-d exchange induced giant Zeeman splitting in the barrier and either normal spin splitting or sp-d exchange effects in the emitter regions. The application of a magnetic field is shown to produce either an enhancement or suppression of the barrier dominated current, dependent on the field orientation and the level of transmission. Current enhancement is seen when the transmission through the barrier is low, i.e. at low fields and voltages, whereas suppression is seen in the high transmission barrier current and in the leak dominated conduction. Comparisons of the experimental and calculated results suggest that the low voltage current through the barrier is dominated by emission from three dimensional states in the CdTe layers.
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Published date: 1999
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Local EPrints ID: 463586
URI: http://eprints.soton.ac.uk/id/eprint/463586
PURE UUID: 41d5c8e8-8403-4a13-a41b-120ec127e6b9
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Date deposited: 04 Jul 2022 20:54
Last modified: 04 Jul 2022 20:54
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Author:
Vivienne Ruth Lyons
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