Roberts, Jason Mark;
(1997)
Electronic properties of quantum wells for field effect transistor applications.
Doctoral thesis (Ph.D.), University College London (United Kingdom).
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Abstract
Several alternative techniques for improving the transport properties of delta-doped quantum well structures have been investigated. The most successful have used edge delta-doping and compositional grading to produce significantly enhanced electron transport characteristics in AlxGa1-xAs/GaAs, AlxGa1-xAs/InyGa1-yAs, and Al xIn1-xAs/InyGa1-yAs quantum well structures. This compositional grading has been achieved using the digital alloying growth technique—which has been confirmed as a viable method of producing good quality, delta-doped material. Improvements of up to 100% in mobility (to 2630cm2/Vs) and 67% in electron saturation drift velocity (to 1.7 × 107 cm/s) have been achieved using these techniques. The dependence of electron saturation drift velocity (vsat) on mobility (μ) has been determined as vsat α μ0.8±0.3. In addition, we present our investigations of the free-carrier loss observed in a series of highly Si delta-doped AlxGa1-xAs/GaAs quantum well structures. We interpret the results of Hall measurements and self-consistent Poisson Schrodinger modelling in terms of a model of DX centre formation which includes Coulomb interactions, a result of the charged nature of the DX state. Our interpretation implies a strongly growth dependent DX centre energy—which explains the range in published values for the GaAs DX centre energy. The data allows investigation of the DX centre distribution between 214 and 249 meV above the F minima, and confirms a considerably broadened DX centre density of states ≥35 meV).
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D. |
| Title: | Electronic properties of quantum wells for field effect transistor applications |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Thesis digitised by ProQuest. |
| Keywords: | (UMI)AAI10045788; Applied sciences; Field effect transistor applications; Quantum wells |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10100241 |
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