This thesis covers research on low electric conductivity wide band gap semiconductors of the group-III nitride material system. The work presented focussed on using multi-mode scanning electron microscope (SEM) techniques to investigate the luminescence properties and their correlation with surface effects, doping concentration and structure of semiconductor structures.The measurement techniques combined cathodoluminescence (CL) for the characterization of luminescence properties, secondary electron (SE) imaging for imaging of the morphology and wavelength dispersive X-ray (WDX) spectroscopy for compositional analysis. The high spatial resolution of CL and SE-imaging allowed for the investigation of nanometer sized features, whilst environmental SEM allowed the characterisation of low conductivity samples.The investigated AlxGa₁₋xN samples showed a strong dependence on the miscut of the substrate, which was proven to influence the surface morphology and the compositional homogeneity. Studying the influence of the AlxGa₁₋xN sample thickness displayed a reduced strain in the samples with increasing thickness as well as an increasing crystalline quality. The analysis of AlxGa₁₋xN:Si samples showed the incorporation properties of Si in AlxGa₁₋xN, the correlation between defect luminescence, Si concentration and resistivity as well as the influence of threading dislocations on the luminescence properties and incorporation of point defects.The characterization of UV-LED structures demonstrated that a change in the band structure is one of the main reasons for a decreasing output power in AlₓGa₁₋ₓN based UV-LEDs. In addition the dependence of the luminescence properties and crystalline quality of InxAl₁₋xN based UV-LEDs on various growth parameters (e.g. growth temperature, quantum well thickness) was investigated.The study of nanorods revealed the influence of the template on the compositional homogeneity and luminescence of InxAl₁₋xN nanorod LEDs. Furthermore,the influence of optical modes in these structures was studied and found to provide an additional engineering parameter for the design of nanorod LEDs.
|Date of Award||12 Oct 2016|
- University Of Strathclyde
|Sponsors||EPSRC (Engineering and Physical Sciences Research Council)|
|Supervisor||Robert Martin (Supervisor) & Carol Trager-Cowan (Supervisor)|