The novel idea of GaSb quantum dots (QDs)1 quantum rings (QRs) stacked layers single junction solar cells have been investigated for the examination and enhancement of the infrared photo response. Initially the investigation used photoluminescence to probe the optical properties of a type-II material interface between GaSb/GaAs using optimum growth temperature for QDs/QRs with two different growth modes (Stranski-Krastanow (SK) and exchange growth); and two different GaSb deposition thickness (1.5ML and 2.IML). The photoluminescence spectra of the stacked epilayers confirmed that the dominant radiative recombination mechanism was band-to-band in the GaSb QDs/QRs stacked layers. Excellent structural quality is observed in each sample with no threading dislocations (by Transmission Electron Microscopy (TEM)). The composition of the QRs is close to 100 % GaSb with high purity GaAs centres. The ring density per layer is approximately 1010 rings/cm2 with no significant variation in size or density in the separate layers. II Rapid thermal annealing (RTA) has been used to tailor the optical properties of 10-layer stacks of type-II GaSb self-assembled QDs and QRs embedded within GaAs grown by molecular beam epitaxy. An increase in PL emission intensity and a blue shift in peak energy in both types of QD stacks were observed, along with changes in the activation energy for PL quenching. These effects were attributed to Sb-As intermixing and size effects with corresponding changes in the band structure and an increase in the oscillator strength associated with the transformation towards type-I behaviour. It has been concluded that postgrowth rapid thermal annealing can be used to tune the spectral response and control carrier recombination and escape properties of stacked GaSb QD for more effective use in devices such as solar cells and lasers. The final part of the investigation examined the properties of multi-layer QDs/QRs single junction solar cells (SC) to obtain an understanding of the operation and characteristics of the devices. Three kinds of solar cells were fabricated; one is intrinsic layer with ? layers of QDs/QRs, another comprises 10 layers and the final one is control cells (without QDs/QRs).
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:658211 |
| Date | January 2013 |
| Creators | Mahajumi, Abu Syed |
| Publisher | Lancaster University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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