Raman spectroscopy of ternary III-V semiconducting films
- Authors: Mashigo, Donald
- Date: 2009
- Subjects: Raman spectroscopy , Semiconductor films , Compound semiconductors
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10522 , http://hdl.handle.net/10948/1011 , Raman spectroscopy , Semiconductor films , Compound semiconductors
- Description: The III-V semiconductor compounds (i.e. In Ga As x 1-x , 1 x x InAs Sb - , In Ga Sb x 1-x and Al Ga As x 1-x ) have been studied using room temperature Raman spectroscopy. X-ray diffraction has been used as a complementary characterization technique. In this study all the III-V semiconductor compounds were grown by metal organic chemical vapour deposition (MOCVD) on GaAs and GaSb substrates. The layers were studied with respect to composition, strain variation and critical thickness. Raman spectroscopy has been employed to assess the composition dependence of optical phonons in the layers. The alloy composition was varied, while the thickness was kept constant in order to investigate compositional effects. A significant frequency shift of the phonon modes were observed as the composition changed. The composition dependence of the phonon frequencies were described by linear and polynomial expressions. The results of this study were compared with previous Raman and infrared work on III-V semiconductor compounds. Strain relaxation in InGaAs and InGaSb has been investigated by Raman and X-ray diffraction. Measurements were performed on several series of layers. For each series, the thickness was varied, while keeping the composition constant. For a given composition, the layer thicknesses were such that some layers should be fully strained, some partially relaxed and some fully relaxed. The Raman peak shifts and XRD confirm that a layer grows up to the critical thickness and then releases the strain as the thickness increases. Critical layer thickness values measured in this study were compared with published data, in which various techniques had been used to estimate the critical thickness.
- Full Text:
- Date Issued: 2009
- Authors: Mashigo, Donald
- Date: 2009
- Subjects: Raman spectroscopy , Semiconductor films , Compound semiconductors
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10522 , http://hdl.handle.net/10948/1011 , Raman spectroscopy , Semiconductor films , Compound semiconductors
- Description: The III-V semiconductor compounds (i.e. In Ga As x 1-x , 1 x x InAs Sb - , In Ga Sb x 1-x and Al Ga As x 1-x ) have been studied using room temperature Raman spectroscopy. X-ray diffraction has been used as a complementary characterization technique. In this study all the III-V semiconductor compounds were grown by metal organic chemical vapour deposition (MOCVD) on GaAs and GaSb substrates. The layers were studied with respect to composition, strain variation and critical thickness. Raman spectroscopy has been employed to assess the composition dependence of optical phonons in the layers. The alloy composition was varied, while the thickness was kept constant in order to investigate compositional effects. A significant frequency shift of the phonon modes were observed as the composition changed. The composition dependence of the phonon frequencies were described by linear and polynomial expressions. The results of this study were compared with previous Raman and infrared work on III-V semiconductor compounds. Strain relaxation in InGaAs and InGaSb has been investigated by Raman and X-ray diffraction. Measurements were performed on several series of layers. For each series, the thickness was varied, while keeping the composition constant. For a given composition, the layer thicknesses were such that some layers should be fully strained, some partially relaxed and some fully relaxed. The Raman peak shifts and XRD confirm that a layer grows up to the critical thickness and then releases the strain as the thickness increases. Critical layer thickness values measured in this study were compared with published data, in which various techniques had been used to estimate the critical thickness.
- Full Text:
- Date Issued: 2009
Service provider's perceptions of the quality and accessiblity of health services under social health insurance in Dar-Es-Salaam
- Authors: Chomi, Eunice Nahyuha
- Date: 2007
- Subjects: Health insurance -- Tanzania , Medical personnel -- Insurance requirements -- Tanzania
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:10079 , http://hdl.handle.net/10948/489 , Health insurance -- Tanzania , Medical personnel -- Insurance requirements -- Tanzania
- Description: Social health insurance is a form of health care financing that has gained increased attention in African countries in the past decade. Tanzania introduced social health insurance by the establishment of the National Health Insurance Fund (NHIF) in 1999 with, inter alia, the objective of improvement of the quality and availability of health services. The goal of this study was to determine the perceptions of services providers on the quality and accessibility of health services following the introduction of social health insurance. A qualitative approach was used to gain an insider's perspective from the service providers of how the services have changed following the introduction of the scheme. Individual interviews, observation and field notes were used to gather information on the quality and accessibility of health services under the policy of social health insurance. Data were analysed using Tesch's method of data analysis. The health workers generally perceived the fund as being beneficial to its members as it reduced the financial barriers to receiving health care. However, the objectives of the NHIF as a health financing mechanism were not adequately understood by the health workers. Although they perceived the quality of health services as having improved compared to previous years, they did not associate this improvement with the NHIF. The health workers also perceived accessibility of health services as having improved for insured patients but not for non-insured patients.
- Full Text:
- Date Issued: 2007
- Authors: Chomi, Eunice Nahyuha
- Date: 2007
- Subjects: Health insurance -- Tanzania , Medical personnel -- Insurance requirements -- Tanzania
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:10079 , http://hdl.handle.net/10948/489 , Health insurance -- Tanzania , Medical personnel -- Insurance requirements -- Tanzania
- Description: Social health insurance is a form of health care financing that has gained increased attention in African countries in the past decade. Tanzania introduced social health insurance by the establishment of the National Health Insurance Fund (NHIF) in 1999 with, inter alia, the objective of improvement of the quality and availability of health services. The goal of this study was to determine the perceptions of services providers on the quality and accessibility of health services following the introduction of social health insurance. A qualitative approach was used to gain an insider's perspective from the service providers of how the services have changed following the introduction of the scheme. Individual interviews, observation and field notes were used to gather information on the quality and accessibility of health services under the policy of social health insurance. Data were analysed using Tesch's method of data analysis. The health workers generally perceived the fund as being beneficial to its members as it reduced the financial barriers to receiving health care. However, the objectives of the NHIF as a health financing mechanism were not adequately understood by the health workers. Although they perceived the quality of health services as having improved compared to previous years, they did not associate this improvement with the NHIF. The health workers also perceived accessibility of health services as having improved for insured patients but not for non-insured patients.
- Full Text:
- Date Issued: 2007
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