Atmospheric pressure metal-organic vapour phase epitaxial growth of InAs/GaSb strained layer superlattices
- Authors: Miya, Senzo Simo
- Date: 2013
- Subjects: Gallium arsenide semiconductors , Organometallic compounds , Compound semiconductors , Metal organic chemical vapor deposition , Superlattices as materials , Epitaxy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10557 , http://hdl.handle.net/10948/d1020866
- Description: The importance of infrared (IR) technology (for detection in the 3-5 μm and 8-14 μm atmospheric windows) has spread from military applications to civilian applications since World War II. The commercial IR detector market in these wavelength ranges is dominated by mercury cadmium telluride (MCT) alloys. The use of these alloys has, however, been faced with technological difficulties. One of the materials that have been tipped to be suitable to replace MCT is InAs/InxGa1-xSb strained layer superlattices (SLS’s). Atmospheric pressure metal-organic vapour phase epitaxy (MOVPE) has been used to grow InAs/GaSb strained layer superlattices (SLS’s) at 510 °C in this study. This is a starting point towards the development of MOVPE InAs/InxGa1-xSb SLS’s using the same system. Before the SLS’s could be attempted, the growth parameters for GaSb were optimised. Growth parameters for InAs were taken from reports on previous studies conducted using the same reactor. Initially, trimethylgallium, a source that has been used extensively in the same growth system for the growth of GaSb and InxGa1-xSb was intended to be used for gallium species. The high growth rates yielded by this source were too large for the growth of SLS structures, however. Thus, triethylgallium (rarely used for atmospheric pressure MOVPE) was utilized. GaSb layers (between 1 and 2 μm thick) were grown at two different temperatures (550 °C and 510 °C) with a varying V/III ratio. A V/III ratio of 1.5 was found to be optimal at 550 °C. However, the low incorporation efficiency of indium into GaSb at this temperature was inadequate to obtain InxGa1-xSb with an indium mole fraction (x) of around 0.3, which had previously been reported to be optimal for the performance of InAs/InxGa1-xSb SLS’s, due to the maximum splitting of the valence mini bands for this composition. The growth temperature was thus lowered to 510 °C. This resulted in an increase in the optimum V/III ratio to 1.75 for GaSb and yielded much higher incorporation efficiencies of indium in InxGa1-xSb. However, this lower growth temperature also produced poorer surface morphologies for both the binary and ternary layers, due to the reduced surface diffusion of the adsorbed species. An interface control study during the growth of InAs/GaSb SLS’s was subsequently conducted, by investigating the influence of different gas switching sequences on the interface type and quality. It was noted that the growth of SLS’s without any growth interruptions at the interfaces leads to tensile strained SLS’s (GaAs-like interfaces) with a rather large lattice mismatch. A 5 second flow of TMSb over the InAs surface and a flow of H2 over GaSb surface yielded compressively strained SLS’s. Flowing TMIn for 1 second and following by a flow of TMSb for 4 seconds over the GaSb surface, while flowing H2 for 5 seconds over the InAs surface, resulted in SLS’s with GaAs-like interfacial layers and a reduced lattice mismatch. Temperature gradients across the surface of the susceptor led to SLS’s with different structural quality. High resolution x-ray diffraction (HRXRD) was used to determine the thicknesses as well as the type of interfacial layers. The physical parameters of the SLS’s obtained from simulating the HRXRD spectra were comparable to the parameters obtained from cross sectional transmission electron microscopy (XTEM) images. The thicknesses of the layers and the interface type played a major role in determining the cut-off wavelength of the SLS’s.
- Full Text:
- Date Issued: 2013
- Authors: Miya, Senzo Simo
- Date: 2013
- Subjects: Gallium arsenide semiconductors , Organometallic compounds , Compound semiconductors , Metal organic chemical vapor deposition , Superlattices as materials , Epitaxy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10557 , http://hdl.handle.net/10948/d1020866
- Description: The importance of infrared (IR) technology (for detection in the 3-5 μm and 8-14 μm atmospheric windows) has spread from military applications to civilian applications since World War II. The commercial IR detector market in these wavelength ranges is dominated by mercury cadmium telluride (MCT) alloys. The use of these alloys has, however, been faced with technological difficulties. One of the materials that have been tipped to be suitable to replace MCT is InAs/InxGa1-xSb strained layer superlattices (SLS’s). Atmospheric pressure metal-organic vapour phase epitaxy (MOVPE) has been used to grow InAs/GaSb strained layer superlattices (SLS’s) at 510 °C in this study. This is a starting point towards the development of MOVPE InAs/InxGa1-xSb SLS’s using the same system. Before the SLS’s could be attempted, the growth parameters for GaSb were optimised. Growth parameters for InAs were taken from reports on previous studies conducted using the same reactor. Initially, trimethylgallium, a source that has been used extensively in the same growth system for the growth of GaSb and InxGa1-xSb was intended to be used for gallium species. The high growth rates yielded by this source were too large for the growth of SLS structures, however. Thus, triethylgallium (rarely used for atmospheric pressure MOVPE) was utilized. GaSb layers (between 1 and 2 μm thick) were grown at two different temperatures (550 °C and 510 °C) with a varying V/III ratio. A V/III ratio of 1.5 was found to be optimal at 550 °C. However, the low incorporation efficiency of indium into GaSb at this temperature was inadequate to obtain InxGa1-xSb with an indium mole fraction (x) of around 0.3, which had previously been reported to be optimal for the performance of InAs/InxGa1-xSb SLS’s, due to the maximum splitting of the valence mini bands for this composition. The growth temperature was thus lowered to 510 °C. This resulted in an increase in the optimum V/III ratio to 1.75 for GaSb and yielded much higher incorporation efficiencies of indium in InxGa1-xSb. However, this lower growth temperature also produced poorer surface morphologies for both the binary and ternary layers, due to the reduced surface diffusion of the adsorbed species. An interface control study during the growth of InAs/GaSb SLS’s was subsequently conducted, by investigating the influence of different gas switching sequences on the interface type and quality. It was noted that the growth of SLS’s without any growth interruptions at the interfaces leads to tensile strained SLS’s (GaAs-like interfaces) with a rather large lattice mismatch. A 5 second flow of TMSb over the InAs surface and a flow of H2 over GaSb surface yielded compressively strained SLS’s. Flowing TMIn for 1 second and following by a flow of TMSb for 4 seconds over the GaSb surface, while flowing H2 for 5 seconds over the InAs surface, resulted in SLS’s with GaAs-like interfacial layers and a reduced lattice mismatch. Temperature gradients across the surface of the susceptor led to SLS’s with different structural quality. High resolution x-ray diffraction (HRXRD) was used to determine the thicknesses as well as the type of interfacial layers. The physical parameters of the SLS’s obtained from simulating the HRXRD spectra were comparable to the parameters obtained from cross sectional transmission electron microscopy (XTEM) images. The thicknesses of the layers and the interface type played a major role in determining the cut-off wavelength of the SLS’s.
- Full Text:
- Date Issued: 2013
Management of political behaviour in organisations
- Authors: Pio, Riaan Johan
- Date: 2000
- Subjects: Organizational behavior , Corporate culture
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10839 , http://hdl.handle.net/10948/33 , Organizational behavior , Corporate culture
- Description: In this research paper, the constructive management of political behaviour in organisations was investigated. A general overview of relevant aspects which specifically relate to the constructive management of political behaviour in the automotive industry was presented. The literature study included a discussion of the nature of political behaviour and guidelines for the management of political behaviour in organisations. The research methodology consisted of three phases: Phase 1: A literature study to determine guidelines to manage political behaviour in organisations constructively. Phase 2: An empirical study to determine the effectiveness of these guidelines in practice by means of a survey amongst role players in the automotive industry in South Africa. Phase 3: The findings from the literature study and empirical study were integrated into guidelines of how managers can manage political behaviour constructively. The study identified nine main strategies for managing political behaviour. They are: Open communication. Communication must be open to keep all parties informed and to prevent distrust. Reduction of uncertainty. This involves preventing employees being unsure of what the future holds. Awareness. The aim of awareness is for managers to be sensitive to and aware of situations that could elicit political behaviours. Furthermore, they must recognize political behaviour for what it is. Setting an example. Managers must set an exemplary example and not engage in political behaviour. An understanding of the reason/motivation for the formation of informal (political) groups or cliques. Having established the reason why political groups form will enable a manager to manage them more effectively. Confront political game players. Managers must address all forms of possible political behaviour in a serious manner. Understanding the organisation’s strategy, goals and action plans. All employees need to know exactly what direction the organization is moving in and what is in it for them. It is management’s task to ensure this open and clear communication, to prevent fears and political behaviour. Tie resource allocation and rewards to strategy. This can be achieved by ensuring that the criteria for the allocation of rewards is straight forward and understood by all. Reward systems must, furthermore, be directly linked to performance. There should also be transparency in decision-making. Isolate resource acquisition from internal operations. It is necessary to clearly specify the conditions and ground rules for the acquisition of resources to ensure that the process is transparent. The conclusion reached is that political behaviour in organizations can be managed constructively to build win-win relationships.
- Full Text:
- Date Issued: 2000
- Authors: Pio, Riaan Johan
- Date: 2000
- Subjects: Organizational behavior , Corporate culture
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10839 , http://hdl.handle.net/10948/33 , Organizational behavior , Corporate culture
- Description: In this research paper, the constructive management of political behaviour in organisations was investigated. A general overview of relevant aspects which specifically relate to the constructive management of political behaviour in the automotive industry was presented. The literature study included a discussion of the nature of political behaviour and guidelines for the management of political behaviour in organisations. The research methodology consisted of three phases: Phase 1: A literature study to determine guidelines to manage political behaviour in organisations constructively. Phase 2: An empirical study to determine the effectiveness of these guidelines in practice by means of a survey amongst role players in the automotive industry in South Africa. Phase 3: The findings from the literature study and empirical study were integrated into guidelines of how managers can manage political behaviour constructively. The study identified nine main strategies for managing political behaviour. They are: Open communication. Communication must be open to keep all parties informed and to prevent distrust. Reduction of uncertainty. This involves preventing employees being unsure of what the future holds. Awareness. The aim of awareness is for managers to be sensitive to and aware of situations that could elicit political behaviours. Furthermore, they must recognize political behaviour for what it is. Setting an example. Managers must set an exemplary example and not engage in political behaviour. An understanding of the reason/motivation for the formation of informal (political) groups or cliques. Having established the reason why political groups form will enable a manager to manage them more effectively. Confront political game players. Managers must address all forms of possible political behaviour in a serious manner. Understanding the organisation’s strategy, goals and action plans. All employees need to know exactly what direction the organization is moving in and what is in it for them. It is management’s task to ensure this open and clear communication, to prevent fears and political behaviour. Tie resource allocation and rewards to strategy. This can be achieved by ensuring that the criteria for the allocation of rewards is straight forward and understood by all. Reward systems must, furthermore, be directly linked to performance. There should also be transparency in decision-making. Isolate resource acquisition from internal operations. It is necessary to clearly specify the conditions and ground rules for the acquisition of resources to ensure that the process is transparent. The conclusion reached is that political behaviour in organizations can be managed constructively to build win-win relationships.
- Full Text:
- Date Issued: 2000
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