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Description
Cubic boron nitride (c-BN), hexagonal boron nitride (h-BN), and semiconducting diamond all have physical properties that make them ideal materials for applications in high power and high frequency electronics, as well as radiation detectors. However, there is limited research on the unique properties and growth of c-BN or h-BN thin films. This dissertation addresses the deposition of c-BN via plasma enhanced chemical vapor deposition (PECVD) on boron doped diamond substrates. In-Situ X-ray photoelectron spectroscopy (XPS) is used to characterize the thickness and hexagonal to cubic ratio of boron nitride thin films. The effects of hydrogen concentration during the deposition of boron nitride are investigated. The boron nitride deposition rate is found to be dependent on the hydrogen gas flow. The sp2 to sp3 bonding is also found to be dependent on the hydrogen gas flow. Preferential growth of h-BN is observed when an excess of hydrogen is supplied to the reaction, while h-BN growth is suppressed when hydrogen flow is reduced to be the limiting reactant. Reduced hydrogen flow is also observed to promote preferential growth of c-BN.
The hydrogen limited reaction is used to deposit c-BN on single crystal (100) boron-doped diamond substrates. In-situ ultra-violet photoelectron spectroscopy (UPS) and XPS are used to deduce the valence band offset of the diamond/c-BN interface. A valence band offset of -0.3 eV is measured with the diamond VBM above the VBM of c-BN. This value is then discussed in context of previous experimental results and theoretical calculations.
Finally, UPS and XPS are used to characterize the surface states of phosphorus-doped diamond. Variations within the processing parameters for surface preparation and the effects on the electronic surface states are presented and discussed.
ContributorsBrown, Jesse (Author) / Nemanich, Robert J (Thesis advisor) / Alarcon, Ricardo (Committee member) / Lindsay, Stuart (Committee member) / Zaniewski, Anna (Committee member) / Arizona State University (Publisher)
Created2021
Description
This work correlates microscopic material changes to short- and long-term performance in modern, Cu-doped, CdTe-based solar cells. Past research on short- and long-term performance emphasized the device-scale impact of Cu, but neglected the microscopic impact of the other chemical species in the system (e.g., Se, Cl, Cu), their distributions, their local atomic environments, or their interactions/reactions. Additionally, technological limitations precluded nanoscale measurements of the Cu distributions in the cell, and microscale measurements of the material properties (i.e. composition, microstructure, charge transport) as the cell operates. This research aims to answer (1) what is the spatial distribution of Cu in the cell, (2) how does its distribution and local environment correlate with cell performance, and (3) how do local material properties change as the cell operates? This work employs a multi-scale, multi-modal, correlative-measurement approach to elucidate microscopic mechanisms. Several analytical techniques are used – including and especially correlative synchrotron X-ray microscopy – and a unique state-of-the-art instrument was developed to access the dynamics of microscopic mechanisms as they proceed. The work shows Cu segregates around CdTe grain boundaries, and Cu-related acceptor penetration into the CdTe layer is crucial for well-performing cells. After long-term operation, the work presents strong evidence of Se migration into the CdTe layer. This redistribution correlates with microstructural changes in the CdTe layer and limited charge transport around the metal-CdTe interface. Finally, the work correlates changes in microstructure, Cu atomic environment, and charge collection as a cell operates. The results suggest that, as the cell ages, a change to Cu local environment limits charge transport through the metal-CdTe interface, and this change could be influenced by Se migration into the CdTe layer of the cell.
ContributorsWalker, Trumann (Author) / Bertoni, Mariana I (Thesis advisor) / Holman, Zachary (Committee member) / Chan, Candace (Committee member) / Colegrove, Eric (Committee member) / Arizona State University (Publisher)
Created2022
Description
Cubic boron nitride (c-BN) has potential for electronic applications as an electron emitter and serving as a base material for diodes, transistors, etc. However, there has been limited research on c-BN reported, and many of the electronic properties of c-BN and c-BN interfaces have yet to be reported. This dissertation focused on probing thin film c-BN deposited via plasma enhanced chemical vapor deposition (PECVD) with in situ photoelectron spectroscopy (PES). PES measurements were used to characterize the electronic properties of c-BN films and interfaces with vacuum and diamond. First, the interface between c-BN and vacuum were characterized with ultraviolet PES (UPS). UPS measurements indicated that as-deposited c-BN, H2 plasma treated c-BN, and annealed c-BN post H2 plasma treatment exhibited negative electron affinity surfaces. A dipole model suggested dipoles from H-terminated N surface sites were found to be responsible for the NEA surface. Then, Si was introduced into c-BN films to realize n-type doped c-BN. The valence structure and work function of c-BN:Si films were characterized with XPS and UPS measurements. Measurements were unable to confirm n-type character, and it is concluded that silicon nitride formation was the primary effect for the observations. Finally, XPS measurements were employed to measure the band offsets at the c-BN/diamond interface. Measurements indicated the valence band maximum (VBM) of c-BN was positioned ~0.8 eV above the VBM of diamond.
ContributorsShammas, Joseph (Author) / Nemanich, Robert J (Thesis advisor) / Ponce, Fernando (Committee member) / Chen, Tingyong (Committee member) / Chamberlin, Ralph (Committee member) / Arizona State University (Publisher)
Created2016
Description
Nanoscale semiconductors with their unique properties and potential applications have been a focus of extensive research in recent years. There are many ways in which semiconductors change the world with computers, cell phones, and solar panels, and nanoscale semiconductors having a promising potential to expand the efficiency, reduce the cost, and improve the flexibility and durability of their design. In this study, theoretical quantum mechanical simulations were performed on several different nanoscale semiconductor materials, including graphene/phosphorene nanoribbons and group III-V nanowires. First principles density functional theory (DFT) was used to study the electronic and structural properties of these nanomaterials in their fully relaxed and strained states. The electronic band gap, effective masses of charge carriers, electronic orbitals, and density of states were most commonly examined with strain, both from intrinsic and external sources. For example, armchair graphene nanoribbons (AGNR) were found to have unprecedented band gap-strain dependence. Phosphorene nanoribbons (PNRs) demonstrate a different behavior, including a chemical scissors effect, and studies revealed a strong relationship between passivation species and band gap tunability. Unlike the super mechanical flexibility of AGNRs and PNRs which can sustain incredible strain, modest yet large strain was applied to group III-V nanowires such as GaAs/InAs. The calculations showed that a direct and indirect band gap transition occurs at some critical strains and the origination of these gap transitions were explored in detail. In addition to the pure nanowires, GaAs/InAs core/shell heterostructure nanowires were also studied. Due to the lattice mismatch between GaAs and InAs, the intrinsic strain in the core/shell nanowires demonstrates an interesting behavior on tuning the electronic properties. This interesting behavior suggests a mechanical way to exert compressive strain on nanowires experimentally, and can create a finite quantum confinement effect on the core.
ContributorsCopple, Andrew (Author) / Peng, Xihong (Thesis advisor) / Chan, Candace (Committee member) / Chizmeshya, Andrew (Committee member) / Ponce, Fernando (Committee member) / Arizona State University (Publisher)
Created2016
Description
In this dissertation, the interface chemistry and electronic structure of plasma-enhanced atomic layer deposited (PEALD) dielectrics on GaN are investigated with x-ray and ultraviolet photoemission spectroscopy (XPS and UPS). Three interrelated issues are discussed in this study: (1) PEALD dielectric growth process optimization, (2) interface electronic structure of comparative PEALD dielectrics on GaN, and (3) interface electronic structure of PEALD dielectrics on Ga- and N-face GaN. The first study involved an in-depth case study of PEALD Al2O3 growth using dimethylaluminum isopropoxide, with a special focus on oxygen plasma effects. Saturated and self-limiting growth of Al2O3 films were obtained with an enhanced growth rate within the PEALD temperature window (25-220 ºC). The properties of Al2O3 deposited at various temperatures were characterized to better understand the relation between the growth parameters and film properties. In the second study, the interface electronic structures of PEALD dielectrics on Ga-face GaN films were measured. Five promising dielectrics (Al2O3, HfO2, SiO2, La2O3, and ZnO) with a range of band gap energies were chosen. Prior to dielectric growth, a combined wet chemical and in-situ H2/N2 plasma clean process was employed to remove the carbon contamination and prepare the surface for dielectric deposition. The surface band bending and band offsets were measured by XPS and UPS for dielectrics on GaN. The trends of the experimental band offsets on GaN were related to the dielectric band gap energies. In addition, the experimental band offsets were near the calculated values based on the charge neutrality level model. The third study focused on the effect of the polarization bound charge of the Ga- and N-face GaN on interface electronic structures. A surface pretreatment process consisting of a NH4OH wet chemical and an in-situ NH3 plasma treatment was applied to remove carbon contamination, retain monolayer oxygen coverage, and potentially passivate N-vacancy related defects. The surface band bending and polarization charge compensation of Ga- and N-face GaN were investigated. The surface band bending and band offsets were determined for Al2O3, HfO2, and SiO2 on Ga- and N-face GaN. Different dielectric thicknesses and post deposition processing were investigated to understand process related defect formation and/or reduction.
ContributorsYang, Jialing (Author) / Nemanich, Robert J (Thesis advisor) / Chen, Tingyong (Committee member) / Peng, Xihong (Committee member) / Ponce, Fernando (Committee member) / Smith, David (Committee member) / Arizona State University (Publisher)
Created2014
Description
GaN and AlGaN have shown great potential in next-generation power and RF electronics. However, these devices are limited by reliability issues such as leakage current and current collapse that result from surface and interface states on GaN and AlGaN. This dissertation, therefore, examined these electronic states, focusing on the following two points:
First, the surface electronic state configuration was examined with regards to the polarization bound 1013 charges/cm2 that increases with aluminum content. This large bound charge requires compensation either externally by surface states or internally by the space charge regions as relates to band bending. In this work, band bending was measured after different surface treatments of GaN and AlGaN to determine the effects of specific surface states on the electronic state configuration. Results showed oxygen-terminated N-face GaN, Ga-face GaN, and Ga-face Al0.25Ga0.75N surface were characterized by similar band bending regardless of the polarization bound charge, suggesting a Fermi level pinning state ~0.4-0.8 eV below the conduction band minimum. On oxygen-free Ga-face GaN, Al0.15Ga0.85N, Al0.25Ga0.75N, and Al0.35Ga0.65N, band bending increased slightly with aluminum content and thus did not exhibit the same pinning behavior; however, there was still significant compensating charge on these surfaces (~1013 charges/cm2). This charge is likely related to nitrogen vacancies and/or gallium dangling bonds.
In addition, this wozrk investigated the interface electronic state configuration of dielectric/GaN and AlGaN interfaces with regards to deposition conditions and aluminum content. Specifically, oxygen plasma-enhanced atomic layer deposited (PEALD) was used to deposit SiO2. Growth temperature was shown to influence the film quality, where room temperature deposition produced the highest quality films in terms of electrical breakdown. In addition, the valence band offsets (VBOs) appeared to decrease with the deposition temperature, which likely related to an electric field across the Ga2O3 interfacial layer. VBOs were also determined with respect to aluminum content at the PEALD-SiO2/AlxGa1-xN interface, giving 3.0, 2.9, 2.9, and 2.8 eV for 0%, 15%, 25%, and 35% aluminum content, respectively—with corresponding conduction band offsets of 2.5, 2.2, 1.9, and 1.8 eV. This suggests the largest difference manifests in the conduction band, which is in agreement with the charge neutrality level model.
First, the surface electronic state configuration was examined with regards to the polarization bound 1013 charges/cm2 that increases with aluminum content. This large bound charge requires compensation either externally by surface states or internally by the space charge regions as relates to band bending. In this work, band bending was measured after different surface treatments of GaN and AlGaN to determine the effects of specific surface states on the electronic state configuration. Results showed oxygen-terminated N-face GaN, Ga-face GaN, and Ga-face Al0.25Ga0.75N surface were characterized by similar band bending regardless of the polarization bound charge, suggesting a Fermi level pinning state ~0.4-0.8 eV below the conduction band minimum. On oxygen-free Ga-face GaN, Al0.15Ga0.85N, Al0.25Ga0.75N, and Al0.35Ga0.65N, band bending increased slightly with aluminum content and thus did not exhibit the same pinning behavior; however, there was still significant compensating charge on these surfaces (~1013 charges/cm2). This charge is likely related to nitrogen vacancies and/or gallium dangling bonds.
In addition, this wozrk investigated the interface electronic state configuration of dielectric/GaN and AlGaN interfaces with regards to deposition conditions and aluminum content. Specifically, oxygen plasma-enhanced atomic layer deposited (PEALD) was used to deposit SiO2. Growth temperature was shown to influence the film quality, where room temperature deposition produced the highest quality films in terms of electrical breakdown. In addition, the valence band offsets (VBOs) appeared to decrease with the deposition temperature, which likely related to an electric field across the Ga2O3 interfacial layer. VBOs were also determined with respect to aluminum content at the PEALD-SiO2/AlxGa1-xN interface, giving 3.0, 2.9, 2.9, and 2.8 eV for 0%, 15%, 25%, and 35% aluminum content, respectively—with corresponding conduction band offsets of 2.5, 2.2, 1.9, and 1.8 eV. This suggests the largest difference manifests in the conduction band, which is in agreement with the charge neutrality level model.
ContributorsEller, Brianna (Author) / Nemanich, Robert J (Thesis advisor) / Chowdhury, Srabanti (Committee member) / McCartney, Martha (Committee member) / Ponce, Fernando (Committee member) / Smith, David (Committee member) / Arizona State University (Publisher)
Created2015
In-situ photoemission spectroscopy characterization of electronic states in semiconductor interfaces
Description
The electronic states of semiconductor interfaces have significant importance for semiconductor device performance, especially due to the continuing miniaturization of device technology.
The application of ultra high vacuum (UHV) enables the preparation and characterization of fresh and cleaned interfaces. In a UHV environment, photoemission spectroscopy (PES) provides a non-destructive method to measure the electronic band structure, which is a crucial component of interface properties.
In this dissertation, three semiconductor interfaces were studies to understand different effects on electronic states. The interfaces studied were freshly grown or pre-treated under UHV. Then in-situ PES measurements, including x-ray photoemission spectroscopy (XPS) and ultra-violet photoemission spectroscopy (UPS), were conducted to obtain electronic states information.
First, the CdTe/InSb (100) heterointerface was employed as a model interface for II-VI and III-V heterojunctions. It was suggested that an interface layer formed, which consisted of In-Te bonding. The non-octal bonding between In and Te atoms has donor-like behavior, which was proposed to result in an electron accumulation layer in InSb. A type-I heterointerface was observed. Second, Cu/ZnO interfaces were studied to understand the interface bonding and the role of polarization on ZnO interfaces. It was shown that on O-face ZnO (0001) and PEALD ZnO, copper contacts had ohmic behavior. However, on Zn-face ZnO (0001), a 0.3 eV Schottky barrier height was observed. The lower than expected barrier heights were attributed to oxygen vacancies introduced by Cu-O bonding during interface formation. In addition, it is suggested that the different barrier heights on two sides of ZnO (0001) are caused by the different behavior for the ZnO (0001) faces. Last, a pulse mode deposition method was applied for P-doped diamond growth on (100) diamond surfaces. Pretreatment effects were studied. It is suggested that an O/H plasma treatment or a short period of H-plasma and CH4/H2 plasma could yield a higher growth rate. PES measurements were conducted on H-terminated intrinsic diamond surface and P-doped/intrinsic diamond (100) interfaces. It was suggested that electronic states near the valence band maximum caused Fermi level pinning effects, independent of the diamond doping.
The application of ultra high vacuum (UHV) enables the preparation and characterization of fresh and cleaned interfaces. In a UHV environment, photoemission spectroscopy (PES) provides a non-destructive method to measure the electronic band structure, which is a crucial component of interface properties.
In this dissertation, three semiconductor interfaces were studies to understand different effects on electronic states. The interfaces studied were freshly grown or pre-treated under UHV. Then in-situ PES measurements, including x-ray photoemission spectroscopy (XPS) and ultra-violet photoemission spectroscopy (UPS), were conducted to obtain electronic states information.
First, the CdTe/InSb (100) heterointerface was employed as a model interface for II-VI and III-V heterojunctions. It was suggested that an interface layer formed, which consisted of In-Te bonding. The non-octal bonding between In and Te atoms has donor-like behavior, which was proposed to result in an electron accumulation layer in InSb. A type-I heterointerface was observed. Second, Cu/ZnO interfaces were studied to understand the interface bonding and the role of polarization on ZnO interfaces. It was shown that on O-face ZnO (0001) and PEALD ZnO, copper contacts had ohmic behavior. However, on Zn-face ZnO (0001), a 0.3 eV Schottky barrier height was observed. The lower than expected barrier heights were attributed to oxygen vacancies introduced by Cu-O bonding during interface formation. In addition, it is suggested that the different barrier heights on two sides of ZnO (0001) are caused by the different behavior for the ZnO (0001) faces. Last, a pulse mode deposition method was applied for P-doped diamond growth on (100) diamond surfaces. Pretreatment effects were studied. It is suggested that an O/H plasma treatment or a short period of H-plasma and CH4/H2 plasma could yield a higher growth rate. PES measurements were conducted on H-terminated intrinsic diamond surface and P-doped/intrinsic diamond (100) interfaces. It was suggested that electronic states near the valence band maximum caused Fermi level pinning effects, independent of the diamond doping.
ContributorsWang, Xingye (Author) / Nemanich, Robert J (Thesis advisor) / Chan, Candace (Committee member) / Ponce, Fernando (Committee member) / Holman, Zachary (Committee member) / Arizona State University (Publisher)
Created2018