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Research and Development of Electrical Contacts to β-Ga2O3 for Power Electronics and UV Photodetectors.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Research and Development of Electrical Contacts to β-Ga2O3 for Power Electronics and UV Photodetectors./
Author:	Lyle, Luke Andrew McClure.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2020,
Description:	168 p.
Notes:	Source: Dissertations Abstracts International, Volume: 82-04, Section: B.
Contained By:	Dissertations Abstracts International82-04B.
Subject:	Materials science. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28094822
ISBN:	9798672190396

Research and Development of Electrical Contacts to β-Ga2O3 for Power Electronics and UV Photodetectors.
Lyle, Luke Andrew McClure.

Research and Development of Electrical Contacts to β-Ga2O3 for Power Electronics and UV Photodetectors. - Ann Arbor : ProQuest Dissertations & Theses, 2020 - 168 p.

Source: Dissertations Abstracts International, Volume: 82-04, Section: B.

Thesis (Ph.D.)--Carnegie Mellon University, 2020.

This item must not be sold to any third party vendors.

Over the past decade beta-gallium oxide (β-Ga2O3) has accrued considerable interest due to its ultrawide bandgap of around 4.6 eV, superior figure of merit for numerous electronic and optoelectronic applications, a wide range of n-type dopants (Sn, Si, Ge) and the ability to produce single-crystal melt-grown substrates. Considering these factors, β-Ga2O3 has been primarily pursued for applications as high-power electronics and UV photodetectors. Understanding the electrical properties of Schottky and ohmic contacts on β-Ga2O3is crucial to developing high-power electronic devices.We examine the electronic behavior of Ti/Au, Mo, Co, Ni, Pd, and Au Schottky contacts on n-type, Czrochralski-grown (100) β-Ga2O3 substrates. J-V (Current Density-Voltage) measurements of these diodes yield nearly ideal diodes (n≤1.15) in the case of Ti/Au, Mo, Co, and Ni diodes and Schottky barrier heights ranging from 0.56 eV to 1.42 eV. C-V (Capacitance-Voltage) measurements of these diodes reveals Schottky barriers heights ranging from 0.70 eV to 1.98 eV. Further, J-V-T (Current Density-Voltage-Temperature) measurements have been performed on Ti/Au, Co, and Pd diodes revealing inhomogenous barriers well fit by a model proposed by Werner et al. [1] and yielding Schottky barrier heights of 0.81, 1.35 and 2.23 eV, respectively with the dominant current transport mechanism being thermionic emission. Corresponding σ0 values of the proposed spatial Gaussian distribution of the barrier is obtained to be 92, 72, and 197 meV for Ti/Au, Co, and Pd, respectively. The voltage dependence of the Schottky barrier height and standard deviation of the distribution of Schottky barrier heights are expressed by ρ2 and ρ3 parameters of 0.23, 0.1, and 0.12 and-19, -5, and -21 meV for Ti/Au, Co, and Pd, respectively. Our results indicate the index of surface behavior on the (100) orientation of β-Ga2O3 for J-V and C-V is 0.58, and 0.99, respectively, a near total agreement with the Schottky-Mott rule. This is in stark contrast with the ( ̄201) and (010) orientations.In addition to Schottky contacts another critical piece of development for β-Ga2O3 is the fabrication of low-resistance ohmic contacts. Ti/Au metallization coupled with an anneal between 400-500◦C is a common ohmic contact for β-Ga2O3. Chemical and electrical analysis of Au/Ti/(010) β-Ga2O3 and Au/Ti/(001) β-Ga2O3 contacts is performed as a function of annealing temperature with x-ray photoelectron spectroscopy (XPS), Current-Voltage (I-V), and Capacitance-Voltage (C-V) measurements. XPS analysis of the Ti 2p spectra reveals stark differences on the amount of Ti oxidation in the as-deposited state, with the (001) exhibiting significantly more oxidized Ti. The Schottky barrier height from I-V and C-V measurements as a function of annealing temperature exhibited near ideal (~1.1) diodes in the as-deposited case. The I-V and C-V determined barrier heights for the Ti/Au/(010) β-Ga2O3 contacts changed from 0.64 to 0.68 eV and 0.82 to 0.90 eV in the as-deposited case to after an anneal at150◦C whereas the I-V and C-V determined barrier heights for the Ti/Au/(001) β-Ga2O3 contacts changed from 0.49 to 0.40 eV and 0.83 to 0.46 eV in the as-deposited case to after an anneal at 250◦C.In addition to its use as a material for high-power devices, β-Ga2O3 has also been demonstrated as the active material in solar-blind UV photodetectors, which are coveted by numerous industries and the military for applications ranging from flame- and missile-plume detection to ozone hole monitoring. Nanocrystalline β-(AlxGa1−x)2O3, β-Ga2O3, and β-(InxGa1−x)2O3 epitaxial films were grown on (0001) sapphire substrates using metalorganic chemical vapor deposition (MOCVD). The films were grown between temperatures of 600-800◦C using triethylgallium and oxygen with trimethylaluminum/trimethylindium for Al/In incorporation. The films were characterized structurally with x-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM), optically with UV-visible spectroscopy (UV-vis) and chemically using energy dispersive x-ray spectroscopy (EDX) and x-ray photoelectron spectroscopy(XPS). Based on XRD and EDX/XPS results the epitaxial films were grown with compositions xAl= 0.57 and 0.76 (for Al) and xIn= 0.12 and 0.21 (for In). The optical bandgap was found to correspondingly vary between 6.0±0.2 and 3.9±0.1 eV, as a function of composition. Schottky- and MSM-based solar-blindUV photodetectors were fabricated on selected films and showed responsivities varying from>104A/W at 20V for the Ga2O3 films, >103A/W at 20V for the (AlxGa1−x)2O3films and >102A/W at 20V for the (InxGa1−x)2O3 films. Time response measurements on Schottky and MSM detectors reveal rise and dwell times on the order of a minute, indicating the strong presence of photoconductive gain. Noise-equivalent-powers (NEP) of are obtained in the fW-pW regime with specific detectivities (D*) of Schottky and MSM detectors between 1010-1012Jones.

ISBN: 9798672190396Subjects--Topical Terms:

543314
Materials science.
Subjects--Index Terms:

Gallium oxide

Research and Development of Electrical Contacts to β-Ga2O3 for Power Electronics and UV Photodetectors.
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500 $a Source: Dissertations Abstracts International, Volume: 82-04, Section: B.
500 $a Advisor: Porter, Lisa M.
502 $a Thesis (Ph.D.)--Carnegie Mellon University, 2020.
506 $a This item must not be sold to any third party vendors.
520 $a Over the past decade beta-gallium oxide (β-Ga2O3) has accrued considerable interest due to its ultrawide bandgap of around 4.6 eV, superior figure of merit for numerous electronic and optoelectronic applications, a wide range of n-type dopants (Sn, Si, Ge) and the ability to produce single-crystal melt-grown substrates. Considering these factors, β-Ga2O3 has been primarily pursued for applications as high-power electronics and UV photodetectors. Understanding the electrical properties of Schottky and ohmic contacts on β-Ga2O3is crucial to developing high-power electronic devices.We examine the electronic behavior of Ti/Au, Mo, Co, Ni, Pd, and Au Schottky contacts on n-type, Czrochralski-grown (100) β-Ga2O3 substrates. J-V (Current Density-Voltage) measurements of these diodes yield nearly ideal diodes (n≤1.15) in the case of Ti/Au, Mo, Co, and Ni diodes and Schottky barrier heights ranging from 0.56 eV to 1.42 eV. C-V (Capacitance-Voltage) measurements of these diodes reveals Schottky barriers heights ranging from 0.70 eV to 1.98 eV. Further, J-V-T (Current Density-Voltage-Temperature) measurements have been performed on Ti/Au, Co, and Pd diodes revealing inhomogenous barriers well fit by a model proposed by Werner et al. [1] and yielding Schottky barrier heights of 0.81, 1.35 and 2.23 eV, respectively with the dominant current transport mechanism being thermionic emission. Corresponding σ0 values of the proposed spatial Gaussian distribution of the barrier is obtained to be 92, 72, and 197 meV for Ti/Au, Co, and Pd, respectively. The voltage dependence of the Schottky barrier height and standard deviation of the distribution of Schottky barrier heights are expressed by ρ2 and ρ3 parameters of 0.23, 0.1, and 0.12 and-19, -5, and -21 meV for Ti/Au, Co, and Pd, respectively. Our results indicate the index of surface behavior on the (100) orientation of β-Ga2O3 for J-V and C-V is 0.58, and 0.99, respectively, a near total agreement with the Schottky-Mott rule. This is in stark contrast with the ( ̄201) and (010) orientations.In addition to Schottky contacts another critical piece of development for β-Ga2O3 is the fabrication of low-resistance ohmic contacts. Ti/Au metallization coupled with an anneal between 400-500◦C is a common ohmic contact for β-Ga2O3. Chemical and electrical analysis of Au/Ti/(010) β-Ga2O3 and Au/Ti/(001) β-Ga2O3 contacts is performed as a function of annealing temperature with x-ray photoelectron spectroscopy (XPS), Current-Voltage (I-V), and Capacitance-Voltage (C-V) measurements. XPS analysis of the Ti 2p spectra reveals stark differences on the amount of Ti oxidation in the as-deposited state, with the (001) exhibiting significantly more oxidized Ti. The Schottky barrier height from I-V and C-V measurements as a function of annealing temperature exhibited near ideal (~1.1) diodes in the as-deposited case. The I-V and C-V determined barrier heights for the Ti/Au/(010) β-Ga2O3 contacts changed from 0.64 to 0.68 eV and 0.82 to 0.90 eV in the as-deposited case to after an anneal at150◦C whereas the I-V and C-V determined barrier heights for the Ti/Au/(001) β-Ga2O3 contacts changed from 0.49 to 0.40 eV and 0.83 to 0.46 eV in the as-deposited case to after an anneal at 250◦C.In addition to its use as a material for high-power devices, β-Ga2O3 has also been demonstrated as the active material in solar-blind UV photodetectors, which are coveted by numerous industries and the military for applications ranging from flame- and missile-plume detection to ozone hole monitoring. Nanocrystalline β-(AlxGa1−x)2O3, β-Ga2O3, and β-(InxGa1−x)2O3 epitaxial films were grown on (0001) sapphire substrates using metalorganic chemical vapor deposition (MOCVD). The films were grown between temperatures of 600-800◦C using triethylgallium and oxygen with trimethylaluminum/trimethylindium for Al/In incorporation. The films were characterized structurally with x-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM), optically with UV-visible spectroscopy (UV-vis) and chemically using energy dispersive x-ray spectroscopy (EDX) and x-ray photoelectron spectroscopy(XPS). Based on XRD and EDX/XPS results the epitaxial films were grown with compositions xAl= 0.57 and 0.76 (for Al) and xIn= 0.12 and 0.21 (for In). The optical bandgap was found to correspondingly vary between 6.0±0.2 and 3.9±0.1 eV, as a function of composition. Schottky- and MSM-based solar-blindUV photodetectors were fabricated on selected films and showed responsivities varying from>104A/W at 20V for the Ga2O3 films, >103A/W at 20V for the (AlxGa1−x)2O3films and >102A/W at 20V for the (InxGa1−x)2O3 films. Time response measurements on Schottky and MSM detectors reveal rise and dwell times on the order of a minute, indicating the strong presence of photoconductive gain. Noise-equivalent-powers (NEP) of are obtained in the fW-pW regime with specific detectivities (D*) of Schottky and MSM detectors between 1010-1012Jones.
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