Md Rezaul Karim

The Ohio State University

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Hongping Zhao

The Ohio State University

Jinwoo Hwang

The Ohio State University

Menglin Zhu

Massachusetts Institute of Technology

Zixuan Feng

Fujian Agriculture and Forestry University

K. Kash

Case Western Reserve University

Benthara Hewage Dinushi Jayatunga

Case Western Reserve University

A F M Anhar Uddin Bhuiyan

University of Massachusetts Lowell

L. J. Brillson

The Ohio State University

Jared M. Johnson

The Ohio State University

Yuxuan Zhang

The Ohio State University

Cooperative Institutions

The Ohio State University

Wright State University

United States Air Force Research Laboratory

Case Western Reserve University

United States Naval Research Laboratory

University at Buffalo, State University of New York

National Institute of Information and Communications Technology

University of Florida

Wright-Patterson Air Force Base

University of California, Santa Barbara

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Two-step growth of β-Ga2O3 films on (100) diamond via low pressure chemical vapor deposition

Journal of Vacuum Science & Technology A Vacuum Surfaces and Films (2021)

Md Rezaul Karim Zhaoying Chen Zixuan Feng Hsien‐Lien Huang Jared M. Johnson

One of the major challenges in β-Ga2O3-based high power and high frequency devices is anticipated to be related to the low thermal conductivity of the material which is on the order of 10–30 W/m K. The use of diamond (thermal conductivity ∼2000 W/m K) as a substrate can be one effective approach for achieving better thermal management in β-Ga2O3-based devices. In this work, low pressure chemical vapor deposition was used to grow β-Ga2O3 films on (100) oriented, single-crystalline diamond substrates. A two-step growth technique was employed to avoid the oxidation of the diamond surface at high temperatures. From x-ray diffraction measurements, the β-Ga2O3 films grew along the ⟨−201⟩ crystalline axis with the β-Ga2O3 (002) planes rotated by ±24.3–27° with respect to the diamond (111) planes. High-magnification scanning transmission electron microscopy imaging revealed an abrupt β-Ga2O3/diamond interface without any voids which is essential for the high rate of heat transfer across the interface. N-type electrical conductivity was measured in a Si-doped β-Ga2O3 film with 1.4 × 1019 cm−3 electron concentration and ∼3 cm2/V s electron mobility. This work demonstrates the feasibility of heteroepitaxy of β-Ga2O3 films on diamond substrates for potential device design and device fabrication with efficient thermal management.

10.1116/6.0000854

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Citations (21)

Band Structure Engineering Based on InGaN/ZnGeN₂ Heterostructure Quantum Wells for Visible Light Emitters

Crystal Growth & Design (2021)

Md Rezaul Karim Benthara Hewage Dinushi Jayatunga Kaitian Zhang Menglin Zhu Jinwoo Hwang

Band structure engineering based on InGaN/ZnGeN2 heterostructure quantum wells (QWs) is proposed to address the long-standing charge separation challenge in visible light emitters using polar InGaN QWs as active media. A nanometer-scale layer of ZnGeN2 is successfully incorporated in InGaN QWs via metalorganic chemical vapor deposition. Understanding the structural properties of the heterostructure QWs reveals that the growth conditions for the GaN barrier layers play an important role in the QW properties. Specifically, the structural quality of the QWs is improved by increasing the thickness and the growth temperature of the GaN barrier layers. Due to the large band offset at the InGaN/ZnGeN2 heterointerface, the position and thickness of the ZnGeN2 sub-layer within the InGaN QWs determine the potential minima and thus the carrier wave functions in both conduction and valence bands. This work demonstrates the effectiveness of emission wavelength tunability of InGaN/ZnGeN2/InGaN heterostructure QWs via tuning of the ZnGeN2 sub-layer properties. More significantly, the peak emission of InGaN/ZnGeN2/InGaN heterostructure QWs can be extended to longer wavelengths without increasing the In composition or the QW thickness. Results from this work provide a new route for addressing the low quantum efficiency of conventional InGaN QWs emitting at green and longer wavelengths.

Band offset

Barrier layer

Wide-bandgap semiconductor

10.1021/acs.cgd.1c00630

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InGaN-ZnSnN2 Quantum Wells for High Efficiency Light Emitters Beyond Green

Conference on Lasers and Electro-Optics (2018)

Md Rezaul Karim Hongping Zhao

A novel quantum well design based on InGaN-ZnSnN2 structures is promising to address the existing challenge to realize high performance InGaN based visible light emitters emitting beyond green spectral regime (3-order enhancement in spontaneous emission).

Green-light

10.1364/cleo_si.2018.sth3i.2

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Depth-resolved cathodoluminescence and surface photovoltage spectroscopies of gallium vacancies in β-Ga2O3 with neutron irradiation and forming gas anneals

Journal of Vacuum Science & Technology B Nanotechnology and Microelectronics Materials Processing Measurement and Phenomena (2021)

Hantian Gao Shreyas Muralidharan Md Rezaul Karim Lei R. Cao Kevin Leedy

The gallium vacancy is one of the dominant native point defects in β-Ga2O3, one that, together with its complexes, can have a major effect on free carrier densities and transport in this wide bandgap semiconductor. We used a combination of depth-resolved cathodoluminescence spectroscopy and surface photovoltage spectroscopy to identify the optical and energy-level properties of these defects as well as how their defect densities and spatial distributions vary with neutron irradiation and temperature-dependent-forming gas anneals. These studies reveal optical signatures that align closely with theoretical energy-level predictions. Likewise, our optical techniques reveal variations in these defect densities that are consistent with hydrogen passivation of gallium vacancies as a function of temperature and depth from the free Ga2O3 surface. These techniques can help guide the understanding and control of dominant native point defects in Ga2O3.

Cathodoluminescence

Surface Photovoltage

Deep-level transient spectroscopy

Passivation

Wide-bandgap semiconductor

10.1116/6.0001240

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Citations (7)

Low pressure chemical vapor deposition of β-Ga2O3 thin films: Dependence on growth parameters

APL Materials (2018)

Zixuan Feng Md Rezaul Karim Hongping Zhao

Low pressure chemical vapor deposition (LPCVD) has been used to produce high quality β-Ga2O3 materials with controllable n-type doping. In this work, we focus on the studies of key LPCVD growth parameters for β-Ga2O3 thin films, including oxygen/carrier gas flow rates, growth temperature, pressure, and the substrate to Ga crucible distance. These growth parameters play important roles during the LPCVD β-Ga2O3 growth and determine the thin film growth rate, n-type dopant incorporation, and electron mobilities. The dependence of the growth parameters on LPCVD of β-Ga2O3 was carried out on both conventional c-plane sapphire and 6 degree off-axis (toward ⟨11-20⟩ direction) sapphire substrates. To better understand the precursor transport and gas phase reaction process during the LPCVD growth, a numerical model for evaluating the growth rate was developed by using a finite element method and taking into account the gas flow rate, chamber pressure, and chamber geometry. The results from this work can provide guidance for the optimization of the LPCVD growth of β-Ga2O3 with targeted growth rate, surface morphology, doping concentration, and mobility. In addition, β-Ga2O3 grown on off-axis c-sapphire substrates features with faster growth rates with higher electron mobilities within a wide growth window.

Electron Mobility

10.1063/1.5054713

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A Two-Step Growth Pathway for High Sb Incorporation in GaAsSb Nanowires in the Telecommunication Wavelength Range

Scientific Reports (2017)

Estiak Ahmad Md Rezaul Karim Shihab Bin Hafiz C. L. Reynolds Yang Liu

Self-catalyzed growth of axial GaAs1-xSbx nanowire (NW) arrays with bandgap tuning corresponding to the telecommunication wavelength of 1.3 µm poses a challenge, as the growth mechanism for axial configuration is primarily thermodynamically driven by the vapor-liquid-solid growth process. A systematic study carried out on the effects of group V/III beam equivalent (BEP) ratios and substrate temperature (Tsub) on the chemical composition in NWs and NW density revealed the efficacy of a two-step growth temperature sequence (initiating the growth at relatively higher Tsub = 620 °C and then continuing the growth at lower Tsub) as a promising approach for obtaining high-density NWs at higher Sb compositions. The dependence of the Sb composition in the NWs on the growth parameters investigated has been explained by an analytical relationship between the effective vapor composition and NW composition using relevant kinetic parameters. A two-step growth approach along with a gradual variation in Ga-BEP for offsetting the consumption of the droplets has been explored to realize long NWs with homogeneous Sb composition up to 34 at.% and photoluminescence emission reaching 1.3 µm at room temperature.

Atmospheric temperature range

10.1038/s41598-017-09280-4

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Citations (34)

Neutron irradiation and forming gas anneal impact on β-Ga₂O₃ deep level defects

Journal of Physics D Applied Physics (2020)

Hantian Gao Shreyas Muralidharan Md Rezaul Karim Susan White Lei R. Cao

We used depth-resolved cathodoluminescence spectroscopy (DRCLS), absorption spectroscopy, and temperature-dependent Hall effect (TDH) measurements to study the effects of fluence dependent neutron irradiations on deep level defects and the associated changes of electrical properties of β-Ga2O3 grown by low pressure chemical vapor deposition and pulsed laser deposition. DRCLS enabled us to monitor systematic increases of three deep level defects after neutron irradiation which correlated with TDH measurements of significant free carrier removal and mobility decrease. The correlations between defect profiles and electrical property changes vs. irradiation dose link these dominant electrically active native point defects in Ga2O3 with their contributions to free carrier mobility, carrier density, and donor/acceptor depth profiles, further revealing their donor/acceptor electrical behavior and physical nature, consistent with the formation of compensating defects. After irradiation, temperature-dependent forming gas (FG) anneals were performed to reverse the radiation-induced damage and carrier removal. The evolution of defect concentrations with increasing neutron dose and their depth-resolved distributions with FG anneal temperature reveal an interplay between specific defects to control electronic properties.

Neutron irradiation

Forming gas

10.1088/1361-6463/aba92f

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Citations (20)

Experimental determination of the valence band offsets of ZnGeN₂ and (ZnGe)_0.94Ga_0.12N₂ with GaN

Journal of Physics D Applied Physics (2021)

Md Rezaul Karim Brenton A. Noesges Benthara Hewage Dinushi Jayatunga Menglin Zhu Jinwoo Hwang

Abstract A predicted type-II staggered band alignment with an approximately 1.4 eV valence band offset at the ZnGeN 2 /GaN heterointerface has inspired novel band-engineered III-N/ZnGeN 2 heterostructure-based device designs for applications in high performance optoelectronics. We report on the determination of the valence band offset between metalorganic chemical vapor deposition grown (ZnGe) 1− x Ga 2 x N 2 , for x = 0 and 0.06, and GaN using x-ray photoemission spectroscopy. The valence band of ZnGeN 2 was found to lie 1.45–1.65 eV above that of GaN. This result agrees well with the value predicted by first-principles density functional theory calculations using the local density approximation for the potential profile and quasiparticle self-consistent GW calculations of the band edge states relative to the potential. For (ZnGe) 0.94 Ga 0.12 N 2 the value was determined to be 1.29 eV, ∼10%–20% lower than that of ZnGeN 2 . The experimental determination of the large band offset between ZnGeN 2 and GaN provides promising alternative solutions to address challenges faced with pure III-nitride-based structures and devices.

Band offset

10.1088/1361-6463/abee45

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Citations (7)

Metal–Organic Chemical Vapor Deposition Growth of ZnGeN₂ Films on Sapphire

Crystal Growth & Design (2019)

Md Rezaul Karim Benthara Hewage Dinushi Jayatunga Zixuan Feng K. Kash Hongping Zhao

Heterovalent ternary ZnGeN2 thin films were grown on c-, r-, and a-sapphire substrates using metalorganic chemical vapor deposition. The crystal structure of the films was identified by X-ray diffraction spectroscopy. It is consistent with orthorhombic Pna21 assuming perfect ordering of the cations. For a fully disordered cation sublattice, the X-ray diffraction spectra correspond to a wurtzitic crystal. The growth directions were determined to be along the c-axis for the films grown on c- and a-sapphire substrates, and along the orthorhombic [010] axis (wurtzite[112̅0]) for films grown on r-sapphire substrates. The Zn/Ge atomic ratios, determined by energy dispersive X-ray spectroscopy, were observed to decrease as growth temperatures were increased. Growth rates for all substrates decreased by approximately 10% with changes in growth temperatures from 600 to 710 °C. Broad photoluminescence peaks at ∼2.05 eV were observed at room temperature. These are associated with transitions involving deep level defects. Room temperature photoluminescence excitation spectra showed peaks at ∼3.4 eV associated with enhanced absorption near the band gap of the orthorhombic Pna21 phase. Broad tails in the excitation spectra observed to persist to approximately 2.8 eV may be band tailing due to disorder on the cation sublattice. The unintentionally doped films are n-type with carrier concentrations varying from 2 × 1018 cm–3 to 2 × 1019 cm–3, decreasing with the increase in growth temperature. Room temperature Hall mobilities of up to 17 cm2/V·s were obtained.

Orthorhombic crystal system

Wurtzite crystal structure

10.1021/acs.cgd.9b00560

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Citations (20)

Te incorporation in GaAs_1−xSb_xnanowires and p-i-n axial structure

Semiconductor Science and Technology (2016)

Estiak Ahmad Pavan Kumar Kasanaboina Md Rezaul Karim Manish Sharma C. L. Reynolds

We report on in situ Te-doping in GaAs1−xSbx nanowires (NWs) grown via self-assisted molecular beam epitaxy. Enhanced Te incorporation in the NW at higher Te cell temperature was attested by the broadening of the x-ray diffraction peak and the presence of a strong coupled-LO phonon mode in the Raman spectra. Te-doping was estimated from the shift in the coupled-LO phonon mode to be ∼2.0 × 1018/cm3. The surfactant nature of the Te modulated the growth kinetics, which was manifested in an enhanced radial growth rate with improved photoluminescence (PL) characteristics at both room temperature (RT) and 4 K. No noticeable planar defects were observed as ascertained from the high-resolution transmission electron microscopy images and selected-area electron diffraction patterns. Finally, we demonstrate the experimental realization of a GaAs1−xSbx axial p-type/intrinsic/n-type (p-i-n) structure on a Si substrate with Te as the n-type dopant. The GaAs1−xSbx p-i-n NW structures exhibited rectifying current–voltage (I–V) behavior. The dopant concentration and the transport parameters estimated from the PL spectra and I–V curve were found to be in good agreement.

10.1088/0268-1242/31/12/125001

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Citations (17)