skip to main content

This content will become publicly available on June 3, 2023

Title: Electrical properties of α-Ga 2 O 3 films grown by halide vapor phase epitaxy on sapphire with α-Cr 2 O 3 buffers

We report on growth and electrical properties of α-Ga2O3films prepared by halide vapor phase epitaxy (HVPE) at 500 °C on α-Cr2O3buffers predeposited on sapphire by magnetron sputtering. The α-Cr2O3buffers showed a wide microcathodoluminescence (MCL) peak near 350 nm corresponding to the α-Cr2O3bandgap and a sharp MCL line near 700 nm due to the Cr+intracenter transition. Ohmic contacts to Cr2O3were made with both Ti/Au or Ni, producing linear current–voltage ( I– V) characteristics over a wide temperature range with an activation energy of conductivity of ∼75 meV. The sign of thermoelectric power indicated p-type conductivity of the buffers. Sn-doped, 2- μm-thick α-Ga2O3films prepared on this buffer by HVPE showed donor ionization energies of 0.2–0.25 eV, while undoped films were resistive with the Fermi level pinned at ECof 0.3 eV. The I– V and capacitance–voltage ( C– V) characteristics of Ni Schottky diodes on Sn-doped samples using a Cr2O3buffer indicated the presence of two face-to-face junctions, one between n-Ga2O3and p-Cr2O3, the other due to the Ni Schottky diode with n-Ga2O3. The spectral dependence of the photocurrent measured on the structure showed the presence of three major deep traps with optical ionization thresholds near 1.3, 2, and 2.8 eV. Photoinduced current transient spectroscopy spectra of the structures were dominated by more » deep traps with an ionization energy of 0.95 eV. These experiments suggest another pathway to obtain p–n heterojunctions in the α-Ga2O3system.

« less
 ;  ;  ;  ;  ;  ;  ;  ;  ;  ;  ;  ;  
Award ID(s):
Publication Date:
Journal Name:
Journal of Applied Physics
Page Range or eLocation-ID:
Article No. 215701
American Institute of Physics
Sponsoring Org:
National Science Foundation
More Like this
  1. Thick (23 µm) films of κ-Ga 2 O 3 were grown by Halide Vapor Phase Epitaxy (HVPE) on GaN/sapphire templates at 630 °C. X-ray analysis confirmed the formation of single-phase κ-Ga 2 O 3 with half-widths of the high-resolution x-ray diffraction (004), (006), and (008) symmetric reflections of 4.5 arc min and asymmetric (027) reflection of 14 arc min. Orthorhombic κ-Ga 2 O 3 polymorph formation was confirmed from analysis of the Kikuchi diffraction pattern in electron backscattering diffraction. Secondary electron imaging indicated a reasonably flat surface morphology with a few (area density ∼10 3  cm −2 ) approximately circular (diameter ∼50–100 µm) uncoalesced regions, containing κ-Ga 2 O 3 columns with in-plane dimensions and a height of about 10 µm. Micro-cathodoluminescence (MCL) spectra showed a wide 2–3.5 eV band that could be deconvoluted into narrower bands peaked at 2.59, 2.66, 2.86, and 3.12 eV. Ni Schottky diodes prepared on the films showed good rectification but a high series resistance. The films had a thin near-surface region dominated by E c − 0.7 eV deep centers and a deeper region (∼2 µm from the surface) dominated by shallow donors with concentrations of ≤10 16  cm −3 . Photocurrent and photocapacitance spectra showed the presence ofmore »deep compensating acceptors with optical ionization energies of ∼1.35 and 2.3 eV, the latter being close to the energy of one of the MCL bands. Deep level transient spectroscopy revealed deep traps with energies near 0.3, 0.6, 0.7, 0.8, and 1 eV from the conduction band edge. The results show the potential of HVPE to grow very thick κ-Ga 2 O 3 on GaN/sapphire templates.« less
  2. Two-inch diameter α -Ga 2 O 3 films with thickness ∼4 μ m were grown on basal plane sapphire by Halide Vapor Phase Epitaxy (HVPE) and doped with Sn in the top ∼1 μ m from the surface. These films were characterized with High-Resolution X-ray Diffraction (HRXRD), Scanning Electron Microscope (SEM) imaging in the Secondary Electron (SE) and Micro-cathodoluminescence (MCL) modes, contactless sheet resistivity mapping, capacitance-voltage, current-voltage, admittance spectra, and Deep Level Transient Spectroscopy (DLTS) measurements. The edge and screw dislocations densities estimated from HRXRD data were respectively 7.4 × 10 9 cm −2 and 1.5 × 10 7 cm −2 , while the films had a smooth surface with a low density (∼10 3 cm −2 ) of circular openings with diameters between 10 and 100 μ m. The sheet resistivity of the films varied over the entire 2-inch diameter from 200 to 500 Ω square −1 . The net donor concentration was ∼10 18 cm −3 near the surface and increased to ∼4 × 10 18 cm −3 deeper inside the sample. The deep traps observed in admittance and DLTS spectra had levels at E c −0.25 eV and E c −0.35 eV, with concentration ∼10 15 cmmore »−3 and E c −1 eV with concentration ∼10 16 cm −3 .« less
  3. Films of α-Ga 2 O 3 grown by Halide Vapor Phase Epitaxy (HVPE) were irradiated with protons at energies of 330, 400, and 460 keV with fluences 6 × 10 15  cm −2 and with 7 MeV C 4+ ions with a fluence of 1.3 × 10 13  cm −2 and characterized by a suite of measurements, including Photoinduced Transient Current Spectroscopy (PICTS), Thermally Stimulated Current (TSC), Microcathodoluminescence (MCL), Capacitance–frequency (C–f), photocapacitance and Admittance Spectroscopy (AS), as well as by Positron Annihilation Spectroscopy (PAS). Proton irradiation creates a conducting layer near the peak of the ion distribution and vacancy defects distribution and introduces deep traps at E c -0.25, 0.8, and 1.4 eV associated with Ga interstitials, gallium–oxygen divacancies V Ga –V O , and oxygen vacancies V O . Similar defects were observed in C implanted samples. The PAS results can also be interpreted by assuming that the observed changes are due to the introduction of V Ga and V Ga –V O .
  4. High crystalline quality thick β-Ga2O3drift layers are essential for multi-kV vertical power devices. Low-pressure chemical vapor deposition (LPCVD) is suitable for achieving high growth rates. This paper presents a systematic study of the Schottky barrier diodes fabricated on four different Si-doped homoepitaxial β-Ga2O3thin films grown on Sn-doped (010) and (001) β-Ga2O3substrates by LPCVD with a fast growth rate varying from 13 to 21  μm/h. A higher temperature growth results in the highest reported growth rate to date. Room temperature current density–voltage data for different Schottky diodes are presented, and diode characteristics, such as ideality factor, barrier height, specific on-resistance, and breakdown voltage are studied. Temperature dependence (25–250 °C) of the ideality factor, barrier height, and specific on-resistance is also analyzed from the J–V–T characteristics of the fabricated Schottky diodes.

  5. The effects of downstream plasma exposure with O 2 , N 2 or CF 4 discharges on Si-doped Ga 2 O 3 Schottky diode forward and reverse current-voltage characteristics were investigated. The samples were exposed to discharges with rf power of 50 W plasma at a pressure of 400 mTorr and a fixed treatment time of 1 min to simulate dielectric layer removal, photoresist ashing or surface cleaning steps. Schottky contacts were deposited through a shadow mask after exposure to avoid any changes to the surface. A Schottky barrier height of 1.1 eV was obtained for the reference sample without plasma treatment, with an ideality factor of 1.0. The diodes exposed to CF 4 showed a 0.25 V shift from the I–V of the reference sample due to a Schottky barrier height lowering around 14%. The diodes showed a decrease of Schottky barrier height of 2.5 and 6.5% with O 2 or N 2 treatments, respectively. The effect of plasma exposure on the ideality factor of diodes treated with these plasmas was minimal; 0.2% for O 2 and N 2 , 0.3% for CF 4 , respectively. The reverse leakage currents were 1.2, 2.2 and 4.8 μ A cm −2more »for the diodes treated with O 2 , and CF 4 , and N 2 respectively. The effect of downstream plasma treatment on diode on-resistance and on-off ratio were also minimal. The changes observed are much less than caused by exposure to hydrogen-containing plasmas and indicate that downstream plasma stripping of films from Ga 2 O 3 during device processing is a relatively benign approach.« less