Electrical properties of α-Ga2O3 films grown by halide vapor phase epitaxy on sapphire with α-Cr2O3 buffers

Abstract

We report on growth and electrical properties of α-Ga2O3 films prepared by halide vapor phase epitaxy (HVPE) at 500 °C on α-Cr2O3 buffers predeposited on sapphire by magnetron sputtering. The α-Cr2O3 buffers showed a wide microcathodoluminescence (MCL) peak near 350 nm corresponding to the α-Cr2O3 bandgap and a sharp MCL line near 700 nm due to the Cr+ intracenter transition. Ohmic contacts to Cr2O3 were 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-Ga2O3 films 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 EC of 0.3 eV. The I– V and capacitance–voltage ( C– V) characteristics of Ni Schottky diodes on Sn-doped samples using a Cr2O3 buffer indicated the presence of two face-to-face junctions, one between n-Ga2O3 and 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 deep traps with an ionization energy of 0.95 eV. These experiments suggest another pathway to obtain p–n heterojunctions in the α-Ga2O3 system.

Electrical and Recombination Properties of Polar Orthorhombic κ-Ga2O3 Films Prepared by Halide Vapor Phase Epitaxy

“…In addition, there is competition with the other metastable polymorph, κ-Ga 2 O 3 , during growth on sapphire [ 14 ]. The high dislocation density problem can be alleviated using strain-relieving α-(Al x Ga 1-x ) 2 O 3 buffers in mist CVD [ 16 ], or via growth using magnetron-sputtered α-Cr 2 O 3 buffers in HVPE [ 17 , 18 ]. A radical decrease in the dislocation density down to 10 6 –10 7 cm −2 can be achieved via the application of the Epitaxial Lateral Overgrowth (ELOG) technique [ 19 ].…”

Atomic Layer Deposition of Ga2O3 from GaI3 and O3: Growth of High-Density Phases

“…In earlier studies, the thin films containing crystalline Ga 2 O 3 have been grown on single crystal α-Al 2 O 3 , ,,− ,,,, GaN, SiC, and Si(111), and on α-Cr 2 O 3 , indium–tin oxide, and Al 2 O 3 buffer layers deposited on single crystal α-Al 2 O 3 , , yttrium stabilized zirconia, and Si(1 1 1), respectively. In the case of most thin-film deposition techniques used for the deposition of crystalline Ga 2 O 3 , substrate temperatures ≥500 °C have been needed for this purpose. ,,− ,,,, The plasma-enhanced ALD (PEALD) method that has enabled the growth of a mixture of α- and β-Ga 2 O 3 at T G ≥ 190 °C and α-Ga 2 O 3 at T G ≥ 250 °C on α-Al 2 O 3 has been a notable exception from this rule. However, for the deposition of crystalline films on substrates that do not support epitaxial growth, markedly higher T G or application of in situ Ar plasma annealing in PEALD (Table ) has been inevitable .…”

“…In earlier studies, the thin films containing crystalline Ga 2 O 3 have been grown on single crystal α-Al 2 O 3 , 5,10,14 −16,27,28,31,38 GaN, 31 SiC, 31 and Si(111), 53 and on α-Cr 2 O 3 , indium−tin oxide, and Al 2 O 3 buffer layers deposited on single crystal α-Al 2 O 3 , 18,19 yttrium stabilized zirconia, 15 and Si(1 1 1), 53 respectively. In the case of most thin-film deposition techniques used for the deposition of crystalline Ga 2 O 3 , substrate temperatures ≥500 °C have been needed for this purpose.…”

“…13−15 Correspondingly, some specific material param- eters like high permittivity values reaching 32 and promising ferroelectric properties, reported for ε-Ga 2 O 3 , characterize the κ-Ga 2 O 3 phase as well. 15,17 Gallium oxide thin films have been prepared by various methods, including magnetron sputtering, 2,4 pulsed laser deposition, 5,6 chemical vapor deposition, 1,7,18,19 and atomic layer deposition (ALD). 20 Among these methods, ALD provides excellent conformity, thickness control, and reproducibility at a nanometer level, which makes this technique most suitable for many applications.…”

Electrical conductive and photoelectrical properties of heterostructures based on gallium and chromium oxides with corundum structure

“…Rise τ 1 and fall τ 2 photoresponse times determined at the levels of 0.9J L (J L is the net electric current in a film under UV irradiation) and 1.1J D , respectively, were 0.1 and ∼ 60 s for α-Ga 2 O 3 films. High values of τ 2 are likely attributable to deep trap centers with different activation energies that, according to [15], are present in the bandgap.…”