Ultrawide bandgap β-(AlxGa1−x)2O3 vertical Schottky barrier diodes on (010) β-Ga2O3 substrates are demonstrated. The β-(AlxGa1−x)2O3 epilayer has an Al composition of 21% and a nominal Si doping of 2 × 1017 cm−3 grown by molecular beam epitaxy. Pt/Ti/Au has been employed as the top Schottky contact, whereas Ti/Au has been utilized as the bottom Ohmic contact. The fabricated devices show excellent rectification with a high on/off ratio of ∼109, a turn-on voltage of 1.5 V, and an on-resistance of 3.4 mΩ cm2. Temperature-dependent forward current-voltage characteristics show effective Schottky barrier height varied from 0.91 to 1.18 eV while the ideality factor from 1.8 to 1.1 with increasing temperatures, which is ascribed to the inhomogeneity of the metal/semiconductor interface. The Schottky barrier height was considered a Gaussian distribution of potential, where the extracted mean barrier height and a standard deviation at zero bias were 1.81 and 0.18 eV, respectively. A comprehensive analysis of the device leakage was performed to identify possible leakage mechanisms by studying temperature-dependent reverse current-voltage characteristics. At reverse bias, due to the large Schottky barrier height, the contributions from thermionic emission and thermionic field emission are negligible. By fitting reverse leakage currents at different temperatures, it was identified that Poole–Frenkel emission and trap-assisted tunneling are the main leakage mechanisms at high- and low-temperature regimes, respectively. Electrons can tunnel through the Schottky barrier assisted by traps at low temperatures, while they can escape these traps at high temperatures and be transported under high electric fields. This work can serve as an important reference for the future development of ultrawide bandgap β-(AlxGa1−x)2O3 power electronics, RF electronics, and ultraviolet photonics.
This content will become publicly available on January 17, 2024
While the properties of β-Ga2O3 continue to be extensively studied for high-power applications, the effects of strong electric fields on the Ga2O3 microstructure and, in particular, the impact of electrically active native point defects have been relatively unexplored. We used cathodoluminescence point spectra and hyperspectral imaging to explore possible nanoscale movements of electrically charged defects in Ga2O3 vertical trench power diodes and observed the spatial rearrangement of optically active defects under strong reverse bias. These observations suggest an unequal migration of donor-related defects in β-Ga2O3 due to the applied electric field. The atomic rearrangement and possible local doping changes under extreme electric fields in β-Ga2O3 demonstrate the potential impact of nanoscale device geometry in other high-power semiconductor devices.
more » « less- Award ID(s):
- 1719875
- NSF-PAR ID:
- 10391762
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- Journal of Applied Physics
- Volume:
- 133
- Issue:
- 3
- ISSN:
- 0021-8979
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
-
This review presents recent research advances in measuring native point defects in ZnO nanostructures, establishing how these defects a ect nanoscale electronic properties, and developing new techniques to manipulate these defects to control nano- and micro- wire electronic properties.From spatially-resolved cathodoluminescence spectroscopy, we now know that electrically-active native point defects are present inside, as well as at the surfaces of, ZnO and other semiconductor nanostructures. These defects within nanowires and at their metal interfaces can dominate electrical contact properties, yet they are sensitive to manipulation by chemical interactions, energy beams, as well as applied electrical fields. Non-uniform defect distributions are common among semiconductors, and their e ects are magnified in semiconductor nanostructures so that their electronic e ects are significant. The ability to measure native point defects directly on a nanoscale and manipulate their spatial distributions by multiple techniques presents exciting possibilities for future ZnO nanoscale electronics.more » « less
-
more » « less
β-Ga2O3 is an emerging ultra-wide bandgap semiconductor, holding a tremendous potential for power-switching devices for next-generation high power electronics. The performance of such devices strongly relies on the precise control of electrical properties of β-Ga2O3, which can be achieved by implantation of dopant ions. However, a detailed understanding of the impact of ion implantation on the structure of β-Ga2O3 remains elusive. Here, using aberration-corrected scanning transmission electron microscopy, we investigate the nature of structural damage in ion-implanted β-Ga2O3 and its recovery upon heat treatment with the atomic-scale spatial resolution. We reveal that upon Sn ion implantation, Ga2O3 films undergo a phase transformation from the monoclinic β-phase to the defective cubic spinel γ-phase, which contains high-density antiphase boundaries. Using the planar defect models proposed for the γ-Al2O3, which has the same space group as β-Ga2O3, and atomic-resolution microscopy images, we identify that the observed antiphase boundaries are the {100}1/4 ⟨110⟩ type in cubic structure. We show that post-implantation annealing at 1100 °C under the N2 atmosphere effectively recovers the β-phase; however, nano-sized voids retained within the β-phase structure and a γ-phase surface layer are identified as remanent damage. Our results offer an atomic-scale insight into the structural evolution of β-Ga2O3 under ion implantation and high-temperature annealing, which is key to the optimization of semiconductor processing conditions for relevant device design and the theoretical understanding of defect formation and phase stability.
-
In this study, we compared the transient self-heating behavior of a homoepitaxial β-Ga2O3 MOSFET and a GaN-on-Si HEMT using nanoparticle-assisted Raman thermometry and thermoreflectance thermal imaging. The effectiveness of bottom-side and double-side cooling schemes using a polycrystalline diamond substrate and a diamond passivation layer were studied via transient thermal modeling. Because of the low thermal diffusivity of β-Ga2O3, the use of a β-Ga2O3 composite substrate (bottom-side cooling) must be augmented by a diamond passivation layer (top-side cooling) to effectively cool the device active region under both steady-state and transient operating conditions. Without no proper cooling applied, the steady-state device-to-package thermal resistance of a homoepitaxial β-Ga2O3 MOSFET is 2.6 times higher than that for a GaN-on-Si HEMT. Replacing the substrate with polycrystalline diamond (under a 6.5 μm-thick β-Ga2O3 layer) could reduce the steady-state temperature rise by 65% compared to that for a homoepitaxial β-Ga2O3 MOSFET. However, for high frequency power switching applications beyond the ~102 kHz range, bottom-side cooling (integration with a high thermal conductivity substrate) does not improve the transient thermal response of the device. Adding a diamond passivation over layer diamond not only suppresses the steadystate temperature rise, but also drastically reduces the transient temperature rise under high frequency operating conditions.more » « less
-
more » « less
Abstract Open-channel microfluidics enables precise positioning and confinement of liquid volume to interface with tightly integrated optics, sensors, and circuit elements. Active actuation via electric fields can offer a reduced footprint compared to passive microfluidic ensembles and removes the burden of intricate mechanical assembly of enclosed systems. Typical systems actuate via manipulating surface wettability (
i.e ., electrowetting), which can render low-voltage but forfeits open-microchannel confinement. The dielectric polarization force is an alternative which can generate open liquid microchannels (sub-100 µm) but requires large operating voltages (50–200 VRMS) and low conductivity solutions. Here we show actuation of microchannels as narrow as 1 µm using voltages as low as 0.5 VRMSfor both deionized water and physiological buffer. This was achieved using resonant, nanoscale focusing of radio frequency power and an electrode geometry designed to abate surface tension. We demonstrate practical fluidic applications including open mixing, lateral-flow protein labeling, filtration, and viral transport for infrared biosensing—known to suffer strong absorption losses from enclosed channel material and water. This tube-free system is coupled with resonant wireless power transfer to remove all obstructing hardware — ideal for high-numerical-aperture microscopy. Wireless, smartphone-driven fluidics is presented to fully showcase the practical application of this technology.
