An official website of the United States government
In this work, we demonstrate the growth and phase stabilization of ultrawide bandgap polycrystalline rutile germanium dioxide (GeO2) thin films. GeO2 thin films were deposited using RF magnetron sputtering on r-plane sapphire (Al2O3) substrates. As-deposited films were x-ray amorphous. Postdeposition annealing was performed at temperatures between 650 and 950 °C in an oxygen or nitrogen ambient. Annealing at temperatures from 750 to 950 °C resulted in mixed-phase polycrystalline films containing tetragonal (rutile) GeO2, hexagonal (α-quartz) GeO2, and/or cubic (diamond) germanium (Ge). When nitrogen was used as the anneal ambient, mixed GeO2 phases were observed. In contrast, annealing in oxygen promoted stabilization of the r-GeO2 phase. Grazing angle x-ray diffraction showed a preferred orientation of (220) r-GeO2 for all crystallized films. The combination of O2 annealing and O2 flux during growth resulted in r-GeO2 films with highly preferential alignment. Using electron microscopy, we observed an interfacial layer of hexagonal-oriented GeO2 with epitaxial alignment to the (11¯02) Al2O3 substrate, which may help stabilize the top polycrystalline r-GeO2 film.
more »
« less
This content will become publicly available on November 1, 2026
Growth and characterization of rutile-type GexSn1−xO2 alloy thin films via RF magnetron sputtering
Ultrawide bandgap (UWBG) semiconductors are increasingly of interest for developing energy-efficient technologies. Among UWBG materials, rutile-type oxides, such as GeO2 and SnO2, exhibit promising characteristics for power electronics and optoelectronics. Here we investigate the structural and morphological properties of rutile GexSn1−xO2 alloy thin films synthesized via RF magnetron co-sputtering with compositions ranging from x = 0.13 to x = 0.84. The films, grown on r-plane sapphire substrates, underwent post-deposition annealing (PDA) at 750, 850, and 950 °C. Epitaxial crystallization occurs at 750 °C for compositions with x = 0.69 and 0.64, exhibiting a (101)-oriented alloy peak. Enhanced epitaxial alignment and increased crystallinity is achieved at higher PDA temperatures of 850 and 950 °C. However, PDA at 950 °C promotes binary SnO2 crystallite formation in certain alloy compositions. As a result, 850 °C PDA is identified as the optimal PDA temperature to achieve (101)-oriented thin films across a range of compositions. The optical bandgap energy of the alloys was found to be tunable from 3.77 to 4.38 eV as Ge(x) composition is increased, opening the door to future heterojunction devices for high-performance power and optoelectronic applications.
more »
« less
- Award ID(s):
- 2328701
- PAR ID:
- 10678441
- Publisher / Repository:
- AIP Publishing
- Date Published:
- Journal Name:
- APL Materials
- Volume:
- 13
- Issue:
- 11
- ISSN:
- 2166-532X
- Page Range / eLocation ID:
- 111115
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Rutile germanium oxide (r-GeO2), an ultrawide bandgap semiconductor, is a promising material for next-generation power electronics. Understanding and controlling the structure and morphology of r-GeO2 thin films are crucial for advancing their integration into future devices. In this work, r-GeO2 thin films were grown using RF magnetron sputtering on r plane sapphire substrates. Postdeposition annealing (PDA) was performed in an oxygen ambient atmosphere to crystallize the films. PDA at 950 °C resulted in the formation of needle-like nanostructures, predominantly originating at the edges of the film and growing inward toward the sample center. Sequential annealing at increasing temperatures indicated that these needle-like structures begin forming at temperatures above 925 °C. Next, the effect of the PDA duration on the structure was studied. It was seen that PDA at 950 °C for durations of 1 to 15 min promoted formation of the rutile phase, and extending the PDA duration allowed greater surface coverage of the nanostructures. However, annealing even longer, i.e., for 120 min, resulted in mixed phases of α-quartz and rutile GeO2. These findings demonstrate that controlling the PDA temperature and duration can effectively modulate the morphology of rutile-phase GeO2 thin films.more » « less
-
Abstract The discovery and development of ultra-wide bandgap (UWBG) semiconductors is crucial to accelerate the adoption of renewable power sources. This necessitates an UWBG semiconductor that exhibits robust doping with high carrier mobility over a wide range of carrier concentrations. Here we demonstrate that epitaxial thin films of the perovskite oxide Nd x Sr 1 − x SnO 3 (SSO) do exactly this. Nd is used as a donor to successfully modulate the carrier concentration over nearly two orders of magnitude, from 3.7 × 10 18 cm −3 to 2.0 × 10 20 cm −3 . Despite being grown on lattice-mismatched substrates and thus having relatively high structural disorder, SSO films exhibited the highest room-temperature mobility, ~70 cm 2 V −1 s −1 , among all known UWBG semiconductors in the range of carrier concentrations studied. The phonon-limited mobility is calculated from first principles and supplemented with a model to treat ionized impurity and Kondo scattering. This produces excellent agreement with experiment over a wide range of temperatures and carrier concentrations, and predicts the room-temperature phonon-limited mobility to be 76–99 cm 2 V −1 s −1 depending on carrier concentration. This work establishes a perovskite oxide as an emerging UWBG semiconductor candidate with potential for applications in power electronics.more » « less
-
Rutile compounds have exotic functional properties that can be applied for various electronic applications; however, the limited availability of epitaxial substrates has restricted the study of rutile thin films to a limited range of lattice parameters. Here, rutile GeO 2 is demonstrated as a new rutile substrate with lattice parameters of [Formula: see text] and [Formula: see text]. Rutile GeO 2 single crystals up to 4 mm in size are grown by the flux method. X-ray diffraction reveals high crystallinity with a rocking curve having a full width half-maximum of 0.0572°. After mechanical polishing, a surface roughness of less than 0.1 nm was obtained, and reflection high-energy electron diffraction shows a crystalline surface. Finally, epitaxial growth of (110)-oriented TiO 2 thin films on GeO 2 substrates was demonstrated using molecular beam epitaxy. Templated by rutile GeO 2 substrates, our findings open the possibility of stabilizing new rutile thin films and strain states for the tuning of physical properties.more » « less
-
β-phase gallium oxide (Ga2O3) is an emerging ultrawide bandgap (UWBG) semiconductor with a bandgap energy of ∼ 4.8 eV and a predicted high critical electric field strength of ∼8 MV/cm, enabling promising applications in next generation high power electronics and deep ultraviolet optoelectronics. The advantages of Ga2O3 also stem from its availability of single crystal bulk native substrates synthesized from melt, and its well-controllable n-type doping from both bulk growth and thin film epitaxy. Among several thin film growth methods, metalorganic chemical vapor deposition (MOCVD) has been demonstrated as an enabling technology for developing high-quality epitaxy of Ga2O3 thin films, (AlxGa1−x)2O3 alloys, and heterostructures along various crystal orientations and with different phases. This tutorial summarizes the recent progresses in the epitaxial growth of β-Ga2O3 thin films via different growth methods, with a focus on the growth of Ga2O3 and its compositional alloys by MOCVD. The challenges for the epitaxial development of β-Ga2O3 are discussed, along with the opportunities of future works to enhance the state-of-the-art device performance based on this emerging UWBG semiconductor material system.more » « less
