High-quality dielectric-semiconductor interfaces are critical for reliable high-performance transistors. We report the in-situ metalorganic chemical vapor deposition (MOCVD) of Al\(_2\)O\(_3\) on ...\(\beta\)-Ga\(_2\)O\(_3\) as a potentially better alternative to the most commonly used atomic layer deposition (ALD). The growth of Al\(_2\)O\(_3\) is performed in the same reactor as Ga\(_2\)O\(_3\) using trimethylaluminum and O\(_2\) as precursors without breaking the vacuum at a growth temperature of 600 \(^0\)C. The fast and slow near interface traps at the Al\(_2\)O\(_3\)/ \(\beta\)-Ga\(_2\)O\(_3\) interface are identified and quantified using stressed capacitance-voltage (CV) measurements on metal oxide semiconductor capacitor (MOSCAP) structures. The density of shallow and deep level initially filled traps (D\(_{it}\)) are measured using ultra-violet (UV) assisted CV technique. The average D\(_{it}\) for the MOSCAP is determined to be 7.8 \(\times\) 10\(^{11}\) cm\(^{-2}\)eV\(^{-1}\). The conduction band offset of the Al\(_2\)O\(_3\)/ Ga\(_2\)O\(_3\) interface is also determined from CV measurements and found out to be 1.7 eV which is in close agreement with the existing literature reports of ALD Al\(_2\)O\(_3\)/ Ga\(_2\)O\(_3\) interface. The current-voltage characteristics are also analyzed and the average breakdown field is extracted to be approximately 5.8 MV/cm. This in-situ Al\(_2\)O\(_3\) dielectric on \(\beta\)-Ga\(_2\)O\(_3\) with improved dielectric properties can enable Ga\(_2\)O\(_3\)-based high performance devices.
We report on the modeling of polarization-induced two-dimensional electron gas (2DEG) formation at \({\epsilon}\)-AlGaO3 / \({\epsilon}\)-Ga2O3 heterointerface and the effect of spontaneous ...polarization (Psp) reversal on 2DEG density in \({\epsilon}\)-Ga2O3 /\({\epsilon}\)-AlGaO3 / \({\epsilon}\)-Ga2O3 double heterostructures. Density-functional theory (DFT) is utilized to calculate the material properties of \({\epsilon}\)-Ga2O3 and \({\epsilon}\)-AlGaO3 alloys. Using Schrodinger-Poisson solver along with DFT calculated parameters, the 2DEG density is calculated as a function of barrier type and thickness. By optimizing the layer thicknesses of \({\epsilon}\)-Ga2O3/\({\epsilon}\)-AlGaO3/\({\epsilon}\)-Ga2O3 heterostructures, charge contrast ratios exceeding 1600 are obtained. This computational study indicates the high potential for \({\epsilon}\)-Ga2O3-based heterostructure devices for non-volatile memories and neuromorphic applications.
We report on the growth and characterization of metalorganic vapor-phase epitaxy-grown \b{eta}-(AlxGa1-x)2O3/\b{eta}-Ga2O3 modulation-doped heterostructures. Electron channel is realized in the ...heterostructure by utilizing a delta-doped \b{eta}-(AlxGa1-x)2O3 barrier. Electron channel characteristics are studied using transfer length method, capacitance-voltage and Hall measurements. Hall sheet charge density of 1.06 x 1013 cm-2 and mobility of 111 cm2/Vs is measured at room temperature. Fabricated transistor showed peak current of 22 mA/mm and on-off ratio of 8 x 106. Sheet resistance of 5.3 k{\Omega}/Square is measured at room temperature, which includes contribution from a parallel channel in \b{eta}-(AlxGa1-x)2O3.
By combining temperature-dependent resistivity and Hall effect measurements, we investigate donor state energy in Si-doped \b{eta}-Ga2O3 films grown using metal-organic vapor phase epitaxy (MOVPE). ...High magnetic field Hall effect measurements (H = +/-90 kOe) showed non-linear Hall resistance for T < 150 K revealing two-band conduction. Further analyses revealed carrier freeze-out characteristics in both bands yielding donor state energies of ~ 33.7 and ~ 45.6 meV. The former is consistent with the donor energy of Si in \b{eta}-Ga2O3 whereas the latter suggests a residual donor state, likely associated with a DX center. This study provides a critical insight into the impurity band conduction and the defect energy states in \b{eta}-Ga2O3 using high-field magnetotransport measurements.
Herein we utilize polarized photoluminescence (PL) microscopy and spectral analysis to locate and characterize many different types of µm-scale extended defects present in melt-grown bulk crystals ...and metal-organic vapor-phase epitaxy (MOVPE)-grown epitaxial thin films of β-Ga 2 O 3 and β-(Al,Ga) 2 O 3 . These include pits, divots, mounds, scratches, rotation domain boundaries, stacking faults, cracks, and other defect categories. Some types of µm-scale defects simply decrease overall PL yield, while others emit different spectra than single crystal regions. We combine PL microscopy with atomic force microscopy (AFM) and scanning electron microscopy (SEM) to provide detailed characteristics of these different types of features which can arise from both bulk crystal growth, surface preparation, and epitaxial growth processes. We show that sample quality (in terms of extended defects) can be determined by using PL and that attributing spectral features to isolated point defects is invalid unless the sample is proven to not contain extended defects.
We report on n-type degenerate doping in MOVPE grown \b{eta}-(Al0.26Ga0.74)2O3 epitaxial thin films and modulation doping in \b{eta}-(Al0.26Ga0.74)2O3/\b{eta}-Ga2O3 heterostructure. Alloy composition ...is confirmed using HRXRD measurements. Carrier concentration in the thin films is proportional to the silane molar flow. Room temperature hall measurements showed a high carrier concentration of 6x1018-7.3x1019 cm-3 with a corresponding electron mobility of 53-27 cm2/V.s in uniformly-doped \b{eta}-(Al0.26Ga0.74)2O3 layers. Modulation doping is used to realize a total electron sheet charge of 2.3x1012 cm-2 in a \b{eta}-(Al0.26Ga0.74)2O3/\b{eta}-Ga2O3 heterostructure using a uniformly-doped \b{eta}-(Al0.26Ga0.74)2O3 barrier layer and a thin spacer layer.
We report on silicon delta doping of metalorganic vapor-phase epitaxy-grown \b{eta}-Ga2O3 thin films using silane precursor. Delta-doped \b{eta}-Ga2O3 epitaxial films are characterized using ...capacitance-voltage profiling and secondary-ion mass spectroscopy. Electron sheet charge density in the range of 2.9e12 cm-2 to 8e12 cm-2 with a half width at half maximum ranging from 6.2 nm to 3.5 nm is measured. We also demonstrate a high density (6.4e12 cm-2) degenerate two-dimensional electron gas using a delta-doped \b{eta}-(Al0.26Ga0.74)2O3/\b{eta}-Ga2O3 heterostructure.The total charge could also include a contribution from a parallel channel in the \b{eta}-(Al0.26Ga0.74)2O3 alloy barrier.
Abstract
High quality dielectric‐semiconductor interfaces are critical for reliable high‐performance transistors. This paper reports the in situ metal–organic chemical vapor deposition of Al
2
O
3
on ...β‐Ga
2
O
3
as a potentially better alternative to the most commonly used atomic layer deposition (ALD). The growth of Al
2
O
3
is performed in the same reactor as Ga
2
O
3
using trimethylaluminum and O
2
as precursors without breaking the vacuum at a growth temperature of 600 °C. The fast and slow near interface traps at the Al
2
O
3
/β‐Ga
2
O
3
interface are identified and quantified using stressed capacitance–voltage (CV) measurements on metal oxide semiconductor capacitor (MOSCAP) structures. The density of shallow and deep level initially filled traps (D
it
) are measured using ultraviolet‐assisted CV technique. The average D
it
for the MOSCAP is determined to be 6.4
×
10
11
cm
−2
eV
−1
. The conduction band offset of the Al
2
O
3
/ Ga
2
O
3
interface is also determined from CV measurements and found out to be 1.7 eV which is in close agreement with the existing literature reports of ALD Al
2
O
3
/Ga
2
O
3
interface. The current–voltage characteristics are also analyzed and the average breakdown field is extracted to be approximately 5.8 MV cm
−1
. This in situ Al
2
O
3
dielectric on β‐Ga
2
O
3
with improved dielectric properties can enable Ga
2
O
3
‐based high‐performance devices.
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