High-Mobility Ge-Doped $\beta$-Ga$_2$O$_3$ Growth on Sapphire by Low-Pressure Chemical Vapor Deposition

Ahmed Ibreljic; Anhar Bhuiyan; Ibrahim Isah; Michael Davenport; Saleh Ahmed Khan; Sourav Sarker; Stephen Lam; Stephen Margiotta

REVIEW 3 major objections 7 minor 1 cited by

High-Mobility Ge-Doped $\beta$-Ga$_2$O$_3$ Growth on Sapphire by Low-Pressure Chemical Vapor Deposition

T0 review · 3 major / 7 minor · reviewed 2026-07-14 · grok-4.5

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Pith's one-line read Sapphire offcut of 6° yields Ge-doped β-Ga₂O₃ films with 117 cm²/V·s room-temperature mobility on low-cost substrates, the highest reported for this heteroepitaxy.

desk verdict Record Ge:β-Ga₂O₃/sapphire Hall numbers are real and useful; the offcut-only causal story is confounded by co-varying source geometry and doping. read the letter →

arxiv 2607.10908 v1 pith:RDPIUXPR submitted 2026-07-12 cond-mat.mtrl-sci physics.app-ph

Ahmed Ibreljic , Saleh Ahmed Khan , Sourav Sarker , Ibrahim Isah , Stephen Margiotta , Michael Davenport , Stephen Lam , Anhar Bhuiyan This is my paper · ORCID

classification cond-mat.mtrl-sciphysics.app-ph

keywords β-Ga₂O₃GedopingLPCVDsapphireoffcutheteroepitaxyHallmobilitystep-flowgrowthultra-widebandgap

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

The paper shows that intentional offcut on c-plane sapphire steers low-pressure chemical vapor deposition of Ge-doped β-Ga₂O₃ into a step-flow growth mode. That change improves terrace alignment, crystalline coherence and surface smoothness, which in turn raises electron mobility. On a 6° offcut the films reach 117 cm²/V·s at room temperature and 337 cm²/V·s at 128 K—numbers that surpass all earlier Ge-doped β-Ga₂O₃ layers grown on sapphire and approach values previously limited to expensive native substrates. Transport modeling extracts shallow donors (12.5–19 meV), a deeper 80 meV level, very low compensation and dislocation densities near 10⁹ cm⁻². The result matters because high-mobility n-type films on scalable sapphire open a practical route to ultra-wide-bandgap power devices without relying on costly bulk Ga₂O₃ wafers.

What carries the argument

Sapphire offcut engineering: intentional substrate miscut toward ⟨11-20⟩ that supplies atomic steps, stabilizes step-flow growth, suppresses rotational domains and thereby lowers the scattering that had previously limited mobility in heteroepitaxial Ge-doped β-Ga₂O₃.

What would settle it

Grow a new set of films that hold Ga–substrate distance, Ge loading, thickness and growth rate fixed while varying only the sapphire offcut; if the mobility peak at 6° disappears, the offcut claim is falsified.

Watch

Extended reading notes

Core claim

LPCVD growth of Ge-doped (-201) β-Ga₂O₃ on 6° offcut c-plane sapphire produces the highest room-temperature (117 cm²/V·s) and low-temperature (337 cm²/V·s) Hall mobilities yet reported for Ge-doped β-Ga₂O₃ on sapphire, by converting multidirectional island growth into ordered step-flow growth that reduces rotational domains and dislocation scattering.

Load-bearing premise

The mobility gain is attributed mainly to the sapphire offcut angle, even though Ga-to-substrate distance, Ge source loading, film thickness and growth rate all change together with offcut in the experimental series.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

The new experimental fact is solid: LPCVD Ge-doped (-201) β-Ga₂O₃ on 6° offcut sapphire reaches 117 cm²/V·s at 1.43×10¹⁷ cm⁻³ (RT) and 337 cm²/V·s at 128 K. That is well above prior Ge-on-sapphire LPCVD (~20–43) and approaches good homoepitaxial Ge values. Structural data (SEM/AFM terrace alignment, rocking-curve narrowing, Raman, near-stoichiometric XPS) are consistent and support better crystallinity at higher offcut.

What the paper does well is the multi-offcut matrix plus temperature-dependent Hall and a standard charge-neutrality + Matthiessen fit (POP, II, NI, ADP, DIS). Extracted shallow donors (12.5–19 meV), a deeper ~80 meV level, low NA, and Ndis ~10⁹ cm⁻² are plausible and match literature ranges. The benchmark plot is honest.

The soft spot is real but not fatal. Table 1 shows Ga–substrate distance, Ge loading, thickness, and growth rate all step with offcut. The record sample is also the lightest-doped and uses a unique source geometry. Structural improvement with offcut is clear; the electrical jump is therefore correlative rather than cleanly isolated. The model also floats ħω₀ differently for 6° vs 8°. That weakens the “offcut is the primary knob” claim but does not erase the mobility numbers themselves.

This is for UWBG materials and device groups who need high-mobility n-type layers on cheap sapphire. Cite the Hall values and the growth recipe; treat the pure-offcut mechanism with the usual caution until a fixed-geometry control series appears. I would send it to peer review—the data are worth referee time and the confound is fixable by clarification or extra experiments.

Referee Report

3 major / 7 minor

Summary. The manuscript reports LPCVD heteroepitaxy of Ge-doped (−201) β-Ga₂O₃ on c-plane sapphire with intentional offcuts of 0°, 2°, 6°, and 8°. Structural data (SEM, AFM, XRD rocking curves, Raman) show a transition toward step-flow growth, improved terrace alignment, lower RMS roughness, and narrower (402) FWHM with increasing offcut. XPS indicates near-stoichiometric O/Ga ≈ 1.48. Hall measurements give room-temperature mobilities from 15 to 117 cm²/V·s over n ≈ 1.43×10¹⁷–2.75×10¹⁸ cm⁻³, with the 6° sample reaching 117 cm²/V·s at 1.43×10¹⁷ cm⁻³ and a peak of 337 cm²/V·s at 128 K. Temperature-dependent n(T) and μ(T) are fit with a two-donor charge-neutrality model plus Matthiessen scattering (POP, II, NI, ADP, dislocation), yielding ED ≈ 12.5–19 and 80 meV, low NA, and Ndis ~ 10⁹ cm⁻². The authors conclude that sapphire offcut engineering enables the highest reported RT and LT mobilities for Ge-doped β-Ga₂O₃ on sapphire and is a scalable path for high-mobility heteroepitaxy.

Significance. If the mobility values and structural trends hold, the work is a useful advance for scalable β-Ga₂O₃ heteroepitaxy: LPCVD Ge doping on low-cost sapphire reaching ~117 cm²/V·s approaches homoepitaxial Ge-doped ranges and substantially exceeds prior Ge-doped β-Ga₂O₃ on sapphire. The multi-technique characterization (phase purity, morphology, composition, T-dependent Hall) and standard transport modeling are appropriate for the field. The result is of practical interest for power-device drift layers on foreign substrates. The main scientific contribution is experimental demonstration and benchmarking rather than a new theoretical framework; its impact depends on how cleanly mobility gains can be attributed to offcut versus co-varying growth parameters.

major comments (3)

Table 1 and §II–III: The central causal claim that sapphire offcut is the primary driver of the mobility rise (15 → 117 cm²/V·s) is not isolated. Ga–substrate distance is stepped 2.5→5.5 cm with offcut, Ge/(Ge+Ga) loading drops from 0.50–0.60 wt% (0°/2°) to 0.05 wt% for the record Sample 4, and thickness/growth rate vary by factors of ~3–5. These parameters independently control Ge flux, residual impurities, strain relaxation, and dislocation filtering. The electrical optimum coincides with the lowest intentional doping and a unique source geometry. Without fixed-geometry / fixed-loading controls (or at least a systematic discussion quantifying each contribution), the attribution to step-flow alone remains correlative. Please either (i) add control growths at fixed Ga–substrate distance and comparable n across offcuts, or (ii) substantially reframe Abstract/Conclusion language to “optimi
§III, Table 1, Fig. 7–8: Mobility comparisons across offcut are confounded by large differences in carrier concentration. The 0° and 2° films sit at n ~ (2.5–2.8)×10¹⁸ cm⁻³ while the 117 cm²/V·s film is at 1.43×10¹⁷ cm⁻³; Fig. 8 already shows that within 6° films, lowering n from 4.24×10¹⁷ to 1.43×10¹⁷ raises RT μ from 78 to 117 cm²/V·s. Ionized-impurity scattering therefore accounts for a substantial fraction of the reported “offcut” gain. Present mobility vs n (as in Fig. 6) with offcut as a parameter, and avoid ranking offcuts by raw μ without n-matching. Clarify which samples establish an offcut benefit at fixed doping.
§III, Eqs. (1)–(3), Tables 2–3, Fig. 9: The transport fit uses several free parameters (ND1, ND2, ED1, ED2, NA, Ndis, and different fitted ħω₀ of 47 vs 39 meV for 6° vs 8°). Different phonon energies for the same material under similar growth conditions need physical justification or a common ħω₀ with uncertainty bounds. Report fit sensitivity / uniqueness (e.g., covariance or constrained fits) so that extracted Ndis ~ 1–1.7×10⁹ cm⁻² and NA < 5×10¹⁵ cm⁻³ are not under-determined. The model is standard and secondary to the experimental claim, but over-interpreted uniqueness would weaken the mechanistic narrative.

minor comments (7)

Notation: The orientation is written inconsistently as (2"01), (−201), and (-201). Standardize to (−201) / (¯201) throughout text, abstract, figures, and tables.
Fig. 3(b): Rocking-curve FWHM values are shown only as a trend; please list numerical FWHM (arcsec) for each offcut in the text or a table so the crystallinity improvement can be cited quantitatively.
Table 1: Sample 7 lists thickness 5.34 µm and growth rate 3.56 µm/h (implying ~1.5 h), while several others equate thickness to growth rate numerically (suggesting 1 h growth). State growth time explicitly for each run.
Fig. 6 caption and legend: Ensure all literature points are correctly attributed (homoepitaxy vs heteroepitaxy; β vs α) and that the “highest on sapphire” claim is restricted to Ge-doped β-Ga₂O₃ as stated, not all Ga₂O₃:Ge.
XPS: O/Ga = 1.48 is near-stoichiometric; briefly note surface sensitivity and whether adventitious C / O–H affect the ratio, and whether Ge is detectable at the doping levels used (or below XPS detection).
§I: Prior LPCVD Si-doped work from the group is appropriately cited; a short explicit contrast (Ge vs Si incorporation efficiency under the same reactor) would help readers place the Ge results.
Typographical: scattered OCR-like artifacts in the provided text (e.g., 10!" cm#$, µ;<;) should be cleaned in the production manuscript; ensure Greek and subscripts render correctly.

Circularity Check

0 steps flagged · score 1.0 of 10

No load-bearing circularity: headline mobilities are direct Hall measurements; charge-neutrality/Boltzmann analysis is post-hoc parameter extraction, not a prediction that reduces to its inputs.

full rationale

This is a standard experimental materials paper. The strongest claim (RT mobility 117 cm²/V·s and LT peak 337 cm²/V·s for the 6° Ge-doped film on sapphire) is obtained from van-der-Pauw Hall data (Table 1, Figs. 7–8); it is not derived from any model equation. The subsequent charge-neutrality (Eqs. 1–2) and Matthiessen-rule mobility (Eq. 3) analysis fits free parameters (ND1/ED1, ND2/ED2, NA, Ndis, and even ħω₀ separately for the 6° and 8° samples—see Table 2) to the already-measured n(T) and µ(T) curves; the paper correctly labels the results as “fitting revealed” and “good agreement with the experimental data” (Fig. 9 caption). No quantity is defined in terms of the quantity it is said to predict, no fitted constant is re-labeled a first-principles prediction, and no uniqueness theorem or ansatz is imported via self-citation to force the result. Minor self-citations of the group’s earlier Si-doped LPCVD work appear in the introduction for context but are not required for the Ge mobility numbers or the offcut comparison. The paper is therefore self-contained against external benchmarks; any residual concerns about co-varying growth parameters (Ga–substrate distance, Ge loading, thickness) are experimental-design issues, not circularity of derivation.

Assumptions & free parameters 7 free parameters · 4 assumptions · 0 invented entities

The paper is experimental; the load-bearing content is measured Hall mobility and structural metrics. The transport analysis imports standard semiconductor scattering formulas and fits several free parameters (donor levels, densities, Ndis, ħω₀) to n(T) and µ(T). No new physical entities are postulated. Domain assumptions are the usual ones for β-Ga₂O₃ transport literature (Matthiessen’s rule, Fermi–Dirac ionization, dislocation acceptor spacing ≈0.47 nm along (-201)).

free parameters (7)

ED1 (shallow donor activation energy) = 12.5–19 meV
Fitted to n(T) via charge-neutrality; reported 12.5 meV (6°) and 19 meV (8°).
ED2 (deeper donor activation energy) = 80 meV
Second donor level fixed/fitted at 80 meV for both samples.
ND1, ND2 (donor concentrations) = ND1 ~1.6–5×10¹⁷ cm⁻³; ND2 ~0.5–1.7×10¹⁷ cm⁻³
Fitted concentrations of the two donor populations (Table 3).
NA (acceptor compensation) = 2–5×10¹⁵ cm⁻³
Bulk acceptor density fitted under charge neutrality; kept low (<5×10¹⁵ cm⁻³).
Ndis (threading dislocation density) = 1.0–1.7×10⁹ cm⁻²
Extracted from mobility fit via dislocation scattering term; order 10⁹ cm⁻².
ħω₀ (polar optical phonon energy) = 47 meV (6°), 39 meV (8°)
Explicitly listed as fitted (Table 2): 47 meV for 6° sample, 39 meV for 8° sample.
Ge/(Ge+Ga) source loading and Ga–substrate distance = 0.05–0.60 wt%; 2.5–5.5 cm
Experimentally chosen control knobs that co-vary with offcut (Table 1) and directly set doping and growth rate.

assumptions (4)

domain assumption Matthiessen’s rule for combining independent scattering rates (POP + II + NI + ADP + DIS)
Used without derivation in Eq. (3) to obtain total mobility; standard but approximate when mechanisms are correlated.
domain assumption Charge-neutrality condition including dislocation-line acceptors with spacing d≈0.47 nm along (-201)
Eq. (1)–(2); d taken from crystallographic periodicity (He 2006, Varley 2010).
domain assumption Literature material parameters for β-Ga₂O₃ (m*=0.313 m0, εs=10.2, ε∞=3.6, EADP=6.9 eV, etc.)
Table 2 values taken from prior transport papers (Feng, Neal, Ma, Zhang et al.).
domain assumption Ge preferentially occupies tetrahedral Ga(I) sites as a shallow donor
Invoked in Introduction from first-principles and prior MBE/MOCVD work (Speck, Alema).

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Pith. "Pith review of High-Mobility Ge-Doped $\beta$-Ga$_2$O$_3$ Growth on Sapphire by Low-Pressure Chemical Vapor Deposition." pith.science (2026). https://pith.science/paper/RDPIUXPR

@misc{pith2026260710908,
  author       = {Pith},
  title        = {Pith review of: High-Mobility Ge-Doped $\beta$-Ga$_2$O$_3$ Growth on Sapphire by Low-Pressure Chemical Vapor Deposition},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/RDPIUXPR}},
  note         = {Machine review of arXiv:2607.10908}
}

abstract

In this work, high-quality Ge-doped (-201) $\beta$-Ga$_2$O$_3$ thin films were heteroepitaxially grown on c-plane sapphire substrates with offcut angles of 0 deg, 2 deg, 6 deg, and 8 deg using low-pressure chemical vapor deposition (LPCVD). Increasing sapphire offcut promoted step-flow growth, resulting in improved terrace alignment, reduced surface roughness, and enhanced crystalline quality. Phase-pure monoclinic $\beta$-Ga$_2$O$_3$ with strong (-201) preferential orientation was confirmed by X-ray diffraction and Raman spectroscopy, while X-ray photoelectron spectroscopy revealed near-stoichiometric composition with an O/Ga ratio of 1.48. Electrical transport properties exhibited a strong dependence on substrate offcut angle, with room-temperature Hall mobility increasing from 15 to 117 cm$^2$/V s as the offcut angle increased from 0 deg to 6 deg, across carrier concentrations spanning $1.43 \times 10^{17}$ to $2.75 \times 10^{18}$ cm$^{-3}$. The 6 deg offcut sample achieved a room-temperature mobility of 117 cm$^2$/V s at a carrier concentration of $1.43 \times 10^{17}$ cm$^{-3}$ and a peak low-temperature mobility of 337 cm$^2$/V s at 128 K with a carrier concentration of $8.96 \times 10^{16}$ cm$^{-3}$, representing the highest reported room-temperature and low-temperature mobilities for Ge-doped $\beta$-Ga$_2$O$_3$ films grown on sapphire substrates. Carrier concentration and mobility data were analyzed using charge-neutrality and Boltzmann transport models incorporating donor activation together with polar optical phonon, ionized impurity, neutral impurity, acoustic deformation potential, and dislocation scattering mechanisms. The fitting revealed shallow donor activation energies of 12.5-19 meV, a deeper donor level at 80 meV, low acceptor compensation ($< 5 \times 10^{15}$ cm$^{-3}$), and threading dislocation densities on the order of $10^9$ cm$^{-2}$.

Figures

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Works this paper leans on

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[1]

Overall, the agreement between the modeled and experimentally measured carrier concentration and mobility indicates that the adopted charge-neutrality and mobility-scattering model captures the dominant transport processes in the present Ge doped β-Ga₂O₃ heteroepitaxial films. IV. Conclusion In summary, high-quality Ge-doped (2"01) β-Ga₂O₃ thin films were...

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[3]

R.; Das, N.; Saha, C

(51) Gilankar, A.; Gervassi-Saga, J.; McCartney, M. R.; Das, N.; Saha, C. N.; Liu, Y .; McComas, D. M.; Smith, D. J.; Kalarickal, N. K. Demonstration of KV-class β-Ga2O3 trench junction barrier Schottky diodes with space-modulated junction termination extension. APL Electron. Devices 2026, 2 (1), 016106. DOI: 10.1063/5.0295311. (52) Wan, H.-H.; Li, J.-S.;...

work page doi:10.1063/5.0295311 2026
[4]

N.; Vaidya, A.; Nipu, N

(54) Saha, C. N.; Vaidya, A.; Nipu, N. J.; Meng, L.; Yu, D. S.; Zhao, H.; Singisetti, U. Thin channel 23 Ga2O3 MOSFET with 55 GHz fMAX and >100 V breakdown. Appl. Phys. Lett. 2024, 125 (6), 062101. DOI: 10.1063/5.0208580. (55) Saha, C. N.; Nipu, N. J.; Singisetti, U. High performance vacuum annealed β-(AlxGa1−x)2O3/Ga2O3 HFET with fT/fMAX of 32/65 GHz....

doi:10.1063/5.0208580 2024
[5]

G.; Shimamura, K.; Yoshikawa, Y .; Ujiie, T.; Aoki, K

(62) Víllora, E. G.; Shimamura, K.; Yoshikawa, Y .; Ujiie, T.; Aoki, K. Electrical conductivity and carrier concentration control in β-Ga2O3 by Si doping. Appl. Phys. Lett. 2008, 92 (20), 202120. DOI: 10.1063/1.2919728. (63) Ranga, P.; Bhattacharyya, A.; Whittaker-Brooks, L.; Scarpulla, M. A.; Krishnamoorthy, S. N-type doping of low-pressure chemical vapo...

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[6]

A.; Pandey, R.; Amzallag, E.; Baraille, I.; Rérat, M

24 (70) He, H.; Orlando, R.; Blanco, M. A.; Pandey, R.; Amzallag, E.; Baraille, I.; Rérat, M. First-principles study of the structural, electronic, and optical properties of ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ in its monoclinic and hexagonal phases. Phys. Rev. B 2006, 74 (19), 195123. DOI: 10.1103/PhysRevB.74.195123. (71) Varley, J. B.; Weber, J. R.; Jano...

work page doi:10.1103/physrevb.74.195123 2006
[7]

Benchmark comparison of room-temperature Hall mobility as a function of carrier concentration for Ge-doped β-Ga₂O₃ and α-Ga₂O₃ films grown by different epitaxial techniques and on different substrates. This work —LPCVD (𝟐01) β-Ga₂O₃:Ge, C-plane sapphire, no oﬀcutThis work —LPCVD (𝟐01) β-Ga₂O₃:Ge, C-plane sapphire, 2°oﬀcutThis work —LPCVD (𝟐01) β-Ga₂O₃:Ge,...

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Pith tools

Reviewed July 14, 2026 · model on record in the stance chip above.

[1] [1]

Overall, the agreement between the modeled and experimentally measured carrier concentration and mobility indicates that the adopted charge-neutrality and mobility-scattering model captures the dominant transport processes in the present Ge doped β-Ga₂O₃ heteroepitaxial films. IV. Conclusion In summary, high-quality Ge-doped (2"01) β-Ga₂O₃ thin films were...

doi:10.1063/5.0060327 2022

[2] [2]

Charge recovery by vacuum annealing in β-Ga2O3 multi-fin trench Schottky barrier diodes

(45) Dhara, S.; Dheenan, A.; Rajan, S. Charge recovery by vacuum annealing in β-Ga2O3 multi-fin trench Schottky barrier diodes. APL Electron. Devices 2025, 1 (2), 026122. DOI: 10.1063/5.0270286. (46) Hollar, E. J.; Farzana, E. Over 3 kV and ultra-low leakage vertical (011) β-Ga2O3 power diodes with engineered Schottky contact and high-permittivity dielect...

arXiv doi:10.1063/5.0270286 2025

[3] [3]

R.; Das, N.; Saha, C

(51) Gilankar, A.; Gervassi-Saga, J.; McCartney, M. R.; Das, N.; Saha, C. N.; Liu, Y .; McComas, D. M.; Smith, D. J.; Kalarickal, N. K. Demonstration of KV-class β-Ga2O3 trench junction barrier Schottky diodes with space-modulated junction termination extension. APL Electron. Devices 2026, 2 (1), 016106. DOI: 10.1063/5.0295311. (52) Wan, H.-H.; Li, J.-S.;...

work page doi:10.1063/5.0295311 2026

[4] [4]

N.; Vaidya, A.; Nipu, N

(54) Saha, C. N.; Vaidya, A.; Nipu, N. J.; Meng, L.; Yu, D. S.; Zhao, H.; Singisetti, U. Thin channel 23 Ga2O3 MOSFET with 55 GHz fMAX and >100 V breakdown. Appl. Phys. Lett. 2024, 125 (6), 062101. DOI: 10.1063/5.0208580. (55) Saha, C. N.; Nipu, N. J.; Singisetti, U. High performance vacuum annealed β-(AlxGa1−x)2O3/Ga2O3 HFET with fT/fMAX of 32/65 GHz....

doi:10.1063/5.0208580 2024

[5] [5]

G.; Shimamura, K.; Yoshikawa, Y .; Ujiie, T.; Aoki, K

(62) Víllora, E. G.; Shimamura, K.; Yoshikawa, Y .; Ujiie, T.; Aoki, K. Electrical conductivity and carrier concentration control in β-Ga2O3 by Si doping. Appl. Phys. Lett. 2008, 92 (20), 202120. DOI: 10.1063/1.2919728. (63) Ranga, P.; Bhattacharyya, A.; Whittaker-Brooks, L.; Scarpulla, M. A.; Krishnamoorthy, S. N-type doping of low-pressure chemical vapo...

doi:10.1063/1.2919728 2008

[6] [6]

A.; Pandey, R.; Amzallag, E.; Baraille, I.; Rérat, M

24 (70) He, H.; Orlando, R.; Blanco, M. A.; Pandey, R.; Amzallag, E.; Baraille, I.; Rérat, M. First-principles study of the structural, electronic, and optical properties of ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ in its monoclinic and hexagonal phases. Phys. Rev. B 2006, 74 (19), 195123. DOI: 10.1103/PhysRevB.74.195123. (71) Varley, J. B.; Weber, J. R.; Jano...

work page doi:10.1103/physrevb.74.195123 2006

[7] [7]

Benchmark comparison of room-temperature Hall mobility as a function of carrier concentration for Ge-doped β-Ga₂O₃ and α-Ga₂O₃ films grown by different epitaxial techniques and on different substrates. This work —LPCVD (𝟐01) β-Ga₂O₃:Ge, C-plane sapphire, no oﬀcutThis work —LPCVD (𝟐01) β-Ga₂O₃:Ge, C-plane sapphire, 2°oﬀcutThis work —LPCVD (𝟐01) β-Ga₂O₃:Ge,...

2021