Intrinsic Electron Mobility Limits in beta-Ga2O3 (1610.04198v2)

Abstract: By systematically comparing experimental and theoretical transport properties, we identify the polar optical phonon scattering as the dominant mechanism limiting electron mobility in beta-Ga2O3 to lower than 200 cm2/Vs at 300 K for donor doping densities lower than 1018 cm-3. In spite of similar electron effective mass of beta-Ga2O3 to GaN, the electron mobility is 10x lower because of a massive Frohlich interaction, due to the low phonon energies stemming from the crystal structure and strong bond ionicity. Based on the theoretical and experimental analysis, we provide an empirical expression for electron mobility in beta-Ga2O3 that should help calibrate its potential in high performance device design and applications.

• The paper identifies polar optical phonon scattering as the main factor limiting electron mobility to below 200 cm²/V·s at room temperature.
• It rigorously combines experimental data and theoretical analysis using the Boltzmann transport equation and relaxation-time approximation to link mobility constraints to low optical phonon energies (~44 meV).
• The study highlights significant implications for device design by suggesting limited mobility enhancement under standard conditions and potential for improvements using strain or 2D heterojunction approaches.

Intrinsic Electron Mobility Limits in $\beta$-Ga$_2$O$_3$

The paper provides a comprehensive investigation into the intrinsic electron mobility limits within $\beta$-Ga$_2$O$_3$, an ultra wide-bandgap semiconductor. By rigorously analyzing both experimental and theoretical transport properties, the paper identifies polar optical phonon scattering as the principal mechanism constraining electron mobility to less than 200 cm$^2$/V·s at room temperature when donor doping densities remain below approximately $10^{18}$ cm$^{-3}$.

Mechanism Limiting Electron Mobility

The authors pinpoint the massive Fröhlich interaction in $\beta$-Ga$_2$O$_3$ as a critical factor whose implications extend beyond simple comparisons to GaN, despite their similar electron effective masses. This interaction is driven by the crystal structure and the strong bond ionicity in $\beta$-Ga$_2$O$_3$, which consequently result in significantly lower electron mobilities. Specifically, the paper estimates that these mobilities are approximately 10 times lower than those observed in GaN. Through a detailed analysis involving the relaxation-time approximation (RTA) solution of the Boltzmann transport equation (BTE), the intrinsic scattering mechanisms, including ionized impurity, neutral impurity, polar optical phonon, and acoustic deformation potential (ADP) scattering, were studied.

Experimental and Theoretical Correspondence

This analysis has not only corroborated experimental results showing maximum room-temperature electron mobility of approximately 110-150 cm$^2$/V·s in $\beta$-Ga$_2$O$_3$ but also aligns well with the theoretical constraints posed by the observed low optical phonon energies, which are about 44 meV, according to the transport property deductions.

Implications and Future Directions

The empirical expression provided for electron mobility could serve as a tool for calibrating $\beta$-Ga$_2$O$_3$'s potential in high-performance device applications. This work suggests that, for low doping densities, the observed electron mobility is near the intrinsic limit. One implication of this finding is that further enhancements in mobility under standard conditions might be challenging. Potential areas for exploration include examining strain as a means of modifying phonon energies or leveraging two-dimensional electron gas structures at Ga$_2$O$_3$ heterojunctions to enhance mobility. Such approaches could alleviate some of the constraints imposed by intrinsic impurity scattering and the strong Fröhlich interaction.

Conclusion

This paper significantly deepens the understanding of intrinsic transport limits in $\beta$-Ga$_2$O$_3$, emphasizing the dominance of electron-PO phonon interactions. The implications of these findings are pertinent to the design of future electronic components which utilize $\beta$-Ga$_2$O$_3$, particularly in contexts where high temperatures and specific doping conditions are endemic. Additionally, this research lays the groundwork for further exploration into materials engineering solutions that might overcome these intrinsic limitations.