Shubnikov-de Haas oscillations of two-dimensional electron gases in AlYN/GaN and AlScN/GaN heterostructures

Abstract

AlYN and AlScN have recently emerged as promising nitride materials that can be integrated with GaN to form two-dimensional electron gases (2DEGs) at heterojunctions. Electron transport properties in these heterostructures have been enhanced through careful design and optimization of epitaxial growth conditions. In this work, we report for the first time Shubnikov-de Haas (SdH) oscillations of 2DEGs in AlYN/GaN and AlScN/GaN heterostructures, grown by metal-organic chemical vapor deposition. SdH oscillations provide direct access to key 2DEG parameters at the Fermi level: (1) carrier density, (2) electron effective mass (m* ~ 0.24 me for AlYN/GaN and m* ~ 0.25 me for AlScN/GaN), and (3) quantum scattering time (~ 68 fs for AlYN/GaN and ~ 70 fs for AlScN/GaN). These measurements of fundamental transport properties provide critical insights for advancing emerging nitride semiconductors for future high-frequency and power electronics.

Figures (4)

• Figure 1: Schematic diagrams of the epitaxial (a) AlYN/GaN and (c) AlScN/GaN heterostructures grown by MOCVD. Longitudinal magnetoresistance $R_{\rm xx}$ of (b) the AlYN/GaN 2DEG and (d) the AlScN/GaN 2DEG, measured over temperatures from 2 to 11 K and magnetic field $B$ from 10 to 14 T. The faint lines show the raw $R_{\rm xx}$ data, while the solid lines represent the data obtained using a Savitzky–Golay filter, which reduces noise while preserving the peak positions and amplitudes.
• Figure 2: The oscillatory component $\Delta R_{\rm xx}$ as a function of $1/B$ for (a) AlYN/GaN and (b) AlScN/GaN heterostructures. For AlYN/GaN, the oscillation period $\Delta(1/B) = 0.0039 \, \text{T}^{-1}$ corresponds to a 2DEG density of $n_s \approx 1.23 \times 10^{13} \, \mathrm{cm}^{-2}$. In contrast, the smaller oscillation period of $\Delta(1/B) = 0.0027 \, \mathrm{T}^{-1}$ in AlScN/GaN reflects a higher 2DEG density of $n_s \approx 1.81 \times 10^{13} \, \mathrm{cm}^{-2}$. Fast Fourier transform (FFT) analysis of $\Delta R_{\rm xx}$ vs. $1/B$ shows a single dominant frequency for both samples. The 2DEG densities extracted from both real-space oscillation period and reciprocal-space FFT analyses are consistent with low-field Hall effect measurements.
• Figure 3: Temperature dependence of peak $\Delta R_{\rm xx}$ at various B fields for (a) AlYN/GaN and (b) AlScN/GaN samples. The solid curves represent the fits to $\chi / \sinh(\chi)$ in Eq.(1) to extract the electron effective mass, yielding $m^* = (0.24 \pm 0.01) \, m_{\rm e}$ for the AlYN/GaN 2DEG and $m^* = (0.25 \pm 0.01) \, m_{\rm e}$ for the AlScN/GaN 2DEG.
• Figure 4: Dingle plots, where $\ln\left(A^* \sinh(\chi) \, / \, \chi\right)$ is plotted versus $1/B$ at 2 K, for both AlYN/GaN and AlScN/GaN 2DEG, allowing for the extraction of quantum scattering time $\tau_{\rm q}$. $A^*$ denotes the absolute value at the valley of $\Delta R_{\rm xx}$. The solid black lines are fits to the disorder damping term $e^{-\pi / (\omega_{\rm c} \tau_{\rm q})}$ from Eq.(1).