Nonresonant hydrogen dopants in In(AsN): A route to high electron concentrations and mobilities

We provide evidence for the unique effect of hydrogen on the transport properties of the mid-infrared alloy In(AsN). High electron concentrations and mobilities are simultaneously achieved in hydrogenated In(AsN), and Shubnikov-de Haas oscillations are observed up to near room temperature. These results can be accounted for by the formation of N-H donor complexes with energy levels well above the Fermi energy, far from resonance with the conduction electrons, thus resulting in weak electron scattering even at high donor concentrations. Similar effects should be found in other narrow band gap dilute nitride alloys.

Figure 1

Low temperature ($T$ $=$ 4.2 K) transverse magnetoresistance, $\Delta R_{xx}/R_{xx}$, versus magnetic field, $B_z$, for an In(AsN) Hall bar with [N] $=$ 1$\%$ before (V) and after (H) hydrogenation ($d_{\mathrm{H}}=4\times {10}^{17}$ ions/cm${}^2$). The top inset sketches a Hall bar and the angle θ between B and the $z$ axis. The right inset shows $d{R}_{xx}/dB$ versus $B^{-1}$ for B tilted at different angles θ ($T=2$ K).

Figure 2

Fast Fourier Transform (FFT) analysis of the SdH oscillations in the resistance ($R_{xx}$) for different angles θ of magnetic field B for an In(AsN) Hall bar with [N] $=$ 1$\%$ and $d_{\mathrm{H}}$ $=$ 4 × 10${}^{17}$ ions/cm${}^2$ ($T$ $=$ 2 K). For $\theta =0^{\circ }$, two peaks are observed at frequencies $B_f$${}_{3\mathrm{D}}$ $=$ (185 ± 5) T and $B_f$${}_{2\mathrm{D}}$ $=$ (230 ± 5) T. $B_f$${}_{3\mathrm{D}}$ is independent of θ (see vertical line), thus indicating that is associated with the SdH effect in a 3D electron gas of density $n_e={\left(2e{B}_{f3\mathrm{D}}/\hslash \right)}^{3/2}/\left(3{\pi }^2\right)=1.4\times {10}^{19}{\mathrm{cm}}^{-3}.$ The peak at $B_f$${}_{2\mathrm{D}}$ is clearly observed only for $\theta =0^{\circ }$ and originates from the SdH effect in a 2D surface accumulation layer with electron density $n_e=2e{B}_{f2\mathrm{D}}/h=1.1\times {10}^{13}{\mathrm{cm}}^{-2}.$ For a 2D surface accumulation, this peak should shift at lower frequency for increasing θ according to $B_f$${}_{2\mathrm{D}}$ ∼ cos(θ) (see blue line and symbols).

Figure 3

Temperature dependence of the resistance $R_{xx}$ versus magnetic field ($B_z$) for a hydrogenated In(AsN) Hall bar with [N] $=$ 1$\%$ ($d_{\mathrm{H}}$ $=$ 4 × 10${}^{17}$ ions/cm${}^2$). To reveal the oscillatory peaks in $R_{xx}$, in the top inset we plot the dependence of $R_{xx}$-$\alpha B_z$ on $B_z$${}^{-1}$ (where α is a constant) at different temperatures. The dependence of $R_{xx}$-$\alpha B_z$ on $B_z$${}^{-1}$ is also shown on the bottom inset at fixed temperature ($T$ $=$ 4.2 K) for hydrogenated In(AsN) Hall bars with [N] $=$ 0$\%$, 0.2$\%$, and 1$\%$ and $d_{\mathrm{H}}$ $=$ 4 × 10${}^{17}$ ions/cm${}^2$.

Figure 4

(a) and (b) Dependence of the electron density ($n_e$) and mobility (${\mu }_e$) on [N] before (V) and after (H) hydrogenation ($d_{\mathrm{H}}$ $=$ 4 × 10${}^{17}$ ions/cm${}^2$) at $T$ $=$ 4.2 K. The values of $n_e$ are derived from the analysis of the Shubnikov-de Haas oscillations (asterisks) and the Hall resistance (dots and circles). Dotted lines are guides to the eye. The continuous line in (a) shows the density of N atoms. (c) Dependence of the electron scattering time (${\tau }_e$) on [N] as derived from ${\tau }_e={\mu }_e{m}_e^{*}/e$ before (V) and after (H) hydrogenation ($d_{\mathrm{H}}$ $=$ 4 × 10${}^{17}$ ions/cm${}^2$) at $T$ $=$ 4.2 K. (d) Calculated dependence of ${\tau }_e$ on the electron density $n_e$ according to the Brooks-Herring model.

Figure 5

(a) Normalized micro-Raman spectra of In(AsN) epilayers before (dotted lines) and after (solid lines) hydrogen incorporation. The spectra were acquired at $T$ $=$ 300 K with a laser of power density $P$ ∼ 10${}^5$ W/cm${}^2$, wavelength λ = 633 nm, and spot diameter $d$ ∼ 1 μm. The H dose (H: 4 × 10${}^{17}$ ions/cm${}^2$ and 25H: 10${}^{19}$ ions/cm${}^2$) is indicated in the figure for each epilayer. (b) Calculated dependence of the frequencies ${\omega }_{\pm }$ of the coupled LO phonon-plasmon modes, $L_{+}$ and $L_{-}$, on the electron density $n_e$ for [N] $=$ 0$\%$ (dashed line) and [N] $=$ 1$\%$ (continuous line). The horizontal lines represent the values of the measured frequencies of the TO and LO modes in InAs. Symbols correspond to the measured values of ${\omega }_{+}$ in hydrogenated In(AsN).

Figure 6

(a) Calculated (lines) and measured (symbols) dependences of the first derivative electron mass ($m_e^{*}$) on the electron density ($n_e$). Dashed and continuous lines correspond to InAs and In(AsN) ([N] $=$ 1$\%$), respectively. Empty symbols correspond to values of $m_e^{*}$ derived from cyclotron resonance studies of virgin samples (see Ref. 25). Full symbols correspond to values of $m_e^{*}$ derived from the $T$ dependence of the Shubnikov-de Haas oscillations. (b) Conduction band minimum ($E_C$), Fermi energy ($E_F$), and energy level ($E_{\mathrm{H}-\mathrm{N}}$) of the H-N donor complex. $E_F-E_C=0.29$ eV and 0.02 eV for [N] $=$ 1$\%$ and 0$\%$, respectively.