We describe a new approach to compute the electron-phonon self-energy and carrier mobilities in semiconductors. Our implementation does not require a localized basis set to interpolate the electron-phonon matrix elements, with the advantage that computations can be easily automated. Scattering potentials are interpolated on dense $\mathbf{q}$ meshes using Fourier transforms and ab initio models to describe the long-range potentials generated by dipoles and quadrupoles. To reduce significantly the computational cost, we take advantage of crystal symmetries and employ the linear tetrahedron method and double-grid integration schemes, in conjunction with filtering techniques in the Brillouin zone. We report results for the electron mobility in Si, GaAs, and GaP obtained with this new methodology.
High quality berylium doped InAs layer grown by MBE on GaAs substrate has been examined via magnetotransport measurements and high resolution quantitative mobility spectrum analysis in the range from 5 to 300 K and up to 15 T magnetic field. The layer homogenity and dopant concentration has been proofed via HR-SIMS. The results shew four channel conductivity and essential splitting of the most populated holelike channel below 55 K. The multilayer model concluded from the QMSA results has been compared with nextnano simulation.
In polar semiconductors and oxides, the long-range nature of the electron-phonon (\textit{e}-ph) interaction is a bottleneck to compute charge transport from first principles. Here, we develop an efficient ab initio scheme to compute and converge the \textit{e}-ph relaxation times (RTs) and electron mobility in polar materials. We apply our approach to GaAs, where using the Boltzmann equation with state-dependent RTs, we compute mobilities in excellent agreement with experiment at 250$-$500~K. The $e$-ph RTs and the phonon contributions to intravalley and intervalley $e$-ph scattering are also…
Strain engineering provides an effective way of tailoring the electronic and optoelectronic properties of semiconductor nanomaterials and nanodevices, giving rise to novel functionalities. Here, we present direct experimental evidence of strain-induced modifications of hole mobility in individual GaAs nanowires, using in situ transmission electron microscopy (TEM). The conductivity of the nanowires varied with applied uniaxial tensile stress, showing an initial decrease of ~5-20% up to a stress of 1~ 2 GPa, subsequently increasing up to the elastic limit of the nanowires. This is attributed to…
Two-dimensional (2D) semiconductors have demonstrated great potential for next-generation electronics and optoelectronics. An important property for these applications is the phonon-limited charge carrier mobility. The common approach to calculate the mobility from first principles relies on the interpolation of the electron-phonon coupling (EPC) matrix. However, it neglects the scattering by the dynamical quadrupoles generated by phonons, limiting its accuracy. Here we present a first-principles method to incorporate the quadrupole scattering, which results in a much better interpolation qual…
Considering scattering by unintentional background charged impurities and by charged dopants in the modulation doping layer as well as by GaAs acoustic phonons, we theoretically consider the practical intrinsic (phonons) and extrinsic (background and dopants) limits to carrier mobility in modulation doped AlGaAs-GaAs 2D semiconductor structures. We find that reducing background impurity density to $10^{12}$ cm$^{-3}$ along with a modulation doping separation of 1000 Åor above will achieve a mobility of $100 \times 10^6$ cm$^2$/Vs at a carrier density of $3\times 10^{11}$ cm$^{-2}$ for T=1K. At…
Photoluminescence and magnetotransport measurements have been performed to assess the quality of modulation doped GaAs/AlGaAs heterostructures. The temporal evolution of the low-temperature electron mobility of samples prepared in a molecular beam epitaxy chamber containing manganese as a source material was studied. Mn contamination was identified to be responsible for the reduction of the electron mobility to 1 x 10^{6} cm^{2}/Vs and the appearance of a distinct photoluminescence band. In contrast, structures in which this signal is absent reach mobility values of 5.4 x 10^{6} cm^{2}/Vs. Thi…
Absence of an efficient technology of GaAs passivation limits the use of III-V semiconductors in modern electronics. The effect reported here can possibly lead to a solution of this long standing problem. We found that an electrically conducting interfacial channel is formed when insulating metal oxide dielectrics are deposited on untreated semi-insulating GaAs wafers by reactive RF sputtering in argon/oxygen plasma. The conducting channel is n-type with the surface charge density of 10^7 to 10^10 cm^-2 and Hall mobility as high as 6000 cm^2/Vsec, depending on the RF plasma excitation power an…
The resistivity and the mobility of Carbon doped GaAs nanowires have been studied for different doping concentrations. Surface effects have been evaluated by comparing upassivated with passivated nanowires. We directly see the influence of the surface: the pinning of the Fermi level and the consequent existence of a depletion region lead to an increase of the mobility up to 30 cm^2/(V*s) for doping concentrations lower than 3*10^18 cm^-3. Electron beam induced current measurements show that the minority carrier diffusion path can be as high as 190 nm for passivated nanowires.
Motivated by recent breakthrough in molecular beam epitaxy of GaAs/AlGaAs quantum wells [Y. J. Chung \textit{et al.}, Nature Materials \textbf{20}, 632 (2021)], we examine contributions to mobility and quantum mobility from various scattering mechanisms and their dependencies on the electron density. We find that at lower electron densities, $n_e \lesssim 1 \times 10^{11}$ cm$^{-2}$, both transport and quantum mobility are limited by unintentional background impurities and follow a power law dependence, $\propto n_e^α$, with $α\approx 0.85$. Our predictions for quantum mobility are in reasonab…
We implement metallic layers of Si-doped (110) GaAs as modulation doping in high mobility p-type heterostructures, changing to p-growth conditions for the doping layer alone. The strongly auto-compensated doping is first characterized in bulk samples, identifying the metal-insulator transition density and confirming classic hopping conduction in the insulating regime. To overcome the poor morphology inherent to Si p-type (110) growth, heterostructures are fabricated with only the modulation doping layer grown under p-type conditions. Such heterostructures show a hole mobility of 1.75x10^2 cm^2…
We include the treatment of quadrupolar fields beyond the Fröhlich interaction in the first-principles electron-phonon vertex in semiconductors. Such quadrupolar fields induce long-range interactions that have to be taken into account for accurate physical results. We apply our formalism to Si (nonpolar), GaAs, and GaP (polar) and demonstrate that electron mobilities show large errors if dynamical quadrupoles are not properly treated.
We provide evidence that gallium purity is the primary impediment to attainment of ultra-high mobility in a two-dimensional electron gas (2DEG) in AlGaAs/GaAs heterostructures grown by molecular beam epitaxy (MBE). The purity of gallium can be enhanced dramatically by in-situ high temperature outgassing within an operating MBE. Based on analysis of data from an initial growth campaign in a new MBE system and modifications employed for a 2nd growth campaign, we have produced 2DEGs with low temperature mobility in excess of 35x10^6cm2/Vs at density n=3.0x10^11/cm2 and mobility 18x10^6cm2/Vs at n…
In order to characterize magnetic-field (B) tunable THz plasmonic detectors, spectroscopy experiments were carried out at liquid helium temperatures and high magnetic fields on devices fabricated on a high electron mobility GaAs/AlGaAs heterostructure. The samples were either gated (the gate of a meander shape) or ungated. Spectra of a photovoltage generated by THz radiation were obtained as a function of B at a fixed THz excitation from a THz laser or as a function of THz photon frequency at a fixed B with a Fourier spectrometer. In the first type of measurements, the wave vector of magnetopl…
We report on the growth and electrical characterization of a series of two-dimensional hole systems (2DHSs) used to study the density dependence of low temperature mobility in 20 nm GaAs/AlGaAs quantum wells. The hole density was controlled by changing the Al mole fraction and the setback of the delta-doping layer. We varied the density over a range from 1.8 $\times$ 10$^{10}$ cm$^{-2}$ to 1.9 $\times$ 10$^{11}$ cm$^{-2}$ finding a nonmonotonic dependence of mobility on density at T = 0.3 K. Surprisingly, a peak mobility of 2.3 $\times$ 10$^6$ cm$^2$/Vs was measured at a density of 6.5 $\times…
We report on a systematic study of the density dependence of mobility in a low-density Carbon-doped (100) GaAs two-dimensional hole system (2DHS). At T= 50 mK, a mobility of 2.6 x 10^6 cm^2/Vs at a density p=6.2 x 10^10 cm^- was measured. This is the highest mobility reported for a 2DHS to date. Using a back-gated sample geometry, the density dependence of mobility was studied from 2.8 x 10^10 cm^-2 to 1 x 10^11 cm^-2. The mobility vs. density cannot be fit to a power law dependence of the form mu ~ p^alpha using a single exponent alpha. Our data indicate a continuous evolution of the power la…
We present a first-principles framework to investigate the electron scattering channels and transport properties for polar material by combining the exact solution of linearized electron-phonon (e-ph) Boltzmann transport equation in its integral-differential form associated with the e-ph coupling matrices obtained from polar Wannier interpolation scheme. No ad hoc parameter is required throughout this calculation, and GaAs, a well-studied polar material, is used as an example to demonstrate this method. In this work, the long-range and short-range contributions as well as the intravalley and i…
In time-resolved Faraday rotation experiments we have detected an inplane anisotropy of the electron spin-dephasing time (SDT) in an $n$--modulation-doped GaAs/Al$_{0.3}$Ga$_{0.7}$As single quantum well. The SDT was measured with magnetic fields of $B\le 1$ T, applied in the $[110]$ and $[1\bar{1}0]$ inplane crystal directions of the GaAs quantum well. For fields along $[1\bar{1}0]$, we have found an up to a factor of about 2 larger SDT than in the perpendicular direction. Fully microscopic calculations, by numerically solving the kinetic spin Bloch equations considering the D'yakonov-Perel' a…
Ideal two-dimensional (2D) semiconductors with high mobility comparable to three-dimensional (3D) Si or GaAs are still lacking, hindering the development of high-performance 2D devices. Here in this work, using first-principles calculations and considering all the electron-phonon couplings, we show that monolayer BX (X = P, As, Sb) with honeycomb lattices have intrinsic phonon-limited carrier mobility reaching record-high values of 1200-14000 $cm^2V^{-1}s^{-1}$ at room temperature. Despite being polar and the band edges located at the K point with multiple valleys, these three systems unusuall…
Time-resolved optical measurements of electron-spin dynamics in a (110) GaAs quantum well are used to study the consequences of a strongly anisotropic electron g-tensor, and the origin of previously discovered all-optical nuclear magnetic resonance. All components of the g-tensor are measured, and a strong anisotropy even along the in-plane directions is found. The amplitudes of the spin signal allow the study of the spatial directions of the injected spin and its precession axis. Surprisingly efficient dynamic nuclear polarization in a geometry where the electron spins are injected almost tra…
We report on time-resolved Kerr rotation measurements of spin coherence of electrons in the first excited subband of a high-mobility low-density two-dimensional electron system in a GaAs/Al0.35Ga0.65As heterostructure. While the transverse spin lifetime (T2*) of electrons decreases monotonically with increasing magnetic field, it has a non-monotonic dependence on the temperature, with a peak value of 596 ps at 36 K, indicating the effect of inter-subband electron-electron scattering on the electron spin relaxation. The spin lifetime may be long enough for potential device application with elec…
We perform a full microscopic investigation on the spin relaxation in $n$-type (001) GaAs quantum wells with Al$_{0.4}$Ga$_{0.6}$As barrier due to the D'yakonov-perel' mechanism from nearly 20 K to the room temperature by constructing and numerically solving the kinetic spin Bloch equations. We consider all the relevant scattering such as the electron--acoustic-phonon, the electron--longitudinal-optical-phonon, the electron--nonmagnetic-impurity and the electron-electron Coulomb scattering to the spin relaxation. The spin relaxation times calculated from our theory with a fitting spin splittin…
Selective area growth (SAG) of nanowires and networks promise a route toward scalable electronics, photonics and quantum devices based on III-V semiconductor materials. The potential of high-mobility SAG nanowires however is not yet fully realized, since interfacial roughness, misfit dislocations at the nanowire/substrate interface and non-uniform composition due to material intermixing all scatter electrons. Here, we explore SAG of highly lattice-mismatched InAs nanowires on insulating GaAs(001) substrates and address these key challenges. Atomically smooth nanowire/substrate interfaces are a…
Space charge formation in chromium-compensated GaAs sensors is investigated by the laser-induced transient current technique applying pulsed and DC bias. Formation of non-standard space charge manifested by an appearance of both negatively and positively charged regions in DC biased sensors was revealed during 5 ms after switching bias. Using Monte Carlo simulations of current transients we determined enhanced electron lifetime τ = 150 ns and electron drift mobility μd = 3650 cm2/Vs. We developed and successfully applied theoretical model based on fast hole trapping in the system with spatiall…
First-principles calculations of $e$-ph interactions are becoming a pillar of electronic structure theory. However, the current approach is incomplete. The piezoelectric (PE) $e$-ph interaction, a long-range scattering mechanism due to acoustic phonons in non-centrosymmetric polar materials, is not accurately described at present. Current calculations include short-range $e$-ph interactions (obtained by interpolation) and the dipole-like Fröhlich long-range coupling in polar materials, but lack important quadrupole effects for acoustic modes and PE materials. Here we derive and compute the lon…
N-type doping of GaAs nanowires has proven to be difficult because the amphoteric character of silicon impurities is enhanced by the nanowire growth mechanism and growth conditions. The controllable growth of n-type GaAs nanowires with carrier density as high as 1020 electron/cm3 by self-assisted molecular beam epitaxy using Te donors is demonstrated here. Carrier density and electron mobility of highly doped nanowires are extracted through a combination of transport measurement and Kelvin probe force microscopy analysis in single-wire field-effect devices. Low-temperature photoluminescence is…
We have observed cyclotron resonance in a high-mobility GaAs/AlGaAs two-dimensional electron gas by using the techniques of terahertz time-domain spectroscopy combined with magnetic fields. From this, we calculate the real and imaginary parts of the diagonal elements of the magnetoconductivity tensor, which in turn allows us to extract the concentration, effective mass, and scattering time of the electrons in the sample. We demonstrate the utility of ultrafast terahertz spectroscopy, which can recover the true linewidth of cyclotron resonance in a high-mobility ($>{10}^{6} \mathrm{cm^{2} V^{-1…
We present a general coupled electron-phonon Boltzmann transport equations (BTEs) scheme designed to capture the mutual drag of the two interacting systems. By combining density functional theory based first principles calculations of anharmonic phonon-phonon interactions with physical models of electron-phonon interactions, we apply our implementation of the coupled BTEs to calculate the thermal conductivity, mobility, Seebeck and Peltier coefficients of n-doped gallium arsenide. The measured low temperature enhancement in the Seebeck coefficient is captured using the solution of the fully co…
The great possibilities for strain engineering in core/shell nanowires have been explored as an alternative route to tailor the properties of binary III-V semiconductors without changing their chemical composition. In particular, we demonstrate that the GaAs core in GaAs/In(x)Ga(1-x)As or GaAs/In(x)Al(1-x)As core/shell nanowires can sustain unusually large misfit strains that would have been impossible in conventional thin-film heterostructures. The built-in strain in the core can be regulated via the composition and the thickness of the shell. Thick enough shells become almost strain-free, wh…
We have studied spin dephasing in a high-mobility two-dimensional electron system (2DES), confined in a GaAs/AlGaAs quantum well grown in the [110] direction, using the resonant spin amplification (RSA) technique. From the characteristic shape of the RSA spectra, we are able to extract the spin dephasing times (SDT) for electron spins aligned along the growth direction or within the sample plane, as well as the $g$ factor. We observe a strong anisotropy in the spin dephasing times. While the in-plane SDT remains almost constant as the temperature is varied between 4 K and 50 K, the out-of-plan…
The frequency dependence of microwave-induced resistance oscillations (MIROs) has been studied experimentally in high-mobility electron GaAs/AlGaAs structures to explore the limits at which these oscillations can be observed. It is found that in dc transport experiments at frequencies above 120 GHz, MIROs start to quench, while above 230 GHz, they completely disappear. The results will need to be understood theoretically but are qualitatively discussed within a model in which forced electronic charge oscillations (plasmons) play an intermediate role in the interaction process between the radia…
In this work we address experimentally a number of unresolved issues related to microwave induced resistance oscillations (MIRO) and the zero-resistance states observed recently on very high-mobility 2D electron gases in GaAs/AlGaAs heterostructures. In particular, we examine electrodynamic effects via reflection/absorption experiments and study the exact waveform of MIRO and their damping due to temperature. It is shown that electrodynamic effects due to metallic-like reflection and plasmons are important producing a wide cyclotron resonance line and a number of oscillations which do not coin…
Quantum devices formed in high-electron-mobility semiconductor heterostructures provide a route through which quantum mechanical effects can be exploited on length scales accessible to lithography and integrated electronics. The electrostatic definition of quantum dots in semiconductor heterostructure devices intrinsically involves the lithographic fabrication of intricate patterns of metallic electrodes. The formation of metal/semiconductor interfaces, growth processes associated with polycrystalline metallic layers, and differential thermal expansion produce elastic distortion in the active …
