GaAs Field Research Articles

Time-dependent Nuclear Spin Polarization, Effects of Device Non-uniformity on the Gunn Effect, and Electron Spin Dynamics at High Electric Fields in GaAs

Time-dependent Nuclear Spin Polarization, Effects of Device Non-uniformity on the Gunn Effect, and Electron Spin Dynamics at High Electric Fields in GaAs

The Temperature Dependences of the Electron-Deformation Potential Phonon Interacting System of Quasi Two Dimensional System Under Circularly Oscillating Fields in GaAs and Ge

The Temperature Dependences of the Electron-Deformation Potential Phonon Interacting System of Quasi Two Dimensional System Under Circularly Oscillating Fields in GaAs and Ge

Temperature behavior of Franz-Keldysh oscillation and evaluation of interface electric fields attributed to strain effect of InAs/GaAs quantum dot

In this work, the electric field-induced Franz-Keldysh effect was used to investigate the localized electric fields in GaAs interfaces attributed to strain effect of InAs/GaAs quantum dots (QD). The electric fields were investigated by photoreflectance spectroscopy (PR). PR spectra of the InAs/GaAs QDs showed complex Franz-Keldysh oscillations (FKOs) with various temperatures. It is suggested that the FKOs originated from the interface electric fields predominately caused by the strain-induced polarization at GaAs interface near the InAs QDs. The InAs/GaAs QDs have a broad range of interface electric fields from ∼104 V/cm to ∼2х105 V/cm. Temperature behavior of FKO amplitude distribution is explained by temperature dependent carrier confinement effect.

Fine structure of the Mn acceptor in GaAs

We reveal the electronic level structure of the Mn acceptor, which consists of a valence-band hole bound to an ${\mathrm{Mn}}^{2+}$ ion, in presence of applied uniaxial stress and an external magnetic field in bulk GaAs. Resonant spin-flip Raman scattering is used to measure the $g$ factor of the ${\mathrm{A}}_{\text{Mn}}^{0}$ center in the ground and excited states with the total angular momenta $F=1$ and $F=2$ and characterize the optical selection rules of the spin-flip transitions between these Mn-acceptor states. We determine the random stress fields near the Mn acceptor, the constant of the antiferromagnetic exchange interaction between the valence-band holes and the electrons of the inner ${\mathrm{Mn}}^{2+}$ shell as well as the deformation potential for the exchange energy. The $p\text{\ensuremath{-}}d$ exchange energy, in particular, decreases significantly with increasing compressive stress. By combining the experimental Raman study with the developed theoretical model on the scattering efficiency, in which also the random local and external uniaxial stresses and magnetic field are considered, the fine structure of the Mn acceptor is determined in full detail.

Photorefractive space charge electric field in GaAs:Cr with external electric and magnetic fields

Using band charge transport model, the effect of external dc electric (E0) and magnetic fields (B0) on photorefractive parameters, viz, space charge electric field (ESC) and gain coefficient in steady state regime is investigated for Cr doped GaAs. In particular, space charge electric field of ∼105 V/cm is obtained for E0=5.0×102 V/cm and B0=0.064 T. ESC obtained is nearly 103 times higher than, in absence of either E0 or B0. The gain coefficient exhibits considerable enhancement at above values of E0 and B0.

Orientational dependencies of space-charge waves under the action of a magnetic field in GaAs:Cr

Space-charge wave (SCW) excitation is studied under the influence of an external magnetic field in GaAs:Cr depending on the orientational angle of the exciting oscillating sinusoidal interference pattern to the external electric field. It was found that the tilt of the SCW propagation direction induced by the magnetic field results in a shift of the orientational dependence curve. This feature allows determining the deviation angle of charge carriers’ trajectory and their sign. A quantitative theoretical explanation of the effects is proposed and a theoretical expression for the SCW ac-current is given.

Analysis of the theory of the electron avalanche domain (EAD) in GaAs photoconductive semiconductor switches

An electron avalanche domain (EAD) theory for the filamentary current (streamer) formation and propagation in semi-insulating (SI) GaAs photoconductive semiconductor switches (PCSS) has been derived from the analysis of the experiments. The theory perfects the EAD concept and reveals that the steady increase of the non-equilibrium carrier density for the strong electric field and the high carrier density effect can lead to form the streamer in the local area of the high gain GaAs PCSS. The EAD theory is used successfully to explain the following experimental phenomena happened in the high gain GaAs PCSS which include the formation and propagation of the current filament, the occurrence of carrier avalanche in SI GaAs PCSS when the bias field across the device is below the threshold electric field in GaAs for intrinsic impact ionization. The results show that the EAD theory is a generalized theory to analyze the streamer formation in such transferred-electron effect semiconductor devices.

Beta-detected NMR study of the local magnetic field in epitaxial GaAs:Mn

A low energy beam of spin polarized 8 Li + has been employed to study the magnetic field distribution in an epitaxial thin film of 5.4% Mn doped GaAs(180nm) on a (100) GaAs substrate via beta-detected NMR. The spectrum is a strong function of the implantation energy in the range 28 keV to 3 keV. In the magnetic layer, there is no indication of a missing fraction, and even more remarkable, there is a broad negatively-shifted resonance. The spin lattice relaxation rate is, however, much faster in the Mn doped layer than in the substrate. A sharp peak characteristic of nonmagnetic GaAs is observed down to the lowest implantation energy, for which none of the Li should reach the substrate. This unexpected depth dependence is discussed.

Electrical detection of spin current and spin relaxation in nonmagnetic semiconductors

We report an electrical method for the detection of spin current and spin relaxation in nonmagnetic semiconductors. Optically polarized spins are dragged by an electric field in GaAs. We use the anomalous Hall effect for the detection of spin current and spin relaxation. It is found that the effect depends on the electric field and doping density as well as on temperature, but not on the excitation power. A calculation for the effect is performed using the measured spin polarization by a pump–probe experiment. The results are also discussed in comparison with a quantitative evaluation of the spin lifetimes of the photogenerated electrons under drift in GaAs.

MONTE CARLO MODELING OF HOT ELECTRON TRANSPORT IN BULK AlAs, AlGaAs AND GaAs AT ROOM TEMPERATURE

The results of an ensemble Monte Carlo simulation of electron drift velocity response on the application field in bulk AlAs , AlGaAs and GaAs are presented. All dominant scattering mechanisms in the structure considered have been taken into account. For all materials, it is found that electron velocity overshoot only occurs when the electric field is increased to a value above a certain critical field, unique to each material. This critical field is strongly dependent on the material parameters. Transient velocity overshoot has also been simulated, with the sudden application of fields up to 1600 kVm-1, appropriate to the gate-drain fields expected within an operational field effect transistor. The electron drift velocity relaxes to the saturation value of ~105 ms-1 within 4 ps, for all crystal structures. The steady state and transient velocity overshoot characteristics are in fair agreement with other recent calculations.

Controlling chaos with magnetic field in semi-insulating GaAs

Chaos control has stimulated a large amount of work. We have studied the effect of an external parallel magnetic field on the low-frequency current oscillations observed on a molecular beam epitaxy GaAs sample grown at 265 deg. C, and we have shown that it can be efficiently used for chaos control. The study of the magnetoresistance indicates that the effect of the magnetic field on the charges of the hopping conduction mechanism induces changes in the low-frequency oscillations. Due to this, we have used the magnetic field to control chaos assessed through direct observation low-frequency oscillations, their attractors, and bifurcation diagrams. We also found that the magnetic field interferes indirectly with the Coulombian interaction between the free charges in the conduction band and the hopping carriers, as well as with the recombination mechanism of field enhanced trapping. Controlling the low-frequency oscillations in semi-insulating GaAs by means of an external magnetic field permits probing the interaction of the slow hopping carriers and the fast free carriers in the electric-field domains.

Residual strain field in indented GaAs

This paper presents an optical mean to probe carefully the strain field generated by a microindentation on [111]-oriented GaAs sample, using micro-Raman spectroscopy and microphotoluminescence spectroscopy. Raman and photoluminescence signals recorded from the same point of the sample are directly compared. The frequency shift of the longitudinal and transverse optical phonons was analyzed in great detail, revealing unambiguously the presence of both compressive and tensile strains within the indented area. Outside the indentation fingerprint, the magnitude of strain deduced from luminescence measurements was found to be lower than the one determined by Raman scattering. The Raman spectra revealed significant variations of the optical phonons polarizability with the deformation. Finally, atomic force microscope images of the indented zone aid in the interpretation.

Full-band matrix solution of the Boltzmann transport equation and electron impact ionization in GaAs

A direct matrix solution of the Boltzmann transport equation is developed to investigate impact ionization and other hot carrier phenomena in compound semiconductor devices. The model is applied to GaAs. A full-band calculation of the semiconductor structure is performed using k · p theory. An original determination of the distribution function in k-space as a function of electric field and temperature is achieved. The dependence of the ionization rate on energy, of the drift velocity and of the ionization coefficient on electric field are in good agreement with Monte Carlo data at 300 K and validate the modeling approach. The variation of the impact ionization coefficient on temperature and electric field in GaAs is discussed.

Distribution of electric field in GaAs diffused structures doped by iron or chromium

An analysis based on numerical calculations has been done for the distribution of an electric field in GaAs diffused by chromium or iron-doped structures. First, a calculation has been carried out for the non-uniform impurity distribution using experimentally measured Fe and Cr profiles. It is shown that a ν-n-junction is formed in chromium-doped structures, and a π-n-junction is formed in iron-doped ones. A conclusion is made that these junctions are graded.

Magneto-plasmon spectrum in a semiconductor under intense laser radiation

We study how a linearly polarised intense laser irradiation affects the magneto-plasmon (MP) modes in a semiconductor. We first evaluate the electron Green's function, the density–density correlation function, and the random-phase approximation (RPA) dielectric function in the (Q,t) representation in the presence of a laser field and a quantizing magnetic field. From these results, we obtain the electron density of states (DOS) and the plasmon spectrum in the (Q,Ω) representation and investigate the dependence of the MP excitations on the frequency and intensity of the laser field in GaAs. The results are pertinent to the application of free-electron lasers developed recently.

Quenching of persistent photoconductivity and decrease of electron concentration by high electric fields in GaAs delta-doped by Sn on vicinal substrate structures

This paper reports the measurements of high electric field transport and the persistent photoconductivity in delta-doped by Sn on vicinal and singular substrate GaAs structures. Transport properties of the hot electron gas were measured in the temperature range 4.2 K < T < 300 K at high electric fields up to E = 10 4 V/cm in darkness and under illumination using a pulse technique. Dependence of the current density J( E) showed an anisotropy in [1 1 0] and [1 − 1 0] directions in GaAs(δ-Sn) on vicinal substrate structures and histeresis in electric field at low temperatures. In GaAs(δ-Sn) on singular substrate structures the anisotropy of conductivity is small. The persistent photoconductivity was observed with well defined threshold T c ≈ 240 K in GaAs(δ-Sn) on vicinal substrate structures. At T = 4.2 K by applying a high voltage the persistent photoconductivity may be quenched and the resistance of the sample increased by an order of magnitude. The high conductivity state arises again due to illumination of the sample or due to heating to temperatures above ≈ 240 K.

Transition-Metal Impurity Luminescence in GaAs and its Application to Material Characterization

AbstractA number of sharp characteristic luminescence lines has been observed for GaAs doped with 3d transition-metal impurities in the near-infrared region, the origin being attributed to the zero-phonon intracenter transitions between the energy levels of the metal ions split by the crystal field of the GaAs lattice. It is also known that these luminescence lines are very sensitive to the surrounding field of the transition-metal impurities. The luminescence of Cr-doped GaAs has been most extensively studied, the spectrum revealing a very sharp luminescence line at 0.839 eV. In this paper we review the results on the successful applications of this Cr-related luminescence line to characterization of in-depth profiles of arsenic vacancy in thermally annealed GaAs, local strain field in In-doped GaAs and interface stress at heterostructures grown on Cr-doped GaAs substrate.

An optically detected cyclotron resonance study of bulk GaAs

We have measured optically detected cyclotron resonance using far-infrared radiation on an exceptionally pure sample of GaAs in fields up to 15.5 T. This relatively new experimental technique is shown to offer high resolution of free and donor impurity-bound electron transitions without the reproducibility problems of photoconductivity. The data confirm the existence of metastable donor states and provide a detailed picture of chemical shifts. The optically detected cyclotron resonance signal represents an interaction between the donor bound electron states which are influenced by the far-infrared radiation and the donor bound exciton states which are responsible for the photoluminescence. Attenuation of the luminescence intensity under far-infrared illumination is primarily the result of a photothermal effect. At high fields, there is indication of an interaction between the electron and excitonic energy levels.

Magnetic field dependence of selective pair luminescence in GaAs

The shift in the final state emission energy, resulting from selective pair luminescence in an applied magnetic field in GaAs, is very small. Any shift that is observed is toward lower energy. The relatively constant emission energy in the presence of an applied magnetic field is realized because the increase in band-gap energy, which would shift the emission toward higher energies, is offset by an increase in the donor binding energy which shifts the emission toward lower energies. The acceptor binding energy is essentially constant with applied field while the change in the Coulomb term, due to a change in the pair separation in a magnetic field, is quite small. As a result, the same acceptor excited states are identified in the presence of an applied magnetic field, as in zero field for the same pump energy. The results of this experiment are limited to applied fields ≤36 kG.

Strain fields due to differential dilatation at metal/semiconductor contacts and resulting piezoelectrical fields in GaAs

Due to the difference in their dilatation coefficients, the deposition of metallic layers on semiconductor substrates induce strain fields. In polar semiconductors these strain fields are coupled with piezoelectrical ones and can disturb the characteristics of devices. We present a calculation of these fields which is valid as long as the deposited layers can be considered as thin films. In this approximation, our method allow the determination of the strain and of the electrical fields created by layers of any geometrical shape. Orientation and shape effects are then discussed.