Effect In GaAs Research Articles

Parity-independent Kondo effect of correlated electrons in electrostatically defined ZnO quantum dots

Quantum devices such as spin qubits have been extensively investigated in electrostatically confined quantum dots using high-quality semiconductor heterostructures like GaAs and Si. Here, we present a demonstration of electrostatically forming the quantum dots in ZnO heterostructures. Through the transport measurement, we uncover the distinctive signature of the Kondo effect independent of the even-odd electron number parity, which contrasts with the typical behavior of the Kondo effect in GaAs. By analyzing temperature and magnetic field dependences, we find that the absence of the even-odd parity in the Kondo effect is not straightforwardly interpreted by the considerations developed for conventional semiconductors. We propose that, based on the unique parameters of ZnO, electron correlation likely plays a fundamental role in this observation. Our study not only clarifies the physics of correlated electrons in the quantum dot but also holds promise for applications in quantum devices, leveraging the unique features of ZnO.

Influence and Optimization of Interference Effect in GaAs p-i-n Structure on Terahertz Wave Generation

Influence and Optimization of Interference Effect in GaAs p-i-n Structure on Terahertz Wave Generation

Anomalous Hall Effect in GaAs–AlGaAs Quantum Wells Doped by Nonmagnetic Impurities near the Metal–Insulator Transition

Anomalous Hall Effect in GaAs–AlGaAs Quantum Wells Doped by Nonmagnetic Impurities near the Metal–Insulator Transition

300 keV Ar ion induced effects in GaAs and 4H-SiC

Radiation damage effects on the structures of GaAs and 4H-SiC single crystals are investigated after irradiation with 300 keV Ar ions at room temperature. It is found that despite having contrasting physical and chemical properties, 0.3 displacement per atom (dpa) is the threshold of fractional disorder above which there is a rapid damage build-up behavior exhibited by both GaAs and 4H-SiC. 1 dpa means that all atoms are displaced at least once from their respective lattice sites. This study reveals that disordering in irradiated binary semiconductor materials is a discontinuous two-step process wherein various stages of irradiation are marked by different damage growth mechanisms.

Quasi-nondegenerate pump–probe magnetooptical experiment in GaAs/AlGaAs heterostructure based on spectral filtration

We report on a quasi-nondegenerate pump–probe technique that is based on spectral-filtration of femtosecond laser pulses by a pair of mutually-spectrally-disjunctive commercially available interference filters. The described technique enables to obtain pump and probe pulses with wavelengths that are spectrally close but distinct. These contradictory requirements, which are dictated, for example, by a suppression of stray pump photons from the probe beam in spin-sensitive magneto-optical experiments in non-magnetic semiconductors, can be fulfilled at very low cost and basically no requirement on space. Especially the second feature is important in pump–probe microscopy where collinear propagation of pump and probe pulses is dictated by utilization of a microscopic objective and where the setups are typically quite complex but suffer from a limited size of optical breadboards. Importantly, this spectral-filtration of 100 fs long laser pulses does not affect considerably the resulting time-resolution, which remains well below 500 fs. We demonstrate the practical applicability of this technique by performing spin-sensitive magnetooptical Kerr effect (MOKE) experiment in GaAs/AlGaAs heterostructure, where a high-mobility spin system is formed after optical injection of electrons at wavelengths close to the MOKE resonance. In particular, we studied the time- and spatial-evolutions of spin-related (MOKE) and charge-related (reflectivity) signals. We revealed that they evolve in a similar but not exactly the same way which we attributed to interplay of several electron many-body effects in GaAs.

Radiation hardness of GaAs: Cr and Si sensors irradiated by electron beam

The interest in using the radiation detectors based on high resistive chromium-compensated GaAs (GaAs:Cr) in high energy physics and others applied fields has been growing steadily due to its numerous advantages over others classical materials. High radiation hardness at room temperature stands out and needs to be systematically investigated. In this paper an experimental study of the effect of 20.9 MeV electrons generated by the LINAC-200 accelerator on some properties of GaAs:Cr based sensors is presented. In parallel, Si sensors were irradiated at the same conditions, measured and analyzed in order to perform a comparative study. The target sensors were irradiated with the dose up to 1.5 MGy. The current–voltage characteristics, resistivity, charge collection efficiency and their dependences on the bias voltage and temperature were measured at different absorbed doses. An analysis of the possible microscopic mechanisms leading to the observed effects in GaAs:Cr sensors is presented in the article.

Growth and Memory Effect of Ge in GaAs Epilayers Grown in UHV Environment Using IBGe

The growth of Germanium (Ge) with iso-butyl germane (IBGe) as germanium source and the study of Ge memory effect in GaAs grown in UHV environment (Chemical beam epitaxy CBE reactor) is presented. High quality Ge epilayers were grown and a strong Ge memory effect was found in GaAs epilayers grown in the same reactor.

Enhanced terahertz emission of a gallium arsenide thin film on a porous silicon distributed Bragg reflector designed at 800nm wavelength

Enhanced terahertz (THz) radiation was generated from a gallium arsenide thin film integrated on top of porous silicon distributed Bragg reflector (GaAs/PSi DBR). The film's thickness was designed to be less than the penetration depth of the 800 nm excitation source, while the PSi DBR was centered at the laser wavelength to reflect the transmitted photons at the film-substrate interface. Reflection-geometry THz time-domain spectroscopy measurement revealed enhancement in THz peak to peak amplitude by 1.67 and 5.7 times as compared to the same thickness of GaAs on silicon (GaAs/Si) and bulk semi-insulating (SI) GaAs, respectively. In comparison with the bulk SI-GaAs, both thin film samples showed an order of magnitude improvement in the THz output power. The excitation-wavelength study also revealed a maximum increase near the design wavelength. The enhancement was attributed to the high reflectivity at the film-substrate interface and optical cavity effect in GaAs. These factors contributed to an effective optical confinement within the film's THz generation region.

Effect of GaAs(100) substrate misorientation on structural, electronic, and optical properties of AlN nano-sized films obtained by reactive plasma-ion deposition

With the use of reactive plasma-ion deposition, thin nano-sized films of AlN were obtained on the substrates of GaAs(100) with a different degree of misorientation relative to the <100> direction.It was shown that the growth of the AlN films on GaAs substrates with a small degree of misorientation resulted in the formation of the AlN films in the nano-crystalline state. Hence, the film with a cubic crystal system was formed on a precisely oriented GaAs substrate, while on the substrate with 2° misorientation, the film consisted of a mixture of the AlN phases with cubic and hexagonal crystal symmetry. At the same time, the growth of the films on the substrates with a high degree of misorientation resulted in the disappearance of the long-range order in the crystalline structure of the AlN films; this implied the formation of the AlN phase in the amorphous state. The misorientation of the GaAs(100) substrate affected the sizes of the nano-islands formed on the surface of the AlN film. The lower the misorientation of the GaAs(100) substrate, the smaller were the lateral sizes of the nano-islands.Comparing our data for the optical band gap and the dispersion of the refractive index obtained by reactive ion-plasma deposition and the results for the AlN films grown by reactive sputtering, which is the closest method to the technology used in our work, we found that depending on the conditions of the reactive sputtering, nano-sized films of AlN with refractive index values within the range of 2.26–2.38 for the energy range of ∼4.7–4.9 eV and optical band gaps within 5.34–5.71 eV, were obtained. It was possible to obtain thin films with refractive index values within the range of 1.65–3.35 for energy values of ∼4.7–4.9 eV and optical band gaps of ∼5–6.2 eV by the application of the AlN deposition on the surface of semiconductor materials proposed in this study.An increase in the misorientation degree for the GaAs substrate was observed along with an improvement in the structural quality of nano-sized AlN films as well as in their electron structure, surface morphology, and optical properties. Thus, the morphology, surface composition, and optical functional characteristics of hetero-phase AlN/GaAs systems can be controlled by using GaAs substrates with a specified degree of misorientation relative to the <100> direction.

Photovoltaic effect in optical transitions for ultraquantum limit between spin areas of Landau levels

The article is devoted to the investigation of the photovoltaic effect in GaAs under optical transitions between the spin sub-bands of the Landau levels for the ultra quantum limit. The geometry is considered, when the polarization is perpendicular, and the current is directed along the magnetic field. The effect is due to the cubic terms in the Hamiltonian that exist due to the absence of an inversion center. The dependence of the current on the magnetic field has a resonance nature. Such an effect is associated with resonance in the intermediate state and interference of the second-order transition amplitudes with respect to relativistic contributions to the Hamiltonian. The aim of the work is a theoretical and experimental study of the photovoltaic effect for spin resonance. The practical value and scientific novelty lies in the study of the photovoltaic effect at spin resonance. Since a weakly absorbing medium is considered, an increase in the photovoltaic effect is observed as a result of the divergence of the mean square electric field modulus. The practical significance of the results lies in the development of a methodology for studying band parameters, and the terms in the Hamiltonian can lead to electro dipole transitions and photocurrents.

Emergence of liquid crystalline order in the lowest Landau level of a quantum Hall system with internal anisotropy

It has now become evident that interplay between internal anisotropy parameters (such as electron mass anisotropy and/or anisotropic coupling of electrons to the substrate) and electron-electron correlation effects can create a rich variety of possibilities especially in quantum Hall systems. The electron mass anisotropy or material substrate effects (for example, the piezoelectric effect in GaAs) can lead to an effective anisotropic interaction potential between electrons. For lack of knowledge of realistic ab-initio potentials that may describe such effects, we adopt a phenomenological approach and assume that an anisotropic Coulomb interaction potential mimics the internal anisotropy of the system. In this work we investigate the emergence of liquid crystalline order at filling factor ν = 1/6 of the lowest Landau level, a state very close to the point where a transition from the liquid to the Wigner solid happens. We consider small finite systems of electrons interacting with an anisotropic Coulomb interaction potential and study the energy stability of an anisotropic liquid crystalline state relative to its isotropic Fermi-liquid counterpart. Quantum Monte Carlo simulation results in disk geometry show stabilization of liquid crystalline order driven by an anisotropic Coulomb interaction potential at all values of the interaction anisotropy parameter studied.

Photovoltage formation across GaAs p–n junction under illumination of intense laser radiation

Peculiarities of photovoltaic effect in GaAs p–n junction under laser excitation at 10.6 and 1.06 μm wavelengths has been investigated experimentally. When photon energy is far less than the forbidden energy gap, the photovoltage is found to be caused by hot carrier electromotive force. When the junction is illuminated with intense Nd:YAG laser radiation, the photovoltage is recognized to consist of two components, U = U f + U ph . The first one U f is the fast component having polarity of thermoelectromotive force of hot carriers. The second one U ph is the slow component of opposite polarity, and it is caused by electron–hole pair generation due to two-photon absorption of laser radiation.

Response of timepix detector with GaAs:Cr and Si sensor to heavy ions

The response of the Timepix detector to neon ions with kinetic energy 77 and 158.4 MeV has been studied at the cyclotron U-400M of the JINR Flerov Laboratory of Nuclear Reaction. Sensors produced from gallium arsenide compensated by chromium and from silicon are used for these measurements. While in Timepix detector with Si sensor the well-known so-called "volcano effect" observed, in Timepix detector with GaAs:Cr sensor such effect was completely absent. In the work the behavior of the Timepix detector with GaAs:Cr sensor under irradiation with heavy ions is described in comparison with the detector based on Si sensor. Also the possible reason for absence of "volcano" effect in GaAs:Cr detector is proposed.

Relaxation oscillations of superluminescence in a semiconductor caused by recovery of the Fermi distribution of nonequilibrium electrons

It is shown that modulation of the superluminescence intensity on a characteristic time scale on the order of a few picoseconds may occur in a semiconductor because of relaxation oscillations that result from the “healing” of local perturbations of the quasi-Fermi distribution of nonequilibrium electrons in energy space. The conditions for observing this effect in GaAs are estimated.

Jack 3/5 State from Two-Body Interaction

We investigate the Read–Rezayi parafermion state of correlated electrons at the fractional Landau level filling ν = 3/5. It is a Jack polynomial generated by contact four-body repulsion. We show by exact diagonalization that it is also emerges from a suitable short-range two-body interaction. We find that it closely matches Coulomb ground state in the second Landau level of non-relativistic fermions, and thus possibly describes the ν = 13/5 (and, by conjugation, ν = 12/5) fractional quantum Hall effect in GaAs.

Effect of gaas intermediary layer thickness on the properties of (Ga,Mn) as tri-layer structures

We have investigated the magnetic properties, current–voltage characteristics, and tunnel magnetoresistance of (Ga,Mn)As/GaAs/(Ga,Mn)As tri-layers having different thickness of the intermediary GaAs layer (1–7 nm). When the thickness of GaAs layer is less than 6 nm, the two (Ga,Mn)As layers couples ferromagnetically. For the tri-layers with thicker GaAs, the GaAs acts as an effective barrier for the carrier transport and decouples the two (Ga,Mn)As layers, which results in tunnel magnetoresistance ratio as high as 100% at 5 K.

Thin-film solar cells with InGaAs/GaAsP multiple quantum wells and a rear surface etched with light trapping micro-hole array

A light trapping effect in GaAs p–i–n solar cells with InGaAs/GaAsP multiple quantum wells (MQWs) in the i-layer was demonstrated by applying a light scattering texture to the rear surface of the cell. A thin-film MQW solar cell was successfully fabricated by metal organic vapor phase epitaxy (MOVPE) to grow an inverted n–i–p photovoltaic (PV) structure; this structure was then transferred to a Si support substrate to prevent optical loss due to free carrier absorption. For the light scattering texture, the use of both the wet-etched micro-hole arrayed SiO2 dielectric layer on the rear surface of the cell and the secondarily etched micro hole array on the GaAs layer was attempted. On the SiO2 layer, the micro hole array pattern was obtained by the radio frequency sputtering of the layer followed by wet etching with photolithographic patterning. On the GaAs layer, the micro-hole array pattern was obtained by direct etching through a SiO2 template. Compared with the light scattering effects of the micro-hole-arrayed SiO2 layer, the secondarily etched GaAs rear contact layer showed a significant improvement in external quantum efficiency (EQE) in the wavelength range from 855 to 1000 nm that corresponds to the photon absorption wavelength in MQWs.

Influence of electrically induced refraction and absorption on the measurement of spin current by pockels effect in GaAs

The pockels effect could be utilized to measure spin current in semiconductors for linear electro-optic coefficient can be induced by spin current. When dc electric field is applied, the carriers will shift in k space, which could lead to the change of refraction and absorption coefficients. In this paper, we investigate the influence of the induced change of the refraction and absorption coefficients on the measurement of spin current by pockels effect in GaAs.

Ultrasonic investigation of the Jahn-Teller effect in GaAs semiconductors doped by transition metals

Transition-metal-doped semiconductor GaAs crystals are used as model systems for spintronic research, as well as in other applications. To explore the structure and properties of such impurities, we extended the methodology of ultrasonic investigation of the Jahn-Teller effect in dielectric impurity-centers to the study of significantly different semiconductor impurities using the GaAs:Cu crystal as an example. Phase velocity and attenuation of ultrasound in this system were measured in the temperature interval of 1.9–80 K at 52 MHz and 156 MHz. The anomaly in the velocity and a peak of attenuation found for the longitudinal and slow shear waves indicate the presence of the Jahn-Teller effect with the e-type local distortions of the CuGa4As impurity complex. The temperature dependence of the elastic modulus and relaxation time shows that below 5 K, the thermal activation mechanism of relaxation is possibly replaced by resonance type transitions. The main parameters of the Jahn-Teller effect, stabilization energy, minima positions and the barrier between them, frequency of pseudorotation of the distortions, and the tunneling splitting of the ground state energy, as well as the constant of exchange interaction between the two holes in Cu2+ centers and the concentration of the centers were estimated.

Electron spin resonance study of Er-concentration effect in GaAs;Er,O containing charge carriers

Er-concentration effect in GaAs;Er,O containing charge carriers (n-type, high resistance, p-type) has been studied by X-band Electron spin resonance (ESR) at low temperature (4.7 K < T < 18 K). Observed A, B, and C types of ESR signals were identical to those observed previously in GaAs:Er,O without carrier. The local structure around Er-2O centers is not affected by carriers because similar angular dependence of g-values was observed in both cases (with/without carrier). For temperature dependence, linewidth and lineshape analysis suggested the existence of Er dimers with antiferromagnetic exchange interaction of about 7 K. Moreover, drastic decrease of ESR intensity for C signal in p-type sample was observed and it correlates with the decrease of photoluminescence (PL) intensity. Possible model for the Er-2O trap level in GaAs:Er,O is discussed from the ESR and PL experimental results.