GaAs Conduction Research Articles

Multi-resonant tunable absorber of terahertz metamaterial based on GaAs and VO2

Based on the fact that the conductivity of photosensitive semiconductors can be regulated by external pump light, a metamaterial absorber with single-band and dual-band switchable in terahertz region is designed by replacing gallium arsenide (GaAs) within the nested cell ring structure. With the power increase of external pump light, the maximum absorptivity would be 99.9% when the conductivity of GaAs is setting as 5 × 105 S/m. Furthermore, based on the fact that the temperature can change the phase transition characteristic of vanadium oxide (VO2) and thus change the conductivity characteristic of VO2, the nested cell ring structure is extended, and a multi-resonant metamaterial absorber with tunable conductivity is proposed. When both GaAs and VO2 are in the metallic state, the absorption can be switched from triple-band to single-band, and when the conductivity of both is 5 × 105 S/m, the absorptivity is more than 99%. The GaAs is in the insulated state when there is no pump light irradiating and the conductivity of VO2 could be changed by temperature, or VO2 is in insulated state at room temperature and the conductivity of GaAs could be changed by pump light irradiation. After such supposed condition, the tunability from triple-band to dual-band shown in the proposed metamaterial absorber can be realized gradually. When the conductivity of VO2 or GaAs is 5 × 105 S/m, the maximum absorptivity of such multi-resonant tunable absorber is above 98%. Based on the controllability of GaAs and VO2 conductivity, the multi-resonant tunable absorber with arbitrary switching of single-band/dual-band/triple-band absorption state could be realized. At the same time, the designed absorber has excellent absorption characteristics about both transverse electric (TE) field and transverse magnetic (TM) one in the wide-angle incidence range, which is expected to be further applied in the research fields of modulator, frequency selector, detector, and so on.

GaAs-enabled tunable multifunctional devices based on three coupling mechanisms for terahertz metamaterials

In this paper, a terahertz metamaterial structure with multiple physical features such as EIT-like resonance, Fano resonance, and terahertz wave absorption, is implemented. The device consists of a metal structure and a GaAs layer. The conductivity of GaAs can be adjusted by optical pump. When the conductivity of GaAs is 10 S/m, with the TE polarization wave incenting, the Fano resonance formed, and when the TM polarization wave was incenting, the EIT-like resonance formed. Modulation of the resonance can be achieved by adjusting the conductivity of GaAs, and a maximum modulation depth of 96.5% is obtained. When the conductivity of GaAs is 2 × 105 S/m, a double narrow-band absorption is obtained with TM polarization wave exciting. The maximum sensitivity reaches 513 GHz/RIU and the maximum FOM value reaches 39.5, which indicates that the device has excellent performance in refractive index sensing. The device also has a wide range of applications in terahertz sensors, slow-light devices, and terahertz modulators.

Plasmon-induced transparency effect in hybrid terahertz metamaterials with active control and multi-dark modes

We numerically demonstrate a photo-excited plasmon-induced transparency (PIT) effect in hybrid terahertz (THz) metamaterials. The proposed metamaterials are regular arrays of hybrid unit cells composed of a metallic cut wire and four metallic split-ring resonators (SRRs) whose gaps are filled with photosensitive semiconductor gallium arsenide (GaAs) patches. We simulate the PIT effect controlled by external infrared light intensity to change the conductivity of GaAs. In the absence of photo excitation, the conductivity of GaAs is 0, thus the SRR gaps are disconnected, and the PIT effect is not observed since the dark resonator (supported by the hybrid SRRs) cannot be stimulated. When the conductivity of GaAs is increased via photo excitation, the conductivity of GaAs can increase rapidly from 0 S/m to 1 × 106 S/m and GaAs can connect the metal aluminum SRR gaps, and the dark resonator is excited through coupling with the bright resonator (supported by the cut wire), which leads to the PIT effect. Therefore, the PIT effect can be dynamically tuned between the on and off states by controlling the intensity of the external infrared light. We also discuss couplings between one bright mode (CW) and several dark modes (SRRs) with different sizes. The interference analytically described by the coupled Lorentz oscillator model elucidates the coupling mechanism between one bright mode and two dark modes. The phenomenon can be considered the result of linear superposition of the coupling between the bright mode and each dark mode. The proposed metamaterials are promising for application in the fields of THz communications, optical storage, optical display, and imaging.

Length-Gauge Optical Matrix Elements in WIEN2k

Hybrid exchange-correlation functionals provide superior electronic structure and optical properties of semiconductors or insulators as compared to semilocal exchange-correlation potentials due to admixing a portion of the non-local exact exchange potential from a Hartree–Fock theory. Since the non-local potential does not commute with the position operator, the momentum matrix elements do not fully capture the oscillator strength, while the length-gauge velocity matrix elements do. So far, length-gauge velocity matrix elements were not accessible in the all-electron full-potential WIEN2k package. We demonstrate the feasibility of computing length-gauge matrix elements in WIEN2k for a hybrid exchange-correlation functional based on a finite difference approach. To illustrate the implementation we determined matrix elements for optical transitions between the conduction and valence bands in GaAs, GaN, (CH3NH3)PbI3 and a monolayer MoS2. The non-locality of the Hartree–Fock exact exchange potential leads to a strong enhancement of the oscillator strength as noticed recently in calculations employing pseudopotentials (Laurien and Rubel: arXiv:2111.14772 (2021)). We obtained an analytical expression for the enhancement factor for the difference in eigenvalues not captured by the kinetic energy. It is expected that these results can also be extended to other non-local potentials, e.g., a many-body GW approximation.

Determination of type-I band offsets in GaBixAs1–x quantum wells using polarisation-resolved photovoltage spectroscopy and 12-band k.p calculations

Using photovoltage (PV) spectroscopy we analyse the electronic structure of a series of GaBixAs/(Al)GaAs dilute bismide quantum well (QW) laser structures. The use of polarisation-resolved PV measurements allows us to separately identify transitions involving bound light- and heavy-hole states in the QWs, as well as bound-to-continuum transitions from the QWs to the barriers. Analysis of these transitions enables us to probe the GaBixAs/(Al)GaAs conduction and valence band offsets, thereby quantifying the band offsets. Using a 12-band Hamiltonian, we extract the band offsets in the QWs explicitly by constraining the Bi-related parameters of the model against the experimentally measured transition energies. The PV measurements and calculations we present provide the first explicit confirmation of a type-I band offset at the GaBixAs/GaAs heterointerface near x = 2%. This result, combined with the theory we present for calculating the band offsets at GaBixAs/(Al)GaAs heterointerfaces, can be used to determine the band offsets at arbitrary Bi composition x.

Comparison of Excitation of Acoustic-Electromagnetic Wave in Piezoelecric Crystal and Crystal with Potential of Deformation

In this article, the comparison of excitation in high frequencies of acoustic-electromagnetic wave in piezoelecric crystal and crystal with potential of deformation GaAs is investigating. Possible mechanisms of coupling different hybrid waves are the piezoeffect and the deformation potential. As a model it is analyzing a film of crystal places between two symmetrical substrates with the other materials without an acoustic contact. This film includes 2D electron gas with a high negative differential conductivity and uniform initial distribution of electrons. The hybrid acoustic-electromagnetic wave and hybrid space charge wave interact. Amplification of space charge wave takes place due to negative differential conductivity in GaAs. This amplification of space charge waves is causing the amplification of acoustic-electromagnetic wave. It is to show that the symmetric modes, emerging as transverse ones, interact more effectively with the space charge waves. Another important result is the following: at the frequencies f ≈ 10 GHz, the excitation efficiency of acoustic-electromagnetic wave with transverse displacement due to piezoeffect is more effective, but at higher frequencies, the deformation potential is dominating.

Segregation of Impurities in GaAs and InAs Nanowires

Using ab initio methods based on the density functional theory, we investigate the segregation and formation energies for various dopants (Si, Be, Zn, Sn), commonly used to obtain p- or ntype conductivity in GaAs and InAs nanowires. The distribution of Au and O atoms, which may be unintentionally incorporated during the wire growth, is also studied. The calculations performed for nanowires of zinc blende and wurtzite structure show that the distribution of most of the impurities depends on the crystal structure of the wires. For example, it is shown that the same growth conditions can lead to lower energy for Si substituting Ga (donor) in the wire of wurtzite structure and substituting As (acceptor) in the wire of zinc blende structure. In contrast, we obtain that gold and oxygen atoms always tend to stay at the lateral surfaces of GaAs and InAs nanowires, in agreement with experimental findings, while for beryllium the lowest energies are found when the impurities are located in sites in the center of the wurtzite wire or along the [1; 0; 1] axis from surface to the center of the zinc blende wire, what can explain the recently observed diffusion of this impurity into the volume of GaAs wires.

Experimental evaluation of the spin-Hall conductivity in Si-doped GaAs

We performed photoinduced inverse spin-Hall effect (ISHE) measurements on Si-doped bulk GaAs at room temperature. The spin current is optically injected in the sample by means of circularly polarized light and is detected through spin-dependent scattering by Si impurities, which provide an electromotive field ${\mathbf{E}}_{\mathrm{ISHE}}$ close to the sample surface. We measured the ISHE signal as a function of the incident photon energy, and we determined the corresponding averaged spin current, flowing through the sample, to experimentally determine the spin-Hall conductivity.

Influence of embedded indium nanocrystals on GaAs thermoelectric properties

We have examined the formation of embedded In nanocrystals (NCs) and their influence on the free carrier concentration, resistivity, thermal conductivity, and Seebeck coefficient (S) of GaAs. The In nanocrystals enhance the free carrier concentration, while electron and phonon scattering at crystallite boundaries increases the resistivity and reduces the thermal conductivity. Furthermore, the room temperature Seebeck coefficient exhibits a 25% increase due to carrier trapping. Application of this approach to more heavily doped GaAs layers will likely lead to further increases in S and reductions in resistivity.

Theoretical investigation of the DC conductivity in GaAs by using the projection-reduction method

Based on the conductivity formalism derived using the Kang-Choi reduction identity [N. L. Kang and S. D. Choi, J. Phys. A 43, 165203 (2010)] and a state-dependent projection operator in the linear response scheme, we investigate the effect of the Rashba spin-orbit interaction (RSOI), Zeeman g-factor, temperature and electron-acoustic phonon interaction on the dc conductivity of a twodimensional electron-phonon system in the presence of a perpendicular magnetic field. We find that the dc conductivity in GaAs oscillates with the inverse magnetic field and that the pattern of the oscillation is sensitive to even small change in the RSOI strength and g factor, while temperature and the deformation potential constant play no role in changing the pattern. From this, we find that the oscillations are due to an inversion of electron population caused by the RSOI.

Ga2O3 films formed by electrochemical oxidation

The effect of oxygen plasma on gallium oxide films formed by electrochemical oxidation of n-GaAs wafers with a donor concentration Nd = (1–2) × 1016 cm−3 has been investigated. It is shown that the treatment in an oxygen plasma at a temperature of 50–90°C increases the concentration of β-phase crystallites, which causes an increase in the permittivity, a decrease in the dielectric dissipation factor, and a change in the conductivity of GaAs-〈gallium oxide〉-metal structures.

Infrared quantum counting by nondegenerate two photon conductivity in GaAs

We report on infrared quantum counting of photons at optical communication wavelengths based on nondegenerate two-photon absorption in a GaAs photomultiplier tube. The detected photon energy is lower than the GaAs band gap and the energy difference is complemented by a high intensity pump field. This detection setup is simple, compact, has a broad spectral bandwidth, and benefits from the intrinsic low noise and dark counts of large band gap semiconductor junctions.

Conductivity, Hall and magnetoresistance effect measurements on SI GaAs and InP

The conductivity, Hall effect and magnetoresistance quantities in semi-insulating undoped GaAs and Fe-doped GaAs and InP grown by the LEC technique have been measured in the temperature range 300–420 K. It is shown that mixed conductivity is present in all samples. The experimental data were analyzed using a two-band model including electron and hole transport. A good fit has been obtained self-consistently to both conductivity and mobility. The single-band parameters have been extracted from the measured data in the studied temperature range. From ln (|RH, 0| T3/2) and σ vs T−1 plots, activation energies of 0.77 and 0.65 eV have also been observed for GaAs and InP, respectively. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Annealing temperature dependence of electric conduction and capacitance dispersion in nitrogen-implanted GaAs

The annealing behavior of nitrogen-implanted GaAs samples has been investigated by secondary ion mass spectroscopy, current-voltage (I-V) and capacitance-frequency (C-F) measurements. The I-V data show that the conductivity of as-implanted samples is dominated by variable-range hopping between defect states below 300 K. The implanted layer becomes highly resistive after annealing. The activation energy of the resistance is found to increase from 0.2 eV for as-implanted samples to 0.71 eV for 950°C-annealed samples. Significant capacitance dispersion is observed over frequency for implanted samples. Based on a proposed equivalent circuit, the high-frequency capacitance dispersion is shown to be the result of resistance-capacitance (RC) time constant effects. The increase of activation energy of the resistance can be explained by the creation of deep traps by high temperature annealing. Traps at 0.69 eV and 0.82 eV are detected for 700°C and 950°C-annealing, respectively.

Thermal Effect and Frequency Response Analyses on Heterojunction Bipolar Power Transistor

Heterojunction bipolar transistors (HBT) based on Npn AlGaAs/GaAs material system have attracted considerable attention for microwave power and digital applications due to their high speed and high current capabilities. In this paper, a numerical model based on the Npn AlGaAs/GaAs HBT structure for the carrier transport is presented. Three figures of merit on device operation, current gain, cut-off frequency and maximum oscillation frequency are calculated. Besides, thermal instability plays an important role on power HBT resulted from the low thermal conductivity in GaAs. The generated heat will increase the junction temperature and cause self-destruction. Therefore, the thermal runaway study of the junction temperature, current–voltage (IV) characteristics and frequency response using an analytical thermal model is described.

Experimental study of negative differential conductivity in GaAs:Cr

We have studied the temperature and illumination dependencies of the current versus voltage characteristics $I(V)$ of a Cr-doped GaAs sample. An S-shaped negative differential conductivity with a threshold at around 1 kV ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ was associated with a trap with activation energy of 90 meV. The low-conductivity state in $I(V)$ characteristics is strongly influenced by illumination and temperature. We also present evidence that the electrical conduction above the threshold electric field occurs by a mechanism that involves free electrons despite the fact that the low-conductivity state is p type. This supports the assumption that the 90 meV trap is a donor.

Conductivity compensation and deep traps in epitaxial n-GaAs irradiated by electrons

A study has been made of electrophysical properties and deep traps in epitaxial n-GaAs grown by the chloride method and irradiated by electrons in the temperature range (20–500)°C. It is shown that the “natural” conductivity of GaAs is attained at irradiation temperatures of 20°C due to the introduction of E traps, and for 300°C≤Tirr≤500°C of high-temperature P traps, presumably defect clusters.

A novel mechanism for parallel conduction in GaAs-(Ga,Al)As heterojunctions

GaAs-(Ga,Al)As heterojunctions often show parallel conduction after illumination with red light (h(cross) omega >Eg). A study of the parallel conduction occurring in planar doped GaAs-(Ga,Al)As heterojunctions with a superlattice buffer is presented. The samples studied are subject to parallel conduction by two different types of carrier. Transport measurements indicate the presence of a very large density of low-mobility carriers, while in addition the presence of some high-mobility carriers is indicated by the appearance of an additional dip in the far-infrared (FIR) transmission. The latter type of carrier is thought to form a secondary low-density two-dimensional electron gas weakly confined behind the superlattice buffer.

Defect pairs and clusters related to the EL2 centre in GaAs

In this article, we attempt to consistently interpret Deep Level Transient Spectroscopy (DLTS), Electron Paramagnetic Resonance (EPR) and electrical conductivity experimental data for irradiated GaAs. Our analysis reveals the occurrence of an irradiation-induced single donor mid-gap level (MG) related to the AsGa antisite defect. We give evidence that MG can be identified with the deep level associated to the native bulk centre EL2. We make use of a model we have recently developed for the calculation of inter-defect phonon-assisted tunnelling rates. We calculate the nearest neighbour defect-induced hopping conductivities. In heavy dose irradiated GaAs, the DC conductivity is attributed to hopping between MG defects. Our calculations provide extremely good fits to the experimental results of Deng et al. for the DC electrical conductivity in GaAs induced by argon ion bombardment for temperatures ranging from around 20 K to 500 K. The phonon energy ħω (20 ± 2 meV) and Franck-Condon shift Sħω (145 ±10 meV) of MG needed to achieve this fit are in very good agreement with the ħω and Sħω values earlier determined for the native EL2 defect. The bulk AC hopping conductivity has also been calculated and found to agree well with experimental results of Mares et al. for high purity semi-insulating GaAs. The corresponding low-frequency AC conductivity is attributed entirely to a homogeneous random distribution of native mid-gap donor defects EL2. We are also led to invoke the mid-gap level MG (identifiable with that of EL2) in order to account for DLTS results. In fast-electron irradiated n-GaAs, the two high temperature DLTS peaks E4 and E5 are both accounted for by two defect pairs each including an MG level component. In heavy-particle bombarded n-GaAs damage clusters including MG defects account for the experimentally recorded high temperature DLTS peak. For these defect pairs and clusters, our DLTS simulations correctly predict the observed peak positions and their dependence on the electric field.

Additional considerations in the analysis of mixed conductivity in GaAs

In an earlier study, Hall-effect and conductivity measurements made on semi-insulating GaAs were examined by a new approach to mixed conduction analysis. The analysis of 400-K measurements was based on the assumption of a fixed electron-to-hole mobility ratio. The effect of uncertainty in this ratio is examined in the present communication, and the nomographic presentation is simplified. The conductivity criterion for the onset of mixed conduction is revised and the quartic used earlier for comparative analysis is corrected.