GaAs Interface Research Articles

Interfacial influence on electrical injection and transport characterization of CoFeB|MgO|GaAs-InGaAs quantum wells hetero-structure

The quality of interfaces is a key factor for efficient electrical spin injection into quantum well light emitting diodes. Here, we investigate the interfacial influence on the electrical transport properties in CoFeB|MgO|GaAs-InGaAs quantum wells hetero-structure, by considering textured MgO tunnel barrier fabricated by two different techniques: sputtering and molecular beam epitaxy (MBE). From forward and reverse current–voltage characteristics, it is found that the threshold voltage decreases as the annealing temperature changes from room temperature to 300 °C for sputtered samples, however there is not much difference in threshold voltage with the annealing temperature for MBE-grown samples. In combination with transmission electron microscope (TEM) studies, it is found the MgO|GaAs interface by MBE is sharp for both grown and annealed states. However, there is a thin (∼0.4 nm) amorphous MgO layer at the MgO|GaAs interface for sputtered samples with grown state, and the amorphous MgO can be improved and crystallized after annealing. The MgO|GaAs interface plays a role in modulating the band structure and has an influence on electrical injection. Our work demonstrated that CoFeB|MgO|GaAs interfaces are important and can be engineered thanks to the use of two types of growth for the textured MgO tunnel barriers, which ensures efficient electrical injection.

Sp3s∗ tight-binding calculation of band edges and effective masses of InAs/GaSb superlattices with different interface structures

The band edge energy and effective mass of InAs/GaSb type II superlattices on a (001) GaSb substrate have been investigated using the empirical sp3s∗ tight-binding method. The influence of interfacial bonds on electronic properties has been clarified in typical superlattices of (InAs)n(GaSb)n with C2v point group symmetry and both (InAs)n(InSb)(GaSb)n and (InAs)n(GaSb)n(GaAs) superlattices with D2d point group symmetry. In the short period region of superlattices, we found that the band offsets in the vicinity of the hetero interfaces significantly impact on the band edges and that interfacial Ga-As bonds specifically cause large anisotropy of in-plane effective masses in (InAs)n(GaSb)n superlattices.

Magnetoelectric Effect in Gallium Arsenide–Nickel–Tin–Nickel Multilayer Structures

Experimental data have been presented for the magnetoelectric effect in nickel–tin–nickel multilayer structures grown on a GaAs substrate by cathodic electrodeposition. The method of fabricating these structures has been described, and the frequency dependence of the effect has been demonstrated. It has been shown that tin used as an intermediate layer reduces mechanical stresses due to the phase mismatch at the Ni–GaAs interface and, thus, makes it possible to grow good structures with a 70-μm-thick Ni layer. The grown structures offer good adhesion between layers and a high Q factor.

Analysis of border and interfacial traps in ALD-Y2O3 and -Al2O3 on GaAs via electrical responses - A comparative study

Y2O3 and Al2O3 were in-situ atomic layer deposited (ALD) on pristine GaAs(001)-4×6 reconstructed surfaces without surface pretreatments. We have studied the border and interfacial traps in both hetero-structures using the measured electrical responses. On the basis of frequency dispersion analysis of the capacitance-voltage (CV) characteristics, we conclude that Y2O3 has effectively passivated GaAs surface with a much lower interfacial trap density (Dit) than Al2O3 as the gate dielectric. The quasi-static CV and conductance measurements are in agreement with the above conclusion. We have demonstrated an excellent ALD-Y2O3/GaAs interface with low Dit's of (0.5–2)×1012eV−1cm−2 through the whole GaAs band gap without a mid-gap peak feature.

Enhanced NMR with Optical Pumping Yields 75As Signals Selectively from a Buried GaAs Interface.

We have measured the 75As signals arising from the interface region of single-crystal semi-insulating GaAs that has been coated and passivated with an aluminum oxide film deposited by atomic layer deposition (ALD) with optically pumped NMR (OPNMR). Using wavelength-selective optical pumping, the laser restricts the volume from which OPNMR signals are collected. Here, OPNMR signals were obtained from the interface region and distinguished from signals arising from the bulk. The interface region is highlighted by interactions that disrupt the cubic symmetry of the GaAs lattice, resulting in quadrupolar satellites for nuclear [Formula: see text] isotopes, whereas NMR of the "bulk" lattice is nominally unsplit. Quadrupolar splitting at the interface arises from strain based on lattice mismatch between the GaAs and ALD-deposited aluminum oxide due to their different coefficients of thermal expansion. Such spectroscopic evidence of strain can be useful for measuring lattice distortions at heterojunction boundaries and interfaces.

Comparison of Ti/Pd/Ag, Pd/Ti/Pd/Ag and Pd/Ge/Ti/Pd/Ag contacts to n-type GaAs for electronic devices handling high current densities

In the quest for metal contacts for electronic devices handling high current densities, we report the results of Pd/Ti/Pd/Ag and Pd/Ge/Ti/Pd/Ag contacts to n-GaAs and compare them to Ti/Pd/Ag and AuGe/Ni/Au. These metal systems have been designed with the goal of producing an electrical contact with (a) low metal–semiconductor specific contact resistance, (b) very high sheet conductance, (c) good bondability, (d) long-term durability and (e) cost-effectiveness. The structure of the contacts consists of an interfacial layer (either Pd or Pd/Ge) intended to produce a low metal–semiconductor specific contact resistance; a diffusion barrier (Ti/Pd) and a thick top layer of Ag to provide the desired high sheet conductance, limited cost and good bondability. The results show that both systems can achieve very low metal resistivity (ρM ∼ 2 × 10−6 Ω cm), reaching values close to that of pure bulk silver. This fact is attributed to the Ti/Pd bilayer acting as an efficient diffusion barrier, and thus the metal sheet resistance can be controlled by the thickness of the deposited silver layer. Moreover, the use of Pd as interfacial layer produces contacts with moderate specific contact resistance (ρC ∼ 10−4 Ω cm2) whilst the use of Pd/Ge decreases the specific contact resistance to ρC ∼ 1.5 × 10−7 Ω cm2, as a result of the formation of a Pd4(GaAs, Ge2) compound at the GaAs interface.

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.

Growth of Metamorphic InGaAs on GaAs (111)A: Counteracting Lattice Mismatch by Inserting a Thin InAs Interlayer

We have successfully grown high quality InxGa1–xAs metamorphic layer on GaAs (111)A using molecular beam epitaxy. Inserting a thin 3.0–7.1 monolayer (ML) InAs interlayer between the In0.25Ga0.75As and GaAs allowed the formation of a nearly lattice-relaxed In0.25Ga0.75As with a very flat upper surface. However, when the thickness of the inserted InAs is thinner or thicker than these values, we observed degradation of crystal quality and/or surface morphology. We also revealed this technique to be applicable to the formation of a high quality metamorphic InxGa1–xAs layer with a range of In compositions (0.25 ≤ x ≤ 0.78) on GaAs (111)A. Cross-sectional scanning transmission electron microscope studies revealed that misfit dislocations formed only at the interface of InAs and GaAs, not at the interface of In0.25Ga0.75As and InAs. From the dislocation density analysis, it is suggested that the dislocation density was decreased by growing In0.25Ga0.75As on InAs, which effectively contribute the strain relaxatio...

Sacrificial Self-Assembled Monolayers for the Passivation of GaAs (100) Surfaces and Interfaces

The use of sacrificial self-assembled monolayers (SAMs) to prepare clean n-type GaAs (100) surfaces without band bending in vacuo is demonstrated. GaAs surface passivation using octadecanethiol SAMs after HCl cleaning is shown to lead to an enhancement of the room-temperature photoluminescence intensity. Synchrotron-radiation photoelectron spectroscopy (SRPES) finds that the interfacial oxide between GaAs and the SAM remains below the detection limit. Evidence for both Ga–S and As–S bonds at the GaAs–thiolate interface is found. The limited thermal stability of the SAM allows the desorption of the alkyl chains by in situ thermal annealing at temperatures above 180 °C, leaving S bonded to Ga behind. The resulting surface contains only a very small amount of O (0.05 ML coverage) and C (about 3% of the SAM remaining) and shows no band bending with the surface Fermi level close to the conduction band. Atomic layer deposition of Al2O3 on this surface occurs via the formation of Al–S bonds without introducing any additional band bending. This indicates that the surface preparation of n-type GaAs (100) using sacrificial octadecanethiol SAMs followed by in situ thermal removal provides a route toward GaAs/oxide interfaces without interfacial oxides and without band bending.

Charge transfer luminescence in (GaIn)As/GaAs/Ga(NAs) double quantum wells

Charge transfer excitons are studied in double quantum well structures consisting of a (GaIn)As and a Ga(NAs) layer separated by a GaAs film of variable thickness. With decreasing barrier thickness, the gradual change from a spatially direct exciton within the (GaIn)As well to a charge transfer exciton bound across the GaAs spacing layer is observed. The optical spectra are well reproduced by a fully microscopic theory and band structure calculations based on the k·p method using a weak type-I valence band offset of approximately (45±40)meV at the Ga(NAs)/GaAs interface.

XPS Analysis of AuGeNi/Cleaved GaAs(110) Interface

The depth composition of the thin layer alloy, AuGeNi, devoted to acting as an ohmic contact on n-GaAs(110) has been investigated by in situ XPS combined with Argon ion sputtering techniques. The fresh cleaved surfaces, supposed to be free of oxygen, were usually deposited with a 200 nm metallic layer in high vacuum conditions (better than 10−7 torr), by thermal evaporation, and annealed at a 430–450° Celsius temperature for 5 minutes. About 18 sessions of ion Ar surfaces etching and intermediate XPS measurements were performed in order to reveal the border of the metal/semiconductor interface. The atomic concentrations of the chemical elements have been approximated. Au4f, Ga3d, Ga2p, As3d, As2p, Ni2p3/2, Ge3d, O1s, and C1s spectral lines were recorded. The Au, Ge, and Ni have a homogenous distribution while Ga and As tend to diffuse to the surface. Oxygen is present in the first layers of the surface while carbon completely disappears after the second etching step. The existence of an Au-Ga alloy was detected and XPS spectra show only metal Ni and Ge within the layer and at the interface. We tried to perform a study about the depth chemical composition profile analysis of AuGeNi layer on cleaved n-GaAs(110) by X-Ray Photoelectron Spectroscopy (XPS) technique.

Oscillatory Tunneling Magnetoresistance in Fe<sub>3</sub>O<sub>4</sub>/n-GaAs/Fe<sub>3</sub>O<sub>4</sub> Junction

Spintronics strives to revolutionize conventional electronics by integrating magnetic materials with semiconductor devices, such as the spin field effect transistor (SFET)[1], which not only improve the capabilities of electronic devices, but develop new functionalities. For electrodes of spin injection and detection in SFET device, half metallic Fe 3 O 4 is an attractive candidate because its high Curie temperature of 858 K, large spin polarization near 100% at the Fermi level and relatively high electronic conductivity at room temperature, which is believed to benefit the injection of spin carriers into the semiconductors.[2] For ferromagnetic metal(FM)/ Semiconductor system, Fe 3 O 4 / GaAs is a very promising system for the fabrication of magnetoelectronic devices due to the Schottky contact of the Fe 3 O 4 /GaAs interface[3,4], which is crucial for studying the behaviors of spin dependent transportation for the devices. It is reported that in a FM/I/NM/I/FM double tunnel junction, where NM is the normal metal, and I the insulating barrier, theories predicted an oscillation of the tunneling magnetoresistance (TMR) effect as a function of the NM layer thickness because the spin polarization of the tunneling electron oscillates as a result of the resonant tunneling. Furthermore, Quantum oscillation of spin polarization in GaAs channel was experimentally demonstrated. In this paper, we have presented a theoretical approach to the tunneling conductance and TMR in a Fe 3 O 4 /GaAs/Fe 3 O 4 magnetic double tunnel junction with both ballistic and diffusive components.

Crystal Phase Quantum Dots in the Ultrathin Core of GaAs-AlGaAs Core-Shell Nanowires.

Semiconductor quantum dots embedded in nanowires (NW-QDs) can be used as efficient sources of nonclassical light with ultrahigh brightness and indistinguishability, needed for photonic quantum information technologies. Although most NW-QDs studied so far focus on heterostructure-type QDs that provide an effective electronic confinement potential using chemically distinct regions with dissimilar electronic structure, homostructure NWs can localize excitons at crystal phase defects in leading to NW-QDs. Here, we optically investigate QD emitters embedded in GaAs-AlGaAs core-shell NWs, where the excitons are confined in an ultrathin-diameter NW core and localized along the axis of the NW core at wurtzite (WZ)/zincblende (ZB) crystal phase defects. Photoluminescence (PL)-excitation measurements performed on the QD-emission reveal sharp resonances arising from excited electronic states of the axial confinement potential. The QD-like nature of the emissive centers are suggested by the observation of a narrow PL line width, as low as ~300 μeV, and confirmed by the observation of clear photon antibunching in autocorrelation measurements. Most interestingly, time-resolved PL measurements reveal a very short radiative lifetime <1 ns, indicative of a transition from a type-II to type-I band alignment of the WZ/ZB crystal interface in GaAs due to the strong quantum confinement in the ultrathin NW core.

Magnetic-field-induced photocurrent in metal-dielectric-semiconductor heterostructures based on cobalt nanoparticles SiO2(Co)/GaAs

Magnetic-field influence on photocurrent in heterostructures of silicon dioxide films with cobalt nanoparticles SiO2(Co) grown on gallium arsenide GaAs substrate has been studied in the avalanche regime at room temperature. High values of magnetic-field-induced photocurrent were found in the vicinity and above the GaAs bandgap of ∼1.4eV. For photon energies E>1.4eV the photocurrent significantly increases, while the avalanche process is suppressed by the magnetic field, and the current flowing through the heterostructure decreases. The photocurrent is enhanced in the SiO2(Co 60at%)/GaAs heterostructure at the magnetic field H=1.65kOe by factor of about 10 for the photon energy E=1.5eV. This phenomenon is explained by a model based on electronic transitions in magnetic fields with the spin-dependent recombination process at deep impurity centers in the SiO2(Co)/GaAs interface region.

Interfacial Ga-As suboxide: Structural and electronic properties

The structural and electronic properties of Ga-As suboxide representative of the transition region at the GaAs/oxide interface are studied through density functional calculations. Two amorphous models generated by quenches from the melt are taken under consideration. The absence of As–O bonds indicates that the structure is a mixture of GaAs and Ga-oxide, in accordance with photoemission experiments. The band edges of the models are found to be closely aligned to those of GaAs. The simulation of charging and discharging processes leads to the identification of an As-related defect with an energy level at ∼0.7 eV above the GaAs valence band maximum, in good agreement with the experimental density of interface states.

First-principles investigation of defects at GaAs/oxide interfaces

First-principles calculations of the ESR parameters of several point defects at GaAs/oxide interfaces and in bulk GaAsO4 are reported. Comparing the theoretical results with recent experimental data, obtained from ESR experiments on thermally oxidized GaAs surfaces, we first confirm the formation of As antisite defects at the GaAs/oxide interface during its thermal oxidation. Two other ESR active defects, which were not identified so far, are tentatively assigned to an As vacancy in the oxide and to a As dangling bond, backbonded to two O atoms and one As atoms, also present in the GaAs oxide layer. The formation of these oxide defects could be correlated to the As enrichment of the GaAs interface during its thermal oxidation.

13.7% Efficiency graphene–gallium arsenide Schottky junction solar cells with a P3HT hole transport layer

Combination of graphene (Gr) with semiconductor to form heterojunction solar cells has recently attracted significant attention due to its simple process with low cost. Here, we have reported a new structure of graphene–gallium arsenide (Gr–GaAs) solar cells using poly(3-hexylthiophene) (P3HT) as hole transport layer. It is found that the open-circuit voltage (Voc) and short-circuit current (Jsc) of the solar cells get significantly increased due to the introduction of P3HT layer. Initial power conversion efficiency (PCE) of 6.84% can be obtained for the Gr–GaAs solar cell with a P3HT layer. The performance improvement of the Gr–GaAs solar cell with a P3HT layer is strongly associated with its small saturation current, due to the increase of built-in barrier and the reduction of the carrier recombination at the Gr–GaAs interface. By doping Gr via bis(trifluoromethanesulfonyl)-amide (TFSA) and utilizing an efficient TiO2 antireflective film (AR film), the PCE of the solar cell with a P3HT layer can reach a maximum value of 13.7%, which is the highest value achieved for the Gr–GaAs solar cells so far. These results pave a new way for the fabrication of high efficiency Gr–GaAs solar cells.

Effect of magnetic field enhancement of the photocurrent in ferromagnetic metal-dielectric heterostructures SiO2(Co)/GaAs

Heterostructures of silicon dioxide films containing cobalt nanoparticles SiO2(Co) grown on GaAs substrate exhibit at room temperature high values of magnetic field enhancement of photocurrent in the vicinity and above the GaAs bandgap of ∼1.4 eV. For photon energies E above the GaAs bandgap, the photocurrent significantly increases, while the avalanche process is suppressed by the magnetic field, and the current flowing through the heterostructure decreases. The photocurrent is enhanced in the SiO2(Co 60 at. %)/GaAs heterostructure at the magnetic field H = 1.65 kOe by a factor of about ten for the photon energy E = 1.5 eV. This phenomenon is explained by a model describing electronic transitions in magnetic fields with the spin-dependent recombination process at deep impurity centers in the GaAs interface region.

Gallium arsenide antireflection layer via direct wet thermal oxidation

Broad bandwidth, low-reflectance, low-cost antireflection (AR) layers on GaAs are demonstrated using a quarter-wave optical thickness dielectric grown by directly oxidising the GaAs through a carefully-balanced oxygen-enhanced wet thermal process at 420°C. For centre design wavelengths between 550 and 800 nm, the native oxide AR layers have a simulated and measured reflectance minima as low as 1.0%, with reflectance <10% over bandwidths as large as 342 nm. The experimental reflectance spectra agree well with the modelling based on the complex optical constants obtained by variable angle spectroscopic ellipsometry, and are consistent with the low GaAs native oxide surface roughness (<0.3 nm) and interface roughness (<2.3 nm) measured by atomic force microscopy.

Electron diffraction study of a high-temperature diamond-like silicon ferromagnet with the self-organized superlattice distribution of manganese impurity

New data on the structure of the diluted magnetic semiconductor Si:Mn with the Curie point to 500 K synthesized by the laser method have been presented. High-resolution electron microscopy and diffraction in the directions 〈110〉 and 〈100〉 of epitaxial layers of the diluted magnetic semiconductor Si:15% Mn with the elimination of the contribution from the GaAs substrate and interface have been applied. It has been established that the diluted magnetic semiconductor Si:Mn is a previously unknown compound with the variable composition Si3 − xMnx (0 < x < 1), single-phase diamond-like structure, high crystal perfection, and self-organized formation of the superlattice structure with the period of the triple distance between the nearest (110) atomic layers and the interval between the (110) layers doped with Mn atoms and oriented along the growth direction of the Si:Mn film. The layers Si:15% Mn (or Si2.5Mn0.5) consist of 15- to 50-nm blocks with the mutually perpendicular orientations of the superlattice modulations. Manganese atoms in the (110) layers doped with this impurity are located in the form of single-atom stripes, which alternate with the silicon single-atom stripes in agreement with the X-ray spectral analysis and ferromagnetic resonance data. The ferromagnetism of Si3 − xMnx is associated with a specific feature of the impurity band.