GaAs Oxide Layer Research Articles

Influences of Native Oxide on the Properties of Ultrathin Al2O3‐Interfaced Si/GaAs Heterojunctions

AbstractThe structure property of non‐ideal Si/GaAs heterostructures that are integrated with the ultra‐thin oxide (UO) tunneling interfacial layer is systematically investigated. Si nanomembranes (NMs) are oxidized in different time periods prior to the hetero‐integration process to create the non‐ideal single‐side passivated Si/GaAs heterostructure. The atomic‐level oxygen distribution and the degree of oxygen content in Si NM and GaAs are carefully investigated using atom probe tomography (APT) and X‐ray photoelectron spectroscopy (XPS) to trace changes in the chemical composition and reactional mechanism across the UO interface when the surface of Si NM is exposed to air for different periods of time. The negatively induced charges at the UO layer cause oxygen diffusion to the GaAs layer and form the unwanted GaAs oxide layer. This native oxide stack noticeably degrades the thermal properties of the Si/GaAs heterostructure as Si NMs become more oxidized. This study reveals that the poor surface passivation on one side of the heterointerface leads to a both‐side oxidation, thus severely deteriorating the transport properties across the heterojunction formed with the UO layer.

Nitrogen Plasma Etching and Surface Passivation of GaAs via Plasma-Enhanced Atomic Layer Deposition

We investigated the suitability of aluminum nitride (AlN) for surface passivation and protection of gallium arsenide (GaAs), using a low-temperature passivation method. By varying the plasma power (100, 200 W) during etching, we found that 200 W produced better passivation. Using X-ray photoelectron spectroscopy, we quantitatively demonstrate that etching the GaAs at 200 W almost removed the GaAs oxide layer. To further study the surface passivation of GaAs, we deposited an AlN film by plasma-enhanced atomic layer deposition using trimethylaluminum and ammonia precursors at 250 °C. AlN passivation did not effectively smooth the GaAs surface, but did increase its photoluminescence intensity. This study shows that AlN coating by plasma-enhanced atomic layer deposition is a promising low-temperature method for GaAs surface passivation.

Periodic nanostructures fabricated on GaAs surface by UV pulsed laser interference

In this paper, periodic nanostructures were fabricated on GaAs wafers by four-beam UV pulsed laser interference patterning. Significant different results were observed on epi-ready and homo-epitaxial GaAs substrate surfaces, which suggests GaAs oxide layer has an important effect on pulsed laser irradiation process. In the case of two-pulse patterning, a noticeable morphology transformation induced by the second pulse was observed on homo-epitaxial GaAs substrate. Based on photo-thermal mode, temperature distribution on sample surface as a function of time and position was calculated by solving the heat diffusion equations.

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.

Smooth GaAs (110) Surface Fabrication Using the Ga-Assisted Deoxidation Method

We have practiced the Ga-assisted deoxidation method on GaAs(110) surface. When the deposit amount of Ga is suitable, flat GaAs(110) surface without any thermal deoxidation induced pits and excrescent GaAs islands obtained with the Ga-assisted deoxidation method. The obtained results suggested that, 9ML Ga was optimized dose for GaAs(110) surface, which is a little more than GaAs(001) surface indicating a thicker oxide layer of GaAs(110) surface.

GaAs metal-oxide-semiconductor devices with a complex gate oxide composed of SiO2 and GaAs oxide grown using a photoelectrochemical oxidation method

In this study, a SiO2/GaAs oxide bi-layer layer was used as the gate oxide in GaAs-based metal-oxide-semiconductor (MOS) devices. The GaAs oxide layer of the bi-layer layer was directly formed on the GaAs surface by using the photoelectrochemical (PEC) oxidation method. Some samples were thermally treated at 200 °C and 300 °C in O2 ambience for 30 min. The surface state density of the oxide/GaAs interface with and without GaAs oxide thermal treatment was 7.2 × 1011 and 7.9 × 1011 cm−2 eV−1, respectively. The GaAs MOS field effect transistors (MOSFETs) with the PEC-deposited GaAs oxide thermally treated showed an output current of 152 mA mm−1 at VDS = 2.4 V and VGS = 0 V and an extrinsic transconductance of 89 mS mm−1.

Properties of the GaAs oxide layer grown by the liquid-phase chemical-enhanced technique on the S-passivated GaAs surface

The properties of GaAs oxide layers prepared by liquid-phase chemical-enhanced oxidation of the (NH4)2Sx-passivated GaAs surface are investigated. The initial oxidation rate is suppressed and the refractive indices of oxide layers are lower after S passivation. In accordance with the depth profiles measured by secondary ion mass spectroscopy (SIMS), a model is proposed to illustrate the chemical composition of the oxide layer grown by liquid-phase chemical-enhanced oxidation after S passivation. Oxidation following different surface treatments was studied by analyzing their activation energies. In addition, we find that the leakage current and the breakdown electric field of oxide layers can be improved significantly with the passivation technique.

Amorphous GaN Grown by Room Temperature Molecular Beam Epitaxy

Amorphous GaN films were grown at room temperature by molecular beam epitaxy on the oxide layer of GaAs(001) substrates. Their properties were investigated by transmission electron microscopy/diffraction and micro-Raman spectroscopy. A broad Raman peak at 650 cm-1 identifies the amorphous GaN. The results suggest that the local short-range bonding structure in amorphous GaN is different from crystalline GaN supporting theoretical predictions [Stumm and Drabold: Phys. Rev. Lett. 79 (1997) 677] that amorphous GaN is attractive for device applications.

Real-time spectroscopic ellipsometry for III–V surface modifications Hydrogen passivation, oxidation and nitridation by plasma processing

Passivation of GaAs surfaces through an initial cleaning step by hydrogen plasmas followed by the formation of an oxide layer by UV-light-assisted oxygen plasma anodization or by the formation of a wide gap GaN layer by N 2 plasma nitridation is presented. The emphasis is on the chemical and microstructural modifications which surfaces undergo during the above passivation processes. In situ spectroscopic ellipsometry is used to monitor the surface in real-time. Specifically, the H 2 remote plasma is operated at 230°C to remove native oxide from GaAs and InP surfaces. Real-time ellipsometry well discriminates the cleaning end-point, the structural damage and the passivation of shallow defects operated by H-atoms, so explaining the observed change of the photoluminescence intensity as a function of hydrogen exposure. O 2 plasma anodization carried out at 130–250°C under UV-light irradiation of the sample is able to change the chemistry of the growing GaAs oxide layer, in that an As 2O 5-rich oxide with reduction of elemental arsenic is obtained. Segregation of As at the GaAs surface is also encountered during N 2 plasma nitridation of GaAs to form a GaN passivating layer. This problem is overcome by low-temperature (250–350°C) nitridation of GaAs with N 2–H 2 plasmas. An attempt is made to correlate the surface chemistry as determined by ellipsometry with the Fermi level unpinning as determined by X-ray photoelectron measurements.

Optical and electronic characterization of transition layer in thin film Au-GaAs Schottky barrier

The possibility of determination of optical parameters and thickness of interfacial oxide (IO) layer by multiple-angle-of-incidence (MAI) ellipsometry has been studied for Au-IO-GaAs structures with different oxide thickness. The films parameters have been calculated by the original program of inverse ellipsometric problem solution. Parameters of oxide layer have been determined both for free GaAs surface and for that covered by Au film. Gold film was prepared by vacuum evaporation on the heated n-n+GaAs substrate. Its parameters have been determined by MAI ellipsometry and transparency measurements of Au-quartz satellite system. The investigation showed the change of optical parameters of GaAs oxide layer after the Au evaporation. In the assumption of invariable thickness of IO layer its optical parameters are : n = 1.0±0.1, k = 0.4 ÷ 0.6. The mechanism of current transport and electrical parameters of Au-IO-GaAs structures have been determined from I-V and C-V characteristics of Schottky diodes. The results of the determination of transition layer thickness to its dielectric constant ratio (d\\εi)) from electrical characteristics of barrier also indicate its difference from initial parameters of oxide layer probably due to interdiffusion of Au, Ga, and As.

Chemistry and kinetics of the GaAs oxidation by plasma anodization: Anin situreal-time ellipsometric study

In situ real-time ellipsometry is used to study the GaAs oxidation process by radio-frequency plasma anodization. The effect of the GaAs surface temperature, the bias potential applied to GaAs substrate, the crystallographic orientation, and UV-light irradiation on the chemistry and kinetics of GaAs oxidation are investigated. Oxide layers from tenths to hundreds of angstroms in thickness are grown at temperatures as low as 130 \ifmmode^\circ\else\textdegree\fi{}C and bias voltages ranging between 5 and 50 V. The rate of oxidation is further increased by irradiation of the GaAs surface with UV light during plasma anodization. The role of the diffusion of oxidizing species and of the drift of gallium and arsenic ions on the oxidation kinetics is discussed and the UV photoenhancement effect is clarified. These plasma-grown GaAs oxide layers have a unique composition in that they are almost stoichiometric and contain ${\mathrm{As}}_{2}{\mathrm{O}}_{5}$ as the main arsenic oxide.

Vertically stacked quantum wires fabricated by an in situ processing technique

We have fabricated vertically stacked structures consisting of two arrays of AlGaAs GaAs quantum wires using a processing technique conducted under an ultra-high vacuum or in a controlled ambient, called in situ electron beam (EB) lithography. In this technique a thin GaAs oxide layer was selectively formed on a clean GaAs surface by EB-stimulated oxidation in an oxygen atmosphere, and then used as a mask material to define mesa stripes by Cl 2 gas etching. Subsequently, ridge structures were formed on the mesa stripes by the MBE growth of a GaAs layer. The first array of quantum wires was formed on the top of the ridges by the growth of an AlGaAs GaAs quantum well. Then, these wire structures were buried and the surface was flattened out by the growth of a thick GaAs layer. The second array of quantum wires was successively formed by a second pattern and regrowth process. The successful fabrication of these structures was confirmed by cathodoluminescence measurements at 77 K.

AlGaAs/GaAs wire and box structures prepared by molecular-beam epitaxial regrowth on in situ patterned GaAs substrates

We have developed a processing technique which is conducted entirely under an ultrahigh vacuum environment, called in situ electron-beam (EB) lithography, to pattern GaAs substrates on which AlGaAs/GaAs wire and box structures are subsequently regrown. In this technique a thin GaAs oxide layer is selectively formed by EB-stimulated oxidation under a controlled oxygen atmosphere, and is then used as a mask material to define mesa stripes and mesa squares by Cl2 gas etching. Subsequently, the initial mesa size is reduced by the regrowth of a GaAs layer. Finally, AlGaAs/GaAs wire and box structures are fabricated on the top of the mesas by the growth of a quantum well. These structures were characterized by cathodoluminescence measurements at 77 K.

Fabrication of quantum wires on GaAs substrates patterned by in situ electron-beam lithography

In situ electron-beam (EB) lithography, a processing technique conducted entirely under an ultra-high vacuum environment, was used to pattern GaAs substrates on which quantum-wire structures were overgrown. First, a GaAs oxide-layer was selectively formed by EB-stimulated oxidation under a controlled oxygen atmosphere; it was then used as a mask material to define mesa stripes by Cl 2 gas-etching. Subsequently, ridge structures were formed on the mesa stripes by the overgrowth of a GaAs layer by molecular-beam epitaxy. Quantum-wire structures were fabricated on the top of the ridges by the growth of an AlGaAs GaAs quantum well. On the narrowest ridge structures, ∼20 nm wide quantum wires were successfully fabricated, as confirmed by cathodoluminescence measurements at 77 K.

Stability of GaAs oxide under metalorganic molecular beam epitaxy process

Well-defined oxide of GaAs can be used as a mask material for selective-area metalorganic molecular beam epitaxy (MOMBE) of GaAs. In this study, the reaction between triethylgallium (TEG) and the GaAs oxide layer was studied using a quadrupole mass spectrometer (QMS) and an atomic force microscope (AFM). Results of the QMS observation showed that TEG was reflected on the GaAs oxide surface until the start of desorption of the GaAs oxide, and the GaAs oxide layer was desorbed from the wafer after a large time delay from the start of TEG supply. AFM images showed that many holes appeared on the GaAs oxide surface during the desorption of the GaAs oxide. The effect of incident TEG upon the stability of the GaAs oxide mask is discussed.

Stability of GaAs oxide under metalorganic molecular beam epitaxy process

Well-defined oxide of GaAs can be used as a mask material for selective-area metalorganic molecular beam epitaxy (MOMBE) of GaAs. In this study, the reaction between triethylgallium (TEG) and the GaAs oxide layer was studied using a quadrupole mass spectrometer (QMS) and an atomic force microscope (AFM). Results of the QMS observation showed that TEG was reflected on the GaAs oxide surface until the start of desorption of the GaAs oxide, and the GaAs oxide layer was desorbed from the wafer after a large time delay from the start of TEG supply. AFM images showed that many holes appeared on the GaAs oxide surface during the desorption of the GaAs oxide. The effect of incident TEG upon the stability of the GaAs oxide mask is discussed.

S2Cl2 treatment: A new sulfur passivation method of GaAs surface

We have developed a new sulfur passivation method—S2Cl2 treatment, which is quite effective for removing the surface oxide layer of GaAs and passivating the surface with monolayer thick sulfides. Photoluminescence (PL) spectroscopy, Auger electron spectroscopy (AES), and x-ray photoelectron spectroscopy (XPS) are used to study the passivated GaAs (100) surfaces. The results of PL reveal that the PL intensity increases by two orders of magnitude, which is indicative of the reduction of surface recombination velocity of GaAs by this treatment. AES data prove that the sulfurized surface contains S, Ga, As, C, and small amount of Cl atoms but no oxygen signal at all. XPS study shows that sulfur atoms bond to both Ga and As atoms more effectively on S2Cl2 treated surfaces than those passivated by (NH4)2Sx.

Growth and characterization of (111) and (001) oriented MgO films on (001) GaAs

The effects of substrate preparation on the structure and orientation of MgO films grown on (001) GaAs using pulsed laser deposition has been investigated. Textured MgO films displaying a (111)MgO∥(001)GaAs orientation relation with x-ray rocking curve full width at half maximum (FWHM) values as low as 1.8° were obtained in cases where the native GaAs surface oxide was only partially desorbed prior to growth. Reflection high-energy electron diffraction, transmission electron microscopy (TEM), and x-ray pole figure analysis of these films reveals a preferential orientation within the plane of the substrate: [11̄0]MgO∥[11̄0]GaAs and [112̄]MgO∥[110]GaAs. An interfacial layer (∼5 nm thick) was observed in high resolution TEM analysis, and was attributed to a remnant native GaAs oxide layer. Complete desorption of the native GaAs oxide at ∼600 °C in vacuum prior to MgO growth led to significant surface roughening due to Langmuir evaporation, and resulted in randomly oriented polycrystalline MgO films. Growth of MgO on Sb-passivated GaAs substrates, which provided smooth, reconstructed surfaces when heated to 350 °C in vacuum, resulted in cube-on-cube oriented films [i.e., (001)MgO∥(001)GaAs,[100]MgO∥[100]GaAs] with x-ray rocking curve FWHM values as low as 0.47°. TEM analysis of the cube-on-cube oriented films revealed evidence of localized strain fields at the MgO/GaAs interface, indicating the presence of misfit dislocations in the MgO layer.

Chemical composition by Auger sputter-depth profiles of GaAs oxide layers formed after chemical or Ar + ion etchings

The oxide formation on the GaAs(100) surface after different etching procedures has been studied using Auger sputter-depth profiles. The etching procedures were either chemical etching (H 3PO 4/H 2O 2/H 2O or NH 3/H 2O 2/H 2O) or low-energy (100 eV) Ar + ion beam etching. An attempt to a quantitative determination of the concentration profiles has been made using the sequential layer sputtering (SLS) model, taking into account the statistical nature of the ion sputtering and the Auger electron escape depth. The chemical composition and the oxide coverage on the GaAs surface have been deduced from the concentration profiles of the elements Ga, As and O. The oxide composition has been also studied after a thermal annealing and compared to an atmospheric native oxide.

Structural properties of GaAs oxide layers grown on polished (100) surfaces

The local structure of GaAs oxides, grown on GaAs (100) wafers by simple exposure to air after chemical etching as well as by heating in air at 250 degrees C and at room temperature in ozone (O3) atmosphere, has been studied by glancing-angle X-ray absorption spectroscopy. The reflection geometry makes it possible to collect the EXAFS (extended X-ray absorption fine-structure) signal related to a thin surface layer (about 30 AA) in such a way as to reduce the unwanted substrate contribution and to collect the signal arising from the oxide grown at the surface. The oxide composition and thickness change as the surface varies from about 5 to 30 AA. An As-enriched oxide is produced by the 30' O3 exposure while the Ga oxide component is more abundant for the sample heated at 250 degrees C in air.