Oxidation Of GaAs Research Articles

Energy barriers at interfaces of (100)GaAs with atomic layer deposited Al2O3 and HfO2

Band alignment at the interfaces of (100)GaAs with Al2O3 and HfO2 grown using atomic layer deposition is determined using internal photoemission and photoconductivity measurements. Though the inferred conduction and valence band offsets for both insulators were found to be close to or larger than 2 eV, the interlayer grown by concomitant oxidation of GaAs reduces the barrier for electrons by approximately 1 eV. The latter may pose significant problems associated with electron injection from GaAs into the oxide.

Capacitance–Voltage Characterization of GaAs–Oxide Interfaces

We will shortly review the basic physics of charge-carrier trapping and emission from trapping states within the bandgap of a semiconductor in order to show that high-temperature capacitance–voltage measurements are necessary for GaAs metal–oxide–semiconductor characterization. The midgap trapping states in GaAs have characteristic emission times on the order of , which makes them extremely complicated to measure at room temperature. Higher substrate temperatures speed up these emission times, which makes measurements of the midgap traps possible with standard measurements. characterizations of , , , and interfaces show the existence of four interface state peaks, independent of the gate oxide deposited: a hole trap peak close to the valence band, a hole trap peak close to midgap energies, an electron trap peak close to midgap energies, and an electron trap peak close to the conduction band.

Gate Dielectrics for High Mobility Semiconductors

In this paper we investigate the impact of charged surface defects on the electronic properties of Ge surface. In addition, we describe new ways of passivating the Ge surface by using reactive rare earth oxides, which catalyze the formation of stable germanates. Their chemical and thermal stability are thought to be responsible for the good electrical properties including very low Dit. In the case of GaAs surface passivation, we show that by optimally adjusting the amorphous Si spacer layer, it is possible to avoid oxidation of GaAs and achieve surface channel inversion.

Comparison of n-type and p-type GaAs oxide growth and its effects on frequency dispersion characteristics

The electrical characteristics of n- and p-type gallium arsenide (GaAs) capacitors show a striking difference in the “accumulation” capacitance frequency dispersion. This difference has been attributed by some to a variation in the oxide growth, possibly due to photoelectrochemical properties of the two substrates. We show that the oxide growth on n- and p-type GaAs substrates is identical when exposed to identical environmental and chemical conditions while still maintaining the diverse electrical characteristics. The difference in electron and hole trap time constants is suggested as the source of the disparity of the frequency dispersion for n-type versus p-type GaAs devices.

Contribution from the solid-phase interactions of activating oxides to their nonlinear joint effect on the thermal oxidation of GaAs

The contribution from the solid-phase interactions in the PbO + Sb2O3 and PbO + Bi2O3 activating compositions to the multichannel process of GaAs thermal oxidation has been determined by spatial separation of the oxides. The solid-phase interactions make a positive contribution to the overall negative nonlinear effect in the dependence of the oxide film thickness on the GaAs surface on the activator batch composition. The contributions from the oxide interactions on the semiconductor surface and in the gas phase have been evaluated for the PbO + Sb2O3 composition.

Diffusion barrier layers for Al on GaAs native oxide grown by liquid phase chemical-enhanced oxidation

Thin films of TiW, TiN/Ti, Pd, and Mo as the diffusion barriers (DB) interposed between the Al layer and GaAs native oxide are examined. The GaAs native oxides are prepared by liquid phase oxidation. The interdiffusion of the Al/GaAs-oxide and Al/DB/GaAs-oxide (DB=TiW, TiN/Ti, Pd or Mo) multilayer structures are investigated by secondary ion mass spectroscopy, X-ray photoelectron spectroscopy, and Auger electron spectroscopy (AES). The results indicate that TiW and Mo films can effectively block Al diffusion and maintain their structural integrity up to 500°C and 400°C for 30min, respectively. However, the thermal stability of TiN/Ti and Pd films cannot be maintained at 400°C for 30min. Moreover, the failure of TiN/Ti barriers due to oxygen incorporated into the barrier layers is observed and the failure of the Pd as the diffusion barrier in the interdiffusion between Al and GaAs oxide, as demonstrated by AES analyses, is also observed.

Role of solid- and gas-phase interactions in the coaction of the oxides in MnO2 + PbO and MnO2 + V2O5 compositions activating the thermal oxidation of GaAs

Spatial separation of the oxides in MnO2 + PbO and MnO2 + V2O5 binary compositions activating the thermal oxidation of GaAs has made it possible to locate the interactions between these oxides that are responsible for the nonlinear effects observed in their coaction. The solid-phase interactions enhance the chemostimulating activities of both oxides (a positive nonlinear effect takes place). The gas-phase interactions cause a marked negative deviation from the additive chemical stimulation effect.

Phosphomolybdic acid-assisted thermal oxidation of GaAs

An experimental investigation is conducted into the thermal oxidation of GaAs assisted by phosphomolybdic acid. The mechanism of the process is identified. It is established that oxide films thus produced consist mainly of GaPO4 and are superior in insulating performance to ones made by conventional thermal oxidation.

Effect of NiO nanolayers on the thermal oxidation of GaAs

It is shown that nickel oxide deposited on GaAs insures rapid growth of oxide layers at low oxidation temperatures, inhibits the degradation of the substrate surface, and contributes to the binding of the volatile component with the formation of As2O3, As2O5, and nickel arsenates. A reaction scheme for the thermal oxidation of NiO(40 and 25 nm)/GaAs heterostructures is proposed which takes into account reactions at the oxide-semiconductor interface.

The oxidation of GaAs(1 0 0) surfaces under atmospheric pressure conditions studied in real time using dynamic reflectance anisotropy spectroscopy at 2.6 and 4 eV

Using real-time, dynamic reflectance anisotropy spectroscopy (RAS) at both 2.6 eV and 4.0 eV, we demonstrate that an anisotropic oxide will form on As rich c(4 × 4)/d(4 × 4) GaAs surfaces when exposed to moisture- free air diluted in inert gases in a metal organic chemical vapour deposition (MOCVD) reactor, and that the initial c(4 × 4)/d(4 × 4) structure effects the resulting optical anisotropy of the oxide. This was achieved by investigating how the RA signals at 2.6 eV and 4 eV of annealed GaAs (1 0 0) surfaces evolve relative to the as-etched and as-annealed signals when exposed to oxygen. It is found that while the 2.6 eV response, which is known to be associated with the As dimers, degrades to pre-process levels indicating their destruction, the 4 eV signal, stabilizes at an intermediate, permanent level, suggesting the formation of an anisotropic oxide film whose structure is determined at least in part, by the initial c(4 × 4)/d(4 × 4) surface.

Characterization of atomic-layer-deposited Al2O3∕GaAs interface improved by NH3 plasma pretreatment

Al 2 O 3 thin films were deposited by atomic layer deposition on HF-cleaned and NH3 plasma-treated GaAs surfaces, respectively. The precursors used for Al2O3 films are trimethylaluminum and water. Effects of NH3 plasma pretreatment on the electrical and structural properties of Al2O3∕GaAs interface were investigated by C-V measurements, high-resolution transmission electron microscopy, and x-ray photoelectron spectroscopy measurements. The C-V measurements showed that the electrical property is improved after NH3 plasma pretreatment. X-ray photo electron spectroscopy analyses confirmed that GaAs oxides and elemental As are greatly decreased and the GaAs surface can be efficiently protected during NH3 plasma pretreatment and atomic layer deposition of Al2O3.

Fabrication of nanostructures on Si(1 0 0) and GaAs(1 0 0) by local anodic oxidation

Atomic force microscopes have become useful tools not only for observing surface morphology and nanostructure topography but also for fabrication of various nanostructures itself. In this paper, the application of AFM for fabrication of nanostructures by local anodic oxidation (LAO) of Si(1 0 0) and GaAs(1 0 0) surfaces is presented. A special attention is paid to finding relations between the size of oxide nanolines (height and half-width) and operational parameters as tip-sample voltage and tip writing speed. It was demonstrated that the formation of silicon oxide lines obeys the Cabrera–Mott theory, i.e. the height of the lines grow, linearly with tip-sample voltage and is inversely proportional to logarithm of tip writing speed. As for GaAs substrates, the oxide line height grows linearly with tip-sample voltage as well but LAO exhibits a certain deviation from this theory. It is shown that the selective chemical etching of Si or GaAs ultrathin films processed by LAO makes it possible to use these films as nanolithographic masks for further nanotechnologies, e.g. fabrication of metallic nanostructures by ion-beam bombardment. The ability to control LAO and tip motion can be utilized in fabrication of complex nanostructures finding their applications in nanoelectronic devices, nanophotonics and other high-tech areas.

XPS analysis of surface chemistry of near surface region of epiready GaAs(1 0 0) surface treated with (NH 4) 2S x solution

In this work we analyze the effect of (NH) 2S x wet treatment on the GaAs(1 0 0) covered with “epiready” oxide layer without any pretreatment in order to check the removal of oxides and carbon-related contamination, and the formation of sulfur species. The sulfidation procedure consisted of epiready sample dipping (at room and 40 °C temperatures) in an ammonium polysulfide solution combined with a UHV flash annealing up to 500 °C. The inspection of the XPS As 2p 3/2 and Ga 2p 3/2 spectra taken at surface sensitive mode revealed: (i) the temperature-dependent reduction of the amount of GaAs oxides and carbon contamination after sulfidation, and almost their complete removal after subsequent annealing, (ii) the creation of sulfur bonds with both Ga and As, with more thermally stable Ga–S bonds, and (iii) the slight reduction in elemental arsenic amount.

Effects of O2 Dissociation on a Porous Platinum Coating in the Thermal Oxidation of GaAs

A -thick porous Pt layer has been sputter-coated on a portion of a GaAs sample and subsequently the sample was oxidized at in followed by -enriched . The oxide formed was characterized by Auger electron spectroscopy, secondary ion mass spectrometry, and X-ray photoelectron spectroscopy, all with a lateral resolution of about . Away from the Pt area, a mm-ranged gradually decreasing degree of As oxidation was observed in the outermost oxide layer. In the Pt area, Ga was preferentially oxidized at the oxide/substrate interface producing a five to seven times thicker oxide than in an area without the influence of Pt. A strongly enhanced dissociation rate of on Pt particles and a subsequent O spillover to adjacent oxide explain the experimental observations. The mm-ranged spillover is believed to take place via fast lateral surface diffusion and results in the observed variation of oxidized As at the gas/oxide interface. In the Pt area, a high concentration gradient of dissociated oxygen across the oxide layer supplies a high flux of dissociated oxygen to the GaAs substrate where Ga is preferentially oxidized. The results clearly demonstrate that both a surface reaction and solid-state diffusion influence the oxidation rate. A localized high effective oxygen (O) activity that spills over to a nearby oxide area is believed to be a general phenomenon that is operating in oxides where a dissociating element such as Pt is present at /oxide interfaces.

The role of nitrogen-containing compounds in the growth of oxide layers on GaAs and InP in the course of their thermal oxidation

Thermal oxidation of GaAs and InP with the participation of nitrogen-containing compounds (such as NH3, N2O, NH4NO3, NH4VO3, and NH3 + V2O5) is investigated. It is found that the rates of growth of oxide layers on the surface of semiconductors increase significantly when the chemical activator undergoes transformations in the reaction zone with the formation of compounds that are active at the instant of formation.

Desorption dynamics of oxide nanostructures fabricated by local anodic oxidation nanolithography

We studied the properties of GaAs oxides which were grown by local anodic oxidation (LAO) nanolithography using an atomic force microscope. We find that the LAO structures desorb under irradiation with soft x-rays (130eV). We analyzed the desorption process in detail by time-resolved photoelectron spectroscopy. We observe that even in the first stages of light exposure the LAO oxide is mainly composed of Ga2O, with a small fraction of Ga2O3 and As oxides. The As oxides are located only in the surface layers of the LAO oxide where they account for 10% of the oxide. Within 160minutes of exposure they completely desorb. Moreover, we find evidence for the presence of unoxidized GaAs embedded in the LAO oxide.

Oxidation Patterning of GaAs by Nanoelectrode Lithography

Nanoelectrode lithography, which transfers patterns from a nanoelectrode to a target via an electrochemical reaction, is employed for patterning GaAs. Gallium oxide and arsenic oxide are produced by the anodic oxidation of GaAs. A-400-nm pitch line and space (L/S) pattern and a closely packed hexagonal pattern with a 500 nm pitch are successfully transferred. For the 400-nm-pitch L/S pattern, a patterned area of 6×8 mm2 is obtained with a reaction time of 30 s. The fabricated pattern can be directly used as an etching mask. Structures with depths of approximately 70 and 10 nm are obtained by wet and dry etchings, respectively. In addition, it is confirmed that multiple patterning is also possible on a GaAs substrate.

Chemical composition of GaAs oxides grown by local anodic oxidation: a spatially resolved Auger study

The chemistry of the GaAs oxides fabricated by local anodic oxidation (LAO) using an atomic force microscope is studied by means of spatially resolved Auger electron spectroscopy. Oxide structures with nanometric size grown at different bias are investigated. We found that the LAO oxide is essentially composed of gallium oxides. The chemical composition of the LAO oxide does not depend on the applied bias.

Chemical and electrical characterization of Gd2O3∕GaAs interface improved by sulfur passivation

We report the formation of a gate dielectric film on the sulfur passivated GaAs(001). The Gd2O3 films were deposited on the n-GaAs substrates using the electron-beam evaporation. The sulfur passivated GaAs metal-oxide-semiconductor diode exhibited the improved electrical properties compared to a similar GaAs diode that was cleaned with HCl including an enhanced conduction-band barrier and a reduced-leakage current. We investigated the relation between the interfacial bonds and the electrical properties by a systematic characterization using the photoemission spectroscopy. Sulfidation was shown to preserve a stable Gd2O3∕GaAs interface and to prevent an interfacial GaAs oxide formation. The stable interface and the passivated surface were caused by the bonding transition from As–S to Ga–S. The As-oxide was dissociated to form the interfacial Ga2O3 and to volatilize the elemental As in the Gd2O3 deposition, conducted without sulfidation. The interfacial oxides and excess As degraded the electrical properties and resulted in the decrease of the conduction-band offset. It was found that the Gd2O3 film was composed of two oxidation states: the amorphous Gd–O and the crystalline Gd2O3. The bonding transition with a substrate heating implies that the Gd2O3 film on the GaAs surface completely crystallizes above 400°C. Electrical properties were understood in relation to the band alignment and were estimated from the valence band and the core-level spectra analysis. The sulfidation introduced a shift of the Fermi level toward the conduction-band minimum on the GaAs surface and increased the conduction-band offset at the Gd2O3∕GaAs interface, followed by a saturated accumulation capacitance with a low-leakage current.

Influence of annealing ambient on GaAs oxide prepared by the liquid phase method

The characteristics of GaAs native oxides prepared by the liquid phase chemical-enhanced oxidation technique annealed at various ambiences including N2, O2, and mixture of N2 (85%) and H2 (15%) are investigated. The annealing temperatures range from 300 to 700 °C. The shrinkage of oxide film thickness, the increase of refractive index, the decrease of surface roughness, the enhancement of breakdown field strength and the reduction of leakage current have been obtained for all annealing conditions, except for annealing in the ambient atmosphere of N2 or O2 at temperature of 700 °C. It is found that annealed oxide films exhibited better thermal stability in an atmosphere of N2/H2 up to an annealing temperature of 700 °C. This is due to the existence of H atoms in the oxide films as demonstrated by SIMS depth profiles.