Ga2O3 Layer Research Articles

Selective Area Growth by Metal Organic Vapor Phase Epitaxy and Atomic Layer Epitaxy Using Ga2O3 as a Novel Mask Layer

A novel technique is proposed for advanced microstructure formation using Ga2O3 as a new mask material. Ga2O3 layers were prepared by RF sputtering with Ga2O3 powder target and patterned using photolithography. Scanning electron microscope (SEM) and Photoluminescence (PL) measurement findings indicate that reasonably high-quality single crystalline GaAs layers could be successfully grown selectively on the unmasked region by metal organic vapor phase epitaxy (MOVPE) and atomic layer epitaxy (ALE). The GaAs/AlGaAs quantum structure was also fabricated by selective area MOVPE, however, at this stage, polycrystalline AlGaAs layers formed on the mask region after the mask removal and the regrowth of AlGaAs overlayers. The key factor in this microstructure fabrication process is the sensitive dependence of Ga oxide layers against the reactor pressure under H2 exposure.

Selective formation of one- and two-dimensional arrayed InGaAs quantum dots using Ga2O3 thin film as a mask material

We report on the selective formation of InGaAs quantum dots (QDs) by molecular beam epitaxy. Nanoscale patterned Ga2O3 thin film deposited on the GaAs (100) substrate was employed as a mask material. Due to the enhanced migration effect of the group-III adatoms, such as Ga and In on Ga2O3 mask layer, the InGaAs QDs formed on the patterned substrate results in coalesced islands unlike those formed on the nonpatterned substrate. The estimation of the relative volume of the islands per unit area revealed that the desorption process as well as the migration of the Ga and In adatoms might occur on the Ga2O3 layer during the growth process, providing a good selective growth of self-assembled QDs.

接着性加熱重合型レジンの貴金属床義歯への応用 表面改質法による改質表面構造と接着性

The present study was conducted to investigate the efficacy of surface modification methods for precious metal alloys, including Adlloy surface modification method, Type I, and Type II tin electroplating methods. The structures of modified surface having an effect on the adhesive ability of 4-META heat-curing resin and Au-Ag-Pd alloy were analyzed by ESCA in order to discuss the relationship between the surface structure and the adhesiveness.The modified surfaces of the alloy showing high shear bond strength were composed of a flat pane covered with a Ga2O3 layer by the Adlloy method and jagged grains covered with SnO layer by the Type II tin electroplating method. On the other hand, the modified surface of the alloy with the Type I tin electroplating method showed no efficacy of adhesion and was composed of polygonal grains covered with an SnO2 layer.It was suggested that the differences of adhesiveness depended on the kind of oxide compounds promoted by each modification methods.

Formation of single-phase MAsx films on GaAs by selective wet-hydrogen oxidation and etching

A technique which shows promise for achieving stable contacts is reported. This technique involves the selective oxidation of Ga in H2O/H2 mixtures simultaneous with the reaction of the metal and As to form a metal arsenide compound. The oxidation step is followed by removing the Ga2O3 layer using an acid etch. The large free energy of formation of gallium oxide enables the adjustment of the partial pressure of H2O to H2 so that only gallium is oxidized, while the GaAs substrate, metal, and metal arsenide are not. This method is discussed for three metal contacts to GaAs: In, Pt, and Cr. The technique was applied to GaPt/PtAs2/GaAs structures. The GaPt phase can be oxidized completely, whereas the inner PtAs2 is left unoxidized. The oxide can be etched off to leave a structure consisting only of platinum-arsenide on the GaAs substrate.

Effects of oxygen impurities in W films on W/GaAs Schottky-barrier contacts

Schottky-barrier characteristics and chemical reactions of contacts between oxygen-contained W films and GaAs substrates annealed up to 800 °C have been investigated. Phase transformation from β-W to α-W of the oxygen-contained W films (3 at. % oxygen), sputter deposited in Ar and O2 gas mixture, is observed at temperatures around 650 °C. Electrical degradation of the contacts, especially in capacitance-voltage (C-V) characteristics, is found after annealing above 650 °C. Oxygen accumulation at the W/GaAs interfacial region and Ga and As atom diffusion into the W films are found by secondary-ion mass spectrometry during annealing. Formation of a Ga2O3 layer at the interfacial region is also detected by x-ray photoemission spectroscopy and transmission electron microscopy. These results suggest that Ga2O3-layer formation is related to the electrical degradation. The C-V characteristics can possibly be explained by series capacitance of an interfacial oxide layer and a depletion layer together with an assumption of nonuniform carrier distribution in the GaAs substrate.

Schottky barrier height variation due to a Mo interfacial layer in W/GaAs systems

The effect of the interfacial Mo-GaAs alloy layer on the Schottky barrier characteristics of W/GaAs contacts is investigated. Variation in Schottky barrier heights is measured by fabricating W(300 nm thick)/Mo(0–10 nm)/GaAs diodes, where a Ga2 O3 layer 0.9 nm thick is previously formed on the GaAs surface. The oxide layer is intended to detect the initial stage of the interfacial reaction which could remove the oxide layer and influence electrical characteristics. The maximum barrier height and the minimum ideality factor are obtained at a Mo layer thickness of 1 nm after annealing at 450 °C. The Mo layer reduces the Ga2 O3 layer on GaAs surfaces and forms the compounds GaMo3 and Mo5 As4 with the GaAs substrates by a solid-phase reaction. The intimate contact of these compounds to the substrates is thought to be formed some distance below the original Mo/GaAs interface. The formation and control of buried Schottky barrier contacts using refractory metals are experimentally verified. This allows more reliable gate barriers for GaAs metal-semiconductor field-effect transistors.

Oxide effects on photoemission from high current GaAs photocathodes

During 4 years of on line operation of the SLAC polarized electron gun (PEGGY) and polarized LEED (PLEED) system, we have observed and characterized the failure modes of the GaAs (100) photocathodes (PC's) used in these systems. Several modes are observed. Gradual decreases in electron polarization and intensity are attributed to the physisorption of CO2 on the PC's during running at LN2 temperatures. Such PC's can be rejuvenated by warming to 90 K, i.e. above the CO2 desorption temperature. These PC's recover 90% of their original intensity. A second well-characterized failure mode results from overheating the PC during in situ heat cleaning prior to activation. In this mode, As is preferentially evaporated from the GaAs, leaving a Ga2O3 layer on the surface. This effect has been studied by AES sputter profiling which indicates that the substantial thickness of the oxide layer blocks photoemission. These PC's may only be recovered by chemically removing the oxide layer. A third mode which is not as well characterized appears for thin Ga oxide layers. Properties of these PC's include reduced emission and the presence of a cutoff bias level. Such PC's are also not recoverable in situ.

Anodic oxide/GaAs and InP interface formation

The initial stages of anodization of GaAs and InP were investigated in order to determine the factors which affect the oxide–semiconductor interface formation. This was accomplished by ESCA profiling thin anodic layers grown on chemomechanically polished wafers. Oxides on both InP and GaAs appear to be initiated by a nucleation and island growth process with the film becoming continuous at a thickness of approximately 40 Å. The oxide/GaAs interface was found to be composed of a Ga2O3 layer with indications of elemental As near the substrate. The oxide/InP interface had a uniform distribution of In2O3 and P2O5. The data indicates that dissolution of As2O3 or P2O5 is not a significant factor in the interface formation but the thermodynamic stability of the oxide could be important.

Effect of vacuum heat treatment on the surface properties of epitaxial GaAs

We have examined the effect of heating under vacuum on the electronic and structural state of the real surface of epitaxial GaAs films. Vacuum heat treatment reduces the height of the surface potential barrier, increases the surface electron affinity, and raises the density of surface recombination centers and traps. The changes in the electrical and physical properties are due to disorder in the subsurface region, which is apparent in the formation of a block GaAs structure and a polycrystalline Ga2O3 layer.

Initial oxidation and oxide/semiconductor interface formation on GaAs

Evolution of the oxide/GaAs interface formation for both thermal and anodic oxides is presented. This is accomplished by examining ESCA profiles of 21–85 Å thick thermal and anodic oxides. The anodic oxide begins with a nucleation and growth process during which the As oxides are leached out leaving a continuous layer of Ga2O3. Oxide growth then proceeds by Ga and As diffusion to the surface where they oxidize leaving the inner layer of Ga2O3 unchanged. Thus the anodic oxide/GaAs interface is formed during the first 40 Å of oxide growth. During thermal oxidation both Ga2O3 and As2O3 are formed but the As2O3 evaporates rapidly leaving the Ga2O3. Once the Ga2O3 layer is formed, the As is excluded from entering the continuous Ga2O3 layer and collects at the oxide/GaAs interface. This occurs after about 40 Å of oxide growth.