Stability Of GaAs Research Articles

Photoelectrochemistry of Self-Limiting Electrodeposition of Ni Film onto GaAs.

Gallium arsenide (GaAs) provides a suitable bandgap (1.43eV) for solar spectrum absorption and allows a larger photovoltage compared to silicon, suggesting great potential as a photoanode toward water splitting. Photocorrosion under water oxidation condition, however, leads to decomposition or the formation of an insulating oxide layer, which limits the photoelectrochemical performance and stability of GaAs. In this work, a self-limiting electrodeposition method of Ni on GaAs is reported to either generate ultra-thin continuous film or nanoislands with high particle density by controlling deposition time. The self-limiting growth mechanism is validated by potential transients, X-ray photoelectron spectroscopy composition and depth profile measurements. This deposition method exhibits a rapid nucleation, forms an initial metallic layer followed by a hydroxide/oxyhydroxide nanofilm on the GaAs surface and is independent of layer thickness versus deposition time when coalescence is reached. A photocurrent up to 8.9mA cm-2 with a photovoltage of 0.11V is obtained for continuous ultrathin films, while a photocurrent density of 9.2mA cm-2 with a photovoltage of 0.50V is reached for the discontinuous nanoislands layers in an aqueous solution containing the reversible redox couple K3 Fe(CN)6 /K4 Fe(CN)6 .

Etching or Stabilization of GaAs(001) under Alkali and Halogen Adsorption

Experimentally and by ab initio calculations it is shown that adsorption of electropositive cesium on the As-rich surface of GaAs(001) and, in a symmetric fashion, adsorption of electronegative iodine on the Ga-rich surface, induce a decrease of the surface stability, thus facilitating surface etching. Conversely, Cs adsorption on the Ga-rich surface and I adsorption on the As-rich surface lead to an increased surface stability. Etching occurs when adsorption-induced charge transfer weakens the backbonds of the top arsenic atoms for the case of Cs on the As-rich β2(2 × 4) surface and the lateral bonds in the topmost surface layer for I on the Ga-rich ζ(4 × 2) surface. The possibilities of reversible transitions between the two reconstructed surfaces and of atomic layer etching with monolayer precision are demonstrated.

The stability of a GaAs(001)-(2 × 4) surface with Si adatoms

The stability of GaAs(001)-(2 × 4) β2 surface with Si adatoms is theoretically investigated using the ab initio pseudopotential method. The calculated results imply that stable lattice sites for Si adatoms strongly depend on the adatom coverage. At lower coverage θ = 0.125, Si adatoms stably reside in the empty Ga sites in the missing dimer trenches. This is consistent with recent STM observations at low coverages. On the other hand, the surface with Si dimers on the upper As dimers are the most stable at higher coverage θ = 0.25. The coverage dependence of adsorption site preferences is qualitatively discussed in terms of energy band structure and excess energy of hetero interatomic bonds such as AsAs, SiAs and GaSi.

Elevated temperature stability of GaAs digital integrated circuits

The elevated temperature stability of a commercial GaAs enhancement-depletion-mode MESFET process has been characterized; the observations made are relevant to device operation at elevated temperatures, with implications for optoelectronic integration on GaAs integrated circuits by selective-area epitaxial growth, and to long term circuit and device reliability. Although the transistor electrical characteristics are stable for up to five hours at 500/spl deg/C, a metallurgical reaction between the interconnect metal AlCu/sub x/ core and WN/sub x/ claddings has been identified which limits circuits to five hour operation at 470/spl deg/C. This later reaction proceeds with an activation energy of 3.5 eV and results in a 15-fold increase in interconnect metal sheet resistance. A geometry-dependent increase in ohmic contact resistance is seen at somewhat higher temperature which is ascribed to the penetration of aluminum-containing compounds to the ohmic contact edge.

InP (and GaAs) substrate stabilization by the presence of GaAs (and InP) in a metal-organic vapour-phase epitaxy system

Metal-organic vapour-phase epitaxy (MOVPE) is a well-established technique for semiconductor growth. Like molecular-beam epitaxy, liquid-phase epitaxy, and vapour-phase epitaxy, it requires a stabilized substrate surface prior to growth to obtain a high-quality crystal. Studies of the stabilization of GaAs and InP substrates placed side by side with their interactions under V-hydride flows can provide valuable information. Here we show the effect of exposing GaAs and InP substrates to AsH3 and (or) PH3 in the temperature range from 550 °C to 750 °C, in an MOVPE reactor. The presence of a GaAs substrate partially stabilizes the InP substrate; the stabilized area decreases when either temperature of AsH3 flow increases. The presence of a stabilized InP substrate (under PH3 flow) also partially stabilizes the GaAs substrate. Surface analysis shows that the stabilized area contains column-V species coming from the neighbouring substrate. These column-V species are competing with species originating from the V hydrides (AsH3 or PH3). From the analysis of these experiments, we conclude that the V-hydride species active in the MOVPE environment are not dimers or tetramers. Annealing the substrates under both AsH3, and PH3 shows preference for As-specics aggregation at the substrate surface. The simple model previously used to prediet stabilization is extended to cover this mixed-hydride situation.

Photocapacitance study of n‐GaAs/electrolyte interfaces

AbstractThe electrochemical photocapacitance spectroscopy (EPS) is used to determine the interface state distribution at n‐GaAs/aqueous electrolyte junctions. Two states (Ec — 1.30eV and Ec — 1.05 eV) are found to be related to corrosion of GaAs. It is also shown that ruthenium induces additional states 0.2 eV above the valence band. A new insight of its effect on the stabilization of GaAs is given.