Publications (7)7.69 Total impact
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Article: Absence of an intrinsic value for the surface recombination velocity in doped semiconductors
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ABSTRACT: A self-consistent expression for the surface recombination velocity $S$ and the surface Fermi level unpinning energy as a function of light excitation power ($P$) is presented for n- and p-type semiconductors doped above the 10$^{16}$ cm$^{-3}$ range. Measurements of $S$ on p-type GaAs films using a novel polarized microluminescence technique are used to illustrate two limiting cases of the model. For a naturally oxidized surface $S$ is described by a power law in $P$ whereas for a passivated surface $S^{-1}$ varies logarithmically with $P$. Furthermore, the variation in $S$ with surface state density and bulk doping level is found to be the result of Fermi level unpinning rather than a change in the intrinsic surface recombination velocity. It is concluded that $S$ depends on $P$ throughout the experimentally accessible range of excitation powers and therefore that no instrinsic value can be determined. Previously reported values of $S$ on a range of semiconducting materials are thus only valid for a specific excitation power.02/2013; -
Article: GaAs(111)A and B in hydrazine sulfide solutions : extreme polarity dependence of surface adsorption processes
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ABSTRACT: Chemical bonds formed by hydrazine-sulfide treatment of GaAs(111) were studied by synchrotron photoemission spectroscopy. At the B surface, the top arsenic atoms are replaced by nitrogen atoms, while GaAs(111)A is covered by sulfur, also bonded to underlying gallium, despite the sulfide molar concentration being 103 times smaller than that of the hydrazine. This extreme dependence on surface polarity is explained by competitive adsorption processes of HS- and OH- anions and of hydrazine molecules, on Ga- adsorption sites, which have distinct configurations on the A and B surfaces.07/2009; -
Article: Soft nitridation of GaAs(100) by hydrazine sulfide solutions: Effect on surface recombination and surface barrier
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ABSTRACT: The effect of nitridation of GaAs(100) by hydrazine sulfide solutions on the surface recombination velocity and surface barrier has been studied using photoluminescence and photoreflectance spectroscopies. Nitridation produces a decrease of surface recombination velocity by a factor of 26. After three years of air exposure, the recombination velocity is still smaller than for the naturally oxidized surface by a factor of 11. The observed effect is caused by a continuous nitride monolayer bonded with the GaAs substrate. The surface Fermi level is still pinned near midgap, which is attributed to residual unpassivated surface defects.Applied Physics Letters 01/2007; 90(2):022104-022104-3. · 3.84 Impact Factor -
Article: Liquid phase epitaxial regrowth on sulfide‐passivated Ga1-xAlxAs
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ABSTRACT: We demonstrate that Na 2 S passivation allows liquid phase epitaxial regrowth of Ga 0.5 Al 0.5 As upon Ga 1-x Al x As (0.3≤x≤0.8) after air exposure. Large aluminum concentrations require concentrated (2.4 M) sulfide solutions. We have also studied the Ga 1-x Al x As etching rate by Na 2 S. For large sulfide concentrations or small aluminum concentrations, the etching process stops after some time. These two phenomena are correlated because both of them require the presence on the surface of a stable protective layer. This can be understood by assuming the existence at the surface of two competing mechanisms: etching and passivation.Applied Physics Letters 09/1993; · 3.84 Impact Factor -
Article: Wet chemical nitridation of GaAs(001) surface
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ABSTRACT: Auger Electron Spectroscopy and Scanning Tunnelling Microscopy were used to study the chemical and structural properties of the GaAs(001) surface after wet chemical nitridation by hydrazine-sulfide solutions. AES results show that the as-nitrided surface is covered by a thin film formed by a layer of nitrogen atoms strongly bonded with the substrate, and by a layer of residual impurities above it. The residual layer consists of oxygen- and sulfur-containing compounds, which are removed by annealing at near 450 and 520$^{\circ}$C respectively. The STM relief of the annealed surface is smooth with the rms roughness of the order of 0.4 nm. It is formed by numerous grain-like features of average lateral size near 5 nm and of 0.5 nm of height. Possible origin of the features is discussed.http://dx.doi.org/10.1051/jp4:2006132050. -
Article: Interface chemistry and epitaxial growth modes of SrF_ {2} on Si (001)
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ABSTRACT: Molecular beam epitaxy has been used to grow SrF2 thin films on Si(001). The growth modes have been investigated by atomic force microscopy, electron diffraction, and photoemission. Two principal growth regimes have been identified: (i) when deposition is carried out with the substrate held at a temperature of 700–750 °C, SrF2 molecules react with the substrate giving rise to a Sr-rich wetting layer on top of which three dimensional bulklike fluoride ridges develop; (ii) when deposition is carried out with the substrate held at 400 °C, a nanopatterned film forms with characteristic triangular islands. Results are compared to the growth mode of CaF2 on Si(001) under analogous deposition conditions. Morphological and structural differences between the two systems are associated with the larger lattice parameter of SrF2 with respect to CaF2, resulting in a larger mismatch with the Si substrate.Phys. Rev. B. 75(7). -
Article: Structural properties of GaAs surfaces nitrided in hydrazine-sulfide solutions
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ABSTRACT: The surface structure of GaAs(1 0 0), (1 1 1)A, and (1 1 1)B substrates nitrided through the wet chemical treatment in hydrazine-sulfide solution have been studied by scanning tunneling microscopy (STM) under annealing in UHV. Such treatment has earlier been shown to produce a monolayer of gallium nitride on the (1 0 0)GaAs surface. The as-nitrided substrates of all surface orientations were found to be covered by an overfilm, which contains thioarsenic compounds and has a smooth relief. Thermal desorption of the overlfilm at about 530 °C opens the own relief of the nitrided surfaces. For the (1 0 0) orientation such relief is not microscopically planar and consists of nano-scale vicinal hillocks. These hillocks occur due to surface microetching which proceeds simultaneously with the formation of the surface nitride layer. We have shown that the wet nitridation procedure forms a monolayer of surface nitride on the (1 1 1)B surface. During nitridation the (1 1 1)B surface, as well as the (1 0 0) one, is affected by the microetching in the hydrazine-sulfide solution. Therefore, it exhibits a characteristic relief formed by triangular vicinal pyramids. At the same time the nitride film is not formed on the (1 1 1)A surface, which is more chemically inert, and where the surface etching is almost absent.Applied Surface Science.
