InSb and InAs1−xSbx epitaxial layers have been successfully grown on (100)GaAs substrates by molecular beam epitaxy. Remarkably good morphologies were obtained despite the large lattice mismatch (14%) between InSb and GaAs. Room-temperature electron mobilities as high as 57 000 cm2/V s were measured in InSb layers of about 5 μm thick with ND−NA∼1.6×1016 cm−3. The substrate temperature and Sb/In flux ratio were found to critically influence the quality of InSb epilayers. By employing dimeric instead of tetrameric sources, the composition of the InAs1−xSbx films was observed to be relatively independent of substrate temperature. Electron mobilities of 20 000 and 8800 cm2/V s, at 300 and 77 K, respectively, were obtained for a 1.6-μm-thick InAs1−xSbx (x=0.67) layer.
We present a new technique for porous semiconductor formation which is based on the exposure of semiconductor surfaces to gas phase etchants. The technique offers the possibility of fabricating light-emitting devices by selectively exposing a silicon surface to HF vapor. Photoluminescence measurements reveal an efficient emission at around 750 nm. FTIR analysis confirm the existence of strong hydrogen incorporation and oxidation as evidenced from the local bonding environment of hydrogen and oxygen atoms.
Abstract:Cryptocrystal layers of ammonium silicon fluoride (NH 4 ) 2 SiF 6 were synthesized on silicon wafers by dry etching method using vapor of the mixture of HF and HNO 3 solutions at room temperature. Crystalline layers having thicknesses of up to 8 m have been produced at growth rates of around 1 m/hour. The crystallinity was analysed by X-ray diffraction that indicates an isometric hexoctahedral system (4/m -32/m) with Fm3m space grouping of (NH 4 ) 2 SiF 6 cryptohalite crystals. These results have been confirmed by the presence of vibrational absorption bands of (NH 4 ) 2 SiF 6 species by Fourier transform infrared (FTIR) spectroscopic measurements. Strong absorption bands were observed in the infrared at 480cm -1 , 725cm -1 , 1433cm -1 and 3327cm -1 and assigned to N-H and Si-F related vibrational modes of (NH 4 ) 2 SiF 6 .Annealing above
The physical properties of black silicon (b-Si) formed on Si wafers by reactive ion etching in chlorine plasma are reported in an attempt to clarify the formation mechanism and the origin of the observed optical and electrical phenomena, which are promising for a variety of applications. The b-Si consisting of high density and high aspect ratio sub-micron length whiskers or pillars with tip diameters of well under 3 nm exhibits strong photoluminescence (PL) both in the visible and the infrared, which is interpreted in conjunction with defects, confinement effects and near band-edge emission. Structural analysis indicates that the whiskers are all crystalline and encapsulated by a thin Si oxide layer. The infrared vibrational spectrum of Si-O-Si bondings in terms of transverse-optic (TO) and longitudinal-optic (LO) phonons indicates that disorder induced LO-TO optical mode coupling can be an effective tool in assessing the structural quality of the b-Si. The same phonons are likely coupled to electrons in visible region PL transitions. Field emission properties of these nanoscopic features are demonstrated indicating the influence of the tip shape on the emission. Overall properties are discussed in terms of the surface morphology of the nanowhiskers.
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