Self-organized nanostructures in Si1-xGex films on Si(001)

Received: 30 July 1998/Accepted: 23 October 1998     

Line-scan sequential lateral solidification of Si thin films

Received: 14 April 1998/Accepted: 22 April 1998     

Monocrystalline Si waffles for thin solar cells fabricated by the novel perforated-silicon process

2 for this waffle-shaped film when it is attached to glass substrates. Received: 15 May 1998/Accepted: 28 May 1998     

Dome-to-pyramid transition induced by alloying of Ge islands on Si(001)

Received: 19 October 1998/Accepted: 19 October 1998     

On the impeded growth of oxide films on Si in N2O ambient

Growth kinetics of thin oxide films on silicon in nitrous oxide were investigated in the very early stage of the process. It was found that the resistance to oxidation reaches an almost stationary value for about 10 s at 1100 °C. The observation is explained by the incorporation of nitrogen atoms at the interface in the film, which impede the further growth. Received: 24 September 1998 / Accepted: 9 December 1998 / Published online: 24 March 1999     

Formation of amorphous layers by solid-state reaction. from thin Ir films on Si(100)

Received: 18 November 1997 / Accepted: 16 October 1998 / Published online: 24 February 1999     

Surface second-harmonic generation spectra of Si(111)-7×7 in the -–1.0 1.7eV fundamental photon energy

Received: 20 September 1998 / Revised version: 23 December 1998     

Magnetic and transport properties of sputtered Fe/Si multilayers

The structural, magnetic and transport properties of sputtered Fe/Si multilayers were studied. The analyses of the data of the X-ray diffraction, resistance and magnetic measurements show that heavy atomic interdiffusion between Fe and Si occurs, resulting in multilayers of different complicated structures according to different sublayer thicknesses. The nominal Fe layers in the multilayers generally consist of Fe layers doped with Si, ferromagnetic Fe-Si silicide layers and nonmagnetic Fe-Si silicide interface layers, while the nominal Si spacers turn out to be Fe-Si compound layers with additional amorphous Si sublayers only under the condition either for the series or for the series multilayers. A strong antiferromagnetic (AFM) coupling and negative magnetoresistance (MR) effect, about 1%, were observed only in multilayers with iron silicide spacers and disappeared when -Si layers appear in the spacers. The dependences of MR on and on bilayer numbers N resemble the dependence of AFM coupling. The increase of MR ratio with increasing N is mainly attributed to the improvement of AFM coupling for multilayers with N. The dependence of MR ratio is similar to that in metal/metal system with predominant bulk spin dependent scattering and is fitted by a phenomenological formula for GMR. At 77 K both the MR effect and saturation field increase. All these facts suggest that the mechanisms of the AFM coupling and MR effect in sputtered Fe/Si multilayers are similar to those in metal/metal system. Received: 11 February 1998 / Revised: 9 March 1998 / Accepted: 9 March 1998     

Surfactant-mediated growth of Si1-xSnx layers by molecular-beam epitaxy

1-x Sn_x (0.01≤x≤0.04) layers on Si(001) and relaxed Si-Ge substrates. The Si_1-xSn_x layers were investigated using Rutherford backscattering spectrometry, atomic force microscopy, transmission electron microscopy and preferential-etching experiments. The investigation of surfactant-mediated growth of epitaxial Si_1-xSn_x was motivated by a possible use of relatively higher growth temperatures without relaxation by surface precipitation. It is demonstrated that higher growth temperatures are attainable when Bi is used as surfactant if the surface-segregated Sn layer is relatively small, equivalent to Si_1-xSn_x layers of low strain. The increase in growth temperature leads to a significant improvement in the crystalline quality of these Si_1-xSn_x layers. Received: 4 December 1998/Accepted: 9 December 1998     

Computer study of boron and phosphorus at the Si(100)̶2 ╳ 1 surface

The AM1 semiempirical numerical method combined with the geometry optimization procedure was used to study the energetics of active impurities (B, P) in substitutional positions at the Si(100)- surface. It has been found that phosphorus prefers to be in the first layer (in dimers). Boron has the lowest energy in the second layer. Energy profits, counting from the fourth bulk-like layer, for B and P are 1.33 eV and 0.56 eV, respectively. Comparing of the P-Si and P-P dimers energetics has shown that P-Si dimers are more preferable energetically. Received: 26 March 1998 / Accepted: 9 June 1998     

Dopant diffusion and segregation in semiconductor heterostructures: Part 2. B in GexSi1-x/Si structures

x Si_1-x/Si heterostructures have been obtained. Here the chemical effects seem to be of less importance. The Fermi-level effect determines the ionized boron solubilities in Ge_xSi_1-x and in Si, as well as the thermal equilibrium concentration of the singly-positively-charged crystal self-interstitials I⁺ which governs the boron diffusion process. The junction carrier concentration affects the concentration of I⁺ and solubility of B in the region and hence controls B diffusion across the heterojunction. Received: 20 August 1998/Accepted: 23 September 1998     

Second-harmonic spectroscopy of Ge/Si(001) and Si1-xGex(001)/Si(001)

0.9 Ge_0.1(001)/Si(001) films with SH photon energies 3.1<2hν<3.5 eV near the bulk E₁ critical point of Si(001) or Si_0.9Ge_0.1(001). Ge was deposited on Si(001) by using atomic layer epitaxy cycles with GeH₄ or Ge₂H₆ deposition at 410 K followed by hydrogen desorption. As Ge coverage increased from 0 to 2 monolayers the SH signal increased uniformly by a factor of seven with no detectable shift in the silicon E₁ resonant peak position. SH signals from Si_0.9Ge_0.1(001)/Si(001) were also stronger than those from intrinsic Si(001). Hydrogen termination of the Si_0.9Ge_0.1(001) and Ge/Si(001) surfaces strongly quenched the SH signals, which is similar to the reported trend on H/Si(001). We attribute the stronger signals from Ge-containingsurfaces to the stronger SH polarizability of asymmetric Ge-Si and Ge-Ge dimers compared to Si-Si dimers. Hydrogen termination symmetrizes all dimers, thus quenching the SH polarizability of all of the surfaces investigated. Received: 13 October 1998 / Revised version: 18 January 1999     

DC-electric-field-modified second-harmonic generation at the Si(100) surface

1 resonances for clean and H covered surfaces shift as a function of the dc field in agreement with experiment. This suggests the presence of built-in electric fields whose strength depends on the H coverage, and which are strongly localized in the subsurface region. Received: 20 September 1998     

Visible photoluminescence from Ge+-implanted SiO2 films thermally grown on crystalline Si

+ -implanted SiO₂ films is studied as a function of different fabricating conditions (implantation dose, annealing temperature and time). The SiO₂ films containing Ge nanocrystals exhibit two photoluminescence (PL) bands peaked at 600 nm and 780 nm. There are two excitation bands in the PL excitation (PLE) spectra. With variation in Ge nanocrystal size, the PL and PLE peak energies show no appreciable shift. The PL and PLE spectral analyses suggest that during the PL process, electron–hole pairs are generated by the E(l) and E(2) direct transitions inside Ge nanocrystals, which then radiatively recombine via luminescent centers in the matrix or at the interface between the nanocrystal/matrix. Received: 27 January 1998/Accepted: 18 March 1998     

Formation of high-conductivity NiSi2 layers on Si at zero-mismatch temperature by high-current Ni-ion implantation

2 and Si lattices at 380 °C, which was defined as zero-mismatch temperature. The implantation was conducted with a metal vapor vacuum arc (MEVVA) ion implanter at an extraction voltage of 45 kV. Based on a thermal conduction estimation, a temperature rise of 380 °C required the Ni-ion current density to be 35 μA/cm². For the Si(111) wafers, the high conducting NiSi₂ layers were indeed directly formed after Ni-ion implantation with this specific current density to a normal dose of 2×10¹⁷ ions/cm² and the resistivity was as low as 9 μΩ cm. For the Si(111) wafers pre-covered with a 10-nm Ni overlayer, the resistivity of the NiSi₂ layers obtained under the same conditions decreased down to about 6 μΩ cm. The superior electrical property of the NiSi₂ was thought to be related to its formation temperature, i.e. at a zero-mismatch temperature of 380 °C, which resulted in minimizing the stress and stress-induced defects involved in its formation as well as cooling process. Received: 27 April 1998 / Accepted: 26 October 1998     

Raman investigation of submicro-grained Si films obtained by incoherent UV photo-CVD of silicon hydrides

Received: 10 February 1998/Accepted: 12 February 1998     

Impedance spectroscopic study of Si/HF-electrolyte system during Si dissolution

Porous silicon (PS) has been synthesized by anodic etching in HF and ethanol electrolyte. The in situ current–voltage characteristic clearly identify the pore formation, transition and electropolishing regimes. The experimentally observed impedance and phase as a function of frequency (Bode plots) reasonably agree with theoretically simulated Bode plots drawn by considering the equivalent circuit for PS/electrolyte. Received: 10 December 1999 / Accepted: 12 February 2000 / Published online: 13 September 2000     

Second-harmonic generation spectroscopy on quantum wells: Au on Si(111)

×):Au-structure prior to film growth leads to increased amplitude in the oscillations indicating improved growth characteristics compared to the 7×7 substrate. The position of the maxima shifts towards lower coverage and the oscillation period decreases with increasing pump frequency. This behaviour is an unambiguous signature of quantum well resonances and, hence, clearly demonstrates that Au deposition on Si(111)(×):Au leads to well-defined quantum well structures with atomically flat interfaces. Furthermore, the rotationally anisotropic contribution to SHG also shows coverage oscillations as a result of quantum well effects and demonstrates the presence of structural order. Received: 12 October 1998     

KrF excimer laser ablation of thin Cr film on glass substrate

Received: 5 October 1998 / Accepted: 14 December 1998 / Published online: 24 February 1999     

Mechanism of conductivity in metal-polymer-metal structures

Received: 25 September 1998 / Accepted: 25 November 1998 / Published online: 24 February 1999