Recrystallization behaviour and electrical properties of germanium ion implanted polycrystalline silicon films

The recrystallization behaviour of undoped and phosphorus-doped polycrystalline silicon films amorphized by germanium ion implantation at doses ranging from 1 × 10¹⁵ to 1 × 10¹⁶cm^-2 are investigated, and the electrical properties of phosphorus-doped films after recrystallization are studied. The phosphorus doping concentration ranges from 3 × 10¹⁸ to 1 × 10²⁰cm^-3. It is found that the nucleation rate decreases for undoped films and increases for phosphorus-doped films with increasing germanium dose; the growth rates decrease for both doped and undoped films. The decrease in nucleation rate is caused by the increase in implantation damage. The decrease in growth rate is considered to be due to the increase in lattice strain. The grain size increases with germanium dose for undoped films, but decreases for phosphorus-doped films. The dependence of the electrical properties of the recrystallized films as a function of phosphorus doping concentration with different germanium doses can be explained in terms of the grain size, crystallinity and grain boundary barrier height.     

Memory switching in polycrystalline silicon films

Non-volatile memory switching has been observed in polycrystalline silicon layers produced by chemical vapor deposition. Evidence for filamentary conduction is found for devices which are in their low impedance state. Devices have been cycled through high and low impedance states up to a maximum of 2x10⁴ times. Exposure to transient ionizing electron radiation caused the devices to switch to their low impedance state.     

Inductivity phenomena in local polycrystalline silicon films

The capacitance-voltage characteristics of epitaxially grown polycrystalline silicon local films were investigated in the frequency range 0.465-10 MHz. A transition in the character of the capacitance from reactive conductivity to inductive behaviour was discovered.It is shown that under illumination the inductance transformed into a capacitance and the negative resistance region disappeared from the current- voltage curve.It is suggested that inductivity phenomena in polycrystalline silicon films occur by processes of recharging of deep levels.     

Amorphous silicon and germanium films for uncooled microbolometers

The possibility of using amorphous silicon and germanium films prepared by magnetron sputtering as components in uncooled microbolometers has been analyzed experimentally and results are presented. Amorphous silicon and germanium films having activation energies of 0.135 and 0.2 eV, and resistivities of 50 and 0.4 kΩ·cm, respectively, were fabricated. Pis’ma Zh. Tekh. Fiz. 23, 21–26 (July 12, 1997)     

Studying the morphology of hemispherical-grain polycrystalline silicon films

The effect of the deposition temperature on the morphology of hemispherical-grain polycrystalline silicon (HSG-Si) films obtained by low-pressure chemical vapor deposition (LPCVD) has been studied using atomic force microscopy. The dependences of the relative surface area increment, density of grains, average height and lateral size of grains, mean square roughness, and correlation length on the deposition temperature have been determined in an interval used for the LPCVD growth of HSG-Si films.     

Preparation of nanostructured silicon oxide and silicon nitride films using nanotechnologies

The synthesis of silicon oxide and silicon nitride surface nanostructures is used as an example to demonstrate the possibility of using correlation relationships with inductive parametric constants for quantitatively assessing the reactivity of surface functional groups and predicting the conditions of surface reactions.     

Investigation of silicon etching and silicon dioxide bubble formation during silicon oxidation in HCl-oxygen atmospheres

Experiments performed to characterize the silicon etching occurring at the silicon-silicon dioxide interface during thermal oxidation of silicon in dry oxygen-HCl atmospheres at 1100 °C are described. The etching was accompanied by bubble formation or bowing of the silicon dioxide film and ultimately by complete loss of adhesion of the thermally grown film. Pre-oxidation experiments with dry oxygen suggest that silicon etching is primarily dependent upon the chlorine concentration at the silicon-silicon dioxide interface, with oxide growth prior to HCl addition having a small effect.     

Epitaxial growth of nanostructured gold films on germanium via galvanic displacement

This work focuses on the synthesis and characterization of gold films grown via galvanic displacement on Ge(111) substrates. The synthetic approach uses galvanic displacement, a type of electroless deposition that takes place in an efficient manner under aqueous, room temperature conditions. Investigations involving X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques were performed to study the crystallinity and orientation of the resulting gold-on-germanium films. A profound effect of HF(aq) concentration was noted, and although the SEM images did not show significant differences in the resulting gold films, a host of X-ray diffraction studies demonstrated that higher concentrations of HF(aq) led to epitaxial gold-on-germanium, whereas in the absence of HF(aq), lower degrees of order (fiber texture) resulted. Cross-sectional nanobeam diffraction analyses of the Au-Ge interface confirmed the epitaxial nature of the gold-on-germanium film. This epitaxial behavior can be attributed to the simultaneous etching of the germanium oxides, formed during the galvanic displacement process, in the presence of HF. High-resolution TEM analyses showed the coincident site lattice (CSL) interface of gold-on-germanium, which results in a small 3.8% lattice mismatch due to the coincidence of four gold lattices with three of germanium.     

Desorption-ionization mass spectrometry using deposited nanostructured silicon films

We present a method for desorption ionization on silicon based on novel column/void-network-deposited silicon thin films. A number of different peptides and proteins in the < or = 6000 Daltons range are analyzed by time-of-flight mass spectrometry in this demonstration of our approach. A variety of sample preparation conditions, including the use of chemical additives, surface treatments, and sample purification are used to show the potential of mass analysis using deposited column/void-network silicon films for high throughput proteomic screening.     

Roughness of amorphous, polycrystalline and hemispherical-grained silicon films

We have performed atomic-force-microscopy studies of the roughness and spatial and correlation properties of the surface for three typical LPCVD films of silicon: amorphous and polycrystalline films with a relatively smooth surface, as well as polycrystalline films with hemispherical grains (HSG-Si) having considerable surface roughness. As follows from analysis of the correlation function and power spectral density function, the model of a self-affine surface is suitable for describing morphology of amorphous and polycrystalline silicon films, while the model of a mounded surface is preferable for HSG-Si films.     

Properties of polycrystalline silicon films prepared from fluorinated precursors

Polycrystalline silicon films have been prepared at low temperature on glass substrate from fluorinated precursors by PECVD technique varying the hydrogen dilution and gas flow rate. Undoped film with dark-conductivity 1.05×10⁻² S cm⁻¹ has been obtained. For n-type poly-Si film the highest conductivity achieved is 2.8 S cm⁻¹. Grain size observed from SEM varies from 4 to 6 μm for undoped and 2 to 3 μm for phosphorous doped films. The main crystalline peak is 〈111〉 whereas the crystallite size calculated from XRD is 350 Å. The optical absorptions and hydrogen contents in the films deposited under different conditions have been studied. Growth kinetics are dominated by the precursors SiF_nH_m (m+n≤3) and concentrations of F and H on the growth surface.     

Structure of diamond polycrystalline films deposited on silicon substrates

The article presents results of structural studies of polycrystalline diamond thin films deposited by hot filament CVD on silicon substrates. The films were characterized using Scanning Electron Microscopy (SEM), Raman Spectroscopy (RS), Electron Backscattered Diffraction (EBSD), Energy Dispersive Spectroscopy (EDS) and Secondary Ion Mass Spectroscopy (SIMS). Both the EBSD patterns and Raman spectra confirm that the grains visible in the electron micrographs are diamond micro-crystallites. The residual stress in the films is found to be in the range between −4.29 GPa and −0.56 GPa depending on the sample thickness. No evidence of lonsdalite and graphite has been registered in the polycrystalline material of the investigated samples. Evidence of the existence of silicon carbide at the diamond/silicon interface is presented. It is also suggested that an amorphous carbonaceous film covers the silicon surface in the regions of holes in the thin diamond layers.     

Band gap profiles of intrinsic amorphous silicon germanium films and their application to amorphous silicon germanium heterojunction solar cells

Intrinsic amorphous silicon germanium (i-a-SiGe:H) films with V, U and VU shape band gap profiles for amorphous silicon germanium (a-SiGe:H) heterojunction solar cells were fabricated. The band gap profiles of i-a-SiGe:H were prepared by varying the GeH₄ and H₂ flow rates during the deposition process. The use of i-a-SiGe:H with band gap profile in an absorber layer for a-SiGe:H heterojunction solar cells was investigated. The solar cell using a VU shape band gap profile shows a higher efficiency compared to other shapes. The highest efficiency obtained for an a-SiGe:H heterojunction solar cell using the VU shape band gap profile technique was 9.4% (V_oc = 0.79 V, J_sc = 19.0 mA/cm² and FF = 0.63).     

The burning rate of energetic films of nanostructured porous silicon

A systematic study of nanoenergetic films consisting of nanostructured porous silicon impregnated with sodium perchlorate is carried out. The explosive properties of these films are investigated as a function of thickness, porosity, and confinement. The films' burning rates are investigated using fiber-optic velocity probes, demonstrating that flame-front velocities vary between approximately 1 and 500 m s(-1) and are very sensitive to the films' structural characteristics. Analysis of the flame profile by high-speed video is also presented, suggesting that the reaction type is a deflagration rather than a detonation. A strong plume of flame is emitted from the surface, indicating the potential for this material to perform useful work either as an initiator or as a propellant. The shape of the flame front transitioned from an inverted V at thin-film thicknesses to a neat square-shaped front once the material became self-confining at 50 μm.     

Thin polycrystalline zinc oxide films obtained by oxidation of metallic zinc films

Thin polycrystalline ZnO films were obtained by thermal oxidation of metallic Zn films, thermally deposited on various substrates, such as silica, sapphire and glass, in both air and pure oxygen atmospheres. The quality of the ZnO layers was asserted by Hall effect, cathodoluminescence and atomic force microscopy measurements. Electron concentration of 7.32×10¹² cm⁻³ and mobility of 14.2 cm²/V s with root mean square roughness of 30 nm were obtained for the 900 °C annealed ZnO films in oxygen. Room temperature cathodoluminescence spectra consisted of a narrow near band edge luminescence band and a broad defect-related green band with peak positions at 380 and 500 nm, respectively. ZnO film luminescence properties improved dramatically with the increase of annealing temperature and decrease of O₂ pressure.     

Radiation-resistant free germanium and silicon films for nuclear physics experiments

The structure, composition, and radiation resistance of free target films of germanium and silicon prepared under various conditions were studied. Under the experimental conditions encountered in nuclear physics, the targets prepared by pulsed thermal deposition in vacuum are stable for a longer period of time as compared to the samples prepared in a continuous deposition regime.     

Characterization of laser annealed polycrystalline silicon films on various substrates

The structure and property of eximer laser annealed poly-Si films on various substrate materials such as MoW, Cr, were studied. It was found that the crystallinity of the film depended on the recrystallization energy density and substrate materials. The crystallinity of the film on substrate was the highest quality, and the higher the thermal conductivity of the substrate, the poorer the crystallinity of the poly-Si films at the same laser energy density. In the lower laser energy region than optimum, the grain size and surface roughness were increased with increasing laser power due to the increase of the crystallinity and decreased intrinsic stress. On the other hand, in the higher power region than optimum, with the increase of laser power, X-ray intensity and grain size were decreased due to the fast solidification velocity. There was no metal diffusion into poly-Si film but small amount of Si, less than 3 atomic percent, diffused into the metal film during the recrystallization process.     

Pore formation in aluminum films on macroporous silicon during high-temperature annealing

The surface of an aluminum metallization coating applied on a macroporous silicon layer and annealed for 10–60 min at 550°C has been studied by atomic-force and electron microscopy techniques. It is established that the annealing results in the formation of through (open) macropores with lateral dimensions within 400–1300 nm in the aluminum film and in the growth of large hillocks with heights of up to 1.2μ m on the surface, which are located at the edges of these macropores. The geometric parameters of large hillocks are independent of the duration of annealing.     

Large-grain polycrystalline silicon thin films obtained by low-temperature stepwise annealing of hydrogenated amorphous silicon

Large grained polycrystalline silicon thin films have been prepared by low-temperature solid phase crystallisation of sputter-deposited hydrogenated amorphous silicon (a-Si:H), with relatively short processing times, and a considerably low thermal budget. Various a-Si:H samples, deposited under different conditions and with varying hydrogen concentrations and hydrogen bonding configurations, were simultaneously annealed. Only a particular set of deposition conditions led to crystallisation. The a-Si:H thin film which was successfully crystallised was prepared in an argon-hydrogen mixture, in which the last few minutes of film deposition occurred in a hydrogen-rich atmosphere. For that film, the hydrogen concentration profile resulted in a much higher hydrogen content on the sample surface than in the bulk, and H-Si bonds were predominantly of the weak type. Crystallisation was accomplished by low-temperature stepwise annealing from 200°C to 600°C at 100°C steps, with samples being cooled down to room-temperature between each annealing step. This resulted in large grained (> 10 μm range) polycrystalline silicon after the 600°C annealing step for a 1.1 μm thick sample. Fourier transform infrared (FTIR) spectroscopy, elastic recoil detection analysis (ERDA) and scanning electron microscopy (SEM) techniques were used to analyse samples before and after crystallisation.