Effect of indium annealing on the electrical properties of polycrystalline n-type CdTe

Polycrystalline n-type CdTe samples were annealed in molten indium at 800°C for different times (150 to 350 h). D.c. conductivity () and Hall coefficient (R_H) studies were made on these samples in the temperature range 77 to 400 K. R_H and data were analysed based on the various models existing for polycrystalline semiconductors. The temperature variation of mobility data were analysed in the light of various scattering mechanisms; the role of grain-boundary scattering being examined in particular detail.     

Defect annealing processes for polycrystalline silicon thin-film solar cells

A variety of defect healing methods was analyzed for optimization of polycrystalline silicon (poly-Si) thin-film solar cells on glass. The films were fabricated by solid phase crystallization of amorphous silicon deposited either by plasma enhanced chemical vapor deposition (PECVD) or by electron-beam evaporation (EBE). Three different rapid thermal processing (RTP) set-ups were compared: A conventional rapid thermal annealing oven, a dual wavelength laser annealing system and a movable two sided halogen lamp oven. The two latter processes utilize focused energy input for reducing the thermal load introduced into the glass substrates and thus lead to less deformation and impurity diffusion. Analysis of the structural and electrical properties of the poly-Si thin films was performed by Suns-V_OC measurements and Raman spectroscopy. 1 cm² cells were prepared for a selection of samples and characterized by I–V-measurements. The poly-Si material quality could be extremely enhanced, resulting in increase of the open circuit voltages from about 100 mV (EBE) and 170 mV (PECVD) in the untreated case up to 480 mV after processing.     

Rapid thermal annealing of in situ p-doped polycrystalline silicon thin-films

Polycrystalline silicon thin films deposited via low-pressure chemical vapour deposition (LPCVD) have a rough surface and a resistance which is too high for use within microelectronic devices. However, both of these problems may be overcome by in situ doping of the polycrystalline silicon films with phosphorus by introducing PH₃/N₂ and SiH₄/N₂ mixtures simultaneously into a LPCVD reactor but, such doping requires a high temperature furnace step (950°C) to bring the resistivity down to the required level. In general, prolonged exposure to high temperature is undesirable since it not only reduces the resistivity of the polycrystalline silicon film but also disturbs the existing dopant profiles and alters the structure of the films deposited. This ultimately makes the devices fabricated unreliable, difficult to reproduce and thus a broad device specification in batch production. The solution is to decrease the furnace temperature or reduce the time the devices are kept at high temperature. The latter may be achieved by using a technique known as rapid thermal annealing (RTA). In this paper we examine rapid thermal annealing as a quick method of redistributing the dopants in order to achieve a lower sheet resistance. The results obtained are compared with conventional furnace annealing. It will be shown that rapid thermal annealing is an attractive and often better alternative to conventional 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.     

Effect of annealing temperature on the performance of water motion energy harvesting in n-type silicon thin film by magnetron sputtering

Journal of Materials Science - Harvesting energy through water motion on solid surface is significantly important due to the energy generation intermittency of the usually used energy transducers....     

Ellipsometric analysis of ion-implanted polycrystalline silicon films before and after annealing

A study of arsenic ion-implanted polycrystalline silicon films before and after annealing at various temperatures has been performed using spectroscopic ellipsometry in the ultraviolet to the visible spectral region. Using the Bruggeman effective medium approximation, an optical/structural model is presented for all the annealed samples explaining the measurements. Ellipsometric measurements reveal important structural changes as a function of annealing temperature which provide an interesting inside into the annealing kinetics of ion-implanted polycrystalline silicon films. This work also demonstrates the importance of spectroscopic ellipsometry in determining non-destructively the dielectric functions in materials that have undergone complex processing.     

Grain growth mechanism in heavily arsenic-doped polycrystalline silicon

The mechanism of grain growth in heavily arsenic-doped polycrystalline silicon has been investigated by developing a kinetic model. A computer simulation technique has been used to determine the grain boundary self-diffusion of the silicon atoms and hence the grain size for different arsenic concentrations, annealing times and temperatures has been estimated. The evaluated numerical values are compared with the available experimental values. Using this model the grain size distribution in arsenic-doped polysilicon for various values of arsenic concentration, annealing time and temperature has been determined. The results are discussed in detail.     

Influence of annealing temperature on the properties of polycrystalline silicon films formed by rapid thermal annealing of a-Si:H films

In this work, rapid thermal annealing (RTA) was employed to crystallize the amorphous silicon films deposited by hot-wire chemical vapor deposition. The influence of annealing temperature on structural and electrical properties was studied by Raman spectroscopy, X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and temperature-dependent conductivity measurement. The results show that the amorphous silicon films can be successfully crystallized by RTA in a very short time. The crystallinity and electrical properties of the poly-Si films was greatly improved as the RTA temperature increasing. When the temperature higher than 900 °C, the poly-Si films obtained the crystalline fraction above 95 %, and the hydrogen atoms almost disappeared in the poly-Si films. At the temperature of 1,100 °C, polycrystalline silicon films with conductivity of 16.4 S cm^?1 is obtained, which is seven orders in magnitude higher than that of the film annealed at 700 °C.     

Thin-film polycrystalline silicon solar cells formed by flash lamp annealing of a-Si films

We have fabricated thin-film solar cells using polycrystalline silicon (poly-Si) films formed by flash lamp annealing (FLA) of 4.5-µm-thick amorphous Si (a-Si) films deposited on Cr-coated glass substrates. High-pressure water-vapor annealing (HPWVA) is effective to improve the minority carrier lifetime of poly-Si films up to 10 µs long. Diode and solar cell characteristics can be seen only in the solar cells formed using poly-Si films after HPWVA, indicating the need for defect termination. The actual solar cell operation demonstrated indicates feasibility of using poly-Si films formed through FLA on glass substrates as a thin-film solar cell material.     

Effect of annealing temperature on electrical characteristics of ruthenium-based Schottky contacts on n-type GaN

The electrical properties of ruthenium (Ru) and ruthenium/gold (Ru/Au) Schottky contacts on n-type GaN are investigated as a function of annealing temperature by current–voltage (I–V) and capacitance–voltage (C–V) techniques. The Schottky barrier height of as-deposited Ru/n-GaN is found to be 0.88 eV (I–V) and 1.10 eV (C–V) respectively. However, after annealing at 500°C for 1 min in the nitrogen ambient, the decrease in barrier height is quite considerable and found to be 0.80 eV (I–V) and 0.86 eV (C–V). In the case of Ru/Au Schottky diode the measured barrier height is 0.75 eV (I–V) and 0.93 eV (C–V). In contrast to the Ru contacts, it is interesting to note that the barrier height of Ru/Au depends on the annealing temperature. Annealing at 300°C improves the barrier height and the corresponding values are 0.99 and 1.34 eV. Further increase in annealing temperature decreases the barrier height and the respective values are 0.72 and 1.08 eV at 500°C. From the above observations, it is clear that the electrical properties of annealed Ru/Au contacts are improved compared to the as-deposited films. However, Ru Schottky contacts exhibit a kind of thermal stability during annealing.     

Effect of electroactive nickel on the low-temperature annealing behavior of silicon

We have studied the effect of low-temperature annealing on the behavior of electroactive nickel in silicon. The results demonstrate that the state of electroactive nickel centers in silicon is stable up to 200°C. Starting at 300°C, the SiNi solid solution decomposes and the electroactive nickel concentration decreases. From low-temperature (t > 200°C) annealing kinetics, the activation energy for the annealing of a deep center at E _c − 0.41 eV is estimated at 1.2–1.5 eV. The decomposition rate of the SiNi solid solution increases with temperature.     

Effect of thermal annealing on the microstructure of ytterbium-implanted silicon wafers

Ytterbium-implanted Si(0 0 1) wafers annealed at different temperatures (800, 900, 1000 and 1200°C) have been examined by means of cross-section transmission electron microscopy (XTEM) and electron diffraction. The results indicate that two layers of defects exist in the samples, one mainly includes microtwins and the other includes ytterbium precipitates. The distribution and morphology of the defects depend mostly on the thermal annealing: the higher the annealing temperature, the larger the size of the defects and the closer are the layers of defects to the wafer surface. High-resolution images show the different characteristics and details of the defects under various annealing conditions. The relation between microstructure and luminescence response is also discussed. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of annealing in various atmospheres on the photoluminescence of porous silicon

The effect of isochronous annealing in various atmospheres on the photoluminescence of porous p-type silicon samples obtained by anodization under identical conditions was studied. Comparative experimental data for the samples annealed in air, nitrogen, and vacuum are presented.     

Control of the morphology of n-type porous silicon

The morphology of layers obtained by anodic etching is related to the current-voltage characteristics of the electrolytic cell during the etching. By etching at various points of the current-voltage characteristic one can obtain porous silicon with various structures. Pis’ma Zh. Tekh. Fiz. 23, 80–84 (March 26, 1997)     

Raman scattering and photoluminescence study of porous silicon formed on n-type silicon

We report Raman scattering and photoluminescence studies on porous silicon film formed on n-type silicon. The Raman spectra over the sample surface exhibit considerable variation whereas the photoluminescence spectra are practically identical. Our results indicate that, well inside the film surface, it consists of spherical nanocrystals of typical diameter ≈ 100Å, while on the edge these nanocrystals are ? 300Å. We further observe that there is no correlation between the photoluminescence peak position and the nanocrystal diameter. This suggests that the origin of the photoluminescence is due to radiative recombination between defect states in the bulk as well as on the surface of the nanocrystal.     

Effect of annealing temperature on the crystal phase fraction in silicon nanoclusters in a silicon oxide matrix

A model of the annealing-induced crystallization of amorphous clusters in a solid matrix is proposed. The calculated dependence of the crystallized phase fraction on the annealing temperature agrees with the available experimental data.     

Study on the effect of annealing on the electrical properties of n-type cuprous oxide

n-Type cuprous oxide was synthesized by controlling the bath pH of the electro-deposition. Thereafter, cuprous oxide films were annealed in nitrogen at different temperatures. The electrical properties of n-type cuprous oxide films before and after annealing were studied by the capacitance-voltage measurements. By analysis of the Mott-Schottky curves, it was found that the carrier concentration of cuprous oxide films varied with the deposition bath pH and the annealing temperature. Also, the flat-band potential shifted with the increasing annealing temperature.     

Orientation analysis of polycrystalline silicon

An analysis of the crystallographic orientation of Wacker “Silso” polycrystalline silicon is reported. It is observed that many grains are penetrated perpendicular to the sample surface by equally oriented lattice planes. No connection could be found between grain size and grain orientation. 50% of adjacent grains in the center of the plate and 16% of adjacent grains in the edge region of the plate share common lattice planes which traverse the grain boundaries undisturbed.     

Photoconductivity studies of n-type hydrogenated amorphous silicon and microcrystalline silicon

Photoconductivity techniques serve as useful tools for the characterization of amorphous and microcrystalline silicon. From the link between the majority carrier mobility–lifetime product from steady-state photoconductivity and the position of the Fermi level, useful insight can be gained when comparing sample properties. The temperature dependence of the minority carrier mobility–lifetime product implies that the band-tail region of the density-of-states (DOS) is steeper in microcrystalline silicon than in amorphous silicon. Transient and modulated photoconductivity determine the DOS in the upper half of the band gap, for which we find an exponential variation. We indicate that the Fermi level or quasi-Fermi level impose limitations on the DOS extraction from the measured data. In samples in which the Fermi level is shifted towards the conduction band, the DOS calculation then yields values that are too low.