Annealing behavior of a void network in amorphous silicon

A void network in a-Si films prepared by vacuum deposition was studied. A close relationship in annealing behavior has been observed between the changes in surface area of voids and in the ESR signal strength.     

Doping of evaporated amorphous silicon films

It is shown that evaporated amorphous silicon films can be doped interstitially by ion implantation and in-diffusion of lithium. The doping effect is smaller than for glow discharge silicon films, and the doped state is less stable at elevated temperature. This is explained by precipitation as well as out-diffusion effects in connection with the high defect concentration in evaporated films.     

Annealing and amorphous silicon passivation of porous silicon with blue light emission

The photoluminescence (PL) of the annealed and amorphous silicon passivated porous silicon with blue emission has been investigated. The N-type and P-type porous silicon fabricated by electrochemical etching was annealed in the temperature range of 700-900 °C, and was coated with amorphous silicon formed in a plasma-enhanced chemical vapor deposition (PECVD) process. After annealing, the variation of PL intensity of N-type porous silicon was different from that of P-type porous silicon, depending on their structure. It was also found that during annealing at 900 °C, the coated amorphous silicon crystallized into polycrystalline silicon, which passivated the irradiative centers on the surface of porous silicon so as to increase the intensity of the blue emission.     

Optically induced electron spin resonance in doped amorphous silicon

We report the first observations of optically induced electron spin resonance signals in doped and undoped amorphous silicon. We also report the observation of equilibrium surface or interface spin densities ～ 10¹³cm^?2 and volume spin densities ～ 6 × 10¹⁵ cm^?3. The small number of spins observed in equilibrium compared to the large optically induced spin density shows that most electrons are spin paired in equilibrium. We conclude that this implies a very small mean effective correlation energy, U ～ kT.     

Annealing behavior ot trap-centers in silicon containing A-swirl defects

The annealing behavior of trap-centers was studied in float-zone silicon wafers containing A-swirl defects. Samples from areas of high and low A-swirl density were annealed in nitrogen ambient between 100° and 900 °C, and analysed using the Deep Level Transient Spectroscopy. The results indicate, that two levels atE _c }-0.07 eV, _n=4.6×10^–16 cm², andE _c–0.49eV, _n=6.6×10^–16cm² are caused by one defect, for which the silicon di-selfinterstitial is a likely interpretation. A level atE _c }-0.11 eV was assigned to interstitial carbon. Both defects annealed out at about 170 °C. After 600 °C annealing an additional level atE _c–0.2 eV was detected, which was attributed to an interstitial silicon carbon complex. Heat treatment at 800 °C generated a new level atE _c–0.49 eV, _n=2.9×10^–16cm² only in the area of high A-swirl defect density. This level was also observed after oxidation and subsequent annealing of silicon.     

Correlation effects and the density of states in amorphous silicon

The evaluation of the density of gap states from the charge density measured in field-effect experiments is considered in terms of a model which incorporates electron correlation effects. Due to the positive Hubbard U a density of states is deduced which differs appreciably from the “field effect” densities published previously. Besides the lack of the E_x and E_y peaks the minimum density is found to be ～ 10¹⁵ ? 10¹⁶ cm^?3 eV^?1.     

High density amorphous form and polyamorphic transformations of silicon

Polyamorphic transformations of silicon have been investigated by constant-pressure first-principles molecular-dynamics simulations. By pressurizing a normal amorphous Si with tetrahedral coordination, a new high density amorphous (HDA) form that has a strong resemblance to HDA water is obtained. We find that the HDA form can be also obtained through vitrification of liquid Si under pressure. Both HDA and liquid Si contain deformed tetrahedral configurations with interstitial atoms. These findings indicate that HDA Si is directly connected with liquid Si, which is of particular importance in understanding phase relations of polyamorphs of Si.     

退火处理对掺铒氢化非晶硅悬挂键密度和光致荧光的影响

采用磁控溅射技术制备了铒掺杂的氢化非晶硅(a-Si∶H(Er))样品.进一步通过200—500℃温度递增的后退火处理，获得了不同的Si悬挂键(Si-DBs)密度，并在此基础上研究了Si-DBs密度改变对其Er光荧光(Er-PL)的影响.退火温度低于350℃时，Er-PL强度持续增加，但Si-DBs密度的变化显得较复杂；350℃以上时，Er-PL强度随Si-DBs密度的增加而减小.在200—250℃的退火温度范围内，Si-DBs是由于结构弛豫而减少；在250—500℃的退火温度范围内，可能由于Si—H键的断 关键词： 氢化非晶硅 铒掺杂 Si悬挂键 光荧光     

Muon spin resonance and repolarization in amorphous silicon monoxide (a-SiO)

Studies of the muonium fractions in the amorphous oxide a-SiO have been carried out by RF resonance at TRIUMF, Canada and LF repolarization techniques at RAL, U.K. The resonance measurements confirm the presence of the interstitial Mu centre in this intermediate oxide of silicon. Analysis of the data gathered at RAL, using a recently-developed fitting technique, reveals that the Mu^* state is present here as well, but with lower relative fractions than in a-Si. However, as in the latter material, but in contrast to c-Si, this bond-centre species appears to be stable up to room temperature.     

Urbach edge and the density of states in hydrogenated amorphous silicon

Photoconductivity measurements of the optical absorption edge and time-of-flight measurements of the hole drift mobility, on the same amorphous silicon film, enable us to identify the origin of the Urbach edge in amorphous silicon with the density of states in the valence band tail.     

Nickel induced lateral crystallization behavior of amorphous silicon films

Nickel induced lateral crystallization of amorphous silicon with and without electric field has been studied. Dendritic silicon growth behavior is observed, with crystallites of a few hundred nanometers in width and up to a few microns in length. The behavior can be understood from the preferential epitaxial growth of silicon from the (1 1 1) facets of the NiSi₂ precipitate, which forms during the early stage of the annealing process. The dendritic growth fronts are different with and without electric field in the nickel induced lateral crystallization process. Electric field is found to be beneficial in increasing the lateral crystallization rate and improving the film crystallinity. Joule heating plays an important role as well to enhance the lateral crystallization.     

Experimental elucidation of hydrogen local density of states in hydrogenated amorphous silicon

Ultraviolet and X-ray photoemission spectroscopies (UPS and XPS) are used to study the valence band in device quality hydrogenated amorphous silicon films (s-Si:H). Their results are combined to obtain estimated information about the hydrogen local density of states (HLDOS). The monohydride bonding configuration and the occurence of interhydride bonding between H atoms are confirmed by the experimental data.     

The density of states in the mobility gap of halogenated amorphous silicon

Summary The density of states in the mobility gap of halogenated amorphous silicon has been measured by the field effect technique. The results are discussed to shed light on the reality of a peak found in the DOS. A comparison is made with the DOS curves obtained by SCLC in the same material. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Segregation of evaporated gallium in laser doped silicon

Silicon wafers of n-type covered with a thin evaporated layer of pure gallium have been exposed to Q-switched Nd : YAG laser pulses (32 ns; 280, 410, $\text{560}\text{MW}\text{cm}{}^2$). Rutherford backscattering measurements with a 3 MeV He⁺ beam show that a significant fraction of the gallium is incorporated in the silicon substrate. A drastic segregation accumulates the Ga atoms near the surface.     

Annealing behaviour of implanted nitrogen in bulk and evaporated Ni

The diffusion coefficients of nitrogen in N-implanted polycrystalline Ni have been deduced. Both bulk and Ni-evaporated samples implanted with nitrogen were annealed at 150–500° C. The nitrogen profiles were probed using the nuclear resonance broadening technique. The value of 0.99±0.12 eV for the activation energy and (3.0 _–2.8 ⁺⁴⁰ )×10^–6 cm²/s for the frequency factor were obtained for implanted N in bulk Ni. The solubilities for both the bulk and evaporated Ni samples are given. In evaporated Ni nitrogen migration is enhanced due to the defects arising during evaporation.     

Kinetics of CoSi2 from evaporated silicon

2 MeV⁴He⁺ backscattering spectrometry and CuK x-ray diffraction were used to study CoSi₂ formed by annealing at temperatures between 405° and 500 °C from CoSi with evaporated Si films. A laterally uniform layer of CoSi₂ forms, in contrast to the laterally nonuniform CoSi₂ layer that is obtained on single crystal Si substrates. The thickness of the CoSi₂ film formed is proportional to the square root of time at a fixed temperature. The activation energy of this reaction is about 2.3 eV.     

Evolution of stress in evaporated silicon dioxide thin films

The evolution of stress in evaporated SiO2, used as optical coatings, is investigated experimentally through in situ stress measurement. A typical evolution pattern consisting of five subprocedures （thin film deposition, stopping deposition, cooling, venting the vacuum chamber, and exposing coated optics to the atmosphere） is put forward. Further investigations into the subprocedures reveal their features. During the deposition stage, the stresses are usually compressive and reach a stable state when the deposited film is thicker than 100 nm. An increment of compressive stress value is observed with the decrease of residual gas pressure or deposition rate. A very low stress of-20 MPa is formed in SiO2 films deposited at 3×10^-2 Pa. After deposition, the stress increases slightly in the compressive direction and is subject to the stabilization in subsequent tens of minutes. In the process of venting and exposure, the compressive component increases rapidly with the admission of room air and then reaches saturation, followed by a logarithmic decrement of the compressive state in the succeeding hours. An initial discussion of these behaviors is given.     

Fundamental absorption edge of evaporated amorphous WO3 films

The fundamental absorption edge of evaporated WO₃ films is investigated. The optical gap of the virgin film is estimated to be 3.41 eV at room temperature and it decreases with increase of annealing temperature up to 200°C. Annealing at 300°C leads to change in the spectral shape, which is caused by crystallization. For the films annealed at 200°C, temperature coefficient of the optical gap is estimated to be ?2×10^?4 eV/K and the slope of Urbach's tail is found to be independent of measuring temperature up to 200°C. With electrolytic coloration, shift of the optical gap toward higher energy is observed. Magnitude of this shift is estimated to be 0.05 eV at the color center concentration of 7.5×10²¹ cm^?3 when H⁺ electrolyte is used. If Li⁺ electrolyte is used, the magnitude of this shift is about three times larger than in the case of H⁺ electrolyte. This fact is interpreted by a small change in the host matrix structure owing to the injection of proton or Li⁺ during coloration.