Strong visible photoluminescence from amorphous silicon grains in a-SiOx:H films

Two strong luminescence bands were observed from a-SiOx:H in the spectral range of 550-900 nm at room temperature. One is a main broad peak which blueshifts with oxygen content and the other is a shoulder fixed at about 835 nm. In conjunction with TR and micro-Raman spectra, we have proposed that the main band may originate from the amorphous silicon grains embedded in SiOx network, while the shoulder might be due to some defects induced by excess-silicon in these films. (C) 1997 Elsevier Science Ltd.

Microcrystalline silicon films and tandem solar cells prepared by triode PECVD

This paper investigates the effects of the diphasic structure on the optoelectronic properties of hydrogenated microcrystalline silicon (mu c-Si:H) films prepared in a triode three-chamber plasma-enhanced chemical vapor deposition (PECVD) system. The influences of boron-compensation doping on the dark-and photo-conductivity of mu c-Si:H films are also described. A tandem solar cell with an entirely mu c-Si:H p-i-n bottom cell and an a-Si:H top cell has been prepared with an initial conversion efficiency of 8.91% (0.126 cm(2), AM1.5, 100 mW/cm(2)).

Polycrystalline silicon thin films and solar cells prepared by rapid thermal CVD

Polycrystalline silicon (poly-Si) films(similar to 10 mu m) were grown from dichlorosilane by a rapid thermal chemical vapor deposition (RTCVD) technique, with a growth rate up to 100 Angstrom/s at the substrate temperature (T-s) of 1030 degrees C. The average grain size and carrier mobility of the films were found to be dependent on the substrate temperature and material. By using the poly-Si films, the first model pn(+) junction solar cell without anti-reflecting (AR) coating has been prepared on an unpolished heavily phosphorus-doped Si wafer, with an energy conversion efficiency of 4.54% (AM 1.5, 100 mW/cm(2), 1 cm(2)).

Low-temperature (10 K) infrared measurement of interstitial oxygen in heavily antimony-doped silicon via wafer thinning

A new technique is reported for the rapid determination of interstitial oxygen in heavily Sb-doped silicon. This technique includes wafer thinning and low-temperature 10 K infrared measurement on highly thinned wafers. The fine structure of the interstitial oxygen absorption band around 1136 cm(-1) is obtained. Our results show that this method efficiently reduces free-carrier absorption interference, allowing a high reliability of measurement, and can be used at resistivities down to 1 x 10(-2) Omega cm for heavily Sb-doped silicon.

Temperature-stimulated abnormal annealing of neutron-induced damage in high-resistivity silicon detectors

Neutron-irradiated high-resistivity silicon detectors have been subjected to elevated temperature annealing (ETA). It has been found that both detector full depletion voltage and leakage current exhibit abnormal annealing (or ''reverse annealing'') behaviour for highly irradiated detectors: increase with ETA. Laser induced current measurements indicate a net increase of acceptor type space charges associated with the full depletion voltage increase after ETA. Current deep level transient spectroscopy (I-DLTS) and thermally stimulated current (TSC) data show that the dominant effect is the increase of a level at 0.39 eV below the conduction band (E(c) - 0.39 eV) or a level above the valence band (E(v) + 0.39 eV). Candidates tentatively identified for this level are the singly charged double vacancy (V-V-) level at E(c) - 0.39 eV, the carbon interstitial-oxygen interstitial (C-i-O-i) level at E(v) + 0.36 eV, and/or the tri-vacancy-oxygen center (V3O) at E(v) + 0.40 eV.

A transmission electron microscopy study of microstructural defects in proton implanted silicon

The microstructure of silicon on defect layer, a new type of silicon-on-insulator material using proton implantation and two-step annealing to obtain a high resistivity buried layer beneath the silicon surface, has been investigated by transmission electron microscopy. Implantation induced a heavily damaged region containing two types of extended defects involving hydrogen: {001} platelets and {111} platelets. During the first step annealing, gas bubbles and {111} precipitates formed. After the second step annealing, {111} precipitates disappeared, while the bubble microstructure still remained and a buried layer consisting of bubbles and dislocations between the bubbles was left. This study shows that the dislocations pinning the bubbles plays an important role in stabilizing the bubbles and in the formation of the defect insulating layer. (C) 1996 American Institute of Physics.

Improvement of the stability of hydrogenated amorphous silicon films by intermittent illumination treatment at elevated temperature

The intermittent illumination treatment by white light at elevated temperature is proved to be a convenient and efficient method for the improvement of the stability of hydrogenated amorphous silicon (a-Si:H) films. The effect of the treatment on electrical properties, light-induced degradation, and gap states of undoped a-Si:H films has been investigated in detail. With the increase of cycling number, the dark- as well as photo-conductivities in annealed state and light-soaked state approach each other, presenting an unique irreversible effect. The stabilization and ordering processes by the present treatment can not be achieved merely by annealing under the same conditions. It is shown that the treatment proposed here results in a shift to higher values of the energy barriers between defects and their precursors, and hence an improved stability of a-Si:H films. (C) 1996 American Institute of Physics.

Investigation on the N-eff reverse annealing effect using TSC/I-DLTS: Relationship between neutron induced microscopic defects and silicon detector electrical degradations

Neutron induced defect levels in high resistivity silicon detectors have been studied using a current-based macroscopic defect analysis system: thermally stimulated current (TSC) and current deep level transient spectroscopy (I-DLTS). These studies have been correlated to the traditional C-V, I-V, and transient current and charge techniques (TCT/TChT) after neutron radiation and subsequent thermal anneals. It has been found that the increases of the space charge density, N-eff, in irradiated detectors after thermal anneals (N-eff reverse anneal) correspond to the increases of deep levels in the silicon bandgap. In particular, increases of the double vacancy center (V-V and V-V-- -) and/or C-i-O-i level have good correlations with the N-eff reverse anneal. It has also been observed that the leakage current of highly irradiated (Phi(n) > 10(13) n/cm(2)) detectors increases after thermal anneals, which is different from the leakage current annealing behavior of slightly irradiated (Phi(n) < 10(13) n/cm(2)) detectors. It is apparent that V-V center and/or C-i-O-i level play important roles in both N-eff and leakage current degradations for highly irradiated high resistivity silicon detectors.

Microscopic analysis of defects in a high resistivity silicon detector irradiated to 1.7x10(15)n/cm(2)

Current-based microscopic defect analysis methods with optical filling techniques, namely current deep level transient spectroscopy (I-DLTS) and thermally stimulated current (TSC), have been used to study defect levels in a high resistivity silicon detector (p(+)-n-n(+)) induced by very high fluence neutron (VHFN) irradiation (1.7x10(15) n/cm(2)). As many as fourteen deep levels have been detected by I-DLTS. Arrhenius plots of the I-DLTS data have shown defects with energy levels ranging from 0.03 eV to 0.5 eV in the energy band gap. Defect concentrations of relatively shallow levels (E(t) < 0.33 eV) are in the order of 10(13)cm(-3), while those for relatively deep levels (E(t) > 0.33 eV) are in the order of 10(14) cm(-3). TSC data have shown similar defect spectra. A full depletion voltage of about 27,000 volts has been estimated by C-V measurements for the as-irradiated detector, which corresponds to an effective space charge density (N-eff) in the order of 2x10(14) cm(-3). Both detector leakage current and full depletion voltage have been observed to increase with elevated temperature annealing (ETA). The increase of the full depletion voltage corresponds to the increase of some deep levels, especially the 0.39 eV level. Results of positron annihilation spectroscopy have shown a decrease of total concentration of vacancy related defects including vacancy clusters with ETA, suggesting the breaking up of vacancy clusters as possible source of vacancies for the formation of single defects during the reverse anneal.

Dislocation movement in nitrogen-doped Czochralski silicon

Dislocation movement in N-doped Czochralski silicon (Cz-Si) was surveyed by four point bend method. Dislocation movement velocities in Cz-Si doped with nitrogen, with both nitrogen and antimony, and with only antimony were investigated. The order of measured dislocation movement velocities, at 700 degrees C less than or equal to T less than or equal to 800 degrees C and under resolved stress sigma=4.1 kg/mm(2), was V-Sb.O > V-n.Sb.O>V-N.O. The experiments showed that nigtrogen doping could retard the movement of dislocations.

DEVELOPMENT OF CURRENT-BASED MICROSCOPIC DEFECT ANALYSIS-METHODS AND ASSOCIATED OPTICAL FILLING TECHNIQUES FOR THE INVESTIGATION ON HIGHLY IRRADIATED HIGH-RESISTIVITY SILICON DETECTORS

Current based microscopic defect analysis methods such as current deep level transient spectroscopy (I-DLTS) and thermally stimulated current (TSC) have been further developed in accordance with the need for the defect analysis of highly irradiated (Phi(n) > 10(13) n/cm(2)) high resistivity silicon detectors. The new I-DLTS/TSC system has a temperature range of 8 K less than or equal to T less than or equal to 450 K and a high sensitivity that can detect a defect concentration of less than 10(10)/cm(3) (background noise as low as 10 fA). A new filling method using different wavelength laser illumination has been applied, which is more efficient and suitable than the traditional voltage pulse filling. It has been found that the filling of a defect level depends on such factors as the total concentration of free carriers generated or injected, the penetration length of the laser (laser wavelength), the temperature at which the filling is taking place, as well as the decay time after the filling (but before the measurement). The mechanism of the defect filling can be explained by the competition between trapping and detrapping of defect levels, possible capture cross section temperature dependence, and interaction among various defect levels in terms of charge transferring. Optimum defect filling conditions have been suggested for highly irradiated high resistivity silicon detectors.

STUDY OF THE LONG-TERM STABILITY OF THE EFFECTIVE CONCENTRATION OF IONIZED SPACE CHARGES (N-EFF) OF NEUTRON-IRRADIATED SILICON DETECTORS FABRICATED BY VARIOUS THERMAL-OXIDATION PROCESSES

Experimental study of the reverse annealing of the effective concentration of ionized space charges (N-eff, also called effective doping or impurity concentration) of neutron irradiated high resistivity silicon detectors fabricated on wafers with various thermal oxides has been conducted at room temperature (RT) and elevated temperature (ET). Various thermal oxidations with temperatures ranging from 975 degrees C to 1200 degrees C with and without trichlorethane (TCA), which result in different concentrations of oxygen and carbon impurities, have been used. It has been found that, the RT annealing of the N-eff is hindered initially (t < 42 days after the radiation) for detectors made on the oxides with high carbon concentrations, and there was no carbon effect on the long term (t > 42 days after the radiation) N-eff reverse annealing. No apparent effect of oxygen on the stability of N-eff has been observed at RT. At elevated temperature (80 degrees C), no significant difference in annealing behavior has been found for detectors fabricated on silicon wafers with various thermal oxides. It is apparent that for the initial stages (first and/or second) of N-eff reverse annealing, there may tie no dependence on the oxygen and carbon concentrations in the ranges studied.

ELECTRON-STATES OF A VACANCY IN THE CORE OF THE 90-DEGREES PARTIAL DISLOCATION IN SILICON

An LCAO scheme (linear combination of atomic orbitals) taking into account ten atomic orbitals (s-, p-, and d-type) is used to calculate the electronic structure of a vacancy present in the core of the reconstructed 90 degrees partial dislocation in silicon. The levels in the band gap are extracted using Lanczos' algorithm and a continued fraction representation of the local density of states. The three-fold degenerate stale of the ideal vacancy is split into three levels with energies 0.26, 1.1, and 1.9 eV measured from the valence band edge.