Qiuyan Hao

The effects of neutron irradiation on the oxygen precipitation in Czochralski-silicon

Abstract The thermal annealing behavior of oxygen in neutron irradiation Czochralski-silicon (CZ-Si) has been investigated systemically. It was found that a heavy dose of neutron irradiation accelerated the oxygen precipitation in CZ-Si under higher annealing temperature (1070–1130°C). We attribute this effect to the form of defect cluster induced by neutron irradiation, it may be as the core for the oxygen precipitation heterogeneous nuclei and those shorten the nucleation time and accelerate oxygen precipitates in the bulk of Si wafer. In addition, the oxygen diffusion is enhanced by the presence of a large quantity of vacancies near the surface of the wafer.

The Marangoni convection and the oxygen concentration in Czochralski-grown silicon

Abstract The Marangoni convection on the silicon melt surface in Czochralski method was investigated. The results showed that Marangoni convection is related strongly to oxygen in silicon. Introducing a magnetic field by NdFeB permanent magnet into the melt, when B → → B → 0 ( B → 0 is the critical value), all the macro-convections were restrained in the melt and the Marangoni convection on the free surface emerges and becomes dominant. The oxygen concentration in silicon can be controlled freely by the Marangoni convection.

Polyol process synthesis of metal selenide nanomaterials and their photovoltaic application

A mixed solvent of monoethanolamine and thioglycolic acid is successfully used to dissolve Se powder to prepare a highly reactive and soluble Se solution at room temperature in air. The as-prepared Se solution is very stable for more than half a year without any observed precipitation even in air. We used the Se precursor solution to synthesize various metal selenide nanomaterials such as Sb2Se3 nanorods, CuSe nanoplates and CuInSe2 nanocrystals by using a facile and environmentally-friendly triethylene glycol process. The structure, morphology, chemical composition and optical properties of the synthesized metal selenide nanomaterials are characterized. Moreover, the CuInSe2 nanocrystals are used to prepare ethanol-based colloidal ink and then deposited thin films by a dip-coating process. The synthesized CuInSe2 nanocrystal thin films are annealed at 550 °C in a selenizing atmosphere. A power conversion efficiency of 2.65% has been achieved by using the CuInSe2 thin films after selenization as a light-absorbing layer under AM 1.5 illumination.

High-Switching-Ratio Photodetectors Based on Perovskite CH3NH3PbI3 Nanowires

Hybrid organic-inorganic perovskite materials have attracted extensive attention due to their impressive performance in photovoltaic devices. One-dimensional perovskite CH3NH3PbI3 nanomaterials, possessing unique structural features such as large surface-to-volume ratio, anisotropic geometry and quantum confinement, may have excellent optoelectronic properties, which could be utilized to fabricate high-performance photodetectors. However, in comparison to CH3NH3PbI3 thin films, reports on the fabrication of CH3NH3PbI3 nanowires for optoelectrical application are rather limited. Herein, a two-step spin-coating process has been utilized to fabricate pure-phase and single-crystalline CH3NH3PbI3 nanowires on a substrate without mesoporous TiO2 or Al2O3. The size and density of CH3NH3PbI3 nanowires can be easily controlled by changing the PbI2 precursor concentration. The as-prepared CH3NH3PbI3 nanowires are utilized to fabricate photodetectors, which exhibit a fairly high switching ratio of ~600, a responsivity of 55 mA/W, and a normalized detectivity of 0.5 × 1011 jones under 532 nm light illumination (40 mW/cm2) at a very low bias voltage of 0.1 V. The as-prepared perovskite CH3NH3PbI3 nanowires with excellent optoelectronic properties are regarded to be a potential candidate for high-performance photodetector application.

Polylol-solution synthesis of CuInSe2 nanoparticles ink for scalable solution-based thin film photovoltaic cells

ABSTRACT A fast and facile ambient pressure solution chemical process was applied to grow chalcopyrite CuInSe2 nanoparticles by using common and inexpensive polylol ethylene glycol(EG), diethylene glycol(DEG) and triethylene glycol(TEG) as solvent, copper(II) chloride, indium(III) chloride and selenium powder as precursors, hydrazine hydrate and ethylenediamine as reducing agent and polyvinylpyrrolidone as capping agent. The products synthesized were characterized by XRD, TEM, HRTEM, EDS and UV-vis measurements based on different solvents EG, DEG and TEG, refluxing temperature and time as well as PVP adding amounts. The well-dispersed and single-phase CuInSe2 nanoparticles synthesized with TEG solvent were used to prepare nanoparticles colloidal ink by ultrasonically dispersing in absolute alcohol solvent and then deposit CuInSe2 thin films by layer-by-layer dip-coating nanoparticles ink. The deposited thin films were annealed in Ar atmosphere at 550°C for 30 min. Photovoltaic test devices with Mo-coated glass/CuInSe2/CdS/i-ZnO/AZO configuration were fabricated using the ink-coated and annealed CuInSe2 light-absorbing thin films, and the corresponding I-V characteristics were evaluated.

Microstructure of flow pattern defects in boron-doped Czochralski-grown silicon

The morphology and microstructure of flow pattern defects (FPDs) in lightly boron-doped Czochralski-grown silicon (Cz-Si) crystals were investigated using optical microscopy and atomic force microscopy. The experimental results showed that the morphology of FPDs was parabola-like with several steps. Single-type and dual-type voids were found on the tip of FPDs and two heaves exist on the left and right sides of the void. All the results have proved that FPDs were void-type defects. These results are very useful to investigate FPDs in Cz-Si wafers further and explain the annihilation of FPDs during high-temperature annealing.

Investigation of oxygen precipitation and intrinsic gettering in heavily Sb-doped silicon

The behavior of oxygen precipitation in heavily doped silicon was investigated. The experimental results showed that the behavior of oxygen precipitation in heavily doped silicon is not only related to initial oxygen concentration, but also is affected by dopant species. The growth of oxygen precipitation was not affected by dopant type. Dopant species only influenced the nucleation of oxygen precipitation, and the time of precipitate nucleus formation is shorter in P+ samples than in N+ samples. The morphology of oxygen precipitation is independent of dopant type and only depends on the heat-treatment cycles. Considering the hanging bond on the interface of Si-SiOx at precipitates embryo and amending the free energy item, an expression of nucleation critical radius associated with dopant species was derived, and the dependent relationship of oxygen precipitation behavior in heavily doped silicon and dopant species was explained by this model. Moreover, an effective intrinsic gettering cycle with suitable width of denuded zone in heavily Sb-doped silicon samples was obtained in order to reduce or eliminate the metallic impurities and unwanted defects in the surface of substrate and device active regions.

Growth of Si-GaAs crystal under the equivalent micro-gravity

When growth of GaAs by method of MLEC and the magnetic intensity is the critical value B/sub 0/, all macro-convections in melt were completely controlled and the transport of mass only depends on diffusion. In this case, Growth of GaAs is under the equivalent micro-gravity. The effective segregation coefficients of impurities trend to one. The homogeneity and micro zone homogeneity of crystals were greatly improved.

Study on the deep energy levels in neutron-irradiated Czochralski-grown silicon

Czochralski-grown crystal silicon (CZSi) was doped by neutron transmutation. The deep energy levels after heat treatment of neutron transmutation doped Czochralski-grown silicon (NTDCZSi) were investigated by photo-induced transient spectroscopy (PITS) and deep level transient spectroscopy (DLTS). The interstitial oxygen concentration and substitutional carbon concentration were measured by Fourier transfer infrared spectrometry (FTIR). The experimental results showed that there are seven deep levels in the band gap of silicon caused by neutron irradiation. The defect centers corresponding to these deep levels were also deduced. The formation and decomposition of these defects during annealing were discussed.