CHARACTERIZATION OF BIDIRECTIONAL TRANSMISSIVE AND REFLECTIVE PROPERTIES OF BLACK SILICON

This paper describes the initial work of characterizing the transmissive and reflective properties of black silicon diffusers. The diffusers were fabricated from a 100 mm diameter black silicon sample at NASA’s Goddard Space Flight Center (GSFC). The directional hemispherical reflectance from 250 nm to 2500 nm and BRDF/BTDF measurements at 632.8 nm, 1064 nm, and 1550 nm were measured using the GSFC Diffuser Calibration Laboratory’s (DCL) spectrophotometer and optical scatterometer. The diffusers exhibit a low level of specular reflection up to ~1100 nm with no evidence of retroscatter. The measurements are traceable to those made at the National Institute of Standards and Technology (NIST).

Влияние никеля на время жизни носителей заряда в кремниевых солнечных элементах

It has been shown experimentally that nickel clusters on the surface of a silicon sample contain a large amount of oxygen and recombination impurities - Cu, Fe, Cr, which shows good gettering properties of clusters. The optimum temperature of nickel diffusion into silicon is determined - Т=800-850 ° С. Doping with impurity nickel atoms with the formation of clusters makes it possible to increase the lifetime of nonequilibrium charge carriers in the base of a solar cell by up to 2 times, while the formation of a nickel-enriched region in the face layer is more efficient. It is shown that the effect of additional doping with nickel weakly depends on the sequence of the processes of nickel diffusion and the creation of a working p–n-junction.

Абляция кремния в воздухе моно- и бихроматическими импульсами лазерного излучения с длинами волн 355 и 532 nm

Ablation of silicon sample in air under irradiance of single and double laser pulses with wavelengths 355 and 532 nm was studied by means of optical and scanning electron microscopy, raman spectroscopy, profilometry of laser craters as well as video registration of plasma’s plume radiation in time. Dependence of specific sample’s material removal on laser fluence and time interval between coupled pulses of bichromatic laser irradiance was established. Spallation of silicon was found in broad range of irradiance parameters and parameters of craters formed by ablation and spallation under the action of bichromatic laser radiation were determined.

Edge Control in the Computer-Controlled Optical Surface

The computer-controlled optical surface (CCOS) can process good optical surfaces, but its edge effect greatly affects its development and application range. In this paper, based on the two fundamental causes of the CCOS’s edge effect—namely the nonlinear variation of edge pressure and the unreachable edge removal—a combined polishing method of double-rotor polishing and spin-polishing is proposed. The model of the combined polishing method is established and theoretically analyzed. Combined with the advantages of double-rotor polishing and spin-polishing, the combined polishing process can achieve full-aperture machining without pressure change. Finally, the single-crystal silicon sample with a diameter of 100 mm is polished by the combined polishing process. The results show that, compared with the traditional CCOS polishing, the residual error of the sample after the combined polishing process is more convergent, and the edge effect is effectively controlled.

Size Effect in Silicon Irradiated with Self Ions

The influence of the thickness of a silicon sample irradiated by silicon ions on the spatial distribution of primary structural defects, phonons, and induced charges is considered. The calculations were performed using the SRIM2013program. The results can be used to analyze the interaction of other types of radiation with silicon wafers, in particular with neutrons.

Development and Comparison of the Techniques for Solving the Inverse Problem in Photoacoustics

In this work, theoretically/mathematically simulated (TMS) model is presented for the photoacoustic (PA) frequency response of a semiconductor in a minimum volume PA cell. By analyzing of the TMS model, the influences of thermal diffusivity and linear coefficient of thermal expansion on silicon sample PA frequency response were investigated and two methods were developed for their estimation. The first one is a self consistent inverse procedure (SCIP) for solving the exponential problems of mathematical physics, based on regression. The second one, a well trained three-layer perceptron with back propagation, based upon theory of artificial neural networks (ANN), is developed and presented. These two inverse problem solving concepts are applied to thermo-elastic characterization of silicon, compared and discussed in the domain of semiconductor characterization.

Low Recombination Firing-Through Al Paste for N-Type Solar Cell with Boron Emitter

A kind of low recombination firing-through screen-printing aluminum (Al) paste is proposed in this work to be used for a boron-diffused N-type solar cell front side metallization. A front side fire-through contact (FTC) approach has been carried out for the formation of local contacts for a front surface passivated solar cell. With a low contact resistivity (ρc) of 1.0 mΩ·cm2, good ohmic contact between the boron-doped front surface of the silicon sample and the Al paste was realized. To obtain a good energy conversion efficiency, a balance can be achieved between the open circuit voltage (Voc) and contact resistivity (ρc) of the cell by combining suitable Al powders and appropriate additives. The detailed micro-contact difference in Si/metallization between the firing-through Al paste and silver-aluminum (Ag-Al) paste was analyzed. The dark saturation current density beneath the metal contact (J0, metal) of the Si/metallization region using our firing-through Al paste was discussed, which was proven to be 61% lower than using Ag-Al paste. The pseudo energy conversion efficiency of the cell using Al paste measured by Suns-VOC was also higher than using Ag-Al paste. The role of Al paste in low surface metal recombination is discussed. The utilization of this new kind of Al paste was much cheaper and more convenient, compared to the traditional process using Ag or Ag-Al paste.

Geometric determination of direction of dislocations using synchrotron X-ray transmission topography

When performing transmission polychromatic beam topography, the extensions to the line segments of the diffraction images of a straight dislocation are shown to intersect at a single point on the X-ray film. The location of this point, together with the diffraction pattern recorded on the film by synchrotron radiation, gives the crystallographic direction [hkl] of the dislocation unambiguously. The results of two synchrotron topography experiments are presented. Very long dislocations found in the center of a large 450 mm-diameter Czochralski silicon crystal align with the growth direction [001]. In the other silicon sample, the dislocations are of mixed type and along the [011] direction.

CONSIDERATION OF SURFACE RECOMBINATION WHEN MEASURING THE RECOMBINATION LIFETIME FROM THE PHOTOCONDUCTIVITY DECAY IN LARGE-THICKNESS SAMPLES

Surface recombination strongly influence on the photoconductivity decay curve. In this work it was shown that usually defined using this curve the effective life time don’t achieve maxima value if silicon sample thickness exceeds six diffusion length. In this case well known formulas for calculation of free carrier recombination lifetime need to be adjusted.