Phosphorus Gettering Research Articles

A Study of the Phosphorus Gettering of Gold in Silicon by Use of Neutron Activation Analysis

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The semiconductor field-emission photocathode

The recently developed large-area field-emission photocathode is described. It consists of a finely spaced array of point emitters fabricated by etching of p-type silicon or other semiconductor. Uniform emission over areas of 6-7 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> have been obtained. For Si, the spectral response extends from 0.4 to 1.1 µm. Quantum yields of 25 percent at 0.86 µm have been measured, which is about five times the value reported for the extended S-20 photocathode and comparable to the best III-V photoemitters. Calculations indicate that quantum yields of up to 40 percent at 0.86 µm and 28 percent at 0.9 µm are attainable with the present photocathode structures. For low dark current densities, photocathode cooling to temperatures approaching 77 K must be employed at present. The dark current is shown to be dominated by surface-generated electrons in the space-chargeregion of the emitters. Effects of phosphorus gettering and annealing treatments on dark current are discussed, and the spatial frequency response of the device is determined. The results of a computer study show that the field intensification factor of p-semiconductor field emitters behaves quite differently from that of metallic emitters.

Quenched-in centers in silicon p+n junctions

Silicon p + n junctions heat treated at high temperatures (1200°C) for a long time (2–20 hr) and then quenched to room temperatures or below shows two deep donor levels ( E C−264meV andE C−542meV) in the n-type side of the junction depletion layer which appear to originate from the same imperfection center. The concentration of these levels ranges from 10 13 to 10 14 cm −3. The junction leakage current comes from carrier generation at the deeper level in the depletion region. Phosphorus gettering was found ineffective in reducing the concentration of these quenched-in levels, but they are annealed out by very slow cooling (25°C/hr to 650°C then quench to room temperatures). The thermal emission and capture rates of electrons and holes at these levels are measured as a function of temperature and electric field by the junction high frequency capacitance and d.c. leakage current transient techniques. It is demonstrated that the detailed balance relationship does not hold. The origin of this double donor center is yet to be identified.

Ion-implantation-damage gettering effect in silicon photodiode array camera target

The use of ion implantation damage to getter deleterious impurities from diode space-charge regions is studied. Ion implantation into the neutral regions near p-n junctions is shown to cause substantial reduction in the incidence of the type of white video defects (excessive-leakage current diodes) caused by impurity precipitation and often found in a cyclonic pattern. It is found that using doses of 1016 cm−2 phosphorus (50 keV), ≥1015 cm−2 arsenic (150 keV), and ≥3×1015 cm−2 argon (50 keV) can completely eliminate these defects. In addition, the dark currents of the targets which receive ion implantation is equivalent to or lower than control slices receiving regular phosphorus gettering. From curves of the dark current vs target voltage, it is estimated that the surface recombination velocity (S0) of the ion-implanted slices is ∼20% lower than S0 in the control slices, while the Si–SiO2 interface fixed-charge density is not affected by ion implantation. By comparing the gettering efficiency of P+-, As+-, and Ar+-implanted slices, it is concluded that the damage layer rather than the presence of an implanted n+ region is responsible for the observed gettering behavior.

Roentgenographic Examination of Dental Gold Alloys

We present a model for predicting the solar cell efficiency potential of multicrystalline silicon bricks prior to sawing. Three model inputs are required: bulk lifetime images from the side faces of the bricks, the cell manufacturing process, and its gettering action. The model is set up with numerical device and circuit simulations, but may afterwards be parameterized for inline application. In the example shown here, we chose literature data to quantify the increase in bulk lifetime caused by phosphorus gettering of impurities during cell manufacturing. Our proposed model enables manufacturers to (i) assess initial brick quality in relation to their specific cell production line, (ii) to exclude certain parts of the bricks from cell manufacturing, and (iii) to adjust cell manufacturing to initial material quality. The specific gettering efficiency and cell process can be fed into the model dynamically and need to be calibrated ideally for each material manufacturer and each cell production line. The model presented here can be extended to cast mono and dendritically grown bricks.