P-type Surface Layer Research Articles

Distribution of Boron-Induced Defects in Shallow Diffused Surface Layers of Silicon

Chemical sectioning of p-type surface layers on silicon is described. The technique is applied to measure the impurity concentration and the defect concentration vs depth in shallow boron-diffused surface layers using electrical measurements and x-ray diffraction microscopy.

P-Type Surface Layers in Ion-Bombarded Silicon

Silicon is bombarded at 400° to 900°C in a glow discharge of hydrogen with phosphine or diborane admixtures. Below 700°C, bombardment of n-type silicon with an initial resistivity of 200 Ω-cm creates deep (0.5–2.5μ) p-type surface layers regardless of gas composition. The concentration NA(x) of the acceptors in the p layers obeys a simple law: NA(x)=N0 exp(−x/L). N0 is the surface concentration at x=0 which increases from 3.5×1016 acceptors cm−3 to 4×1018 acceptors cm−3 for bombardment temperatures increasing from 500° to 650°C. The decay constant L is found to be 0.2 μ. Annealing experiments rule out the hypothesis that the p layers are caused by fast-diffusing acceptor impurities, e.g. aluminum or boron. It is proposed that the p layers are formed by vacancies which act as acceptor-like defects.

Oxygen chemisorption and surface p-type behavior of zinc oxide powders

It is shown that the weak chemisorption of oxygen which is observed in the temperature range 20–130 °C on powder samples of zinc oxide, either pure or with additions of Li + or Ga 3+, can exert a positive influence on the electrical conductivity of the oxide. The dependence of the conductivity on the oxygen pressure, as well as the sign of the Seebeck voltage, points to the presence of p-type inversion layers on the surface. Treatment of the samples in high vacuum at 450 °C removes the p-type surface layers and the normal n-type behavior can thereafter be observed.

Nachweis von bor auf silizium—oberflächen mit aktivierungsanalyse

We have shown that the highly conductive p-type surface layer which forms on silicon heated in borosilicate glass vacuum systems is due to boron. The boron was identified and its concentration within this layer was determined by radiochemical activation analysis. Agreement with the concentration deduced from electrical conductivity measurements is satisfactory.

The Use of an Interference Microscope for Measurement of Extremely Thin Surface Layers

A method is given for the thickness measurement of p-type or n-type surface layers on semiconductors. This method requires the use of samples with optically flat and reflecting surfaces. The surface is lapped at a small angle in order to expose the p-n junction. After detecting and marking the p-n junction, the thickness is measured by an interference microscope. Another application of the equipment is the measurement of steps in a surface. The thickness range measurable is from 5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−6</sup> cm to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> cm.

The Effective Surface Recombination of a Germaniun Surface with a Floating Barrier

The effect of heavily doped (alloyed) p-type and n-type surface layers on n-type base, and of metallic plating on n-type base, on the surface recombination velocity s has been computed on the basis of one-dimensional junction theory. The results indicate that s should be of the order 1 cm/sec for the heavily doped surfaces, and several thousand cm/sec for the electroplated surface. The low s comes about for the same reason that the injection efficiency of alloy junctions is high; the alloy junction is a very efficient emitter of minority carriers into the base and a poor acceptor of majority carriers from the base because of the high doping level in the alloyed region. Since recombination in the surface layer of minority carriers from the base requires both majority and minority carriers, the restriction of the flow of either reduces the surface recombination. However, measurements of s by diffusion and pulse methods on alloy junction surfaces indicate that their apparent recombination is almost the same as adjacent untreated surface, e.g., 300-500 cm/sec. It is shown that lateral current flow, due to minority carrier gradients parallel to the junction interface, and neglected in one-dimensional theory, gives rise to circulating currents which translate the minority carriers to the nearest high recombination surface. This hole translation property of the floating p-layer is used to explain the erroneously high lifetimes often observed by diffusion measurements on silicon and p-type germanium, and certain discrepancies in effective life measurement on completed transistors.

Measurement of the Surface Properties of Germanium

New techniques are described for the measurement of the surface properties of n-type germanium. These make use of the properties of a new type of rectifying contact. Some preliminary results are given, which are interpreted as demonstrating the existence of a p-type surface layer separated from the interior of the specimen by a rectifying barrier. The observed properties of the surface layer do not support existing theories of rectification at a point contact, and are found to depend sensitively on surface condition. Two new types of transistor are described whose mechanism depends on the presence of the surface layer.