Distribution Of Impurity Atoms Research Articles

Calculations of Impurity Atom Diffusion Through a Narrow Diffusion Mask Opening

Relaxation methods have been used to solve a mixed boundary value problem arising in the fabrication of junction transistors: impurity atom diffusion through a narrow diffusion mask opening. This particular problem is encountered in the fabrication of very narrow diffused p-n junctions. It is shown that the depth of a very narrow junction cannot always be determined from an elementary one-dimensional analysis of this diffusion process. If the width of a diffusion mask opening is less than two impurity atom diffusion lengths, the junction depth becomes geometry dependent. Normalized graphs are presented to illustrate the impurity atom distribution resulting from this particular geometric configuration.

Comparison of simple models of cylindrical and plane field-effect transistors

The electrical properties of plane field-effect transistors with different assumed impurity-atom distributions in their channel regions, corresponding to either an alloyed- or a diffused-gate p-n junction, are compared with those of the cylindrical type, with a uniform distribution of impurities in the channel. It is shown that the electrical properties of different types of field-effect transistors with the same pinchoff voltage and transconductance are quite similar.

Analysis of the Impurity Atom Distribution Near the Diffusion Mask for a Planar p-n Junction

Presented here are the results from a mathematical investigation of the impurity atom distribution within a planar p-n junction. Two fundamentally different diffusion processes are considered: In the first, a constant impurity atom concentration is maintained at the semiconductor surface; in the second, a fixed quantity of impurity atoms is involved in the entire diffusion process. The results of this investigation show than a one-dimensional approximation inadequately characterizes the impurity atom distribution within a planar junction, and that in theory, the planar junction is not at a constant distance from its impurity atom source. Instead, the junction is closer to its source at the semiconductor surface than deep within the bulk material. Further, it is shown that when diffusion takes place from a source of constant concentration density, the junction impurity atom gradient is maximum at the semiconductor surface. In contrast, this junction impurity atom gradient is shown to exhibit a minimum at the semiconductor surface when the total number of impurity atoms is time invariant throughout the entire semiconductor material.

Neutron irradiation damage in molybdenum

Abstract The technique of transmission electron microscopy has been used to study neutron irradiation damage and its behaviour on annealing in molybdenum. Micro-hardness tests were carried out on all specimens before thinning to obtain some indication of the relation between structural effects and the mechanical properties. The results show that part of the damage in molybdenum neutron irradiated to a dose of 2 × 1022 n cm−2 (fission) is in the form of point defect clusters which are deduced to be interstitial. The interstitial point defects must therefore be sufficiently mobile during irradiation at 60°c to form into these clusters. However, the experimentally estimated point defect density only accounts for a small proportion of the theoretical number suggesting that most of the interstitials are present singly or as sub-microscopic clusters. On annealing there is little change in the observable damage up to 800°c but the micro-hardness shows a peak at 170°c followed by steady recovery. Above 800°c the loops grow rapidly and finally join up to form dislocation networks. This stage is accompanied by an increase in the rate of recovery of the micro-hardness. The loops are shown to be interstitial in nature with Burgers vector a/2〈111〉, though during the early stages of network formation some 〈100〉 type dislocations form through the reaction:a/2[111]+a/2[11 1]→a[100]. These results are discussed in conjunction with other more indirect recovery data and a model is proposed for the annealing of irradiation damage in molybdenum above room temperature. The general conclusion is that the initial damage structure and its subsequent behaviour on annealing are largely governed by the distribution and mobility of interstitial impurity atoms during irradiation.

Impurity atom distribution from a two-step diffusion process

Impurity atom distribution from a two-step diffusion process

Depletion Layer Properties in Double Diffused Transistors†

ABSTRACT For the double diffused transistor, Poisson's equation is solved in one dimension; this solution is used to determine depletion layer properties of its collector and emitter junctions. Assuming an impurity atom distribution characterized by the summation of complementary error functions, depletion layer widths are established far the equilibrium emitter junction and for the reverse biased collector junction. Applications of this analysis are presented throughout a wide range of physical and geometrical parameters; graphical illustrations are given for the electrical base width, the collector ‘ punch-through ’ voltage, and others.

On the distribution of impurity atoms in the stress field of a dislocation

It is shown that impurity atoms distributed in the stress field of a dislocation obey Fermi-Dirac statistics. This result is applied to two experimental situations. In the first case, it enables us to determine the binding energy of an impurity to a dislocation, and in the second we see why another attempt to do this went astray.