Reversible temperature induced inversion in the thermionic emission current anisotropy pattern emitted by atomically clean silicon cathodes

Abstract A reviersible temperature induced inversion in the thermionic emission anisotropy pattern emitted by cylindrical silicon cathodes with axial direction [111] is described. At 1320°K both the {110} and the {112} facets yield emission minima. The {110} emission remains the pattern minimum throughout the temperature range investigated. But an inversion occurs for {112} so that at 1495°K, when this inversion is fully developed, the emission from these planes of silicon yield pronounced maxima in the anisotropy pattern of the thermionic emission current. The effect, is completely reversible. When the temperature is lowered to 1320°K, the anisotropy again reverts to that at the starting point. The cycle can be repeated many times with identical results. The individual patterns are reproducible within limits of error set by the accuracy with which the temperature can be reset during the series of measurements. This reversibility allows the conclusion that irreversible changes in surface structure, such as those arising from diffusion and evaporation processes, can be ruled out as an explanation of the phenomenon. In addition, the ‘practical’ emission parameters for the ‘real’ surfaces involved are compiled for both n -type and p -type silicon. ‘Practical’ and ‘real’ are used within this context to stress that the measurements do not necessarily pertain to ideal crystallographic planes, but, as is usual with all such thermionic data, are characteristic of those surface structures that result when single crystal cathodes are heated to incandescence. The measurements relating to n -type silicon represent first therminonic emission results. All previous data pertaining to thermionic emission from silicon that appeared in literature refers to electron emission from silicon cathodes of extreme boron doping.