Influence of the absorption locus of γ-quantor on the energy resolution of diffused semiconductor detectors with internal multiplication

The noise contribution is determined which is generated by the incomplete collection, as a result of structure, and locally different multiplication of the primary charge carriers as a consequence of the difference in the ionization coefficients of electrons and holes. This contribution is a function only of the structure and the geometry of the multiplying detector. First of all, the most important criteria are discussed which, in general terms, affect the usefulness of a diode structure as a multiplying detector, namely the counting volume, breakdown behavior, homogeneity of multiplication, etc. On the basis of these considerations, four specific structures are calculated: Ga-diffused p+n diodes (structure I); p-diffused n+p structures (structure II); planar n+πp+ punch-through diodes (structure III); n+pπp+ Read structure (structure IV). With the drift zone optimally etched, the ratio between the width of the non-multiplying p-space charge zone and the remaining space charge zone is the decisive parameter governing the signal-to-noise ratio (SNR) from the two variation contributions considered. The best SNR values are furnished by structure IV while structure I, because of the insufficient p-width, is completely unsuited to radiation detection proportional to energy. However, it must also be doubted whether detectors of structure IV will become significant for practical purposes of gamma spectroscopy at room temperature in the light of the data presently technically attainable, with respect to the other noise contributions. But all the diodes considered can be used for intensity-proportional light detection. (orig./RF)