A high speed power semiconductor diode has a lightly doped first conductivity type middle layer between a heavily doped first conductivity type first outer zone and a second conductivity type second outer zone including a p-n junction, the middle zone thickness and doping concentration Nd being chosen to achieve a defined blocking voltage at a voltage Ur and the entire middle zone containing recombination centres produced at least partially by accelerated particle irradiation. The novelty is that the middle zone contains, in addition to the doping concentration Nd, donors of density Nz+ which are produced by irradiation at below 300 K and which are intermittently provided at less than 300 K after forward current application, the density maximum being sufficiently high to produce avalanche breakdown at -40 deg C by triangular field progress and at 75% of the room temperature specified blocking voltage UR and the density minimum being 20% of the maximum value. Also claimed is a method of measuring the carbon content in silicon by exposing a silicon diode structure to thorough irradiation with fast particles of chosen energy and dose so that the number of radiation-induced donors approaches a saturation value, followed by calculating the carbon concentration from this donor density measurement by deep level transient capacitive spectrometry (DLTS) or by means of the voltage of onset of dynamic IMPATT oscillation.
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