Application of open circuit voltage decay to the characterisation of heavy doping parameters in a p+ emitter of a junction diode

Abstract

Open circuit voltage decay measurements have been carried out on ion implanted diodes having heavily doped emitters and lightly doped bases which are used as nuclear radiation detectors. A theory has been developed to account for the initial rapid voltage decay associated with the emitter, following the interruption of the forward current. The theory neglects recombination in the lightly doped base region because of the large minority carrier lifetime, compared to the effective lifetime in the emitter region. The magnitude of the emitter leakage current obtained from the theory and the OCVD data is 8.6 pA cm −2. This is about a factor 2.5 smaller than the leakage current obtained using the recent values of hole mobility and band gap narrowing reported in the literature. The difference is attributed to trapping of carriers in the band tails. Annealing the diodes at higher temperatures increases the initial slope of the OCVD plot and increases considerably the dark current of the emitter. This result is in complete agreement with the annealing effects on dark current of the emitter reported by Grup, Slotboom and Smolders.