The electrical activity of IMPATT diodes on a nanometric scale by X-STEBIC method

Abstract

The Scanning Transmission Electron Beam Induced Current Technique (STEBIC) was adapted to allow the analysis of local electrical activity in semiconductor diodes. This technique enabled us to analyse the in situ properties of IMPATT junctions (IMPact Avalanche Transit Time: which are Si doped $p^+/p/n/n^+$ multijunctions). The samples were thinned down as cross-sections, to be observed and analysed in transmission electron microscopy. The current induced by the electron beam was collected by the depleted zone. By synchronising measurements with each scan of the electron beam, the electrical activity can be viewed at a very local scale. The STEBIC signal was simulated by using a model of drift- diffusion. The prevailing role of the recombination rate on the form of the STEBIC profile was evidenced. We found that the spatial resolution of this method depends on the thickness of the sample and on the zone where the measurement is taken. We show that the spatial resolution of this method is optimal when the electron beam is localised in the p/n depleted zone. In thin areas, the maximum spatial resolution is calculated to be $\le 20$ nm. Outside the electric field the transport phenomena are governed by the diffusion of carriers and the signal width is widened.