A new recombination model describing heavy-doping effects and low-temperature behaviour

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Measurements on the reverse and nonideal forward currents in heavily doped diodes and in advanced bipolar transistors in the temperature range from 77 K to 300 K are presented. A detailed comparison is made between these measurements and various models. It is shown that models from the literature fail to describe all observed phenomena. A model is proposed which is shown to provide a good description of the measured heavy-doping effects on recombination. The model describes the experimentally observed voltage and temperature dependence of both the nonideal forward and the reverse currents without the introduction of fitting parameters. It is shown that, for zero-bias depletion widths between 300 AA and about 700 AA, trap-assisted tunneling is important for reverse-biased junctions at room temperature. For zero-bias depletion widths less than 300 AA, the tunneling effects increase dramatically. Whereas trap-assisted tunneling has to be taken into account for the forward characteristic, the reverse characteristic is dominated by band-to-band tunneling. >