Dielectric response of p- n junctions

Abstract

An understanding of the dynamics of recombination and trapping of excess charge carriers in p- n junctions and Schottky diodes is important in the application of these devices, especially under transient conditions. One method of characterising these processes is the “dielectric” measurement of their complex capacitance C ̃ (ω) in a wide range of frequencies ω. Simple generation-recombination or trapping-detrapping processes would give Debye-like behaviour of C ̃ (ω) in frequency. The observed behaviour of p- n junctions and Schottky diodes ranges from nearly Debye-like through broadened loss C″( ω) peaks to almost frequency-independent loss, which cannot easily be interpreted in conventional terms. The behaviour may be described in terms of the so-called “universal” fractional power-law dependence on frequency, corresponding to a constant phase delay between the polarisation and the driving sinusoidal potential. The present paper proposes a novel interpretation of this universal behaviour in terms of the “energy criterion” approach which relies on the independence of frequency of the ratio energy lost per reversal of polarisation to the energy stored. This mechanism is contrasted with the classical Debye process in which the loss arises from a constant time delay between the applied potential and the release of trapped carriers. At frequencies in excess of the loss peak frequency ω p the universal process dominates over the classical process and it is posible to interpret the results in the light of the theory in terms of the density of deep trapping levels and their energetic position.