Non-radiative transitions in semiconductors

Abstract

Non-radiative transitions affect many aspects of semiconductor performance. Normally they reduce device efficiency by suppressing luminescence, creating defects, reducing carrier lifetimes, or enhancing diffusion during operation. The present review surveys both the theoretical and practical understanding of non-radiative transitions. It includes general theoretical results and the associated ideas, with the emphasis on phonon-induced and defect Auger processes. Most of the purely formal aspects are omitted, but the points of principle where uncertainties remain are discussed. The review also covers the relation between basic theoretical studies and practical applied work on device degradation. This includes a description of the atomic processes involved in the more important mechanism of device deterioration and the theoretical understanding of the mechanism of these underlying processes. Finally, there is a survey of models proposed for 'killer' centres.

Odour character differences for enantiomers correlate with molecular flexibility

“…In solid-state physics, there is a well-known role for what are termed promoting modes, which affect the rate of some processes. The promoting mode (Stoneham 1981) is not the reaction coordinate, but makes a key step easier. In solid-state diffusion, a promoting mode might open a gap between atoms, so a diffusing atom can migrate more easily.…”

Understanding electron flow in conducting polymer films: injection, mobility, recombination and mesostructure

“…This is important for two reasons. First, they relate to the optical spectrum of a single chain in a way which is often described by Huang-Rhys theory (Stoneham 1975). However, we note that a conjugated polymer is not a system to which Huang-Rhys theory strictly applies (because there are many electronic states, and many modes with different frequencies, involved), so Huang-Rhys factors from observables (zero-phonon-line fraction, Stokes shift, linewidth) may not agree.…”

“…Within the bulk of the organic semiconductor, the important competition in electron-hole recombination is between the emission of light and the creation of heat. In principle, an important factor in both processes is the line-shape function G(E) (see, e.g., Stoneham 1975, 1981, Itoh and Stoneham 2001, which measures how the system (here the chain plus its environment) responds to the almost instantaneous forces on change of electronic state. In essence, G(E) relates to the ease with which energy E can be taken up by the vibrational system.…”

“…The rule assumes that either phonons of a single frequency (usually the largest available) dominate, or that the proportions of the various frequencies are the same for different values of n. It is not clear from the data of Wilson et al (2001aWilson et al ( , 2001b whether there is a promoting mode as well as the accepting mode, nor is it certain that the accepting modes are the same for radiative and non-radiative transitions. Certainly, there are vibrations of several different energies in the observed optical spectrum, and these correspond to smaller energies than one would estimate from direct application of the energy gap analysis (Wilson et al 2001a(Wilson et al , 2001b) and the observation that it is hard to understand the energy gap rule unless γ is in a range of order 1-2 (see, e.g., Stoneham 1981). Using the observed slopes, this range of γ implies, for the non-radiative transitions, polymer phonon energy from 0.17 to 0.34 eV and monomer phonon energies from 0.26 to 0.52 eV.…”

“…The tunnelling matrix element will be determined by the longer-range parts of the wavefunction, rather than the shorter-range terms which dominate in the energy. The longest-range component has an exponent which is proportional to the square root of the binding energy (see Stoneham (1975), p 131, or Newton (1960). …”