Interpretation of Carrier Recombination Lifetime and Diffusion Length Measurements in Silicon

Abstract

Reduced metal contamination levels become ever more critical as ultralarge scale integrated device feature sizes shrink to 0.25 p.m. Wafers may be contaminated with metals during their manufacture, but metals are more likely to be introduced at the wafer surface during integrated circuit processing. During high-temperature processing steps, the surface contaminants diffuse rapidly into the wafer bulk. Because carrier lifetime and diffusion length are strongly affected by the presence of parts per trillion levels of electrically active metal-related defect centers in the bulk of the wafer, these properties can be used to detect the presence of metal contamination. Unfortunately, these techniques are sometimes misused and misinterpreted. The more common techniques, their benefits, and limitations on their interpretation are discussed. A unified taxonomy to describe carrier lifetime characteristics is also proposed.

Theory of lifetime spectroscopy

“…The deviation term depends on two defect-specific quantities: the relative energy distance ∆E t A -∆E t B of both defects and a ratio V which is defined as . In addition it depends on 21 The discussion below reveals that Eq. (3.61) is generally valid and not restricted to the case of dominance by defect A, which is only used as a starting point.…”

“…A fundamental discussion of the injection and temperature dependence of SRH lifetime has already been published by Bullis and Huff in 1997 within a review of problems associated with the interpretation of carrier lifetime [21]. In the present chapter -which is based on the results published in [22] -the general impact of the defect and material parameters on the injection and temperature dependence of SRH lifetime is investigated in more detail, showing on the one hand the variety of attainable curve shapes and evaluating on the other hand their suitability for a spectroscopic determination of defect parameters.…”

External and Internal Gettering of Interstitial Iron in Silicon for Solar Cells

“…Here a doping concentration of 10 16 cm -3 is assumed, and a generation rate of 0.1 suns is used, which approximates the injection level at maximum power point. The QSS-Model software was used for these simulations [11], assuming a thermal velocity of 1.1×10 7 cm/s [12]. Auger recombination [13] is also included in the calculation, which causes the saturation at lower Fe concentrations.…”

Recombination in compensated crystalline silicon for solar cells

“…15 For calculating recombination lifetimes via the Shockley-Read-Hall model, 16,17 energy levels E T and capture cross sections for electrons and holes r n and r p for two iron-related levels were E T ¼ E V þ 0.38 eV, r n ¼ 1.4 Â 10 À14 cm 2 , and r p ¼ 7 Â 10 À17 cm 2 for interstitial Fe (Fe i ), 18,19 and E T ¼ E C -0.26 eV, r n ¼ 5 Â 10 À15 cm 2 , and r p ¼ 3 Â 10 À 15 cm 2 for the acceptor level for iron-boron pairs (FeB). 22 For simulating solar cell performance, the front and rear surfaces were modeled with a saturation current density of J 0E ¼ 10 À13 A cm À2 each, representative of standard modern solar cell technology. These values are very similar to those of the acceptor level of substitutional gold 21 Au S (E T ¼ E C -0.55 eV, r n ¼ 1.4 Â 10 À16 cm 2 , and r p ¼ 7.6 Â 10 À 15 cm 2 ).…”