Carrier lifetime measurements using free carrier absorption transients. II. Lifetime mapping and effects of surface recombination

Abstract

A novel noncontact technique for semiconductor wafer mapping of the charge carrier lifetime is reviewed. The principle is based upon measurements of free carrier absorption transients by an infrared probe beam following electron-hole pair excitation by a pulsed laser beam. The technique is demonstrated here for Si wafer lifetime mapping, both for homogenous wafers as well as for wafers having pn junctions, and the performance and limitations are addressed. In a companion article J. Appl. Phys. 84, 275 (1998), (part I), the injection dependence is treated in more detail. We demonstrate the broad range of accessible injections, allowing on-wafer lifetime mapping both of the minority carrier lifetime and of the high injection lifetime as well as of Auger recombination effects. Furthermore, problems of surface recombination for bare Si surfaces are elucidated while pn junctions or other barriers are shown to suppress diffusion of carriers to surfaces. Also, a scheme for low temperature surface passivation is demonstrated and the resulting surface recombination velocity is derived. Finally, a few examples of characteristic lifetime maps from processed samples are discussed. We conclude that the technique is one of the few available for monitoring of the carrier lifetime during a full device process sequence.

Assessment of plantar flexors activation capacity: nerve versus muscle stimulation by single versus double pulse

“…The present investigation corroborates the assumption of a non-linear relationship for PFs as was earlier observed for elbow flexors, ankle dorsiflexors and knee extensors (Allen et al 1995;Behm et al 1996;Belanger and McComas 1981;Bulow et al 1993;De Serres and Enoka 1998;Dowling et al 1994;Folland and Williams 2007;Phillips et al 1992;Rutherford et al 1986;Stackhouse et al 2000Stackhouse et al , 2003Todd et al 2004;Yue et al 2000). In particular, a negative linear relationship is observed between IT and torque in the submaximal range of efforts, but the relationship progressively smoothes out approaching the MVT, denoting a level of activation nearmaximal or maximal for a submaximal voluntary torque.…”

“…The number of electrical pulses represents the first methodological concern. Some authors report that the use of interpolated multiple-pulse stimulation (as opposed to single pulse) (i) incorporates recruitment and rate coding, and (ii) increases the technique's sensitivity (Behm et al 2001;De Serres and Enoka 1998;Kent-Braun and Ng 1999;Miller et al 1999;Stackhouse et al 2000). Nevertheless, other investigations demonstrate that the level of activation is similar when using single or multiple pulse stimulations, if the interpolated twitch torque (IT) is normalized to the corresponding resting mechanical response (Allen et al 1998;Behm et al 1996;Gandevia 2001;Herbert and Gandevia 1999;Shield and Zhou 2004).…”

“…There is also some controversy over the assessment of voluntary activation from a single datum point (Behm et al 1996(Behm et al , 2001De Serres and Enoka 1998). This method implies a linear relation between the IT and the level of voluntary activation.…”

“…Several models have thus been proposed to describe this relationship. Some authors, using the best curve fitting procedure, have fitted the experimental data points with exponential (Behm et al 2001;Dowling et al 1994) or polynomial functions (Behm et al 1996(Behm et al , 2001De Serres and Enoka 1998). One major critique to the curvilinear fitting is that it may not always provide equations that cross the x-axis and consequently does not always allow quantification of the torque that the subject would be able to produce for a total IT occlusion (i.e.…”

Optical Measurement Techniques of Recombination Lifetime Based on the Free Carriers Absorption Effect

“…Two schemes of Pump and Probe setup have been proposed, depending on the angle between the pump and probe beams: the transverse configuration and the parallel configuration. The parallel configuration is more suitable for wafer lifetime mapping, obtained by scanning the sample along the plane orthogonal to the beams incidence plane [56,57]. In this case the diffusion length of the free carriers in the sample, = √ , limits the resolution of the system.…”