TY - JOUR

T1 - The effect of sample edge recombination on the averaged injection-dependent carrier lifetime in silicon

AU - Kessler, Michael

AU - Ohrdes, Tobias

AU - Altermatt, Pietro P.

AU - Brendel, Rolf

PY - 2012/3/8

Y1 - 2012/3/8

N2 - In semiconductors, the effective excess carrier lifetime, τ eff, measured in dependence on the injection density, n, is an important parameter. It is frequently observed that τ eff decreases with decreasing n at low-level injection conditions (where Δn is smaller than the dopant density N dop), which has been difficult to explain. We compare measurements with numerical device simulations to demonstrate that this observed reduction of τ eff is caused by a combination of (i) Shockley-Read-Hall (SRH) recombination at the edges of the sample and (ii) transport effects of the carriers toward the edges. We measure τ eff(Δn) of boron-diffused and surface-passivated p +np ++ and p +pp ++ silicon wafers with the commonly applied photo-conductance decay technique, and we vary the sample size. The photo-conductance is probed by inductive coupling within a sample region of about 3 × 3 cm 2; hence, the measurements yield an average value of both τ eff,av and Δn av within that region. For a detailed analysis, we determine τ eff with a high spatial resolution using the dynamic infrared lifetime mapping technique, which shows a strong decrease of τ eff toward the edges of the p np samples at low-level injection. We analyze the measurements by numerical device modeling and circuit simulation. We conclude that the sample size should be at least 6 6 cm 2 for reliable τ eff(n) measurements at low injection conditions. However, at high-injection conditions, the recombination usually dominates at the dopant-diffused surfaces. Therefore, the saturation current-density, J 0, can be extracted from the τ eff(Δn) measurements in samples as small as 3 × 3 cm 2, with a measurement error due to edge recombination below 10%.

AB - In semiconductors, the effective excess carrier lifetime, τ eff, measured in dependence on the injection density, n, is an important parameter. It is frequently observed that τ eff decreases with decreasing n at low-level injection conditions (where Δn is smaller than the dopant density N dop), which has been difficult to explain. We compare measurements with numerical device simulations to demonstrate that this observed reduction of τ eff is caused by a combination of (i) Shockley-Read-Hall (SRH) recombination at the edges of the sample and (ii) transport effects of the carriers toward the edges. We measure τ eff(Δn) of boron-diffused and surface-passivated p +np ++ and p +pp ++ silicon wafers with the commonly applied photo-conductance decay technique, and we vary the sample size. The photo-conductance is probed by inductive coupling within a sample region of about 3 × 3 cm 2; hence, the measurements yield an average value of both τ eff,av and Δn av within that region. For a detailed analysis, we determine τ eff with a high spatial resolution using the dynamic infrared lifetime mapping technique, which shows a strong decrease of τ eff toward the edges of the p np samples at low-level injection. We analyze the measurements by numerical device modeling and circuit simulation. We conclude that the sample size should be at least 6 6 cm 2 for reliable τ eff(n) measurements at low injection conditions. However, at high-injection conditions, the recombination usually dominates at the dopant-diffused surfaces. Therefore, the saturation current-density, J 0, can be extracted from the τ eff(Δn) measurements in samples as small as 3 × 3 cm 2, with a measurement error due to edge recombination below 10%.

UR - http://www.scopus.com/inward/record.url?scp=84858975993&partnerID=8YFLogxK

U2 - 10.1063/1.3691230

DO - 10.1063/1.3691230

M3 - Article

AN - SCOPUS:84858975993

VL - 111

JO - Journal of Applied Physics

JF - Journal of Applied Physics

SN - 0021-8979

IS - 5

M1 - 054508

ER -