Minority Carrier Lifetime Estimation by Photoconductance Decay for Silicon Wafers Immersed in HF

Abstract

The measurement of minority carrier bulk lifetimes of Si wafers immersed in HF is known to have an immersion time dependence, which is specially strong for high lifetime wafers and can vary significantly for different surface treatments performed previously. These complications can make the lifetime measurement become difficult to interpret and inaccurate. Therefore, a method for extracting the bulk lifetime from the measured curves of lifetime versus immersion time is suggested. A model of the reaction between Si and HF is considered, consisting in a first-order reaction between Si and HF for polished wafers and two first-order reactions for textured wafers. Experiments on polished and textured p-type Si wafers were conducted with the photoconductance decay technique to test the model proposed and to show that it is more adequate to estimate the bulk lifetime by using the reactions models than to report it as the lifetime measured at a particular immersion time, which is the usual procedure.

Temporary Surface Passivation for Characterisation of Bulk Defects in Silicon: A Review

“…In this regard, temporary passivation techniques which can passivate such surfaces are of interest in terms of material properties and surface roughness/ability to passivate. The lowest reported S for textured silicon wafers is 1.9 cm s −1 , once accounting for the additional surface area (1.73) . Baker‐Finch examined the dependence of S on the (111) surface area proportion, and found that S increased from ≈1 cm s −1 to 4–5 cm s −1 when the (111) proportion was increased from 0.4 to 1 respectively .…”

“…While HF based techniques in general provide the highest level of surface passivation (see Figure ), the instability of the passivation whilst silicon wafers are immersed in HF is undesirable for long term measurements. Recently, Razera et al examined the time dependence of silicon wafers immersed in 48% HF, and demonstrated that for planar (100) silicon wafers, the lifetime decays steadily for the first 6 min and then stabilises beyond this time. It was proposed that the initial high lifetime at t = 0 min represents a fluorine passivated surface, while for t > 6 min the passivation is attributed to hydrogen termination of silicon surface states, resulting in a lower, but stable surface lifetime .…”

“…Recently, Razera et al examined the time dependence of silicon wafers immersed in 48% HF, and demonstrated that for planar (100) silicon wafers, the lifetime decays steadily for the first 6 min and then stabilises beyond this time. It was proposed that the initial high lifetime at t = 0 min represents a fluorine passivated surface, while for t > 6 min the passivation is attributed to hydrogen termination of silicon surface states, resulting in a lower, but stable surface lifetime . In contrast, when textured silicon wafers are immersed in 48% HF, the initial lifetime is low, but quickly increases, reaching its peak lifetime after ≈3 min of immersion, and then drops again where it finally stabilises for t > 8 min.…”

“…In contrast, when textured silicon wafers are immersed in 48% HF, the initial lifetime is low, but quickly increases, reaching its peak lifetime after ≈3 min of immersion, and then drops again where it finally stabilises for t > 8 min. The different behavior in the time dependent lifetime measurements, suggests formation of SiF bonds is slower on textured wafers, which has been attributed to a delay in the reaction that substitutes the OH (formed during chemical oxidation) group with F …”

Exceptional Hole‐Selective Properties of Ta2O5 Films via Sn4+ Doping for High Performance Silicon Heterojunction Solar Cells

“…Figure a shows the effective carrier lifetime ( τ eff ) of p‐Si wafers coated with and without Ta 2 O 5 films. Note that the bare c‐Si wafer has a moderate surface passivation provided by the HF treatment, [ 24 ] with the measured τ eff of 36.4 µs at the injection concentration of 1 × 10 15 cm −3 . The τ eff is increased to 66.7 µs after the deposition of Ta 2 O 5 films, and it is further improved to 90.4 µs with the introduction of SiO 2 interfacial layer, exhibiting a high surface passivation quality for p‐Si wafers.…”