Surface photovoltage analysis of phase transformation of copper in p-type silicon

Abstract

Surface photovoltage minority carrier lifetime/diffusion length analysis of copper contaminated p-type silicon was performed. It was observed that an optical or low-temperature thermal activation procedure on Cu-doped silicon significantly degrades the diffusion length. Unlike iron doped p-type silicon no recovery of diffusion length was observed following such an activation procedure. It is proposed that the activation procedure dissociates interstitial copper agglomerations and forms extended substitutional defects in silicon, which have much greater recombination efficiency. The change in phase of copper and the formation of associated defects is a function of activation light intensity, annealing time, and temperature. An activation energy of 0.419 eV is obtained for the process, which is in good agreement with copper diffusivity value in silicon. It is thus concluded that the change in phase of copper and the formation of extended defects with activation is a diffusion limited process.

Formation kinetics of copper-related light-induced degradation in crystalline silicon

“…During 1000 min of dark annealing, the lifetime decreases in all samples. A lifetime decrease is expected, as increased recombination has previously been observed in copper-contaminated FZ 8 and Cz-Si 16 during dark annealing at 210 C. However, after only a short anneal of 2 min, a lifetime increase is observed in the low-res samples. This increase is probably caused by the dissociation of boronoxygen defects formed during sample preparation.…”

“…7 Copper is a common 3d transition metal impurity in industrial silicon solar cells, which under illumination also causes lifetime degradation (Cu-LID). [8][9][10] Hence, crystalline silicon can suffer from BO-LID, Cu-LID, or a combination of both degradation effects. In Cu-LID, illumination is proposed to enable the growth of recombination-active copper precipitates (Cu 3 Si) by lowering the repulsion between Cu þ i and Cu 3 Si 0=þ , 11 but the formation kinetics of Cu-LID remain unclear.…”

Accelerated light-induced degradation for detecting copper contamination in p-type silicon

“…The Cu-LID has been confirmed to originate from bulk recombination, 5 which is proposed to be caused by copper precipitation 7 or substitutional copper release through copper complex dissociation during illumination. 8,9 The formed defects have been found to be stable at 200 C in wafers with initial interstitial copper concentration of 10 14 cm À3 . 10 In addition to copper defects, the involvement of boron and oxygen in the formation of a metastable recombinationactive defect (BO-LID) has been extensively reported as the major cause of degradation in low-resistivity boron-doped Czochralski (Cz) silicon.…”

“…By comparing the lifetime values measured during ALID and RT-LID after identical degradation time steps, it becomes evident that ALID results in almost complete lifetime saturation within 1 h, whereas RT-LID requires almost a whole day to reach similar degradation. Note that the Cu-related degradation rate depends on the annealing temperature, 10 light intensity, 9,14 and impurity concentration, 7 enabling probably even faster lifetime saturation at higher temperatures, illumination intensities, or copper concentrations.…”

Preventing light-induced degradation in multicrystalline silicon

“…Copper is a common 3d transition metal impurity in silicon, which in its interstitial state has been observed to cause similar degradation in single crystalline silicon under illumination, 12 even without the presence of boron 13 or oxygen. 14 Illumination of copper-contaminated silicon is proposed to enable the formation of recombination-active copper precipitates (Cu 3 Si), 15 and bulk microdefects 14 are suggested to provide nucleation sites for copper precipitation.…”