The effect of oxide precipitates on minority carrier lifetime in p-type silicon

Abstract

Transient and quasi-steady-state photoconductance methods were used to measure minority carrier lifetime in ∼10 Ω cm p-type Czochralski silicon processed in very clean conditions to contain oxide precipitates. The nucleation and growth times for precipitation were varied to produce 35 samples, which were then characterised by chemical etching and transmission electron microscopy to determine the density and morphology of the precipitates. The effects of other known recombination mechanisms (band-to-band, Coulomb-enhanced Auger, iron-related, and boron-oxygen related) were factored out to isolate the lifetime component associated with the precipitates as accurately as possible. In the samples processed to contain mainly unstrained precipitates, it was shown that the lifetime component due to the precipitates could be extremely high (up to ∼4.5 ms). Recombination at unstrained precipitates is weak and it is estimated that the capture coefficient lies between 3 × 10−8 cm3 s−1 and 1.3 × 10−7 cm3 s−1 at an injection level corresponding to half the doping level. Strained precipitates act as strong recombination centres with a capture coefficient of ∼1 × 10−6 cm3 s−1 at the same level of injection. For the samples investigated, the effective capture coefficient is increased by a factor of ∼3 to 4 when other extended defects (such as dislocations and stacking faults) accompany the strained precipitates. The shape of the injection level dependence of lifetime was similar for all the specimens studied, with the magnitude of the lifetime being dependent on the precipitate density and strain state but approximately independent of precipitate size.

Competitive gettering of iron in silicon photovoltaics: Oxide precipitates versus phosphorus diffusion

“…Details of these corrections are given in Ref. 18. Throughout this study, we use a linear formulation of Shockley-Read-Hall (SRH) statistics (described in detail in Ref.…”

“…The lifetime change was analysed to give the bulk interstitial iron concentration in the samples, using a specific method described in Ref. 18. Before entering the next sample processing stage, the silicon nitride passivation film was removed with concentrated HF.…”

“…18. The $700 lm thick wafers were cross-sectioned and then subjected to a defect revealing etch, which allowed the oxide precipitate density to be determined.…”

Hydrogénation effect on low temperature internal gettering in multicrystalline silicon

“…Lifetimes in this paper are the effective lifetime with bulk iron in the Fei state at an injection level of 1  10 15 cm -3 , and are denoted by Fei. The interstitial iron concentration (denoted by [Fei]) was measured at an injection level of ∆n = 1  10 15 cm -3 based on the carrier lifetime changes before and after the photodissociation of the FeB complexes using a method published previously [31]. The spatial distribution of carrier lifetime was measured using a BT Imaging LIS-L1 photoluminescence (PL) imaging tool with a spatial resolution of ~160 µm.…”

Evaluation of oxygen precipitation behavior in n-type Czochralski-Si for photovoltaic by infrared tomography: Effects of carbon concentration and annealing process conditions

“…Thereafter, various thermal processes (e.g., boron diffusion and electrode formation) are added in the solar cell manufacturing process, and oxygen precipitation progresses. 2,[5][6][7][8][9] The oxygen precipitate acts as a carrier recombination center, 6,[9][10][11][12][13][14][15][16][17][18][19][20][21][22] which can a cause reduction in solar cell conversion efficiency. Therefore, in order to improve solar cell conversion efficiency, it is important to understand and control the oxygen precipitation behavior.…”