Minority Carrier Lifetime in Czochralski Silicon Containing Oxide Precipitates

Abstract

Photoconductance methods were used to measure minority carrier lifetime in p-type Czochralski silicon processed under very clean conditions to contain oxide precipitates. 24 different sample types were characterised by chemical etching and transmission electron microscopy to determine the density and morphology of the precipitates. For samples processed to contain mainly unstrained precipitates, the lifetime component associated with oxide precipitates was extremely high (up to 4.5ms at an injection level corresponding to half of the doping level). The lifetime results show that rate of recombination depends upon the strain state of the precipitates. Recombination at unstrained oxide precipitates (sometimes referred to as "ninja particles") is weak, with a capture coefficient of approximately 1 x 10-7cm3s-1. Strained oxide precipitates and defects associated with them (dislocations and stacking faults) act as much stronger recombination centres with a capture coefficient of approximately 3 x 10-6cm3s-1. Recombination at strained precipitates and associated defects was found to depend mainly on their density (as opposed to size).

IR studies of the oxygen and carbon precipitation processes in electron irradiated tin-doped silicon

“…In the course of thermal treatments at elevated temperatures supersaturated oxygen impurities tend to aggregate leading to the formation of SiO x precipitates [10,11]. Oxide precipitates can have positive but also negative effects in the functionality of devices [26][27][28][29][30][31]. Indeed they may be beneficial by acting as sinks for detrimental metallic impurities (internal gettering) and also can enhance the mechanical strength and stability of Si wafers by preventing dislocation movement.…”

(Invited) The Impact of Oxide Precipitates on Minority Carrier Lifetime in Czochralski Silicon

“…The morphology of the precipitates evolves during growth from an unstrained to a strained state, and strained precipitates can be surrounded by dislocations and stacking faults [8,9]. Oxide precipitates and surrounding defects are strong recombination centres [10][11][12][13][14][15][16][17][18][19][20][21] and hence can limit the conversion efficiency of silicon solar cells [4].…”

“…The approximate energy level and the ratio of the capture coefficient for electrons to that of holes can be determined using temperature-and injectiondependent lifetime spectroscopy (TIDLS) [24][25][26]. We have used TIDLS to parameterize recombination at oxide precipitates and surrounding defects in terms of SRH statistics [17,[19][20][21]. We review some of our results in this paper.…”

Finding unstrained 10 -nm lattice defects in silicon, given 1011 per cubic centimeter

“…This unexpected break in symmetry might be explained by anecdotal evidence [5] that unstrained monolayer oxygen-molecule or "ninja-plates" naturally form on (100) because of lattice potential considerations, but are very hard to find given their lack of strain. At some point these "decloak" [6] to form strained octahedra (cf. Fig.…”

“…Around it are interstitial dislocation loops created by the volume-excess associated with interstitial oxygen precipitation. Field width is about 1.16μm[6]…”