Oxidation-induced stacking faults in silicon. II. Electrical effects in P N diodes

Abstract

The electrical characteristics of boron-diffused P+N diodes containing electrically active stacking faults (EASF) are investigated. The method combines an analysis of the I-V characteristics of the diodes with information derived from a scanning-electron-beam technique, the electron-beam-induced current (EBIC) mode. Stacking faults (SF) measuring 1–2 μm in length nucleate and develop in the near-surface region of the silicon slice during the initial oxidation process. Subsequent to the boron diffusion, the SF are heavily decorated with impurity precipitates. Excess reverse currents are measured at room temperature over a broad range of voltage from the very-low-voltage region where VR < kT/q to the high-voltage preavalanche region where VR≫kT/q. Two distinct regions are observed in the I-V characteristics of all diodes containing EASF's. These regions are separated by an effective threshold voltage VTHE, which is characteristic of the EASF's in the particular diode. For typical diodes with a junction depth Xj=0.4 μm, experimentally determined values for VTHE are in the range 0.1–10.0 V. When the applied reverse voltage VR < VTHE the diode exhibits the two regions characteristic of silicon diodes at room temperature; a low-field Ohmic conductance region when VR < k T/q and a space-charge-generation region when VR > k T/q, which is similiar to a modified form of SNS theory. In this region, the excess generation currents are found to correlate with the threshold voltage of the EASF's. When VR > VTHE a voltage power-law dependence is observed where IRαVn, n≈4.75±0.25. This carrier-generation effect results from the interaction between the strain field and/or the impurity atmosphere surrounding the EASF and the depletion field of the P N junction. The composite defect introduces a local high-density zone of g-r centers which reduce the effective lifetime of minority charge carriers in the region of the SF. The localized g-r zones are typically 20 μm2 in cross-sectional area with an effective lifetime of 4 – 400 ps. They are distributed nonuniformly, and are the direct source of excess IR currents measured at room temperature.

Physical mechanisms of breakdown in multicrystalline silicon solar cells

“…Further µ-XRF measurements along the grain boundary (labelled with A) revealed no other metal clusters. The one to one concurrence of the precipitates and breakdown gives strong evidence that metal clusters in or close to the p-n junction induce variations in the space charge region which causes pre-breakdown which now experimentally confirms earlier conjections [11,12]. TC-DLIT measurements in soft breakdown regions reveal a temperature coefficient which is zero or slightly negative.…”

“…The effect of metal impurities in silicon diodes was studied by a number of authors (see e.g. [11,12]). They suspected that metal precipitates cause soft diode breakdown behaviour.…”

Observation of metal precipitates at prebreakdown sites in multicrystalline silicon solar cells

“…[7][8][9][10]22 In addition, the space charge region is influenced by the threedimensional formation of the emitter, which in turn is related to the surface morphology. Then the modification of the space charge region, which eventually leads to locally decreased breakdown voltage, is a result of the complex interaction between the local surface structure ͑as evidenced for example in Ref.…”

A linear and compact charge-coupled charge packet differencer/replicator

“…Diode and channel stop diffusions were performed using a spin-on dopant source. All wet oxidations were carried out at 900°C to reduce oxidation induced silicon defects and suppress bucket dark current [2] . The gate oxide was grown at 1000°C in dry oxygen.…”