On the impact of substrate contact resistance in bifacial MIS-type lifetime structures
2022, Herguth, Axel, Kostrzewa, Fabian, Sperber, David
Bifacial metal-insulator-semiconductor (MIS) structures are used to intentionally manipulate field-effect passivation of dielectric layers on crystalline silicon substrates during lifetime measurements by external biasing. It is found that the impact of biasing on surface passivation depends on the quality of the substrate contact, in particular in asymmetric front/rear biasing conditions. A mathematical model is presented and used to demonstrate the problems arising from a high substrate contact resistance.
Bulk and surface instabilities in boron doped float-zone samples during light induced degradation treatments
2017, Sperber, David, Graf, Alexander, Heilemann, Adrian, Herguth, Axel, Hahn, Giso
Float-zone silicon is often used as a supposedly stable high lifetime reference material. Here it is shown, however, that boron doped float-zone samples that underwent a fast firing step may suffer from a severe degradation in bulk lifetime during illumination at elevated temperatures. Furthermore, it is observed that silicon nitride related passivation may be affected by a long-term decrease in chemical passivation quality. A time and injection resolved visualization is introduced to quickly distinguish between these degradation features. Both bulk lifetime and chemical passivation quality are shown to recover at the same treatment conditions after longer treatment times.
Does LeTID occur in c-Si even without a firing step?
2019, Sperber, David, Furtwängler, Florian, Herguth, Axel, Hahn, Giso
It is shown that a non-fired B-doped floatzone silicon sample coated with SiNx:H may show severe bulk related degradation and regeneration during illuminated treatment at elevated temperature. It is discussed that the likely cause is light and elevated temperature induced degradation (LeTID) in the silicon bulk. Firing is found to modulate the extent of LeTID so that degradation may either be weaker or stronger compared to the non-fired sample depending on firing parameters. A sample which was annealed instead of fired is found to be stable for up to 1,000 h of treatment time.
On the stability of dielectric passivation layers under illumination and temperature treatment
2016, Sperber, David, Furtwängler, Florian, Herguth, Axel, Hahn, Giso
Different dielectric layers were deposited onto boron doped floatzone silicon wafers and the stability of the effective lifetime was investigated at elevated temperatures ranging from 75°C to 250°C with and without illumination. It was found that samples fired in a belt furnace show an instable behavior on a timescale of minutes to months. The short term behavior of a sample is strongly influenced by the peak firing temperature whereas the long term behavior appears to be less influenced by this parameter. Different chemical cleaning procedures during sample preparation show no significant influence on stability. Via corona charging, the changes at 250°C in darkness could be associated with changes in chemical passivation quality. It could be shown that a non-fired sample shows a similar, but less pronounced instability whereas an annealed sample is stable under the given treatment conditions.
Investigating possible causes of light induced degradation in boron-doped Float-Zone silicon
2017, Sperber, David, Herguth, Axel, Hahn, Giso
The use of different silicon nitride deposition tools is found to change the degree of light induced degradation (LID) of B-doped float-zone silicon after a fast firing step. In addition, a thermally grown SiO2 interlayer further suppresses LID after firing. Possible mechanisms and a potential link to Light and elevated Temperature Induced Degradation (LeTID) are discussed. Furthermore, it is shown that LID is not related to an earlier described class of thermally activated defects in float-zone silicon and that phosphorous gettering does not influence the occurrence of LID in B-doped float-zone silicon significantly.