# Presentation: 567164

## New Insights into the Role of Hydrogen in the Staebler-Wronski Effect in a-Si:H

**New Insights into the Role of Hydrogen in the Staebler-Wronski Effect in a-Si:H**

**P. Craig Taylor**
**Department of Physics**
**Colorado School of Mines**

**Amorphous and Nanocrystalline Silicon Team Meeting**
**April 7, 2006**
**San Francisco, CA**

## Outline

**Outline**

- The Story of Silicon Dihydride (SiH2)
- NMR lineshapes
- Calculations
- Relationship to Metastable Doublet

- H and Dangling Bonds in Tritiated a-Si:H
- Temperature Dependence of Creation
- Annealing
- Possible H-Related Site

- Light Soaking at 77 K

## Paired Hydrogen Bonding Sites

**Paired Hydrogen Bonding Sites**
**Metastable Site**
**Polysilane (SiH****2****)****n**
**Silicon Dihydride (SiH****2****)**

## 1H NMR Lineshapes in a-Si:H due to Bonded Hydrogen

**1****H NMR Lineshapes in a-Si:H due to Bonded Hydrogen**

**Narrow line:  dilute or “random” phase (Lorentzian)**
**Broad line: clustered phase (Gaussian)**

## Slide 5

## NMR Lineshapes in a-Si:H due to Paired Hydrogen Site

**NMR Lineshapes in a-Si:H due to Paired Hydrogen Site**

- T. Su, P. C. Taylor, G. Ganguly and D. E. Carlson, Phys. Rev. Lett. **89**, 015502-1 (2002).

## Slide 7

## Slide 8

## The Microscopic Picture: What Stabilizes the “Dangling Bond”?

**2.3 ****Å**

## Stabilization of the Staebler-Wronski Effect in a-Si:H

**Lineshape indicates site is a doublet**
**Two hydrogen atoms are 2.3 ****Å apart**
**Density of paired hydrogen sites is consistent with the density of dangling bonds from ESR**
**Much different T****1**** and much longer T****1d**** for paired H site indicates that it is decoupled from bonded H**

**Stabilization of the Staebler-Wronski Effect in a-Si:H**

## Lineshape Fitting of Silicon Dihydride 1H NMR Doublet

**Lineshape Fitting of Silicon Dihydride ****1****H NMR Doublet**

**Assume SiH****2**** with distribution of *****r(H-H) *****centered at***** *****1.8 ****Å with a width (FWHM) of 0.5 Å and minimal isotropic broadening of 1 kHz (FWHM).**

- D. Bobela et al. **W06.2 This meeting, Wednesday morning**

## Lineshape Fitting of Silicon Dihydride 1H NMR Doublet

**Lineshape Fitting of Silicon Dihydride ****1****H NMR Doublet**

**Assume unique SiH****2**** with *****r(H-H) = *****1.8 ****Å and isotropic broadening of 12 kHz (FWHM) to account for randomly occurring nearby H**

## Title

**Title**

**Table 1.****   **Summary of (SiH2)n concentration measured from NMR and IR. The reported value is the percent concentration relative to the total hydrogen concentration observable by NMR and IR. “Min %” refers to the minimum concentration estimate, within experimental uncertainty. Details of the growth conditions are also provided.

** **

## Possible SiH2 Sites in a-Si:H

**Possible SiH****2**** Sites in a-Si:H**

- T. A. Abtew, D. A. Drabold, and P. C. Taylor, Appl. Phys. Lett. **86**, 241916 (2005).

- Silicon dangling bond

## Calculated H-H Separation in SiH2

**Calculated H-H Separation in SiH****2**

- T. A. Abtew, D. A. Drabold, and P. C. Taylor, Appl. Physl Lett. **86**, 241916 (2005).

## Summary of SiH2 Sites in a-Si:H

**Summary of SiH****2**** Sites in a-Si:H**

- Significant SiH2 in most, if not all, films
- Calculations yield H-H distances too large
- What is metastable paired hydrogen site?

## Hydrogen and Dangling Bonds in Tritiated a-Si:H

**Hydrogen and Dangling Bonds in Tritiated a-Si:H**

## t1/3

**Stretched Exponential with ****β = 0.6**

**t****1/3**

**Defects expected from ****3****H decays**

**Growth of ****ESR**** and ****PDS**** in Tritiated a-Si:H at Different Temperatures**

## Growth of ESR in Tritiated a-Si:H

**Growth of ESR in Tritiated a-Si:H**
**“****device quality” sample**

## ESR in Tritiated a-Si:H

**ESR in Tritiated a-Si:H**
**“****high defect density” sample**

## ESR in Tritiated a-Si:H

**ESR in Tritiated a-Si:H**
**“****device quality” sample**

## Summary

**Summary**

**In tritiated a-Si:H defects created more slowly than expected from ****3****He production.  **
**Growth is dispersive and saturates at values similar to those produced optically (Staebler-Wronski effect).**
**Most defects are neutral.**
**At room temperature and above there is significant annealing of dangling bonds.**
**No apparent saturation at 77 K at long times.**
**New H-related ESR tentatively identified.**
**Optically induced ESR at 77 K also appears not to saturate.**

## Major Conclusions

**Major Conclusions**

- More Silicon Dihydride Sites in “Device Quality” Films than Previously Assumed
- Relationship of Silicon Dihydride to Metastable H Doublet Sites Unclear
- Dangling Bond Creation in Tritiated a-Si:H Yielding Interesting Results (Possible H related ESR Site)
- Light Soaking at77 K for Long Times Initiated

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**Title**

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