Photoluminescence of Amorphous Silicon

Overview l Amorphous Silicon l The Problem l Photoluminescence l Conclusion

Amorphous Silicon l Short range order only l Band tails –Localized electronic states Density of States Energy Energy

Staebler-Wronski Effect l Degradation of luminescence intensity l Reversible process

Photoluminescence l Laser light is incident on sample l Emitted light is analyzed l Intensity vs. Wavelength is plotted

Photoluminescence of Amorphous Silicon l As grown a-Si:H l Light soaked a- Si:H for 600 hours l Annealed a-Si:H 170 ºC 4-hours

ESR l Counts unpaired electrons/dangling bonds l As-grown 2 x10 16 cm -3 l Light soaked 5 x10 16 cm -3 l Annealed 2 x cm -3

NMR l Sensitive to local hydrogen environment l Metastable change in the hydrogen NMR line shape l Measure increase in the number of hydrogen doublets –On same order as number of defects from ESR

Interpretation of Results l Light soaking causes: –Decrease in intensity of emitted light (measured by photoluminescence) –Increase in dangling bonds (measured by ESR) –Movement of hydrogen atoms (measured by NMR) l All revert back to “normal” after annealing

Acknowledgments l Weber State University Physics Dept. l University of Utah Physics Dept. l BP Solar l Four Corners Section APS l Trisha and Annie