Metastable defects by low-intensity pulsed illumination of hydrogenated amorphous silicon

2000 ◽  
Vol 609 ◽  
Author(s):  
Stephan Heck ◽  
Howard M. Branz
Keyword(s):  
Amorphous Silicon ◽  
Exposure Time ◽  
Red Light ◽  
Hydrogenated Amorphous Silicon ◽  
Continuous Illumination ◽  
Defect Region ◽  
Absorption Increase ◽  
Low Intensity ◽  
Careful Measurement ◽  
Hydrogenated Amorphous

ABSTRACTIllumination of hydrogenated amorphous silicon (a-Si:H) samples with short (e.g., 40 microsecond) pulses of red light produces a smaller metastable absorption increase in the defect region than continuous illumination of the same intensity for the same integrated exposure time. The defect absorption was measured at 1.3 and 1.4 eV by use of the constant photocurrent method (CPM). This smaller degradation is also observed in the photoconductivity. Careful measurement of the film temperature with several techniques confirm that the film temperature rises by less than 5 °C, under continuous illumination. However, several experiments suggest that the suppressed degradation during pulsed illumination is caused primarily by annealing during the dark time between pulses, even at 15 to 26 °C.

Slow Degradation of Hydrogenated Amorphous Silicon Photoconductivity Under Pulsed Illumination

1999 ◽  
Vol 557 ◽  
Author(s):  
Stephan Heck ◽  
Howard M. Branz
Keyword(s):  
Amorphous Silicon ◽  
Exposure Time ◽  
Degradation Mechanism ◽  
Red Light ◽  
Hydrogenated Amorphous Silicon ◽  
Continuous Light ◽  
Continuous Illumination ◽  
Light Pulses ◽  
Carrier Recombination ◽  
Hydrogenated Amorphous

AbstractWe degraded hydrogenated amorphous silicon (a-Si:H) using red light pulses of 32 microseconds to 2 milliseconds. These metastable photoconductivity degradations were compared to degradation with continuous light of the same intensity and same exposure time. For a given integrated exposure time we observe higher degraded photoconductivities (by up to 40 %) as we shorten the pulses. For example, to obtain the same amount of degradation with 120 microsecond pulses as with continuous illumination, the integrated sample exposure time must be doubled. Experiments were conducted to exclude thermal effects. Our result cannot be explained with a simple recombination-driven degradation mechanism, because electron and hole populations rise and fall to steady-state values in only a few microseconds. We conclude that carrier recombination creates a more proximate precursor to metastable degradation of a-Si:H. When illumination begins, this precursor's density rises more slowly than the density of photocarriers and therefore degradation is delayed.

New Results on Enhanced Deuterium Diffusion Under Illumination in Amorphous Silicon

1992 ◽  
Vol 258 ◽  
Author(s):  
Howard M. Branz ◽  
Sally E. Asher ◽  
Brent P. Nelson
Keyword(s):  
Amorphous Silicon ◽  
Room Temperature ◽  
Red Light ◽  
Hydrogenated Amorphous Silicon ◽  
Dissimilar Materials ◽  
Bond Breaking ◽  
Light Enhancement ◽  
Staebler Wronski Effect ◽  
Hydrogenated Amorphous ◽  
Bulk Effect

ABSTRACTWe measure the light-enhancement of D diffusion in hydrogenated amorphous silicon and determine that the mechanism for the effect is an increase of the rate of Si-D bond breaking under illumination. We exclude light-induced heating of the sample and light-induced excitation of D between dissimilar materials as sources of the light-enhancement. It is a bulk effect, most likely caused by excess carriers. We are able to observe the light-induced effect with 380 mW-cm-2 of red light, an intensity only slightly larger than the intensity normally used to induce the Staebler-Wronski effect. At room temperature, the effect is unobservable and we derive an upper bound of 2 × 10-8 photon-1 for the efficiency of light-induced Si-D bond breaking. Implications for the Staebler-Wronski effect are discussed.

Photoconductivity Stability Improvement in Hydrogenated Amorphous Silicon by Ultraviolet Illumination

2002 ◽  
Vol 715 ◽  
Author(s):  
Howard M. Branz ◽  
Yueqin Xu ◽  
Stephan Heck ◽  
Qi Wang ◽  
Wei Gao ◽  
...  
Keyword(s):  
Amorphous Silicon ◽  
Red Light ◽  
Hydrogenated Amorphous Silicon ◽  
Control Sample ◽  
Open Circuit ◽  
Silicon Thin Films ◽  
Uv Illumination ◽  
Treated Sample ◽  
Mobile Hydrogen ◽  
Hydrogenated Amorphous

AbstractWe observe improved photoconductivity stability against light-soaking in hydrogenated amorphous silicon thin films as a result of an ultraviolet (UV) illumination and etch treatment. UV-etch treated samples begins with red-light photoconductivities inferior to that of a control sample which is only etched. After less than an hour of 1 sun red light-soaking, the photoconductivity of the etched-only control falls below that of the UV-etch treated sample. After 2 to 3 days light soaking, the UV-etch films can have a photosensitivity 20 to 38% above their control. We observe no corresponding improvement of defect optical absorption by constant photocurrent method spectroscopy. The UV-etch treatment also produces small improvements in the stabilized open-circuit voltage of Schottky barier solar cells. We speculate that mobile hydrogen produced during UV illumination is penetrating the film and improving stability.

BONDING IN HYDROGENATED AMORPHOUS SILICON

1981 ◽  
Vol 42 (C4) ◽  
pp. C4-773-C4-777 ◽  
Author(s):  
H. R. Shanks ◽  
F. R. Jeffrey ◽  
M. E. Lowry
Keyword(s):  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Hydrogenated Amorphous

High Rate Deposition of Stable Hydrogenated Amorphous Silicon in Transition from Amorphous to Microcrystalline Silicon

2003 ◽  
Vol 762 ◽  
Author(s):  
Guofu Hou ◽  
Xinhua Geng ◽  
Xiaodan Zhang ◽  
Ying Zhao ◽  
Junming Xue ◽  
...  
Keyword(s):  
Phase Transition ◽  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Chemical Vapor ◽  
High Rate ◽  
Very High Frequency ◽  
High Quality ◽  
Working Pressure ◽  
Hydrogen Dilution ◽  
Hydrogenated Amorphous

AbstractHigh rate deposition of high quality and stable hydrogenated amorphous silicon (a-Si:H) films were performed near the threshold of amorphous to microcrystalline phase transition using a very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) method. The effect of hydrogen dilution on optic-electronic and structural properties of these films was investigated by Fourier-transform infrared (FTIR) spectroscopy, Raman scattering and constant photocurrent method (CPM). Experiment showed that although the phase transition was much influenced by hydrogen dilution, it also strongly depended on substrate temperature, working pressure and plasma power. With optimized condition high quality and high stable a-Si:H films, which exhibit σph/σd of 4.4×106 and deposition rate of 28.8Å/s, have been obtained.

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