Experimental evidence of photoinduced expansion in hydrogenated amorphous silicon using bending detected optical lever method

Abstract

Photoinduced structural change in hydrogenated amorphous silicon (a-Si:H) has been studied by a sensitive bending detection method using an optical lever. We observed that a-Si:H films show not only thermal expansion due to a photothermal effect but also residual and persistent expansion after light soaking. The volume change is recovered by thermal annealing at 200 °C. A dehydrogenated sample annealed at 550 °C and a microcrystalline sample, in which photoinduced defects are not created, show little photoinduced expansion. The photoinduced expansion and photoinduced defect density show identical time evolution. These results suggest that the photoinduced expansion is related to the photoinduced defect creation. A quantitative evaluation of the photoinduced expansion indicates that the photoinduced structural change is spread over several molecular volumes around a photocreated defect.

Light induced electrical and macroscopic changes in hydrogenated polymorphous silicon solar cells

“…As a matter of fact, there has been a great deal of research on lightinduced volume changes [50]. Various beam bending experiments have been performed using samples consisting of long and narrow pieces of thin glass or quartz substrates coated with a-Si:H [51][52][53][54][55][56][57]. These results reveal that lightinduced volume expansion follows a stretched exponential behavior, usually showing saturation at dV /V ∼ 10 −3 [29].…”

A change of photoinduced dilation of a-Si:H by cyanide treatment

“…We have previously reported that there exists some correlation between the photoinduced dilation and the photodegradation in undoped a-Si:H films [3][4][5]. A simple scenario to understand this correlation is that the creation of dangling bonds DN d itself brings the dilation DV =V of amorphous Si network.…”

“…On the other hand, photoinduced volume changes (photoinduced structural changes) in a-Si:H films have been investigated by some groups [3][4][5][6][7]. We have previously reported that there exists some correlation between the photoinduced dilation and the photodegradation in undoped a-Si:H films [3][4][5].…”

Depth profile study on Raman spectra of high-energy-electron-irradiated hydrogenated amorphous silicon films

“…It is reported that light soaking or high-energy-particle irradiation made the amorphous network of a-Si:H films to be reorganized, leading to a change in the structural order of the films [5][6][7][8][9] . The local distortions of amorphous network due to higher density defects in the irradiated a-Si:H films result in a change of structural order [9] and a macroscopic volume expansion [10] . Chini et al [11] have reported the formation of 50-260 nm a-Si:H layers on the high-energy-particle-irradiated crystalline silicon surfaces by means of transmission electron microscopy, despite the fact that the penetration depth of high energy particles in crystalline silicon was far beyond the formed amorphous-layer thickness.…”