ESR observations of paramagnetic centers in intrinsic hydrogenated microcrystalline silicon

Abstract

Paramagnetic centers in hydrogenated microcrystalline silicon, c-Si:H have been studied using dark and light-induced electron-spin resonance ͑ESR͒. In dark ESR measurements only one center is observed. The g values obtained empirically from powder-pattern line-shape simulations are g ʈ ϭ2.0096 and g Ќ ϭ2.0031. We suggest that this center may be due to defects in the crystalline phase. During illumination at low temperatures, an additional ESR signal appears. This signal is best described by two powder patterns indicating the presence of two centers. One center is asymmetric (g ʈ ϭ1.999, g Ќ ϭ1.996), while the other is characterized by large, unresolved broadening such that unique g values cannot be obtained. The average g value for this center is 1.998. The light-induced signal, which we interpret as coming from carriers trapped in the band tails at the crystalline grain boundaries, remains for at least several minutes after the light is turned off. Although the time scales of the decay curves are very different for two samples prepared by different techniques, both decays can be fitted using the assumption of recombination due to distant pairs of electrons and holes trapped in localized band-tail states.

Paramagnetic defects in undoped microcrystalline silicon

“…However, an identification and location of the defects corresponding to the resonance contributions at 2.0052 and 2.0043 is not possible at present. The results from adsorption and oxidation studies [22,23], from studies on doped [15,42] and electron bombarded material [9] strongly suggest that there are really two independent resonances at 2.0043 and 2.0052 and not, as was suggested [27,33] and as one could expect in a polycrystalline material, a single resonance with an anisotropic g-tensor.…”

“…A further interesting observation is the fact, that material which is still prepared with high hydrogen dilution of the silane process gas, but which shows already a complete amorphous signature in Raman spectroscopy, does not show the typical amorphous silicon (a-Si:H) dangling bond resonance at g = 2.0055 but a slightly lower gvalue of 2.0052. Attempts for more analytical descriptions of the experimental results [27,33] have been made. However, in view of conflicting experimental results, the validity of these interpretations remains questionable.…”

Electrical detection of electron spin resonance in microcrystalline silicon pin solar cells

“…In intrinsic and n-doped µc-Si:H an ESR resonance at g = 1.997 − 1.998 is reported in various studies which is associated with shallow localised states in energetic proximity to the conduction band, typically referred to as CE states [2,[19][20][21][22][23]. It was demonstrated by cw-and pEDMR measurements on µc-Si:H films that these states are involved in hopping transport at low temperatures as well as in tunnelling recombination between CE and dangling bond states [3,22].…”

Innovative Characterization of Amorphous and Thin-Film Silicon for Improved Module Performance: 1 February 2005 - 31 July 2008

“…Figure 24 shows the comparison of the lineshapes of the ESR signals in H-effused and crystallized samples to that in a typical a-Si:H sample. In trace (a), which is from a typical aSi:H sample, the peak-to-peak width is about 7 G. Trace (b) is from the sample in the H-effused state before crystallization, the line-width is about 5 G. The line-width of the crystallized sample (6.5 G) is much smaller than previously reported values in micro-crystalline silicon (µc-Si:H) samples [77,78,79]. The lineshape changes can be attributed to exchange-narrowing that is well known for high defect density films [80].…”