The effect of variation in hydrogen dilution and RF power density on the properties of a-SiGe:H and related solar cells

Abstract

The effect of systematic variation in hydrogen dilution and RF power density on the different properties (such as optoelectronic and structural properties and defect density) of hydrogenated amorphous silicon germanium alloy (a-SiGe:H) films, prepared at ultra-high vacuum () in a plasma-enhanced chemical vapour deposition multichamber system with a load - lock facility has been studied. Proper structural relaxation of the alloy matrix is controlled by the growth zone reactions. These grown zone reactions depend on the type and number density of reactive radicals and on their energy and momentum. All these factors, hence growth zone reactions, may be changed by variation of the interlinked parameters hydrogen dilution and RF power density. Another noteworthy point is the investigation of the dependence of the improvement in characteristics of single junction solar cells having a-SiGe:H intrinsic layers on that of material quality. Improvement of material quality may or may not be reflected in cell performances.

Improvement of a-Si1−xGex:H single-junction thin-film solar cell performance by bandgap profiling techniques

“…enhanced the surface mobility of the precursors and induced etching effect which selectively etched the undesirable bonding as observed from the reduction in deposition rate [12]. The smaller deposition rate also assisted the atomic relaxation [11]. As a result, the bonding of Ge related species might be strengthened which resulted in a better resistance to the H etching, thereby increased the film Ge content.…”

“…1, the increase in H 2 dilution ratio increased the film Ge content in different R. The mechanism of H 2 on film Ge content is still not well understood. One possibility is that H 2 may shift the gas phase reaction from the formation of dihydride/polyhydride precursors to the formation of trihydride precursors [11]. The GeH 3 precursors had longer lifetime at the growing surface which enabled them to bond in the lower free energy sites.…”

High‐performance a‐SiGe:H thin film prepared by plasma‐enhanced chemical vapor deposition with high plasma power for solar‐cell application

“…The increase of the plasma power increases the average energy of the electrons in the plasma and thus enhances the dissociation cross sections of silane and germane into neutral as well as ionic radicals. Besides, the increasing plasma power transfers high momentum and energy to the precursors in the growing surface, and promotes the surface diffusion of the reactive radicals 3, 15, 16. All these lead to the above growth‐rate enhancement.…”

“…The increased plasma power also transfers high momentum and energy to the precursors in the growing surface, and promotes the surface diffusion of the reactive radicals, especially intrinsically heavy sticky radicals. So the proper structural relaxation in the growing film takes place, the excess hydrogen atoms are eliminated effectively from the surface and the microstructure of the alloy film improves 15, 16. However, excess energy transfer in the growing surface can disturb the network formation, and consequently increase the tail‐state carrier density and dangling‐bond density owing to high ion bombardment damage.…”

Optimization ofμc-Si1−xGex:H Single-Junction Solar Cells with Enhanced Spectral Response and Improved Film Quality

“…As RF power was less than 80 W, the GeH bonding was absent. This result suggested that sufficient power is beneficial in providing energy for structure relaxation of Ge-related precursors [38]. A lower RF power for c-Si 1−x Ge x :H growth provided less energy to the precursors and shortened the diffusion lengths for the precursors, especially in sticky Ge-related precursors.…”