Nanocrystal Formation in Silicon Oxy-Nitride Films for Photovoltaic Applications: Optical and Electrical Properties

Abstract

Thin films of nanocrystalline SiO x N y are studied in view of their application in silicon heterojunction (SHJ) solar cells. In particular, the formation of the nanocrystals and their effects on the electrical and optical properties of the films are investigated. The role of the oxygen content on the properties of the layers is clarified as well. The obtained layers show very high conductivity (44 S/cm), low activation energy (1.85 meV) and high Tauc gap (2.5 eV), promising features for their application in photovoltaics.

Formation of high conductive nano-crystalline silicon embedded in amorphous silicon-carbide films with large optical band gap

“…5(b) that the sample becomes more transparent after annealing. It has been reported that optical band gap is enlarged after annealing in B-doped nc-SiO x N y films, 13 which was explained as the contribution both from the quantum confinement effects and the increased amount of SiO x composition due to formation of Si nano-crystals. In our previous work, we also found that the existence of grain boundary after annealing can influence the optical band gap obviously.…”

“…As shown in Fig. 7, when doping ratio R is lower than 0.6, the relationship between dark conductivity σ and the temperature T can be well described as the formula, which usually used to describe the transport process in micro-crystalline and nano-crystalline Si-based materials: 13,28 …”

“…However, the SiC matrix with a large band gap usually has a poor conductive property and in turn impedes the carrier transport process which will deteriorate the device performance. 13,14 Lechner et al fabricated the doped nc-Si films and they obtained the maximum conductivity up to about 5 S/cm with the very small conductivity activation energy. 15 From the view point of device application, it is highly desired to get nc-Si:SiC films with high conductivity at the suitable optical band gap (>2.5 eV) so that they can act as the window layer or the conductive layer in nano-crystalline SiC film-based optoelectronic devices without absorbing incident (or emitted) light too much.…”

“…15 From the view point of device application, it is highly desired to get nc-Si:SiC films with high conductivity at the suitable optical band gap (>2.5 eV) so that they can act as the window layer or the conductive layer in nano-crystalline SiC film-based optoelectronic devices without absorbing incident (or emitted) light too much. 13,16 In our previous work, hydrogenated amorphous silicon carbide (a-SiC:H) films were prepared in a plasma-enhanced chemical vapor deposition (PECVD) system. Nc-Si:SiC films were fabricated after annealing at 900 • C and 1000 • C. It was found that for samples annealed at 1000 • C, the average size of nc-Si is 9 nm and the crystallinity is reached to 70 %.…”

Annealing effects on SiOxNy thin films: Optical and morphological properties

“…Due to coexistence of different phases and compositions upon annealing, the structure and the formation of SiO x N y together with the role of crystalline fraction and oxygen content in changing optical and electrical properties are still unclear. The dependence of conductivity and optical band gap from oxygen content has been investigated only recently in amorphous and annealed SiO x N y [2,16,[20][21][22].…”