Influences of hydrogen dilution on microstructure and optical absorption characteristics of nc-SiO_x:H film

By using the plasma enhanced chemical vapor deposition（PECVD） technique, amorphous silicon oxide films containing nanocrystalline silicon grain（nc-Si O x：H） are deposited, and the bonding configurations and optical absorption properties of the films are investigated. The grain size can be well controlled by varying the hydrogen and oxygen content,and the largest size is obtained when the hydrogen dilution ratio R is 33. The results show that the crystallinity and the grain size of the film first increased and then decreased as R increased. The highest degree of crystallinity is obtained at R = 30.The analyses of bonding characteristics and light absorption characteristics show that the incorporation of hydrogen leads to an increase of overall bonding oxygen content in the film, and the film porosity first increases and then decreases. When R = 30, the film can be more compact, the optical absorption edge of the film is blue shifted, and the film has a lower activation energy.

Influence of substrate bias voltage on the microstructure of nc-SiO_x:H film

Amorphous silicon oxide containing nanocrystalline silicon grain（nc-SiOx：H） films are prepared by a plasmaenhanced chemical vapor deposition technique at different negative substrate bias voltages.The influence of the bias voltage applied to the substrate on the microstructure is investigated.The analysis of x-ray diffraction spectra evidences the in situ growth of nanocrystalline Si.The grain size can be well controlled by varying the substrate bias voltage,and the largest size is obtained at 60 V.Fourier transform infrared spectra studies on the microstructure evolutions of the nc-SiOx：H films suggest that the absorption peak intensities,which are related to the defect densities,can be well controlled.It can be attributed to the fact that the negative bias voltage provides a useful way to change the energies of the particles in the deposition process,which can provide sufficient driving force for the diffusion and movement for the species on the growing surface and effectively passivate the dangling bonds.Also the larger grain size and lower band gap,which will result in better photosensitivity,can also be obtained with a moderate substrate bias voltage of 60 V.

Microstructure and lateral conductivity control of hydrogenated nanocrystalline silicon oxide and its application in a-Si：H/a-SiGe：H tandem solar cells

Phosphorous-doped hydrogenated nanocrystalline silicon oxide （n-nc-SiOx：H） films are prepared via radio frequency plasma enhanced chemical vapor deposition （RF-PECVD）. Increasing deposition power during n-nc-SiOx：H film growth process can enhance the formation of nanocrystalline and obtain a uniform microstructure of n-nc-SiOx：H film. In addition, in 20s interval before increasing the deposition power, high density small grains are formed in amorphous SiOx matrix with higher crystalline volume fraction （Ic） and have a lower lateral conductivity. This uniform microstructure indicates that the higher Ic can leads to better vertical conductivity, lower refractive index, wider optical band-gap. It improves the back reflection in a-Si：H/a-SiGe：H tandem solar cells acting as an n-nc-SiOx：H back reflector prepared by the gradient power during deposition. Compared with the sample with SiOx back reflector, with a constant power used in deposition process, the sample with gradient power SiOx back reflector can enhance the total short-circuit current density （Jsc） and the initial efficiency of a-Si：H/a-SiGe：H tandem solar cells by 8.3% and 15.5%, respectively.