We report a study by photoluminescence (PL), Raman scattering, and highly resolved X‐ray diffraction (HRXRD) of a series of Si‐doped n‐type GaN layers grown by metalorganic vapor phase epitaxy (MOVPE) on sapphire (0001) with the carrier concentration of 2.3 × 1017 – 9 × 1018 cm–3. We found that the band gap reduction deduced from the PL spectra analysis is due to both band gap narrowing (BGN) effect and change of the nature of stress in the GaN:Si layers. The HRXRD spectra show that at high Si‐doping levels (>1.6 × 1018 cm–3) the GaN films become under tensile stress. Progressive decreases of the E2 Raman mode frequency with Si concentration confirm this observation. The stress induced E2 mode frequency shift is estimated to 1.6 cm–1/GPa. Additionally, dislocation densities are determined by HRXRD by employing a model that uses the line width of X‐ray rocking curves. Atomic force microscopy (AFM) is also used to investigate the defect surface structures of GaN:Si layers which are dominated by pinned steps and surface depressions related to threading dislocations. We find that dislocation densities given by AFM measurements are in agreement with those obtained from rocking curve line widths. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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This paper describes an investigation, by using numerical simulation, into the impacts of i-nc-Si : H buffer layer band gap on the photovoltaic parameters of n-i-p hydrogenated nanocrystalline silicon (nc-Si : H) solar cells. The output external cell parameters, like, the short-circuit current (JSC), the open circuit voltage (VOC), the fill factor (FF) and efficiency (Eff) are simulated by varying the mobility band gap (Eg) of i-nc-Si : H buffer layer. Also, the band diagram of nc-Si : H n-i-p solar cell, the electric field and the traped hole density at i/p interface, and the external quantum efficiency, with different values of buffer layer band gap where optimized. The simulation result shows that in valence band and for both interfaces, the band offsets ΔEV1 at p-nc-Si : H (window layer) / i-nc-Si : H (buffer layer) and ΔEV2 at i-nc-Si : H (buffer layer) / i-nc-Si : H (absorber layer) can be affected by varying Eg. It is obtained that the values efficiency are 10.89 % and 11.33 % when the value of i-nc-Si : H buffer layer band gap are 1.4 eV and 1.55 eV, respectively. However, the i-nc-Si : H buffer layer band gap of 1.55 eV was optimized for obtaining a better efficiency for n-i-p solar cell based on hydrogenated nanocrystalline silicon.