Understanding the Potential and Limitations of Dilute Nitride Alloys for Solar Cells (original) (raw)
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Dilute nitride GaInNAs and GaInNAsSb for solar cell applications
The dilute nitride GaInNAs(Sb) alloy system is challenging to grow and defects can cause short diffusion lengths and high background doping densities. Despite these difficulties, extremely high cell efficiencies have recently been achieved in multi-junction solar cells utilising 1 eV GaInNAs absorber layers. This study aims to highlight the trade-offs between the electrical and optical characteristics related to the performance of GaInNAs(Sb) diode structures grown by molecular beam epitaxy , with band gaps ranging from 0.90 to 1.04 eV. Post-growth annealing was necessary in some instances to reduce the background doping and dark current densities. The incorporation of Sb into GaInNAs has enabled the possibility of producing a dilute nitride cell with a band gap lower than 0.80 eV, although with an increased dark current.
Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, 2016
Dilute-nitride GaAsNx epilayers were grown on GaAs (001) substrates at temperatures of ∼450 °C using a radio-frequency plasma-assisted molecular/chemical beam exitaxy system. The concentration of nitrogen incorporated into the films was varied in the range between 0.01 and 0.04. High-resolution electron microscopy was used to determine the cross-sectional morphology of the epilayers, and Z-contrast imaging showed that the incorporated nitrogen was primarily interstitial. {110}-oriented microcracks, which resulted in strain relaxation, were observed in the sample with the highest N concentration ([N] ∼ 3.7%). Additionally, Z-contrast imaging indicated the formation of a thin, high-N quantum-well-like layer associated with initial ignition of the N-plasma. Significant N contamination of the GaAs barrier layers was observed in all samples, and could severely affect the carrier extraction and transport properties in future targeted devices. Dilute-nitride quantum-well-based photovoltaic...
Using large (500-1000 atoms) pseudopotential supercell calculations, we have investigated the effects of atomic short-range order SRO on the electronic and optical properties of dilute and concentrated GaAsN, GaInN, and GaInAs alloys. We find that in concentrated alloys the clustering of like atoms in the first neighbor fcc shell e.g., N-N in GaAsN alloys leads to a large decrease of both the band-gap and the valence-to-conduction dipole transition-matrix element in GaAsN and in GaInN. On the other hand, the optical properties of GaInAs depend only weakly on the atomic SRO. The reason that the nitride alloys are affected strongly by SRO while GaInAs is affected to a much lesser extent is that in the former case there are band-edge wave-function localizations around specific atoms in the concentrated random alloys. The property for such local-ization is already evident at the dilute isolated impurity and impurity-pair limits.
Structural Characterization of Doped Thick Gainnas Layers - Ambiguities and Challenges
Journal of Electrical Engineering, 2014
GaInNAs alloys are mostly used as an active part of light sources for long wavelength telecom applications. Beside this, these materials are used as thin quantum wells (QWs), and a need is to grow thick layers of such semiconductor alloys for photodetectors and photovoltaic cells applications. However, structural characterization of the GaInNAs layers is hindered by non-homogeneity of the In and N distributions along the layer. In this work the challenges of the structural characterization of doped thick GaInNAs layers grown by atmospheric pressure metalorganic vapour phase epitaxy (APMOVPE) will be presented