This paper reports the reduced-stress GaN epitaxial growth on Si (1 1 1) using a porous GaN interlayer which is formed from GaAs layer by a novel nitridation process. Initially a 2 μm thick GaAs layer is grown on a Si(1 1 1) substrate by MBE. Then, a GaN buffer layer of 20 nm thick is grown on the GaAs layer at 550°C in a MOVPE reactor. The GaAs layer capped with the GaN buffer layer is annealed in NH3 to 1000°C. Through this process, a porous GaN layer is formed beneath the GaN cap layer. An epitaxial GaN layer is grown on the GaN buffer layer at 1000°C in the MOVPE reactor. The epitaxial layer grown on the porous-GaN/Si(1 1 1) structure is found to have no cracks on the surface. In contrast, an epitaxial layer grown on the GaAs layer nitrated without a cap layer many cracks are found in the epilayer and the layer is sometimes peeled off from the substrate. It is found that the surface morphology of the GaN/porous-GaN/Si(1 1 1) sample is markedly improved by employing a 40 nm-thick interlayer grown at 800°C in addition to the above processes. A PL spectrum with a high intensity ratio between the excitonic emission and the deep yellow emission is obtained for the GaN/porous-GaN/Si(1 1 1) sample. E2 peak position in Raman scattering spectrum also shows a reduced stress for the GaN epilayers grown on the porous-GaN/Si(1 1 1).
Currently single junction Si solar photovoltaic limitation and scope of Si hetero-junction cell has driven research towards advanced solar cell. Successful absorption of high energy band and its apposite photonic conversion by high band gap Si nanostructure favors to minimize thermalization and carrier recombination problem thus progress efficiency significantly. Inclusion of indium molar fraction in GaN and its variance for wide band gap III-Ns (InGaN/GaN) on Si cell considerably improves opto-electric properties. Theoretically series model is revealed by novel approach to realize current density matching in III-N/Si hetero-junction tandem cell that has potential to moderate the tunneling difficulty. Hence, cutting edge surface processing techniques to improve the photonic properties of Si and InGaN nanostructures on Si cell have been reviewed comprehensively. Simulated and practical efficiency of different nanostructures have been investigated to analyze the practical efficiency limiting issues. Finally, key materials absorption edge, drift velocity, efficiency progress and present market share related utilization factor have been addressed.
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