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Dependence of carbon doping concentration on the strain-state and properties was studied in detail for the GaN on Si system. Combining the results of XRD and Raman spectra, it is found that compressive stress is introduced into the GaN with a moderate carbon concentration, while it turns into tensile stress when the carbon concentration is higher than a critical point. A possible mechanism is that the carbon tend to replace the N atom in GaN at a relative lower carbon concentration because of the relatively smaller formation energy, while it turned to replace the Ga atom after the carbon concentration is higher than a critical level. Those results are also confirmed by the photoluminescence spectrum. [ABSTRACT FROM AUTHOR]

The influence of AlN/GaN superlattices (SL) buffer on the characteristics of AlGaN/GaN-on-Si (1 1 1) template was studied in detail. There existed an optimized Relative AlN Thickness (RAT) in the superlattices buffer which can not only further filtering the edge- and screw-type dislocations to the upper epilayer and lead to a good crystal quality with narrowest (0 0 0 2) and (1 0 −1 2) full width of half maximum (FWHMs), 439″ and 843″, but also improve the surface roughness to enhance the Two dimensional electron gas (2DEG) mobility and superior electrical properties were achieved. Moreover, an optimized RAT in SL can induce a proper compressive stress to the subsequently grown GaN epilayer and protect it from crack during the cooling step, which can also lead to a better wafer bending. [ABSTRACT FROM AUTHOR]