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Ratio of the hexagonal-to-cubic GaN volume fractions determined by ellipsometric analysis for thin GaN layers grown on – and substrates pretreated differently.
(Color online) (a) AFM morphologies of GaN nucleation layers on – and substrates that underwent different treatments. Vertical scale is for and for . (b) Surface potential measured by electrical force microscopy (Kelvin-probe) for the – and substrates that underwent different treatments and for the corresponding GaN nucleation layer grown on them.
(Color online) (a) real time variation of the imaginary part of the pseudodielectric function recorded at during GaN nucleation on – (black curves) and (red curves) nitrided at 200 and . (b) Spectra of the real and imaginary part of the pseudodielectric function acquired at the end of curves in Fig. 2(a), when the nucleation layer is approximately , for nitrided at (black curve) and (red curve); features due to the GaN band gap and to Ga are indicated. (c) Pseudodielectric function of Ga clusters deposited on a sapphire substrate. (d) Pseudodielectric function of a GaN template.
(Color online) 3D plots of the real and imaginary part of the pseudodielectric function acquired during GaN growth; (a) is for the nucleation layer evolving to (b) which is a GaN film approximately thick. The inset indicates values of the evolution of the GaN thickness and of the corresponding Ga wetting layer.
FWHM of the symmetric (0002) and asymmetric (10–12) XRD reflections as a function of the – and treatments.
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