Substrate-dependent wetting layer formation during GaN growth: Impact on the morphology of the films

Abstract

We have compared epitaxial growth of GaN films on 6H-SiC(0001)-(3×3)R30°−Ga and on (0001)-sapphire. Predeposited Ga layers were nitrided by ion beam assisted molecular beam epitaxy. Whereas on SiC the initially deposited Ga covers the substrate surface completely, on sapphire only Ga droplets are present. The different distribution of the predeposited Ga affects the morphology of GaN significantly. Scanning electron microscopy and atomic force microscopy analysis of the grown films show that the complete wetting of the SiC substrate with Ga enhances finally the size and the flatness of GaN terraces and thus the quality of the film. X-ray photoelectron spectroscopy measurements reveal that metallic Ga resides also on top of the GaN films during the growth.

Formation of GaN nanodots on Si (111) by droplet nitridation

“…4. This reactive spreading of Ga from droplets to form a rough layer in-between dots was also observed in the GaAs/Al 0.3 Ga 0.7 As system [9] and for GaN dots obtained from Ga droplets on sapphire [12]. However, further investigations will be necessary to elucidate completely the phenomena involved in droplet-induced GaN dot formation.…”

“…The detection limit of our technique does not allow evaluating the presence of an eventual metallic layer in between the droplets. Si-2p peak is almost suppressed for the nitridated samples and it seems that a redistribution of Ga has taken place, similar to GaN nucleation on SiC [12]. The N-1s peak gradually develops with increasing nitridation time.…”

“…Signals observed in an XPS spectrum at different energy positions correspond to different surface sensitivities. For example, the IMFP values of Ga-2p and Ga-3d in Ga during Mg-K a radiation are 0.63 and 2.7 nm, respectively, and for GaN, they are 0.55 and 2.2 nm, respectively [12]. It means that Ga-3d spectrum is bulk sensitive as compared to Ga-2p, which is surface sensitive.…”

Effect of etching with cysteamine assisted phosphoric acid on gallium nitride surface oxide formation

“…The Ga-Ga bonding is cited at 1116 eV, 42,43 the Ga-N bonding at 1117.5 eV, 44,45 and the gallium oxide at 1119 eV. 46,47 The deconvoluted peaks are limited to 60.5 eV of the respective binding energy to prevent peak overlapping.…”