Direct MOVPE‐ and MBE‐growth of a‐plane GaN on r‐plane sapphire

Abstract

We report on the growth of pit‐free a‐plane GaN on (1$ \bar 1 $02) sapphire (r‐plane) substrates by metal organic vapor phase epitaxy (MOVPE) using a three step growth method without low temperature nucleation layer. X‐ray diffraction ω ‐scans of the symmetric GaN (11‐20) reflex revealed for 1.2 μm thick crack‐ and pit‐free GaN layers low FWHM of 885 arcsec and 2484 arcsec measured by inclination in c‐ and m‐direction, respectively. To analyze the evolution growth was stopped at different stages and the samples were measured with AFM, SEM, and XRD. Furthermore, we discuss the overgrowth of MOVPE GaN layer with molecular beam epitaxy (MBE). For smooth MOVPE templates with closed surfaces the morphology was reproduced, whereas for not coalesced thinner layers a different growth mode and a smoothening of the layers occurred. We will discuss SEM‐ and AFMdata in detail to examine this overgrowth procedure. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Catalyst free self‐organized grown high‐quality GaN nanorods

“…1(a)-(c). In a first step, r-plane sapphire substrates were nitridated in a Thomas Swan 3 Â 2 00 close coupled vertical showerhead reactor, using a mixed NH 3 /H 2 ambient with a ratio of 1:1 at 1323 K [13]. Afterwards, for some samples, GaN islands ( Fig.…”

TEM characterization of catalyst- and mask-free grown GaN nanorods

“…The origin of the nanorods appears to be within the a-plane GaN layer, but could also be at the a-plane GaN/sapphire interface as proposed by Aschenbrenner et al [10]. Due to TEM specimen preparation parts of the nanorods may be truncated in such a way that the origin of the rods is outside of the TEM specimen.…”

“…Figure 3 shows a STEM micrograph of the structure after the overgrowth. From a first inspection one can see that the sapphire substrate is covered by a smooth layer of GaN [10], on which the nanorods are visible. From diffraction patterns we found that the layer was a-plane GaN, as one can expect from growth on r-plane sapphire.…”

“…The r-plane sapphire substrates were nitridated in a Thomas Swan vertical shower head reactor using a mixed NH 3 /H 2 ambient with a ratio of 1:1 at 1050 °C [10] and overgrown with a thin GaN layer. In a second step the nitridated substrates were transferred to a molecular beam epitaxy (MBE) reactor and the nanorods were grown at a temperature of 830 °C with a background pressure of 1.3·10 -4 Pa and 6·10 -5 Pa of the N and Ga flux, respectively.…”

“…In contrast, Aschenbrenner et al [9] recently showed that highly ordered nanorods can be achieved by growth on nitridated rplane sapphire substrates. In this paper, we report on the structural characterization of the catalyst-free grown GaN nanorods of Aschenbrenner et al [9,10] using transmission electron microscopy (TEM) and related techniques. We determine the epitaxial relationship between the GaN nanorods with the …”