HVPE growth of self-aligned GaN nanorods on c-plane, a-plane, r-plane, and m-plane sapphire wafers

Abstract

Herein, we report the self-aligned growth of GaN nanorods on different orientations of sapphire like c-, a-, rand m-plane substrates by hydride vapor phase epitaxy. Vertical c-axis orientation of GaN NRs is obtained on c-plane [0001] and a-plane 11 20 ½ sapphire and a skew or inclined NRs on r-plane, and inclined intertwined but self-aligned NR array was formed on m-plane sapphire. GaN (002) and (004) peaks were obtained on c-and a-plane sapphire, whereas (110), (103), and (103) only were observed on r-and mplanes, respectively. In the case of r-and m-plane-grown GaN, A 1 transverse optical mode is dominant, and the A 1 longitudinal optical mode is suppressed. Conversely, in the case of c-and a-plane, it is reversed. The probable reason is the optical mode vibrations difference along the differently inclined NRs surfaces. In addition, the specimen exhibits surface optical modes too. The optical behavior of GaN NR on m-sapphire shows an intensity variation when measured in different angular rotations of the specimen by photoluminescence which is because of the higher area of excitation in the case of axial surfaces and lower area of excitation in radial surface. Their epitaxial crystallographic relationship with the substrates and the reasons for the self-aligned orientations are discussed. The anomalies found in the optical behavior are attributed to Raman antenna effect and so on. The self-aligned intertwined GaN NRs find suitable applications in polarizer.

Inhomogeneity-mediated systematic reduction of the Schottky barrier in a Au/GaN nanorod film interface

“…The angle between the grown nanorods and the substrate has been approximated with the help of crosssection SEM images (figure 4, Nano1). When the sample is seen perpendicular to the [0002] azimuth direction, it can be inferred from the cross-section SEM images (figures 3 and 4) that the nanorods have an inclination of around 60 • , which is consistent with the previous reports when similar attempts were made on r-plane Al 2 O 3 [39,41,42,48,54,55]. It should also be noted that in some of the SEM images the angle between the nanorods and the thin film does not appear exactly as ∼60 • as it depends on the line of sight of the SEM.…”

“…One of the plausible solutions to this problem is the introduction of nanostructures at the top of the thin film without breaking the growth process; this would induce a type of inhomogeneity by altering the topography significantly. The use of nanostructures for this purpose looks very promising because of their extremely low defect densities, selection of wide variety substrates (as they can be grown on epitaxially mismatched substrates very easily), very high carrier mobility, etc [39][40][41][42][43][44]. Thus the combination of thin films and nanostructures is very compelling to make Ohmic devices with high-quality metal electrodes which show Schottky behavior otherwise.…”

Electronic Transport Mechanism for Schottky Diodes Formed by Au/HVPE a-Plane GaN Templates Grown via In Situ GaN Nanodot Formation

“…Nonpolar GaN-based electronic devices, including high-electron-mobility transistors (HEMT), Schottky diodes, and metal–oxide–semiconductor field-effect transistor (MOSFET) sensors have been investigated to achieve enhanced performance such as enhancement mode (normally-off), temperature-stable characteristics with less pronounced hysteresis, and high sensitivity [ 3 , 4 , 5 , 6 ]. Due to the lack of native bulk GaN, researchers have been investigating the growth of a-plane GaN with improved structural properties grown on foreign substrates, using metal organic vapor phase epitaxy (MOCVD), molecular beam epitaxy (MBE), or hydride vapor phase epitaxy (HVPE) [ 7 , 8 , 9 , 10 ]. Among these methods, HVPE nonpolar a-plane GaN templates have attracted considerable attention for their high throughput and relatively good crystal quality, and in view of their efficient and effective commercial advantages [ 11 , 12 ].…”

Growth of GaN micro/nanolaser arrays by chemical vapor deposition

“…For the construction of GaN micro/nanolaser arrays, the substrates have a significant influence on epitaxial quality. So far, Si [11], GaN [12], LiAlO 2 [13], graphene [3], and sapphire [14] substrates have been utilized for growing GaN nanowire arrays. Meanwhile, chemical vapor deposition (CVD) with a vaporsolid (VS) [15] process is the most generally utilized method to grow micro/nanowires due to its relatively low cost and facile procedure, in comparison with other methods, e.g.…”