Electron microscopy investigation of extended defects in a‐plane gallium nitride layers grown on r‐plane sapphire by molecular beam epitaxy

Abstract

The interfacial structure and extended defects in a‐plane (1120)‐oriented GaN layers are investigated using conventional and high resolution transmission electron microscopy (HRTEM). The a‐plane GaN epilayers have been grown by nitrogen rf plasma source molecular beam epitaxy (RFMBE) on r‐plane sapphire substrates, which have been nitrided either at 200 °C or at 800 °C for one hour. A thin interfacial layer of strained AlN, with an average thickness of about 1 nm, was formed during nitridation of the sapphire surface at both temperatures. The extended defects observed in the GaN layers are predominantly threading dislocations and basal stacking faults (BSFs), which originate from the GaN/sapphire interface. The threading dislocation density is slightly reduced in the film nitrided at 800 °C, as is the density of inversion domains, although stacking fault density does not appear to change with nitridation conditions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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

“…The tilt angle as reported by many other groups is 58.9° [17,18]. The knowledge of the sap- Photoluminescence spectra of [11][12][13][14][15][16][17][18][19][20][21][22] inclined intertwined GaN nanorods on m-plane sapphire. The left-hand side shows the schematic variation in the incidence area, when the specimen is rotated through 0 to 360°in steps of 90°.…”

“…This can reduce the mismatch between the a-plane GaN epilayer and the r-plane sapphire substrates due to the misfit dislocations. Similar to the case of Nitridation in c- plane sapphire, here also, a parasitic semipolar (103) nanocrystals are formed, which is really a side effect [15,16]. The epitaxial relationship is given as 1 120 ½ nÀGaN k 1 102 ½ Sap and 1 100 ½ GaN k 1 120 ½ Sap .…”

Interfacial structure of semipolar AlN grown on m -plane sapphire by MBE

“…4(b). Figure 4(c) shows a brighter N‐rich interfacial zone of thickness ∼2 ML that is characteristic of nitridated substrates 12, 13. This zone is formed due to the substitution of oxygen atoms by nitrogen atoms 14.…”

Effect of vicinal off-cut substrates on the basal stacking fault density in nonpolar a-GaN epilayers

“…BSFs and partial dislocations alter the electric and optical properties of GaN-based devices acting as carrier scattering centers by forming nonradiative centers within the band gap [7][8][9]. These carrier scattering and nonradiative recombination centers reduce the emission efficiency and cause a reduction in the lifetime of LED devices [7,10]. It was also reported that the BSFs in the c-GaN epilayers produced a donor-acceptor pair transition peak at 3.27 eV [9].…”

“…However, nonpolar GaN films still suffer from high densities of structural defects, such as basal stacking faults (BSFs) and partial dislocations, compared to the polar c-GaN films with high densities of threading dislocations [5,6]. BSFs and partial dislocations alter the electric and optical properties of GaN-based devices acting as carrier scattering centers by forming nonradiative centers within the band gap [7][8][9]. These carrier scattering and nonradiative recombination centers reduce the emission efficiency and cause a reduction in the lifetime of LED devices [7,10].…”