Formation Mechanism of Nanotubes in GaN

Liliental‐Weber, Z.; Chen, Yinwei; Ruvimov, S.; Washburn, J.

doi:10.1103/physrevlett.79.2835

Cited by 315 publications

(97 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…2(a) GaN was cooled from elevated temperatures, the previously empty cores were filled with liquid Ga which then reacted with gaseous nitrogen to form GaN [12]. This result could also be consistent with the pinholes observed by Liliental-Weber et al where the dislocation is observed to open and close during growth [13].…”

supporting

confidence: 79%

Role of Oxygen at Screw Dislocations in GaN

2003

View full text Add to dashboard Cite

Here we report the first direct atomic scale experimental observations of oxygen segregation to screw dislocations in GaN using correlated techniques in the scanning transmission electron microscope. The amount of oxygen present in each of the three distinct types of screw dislocation core is found to depend on the evolution and structure of the core, and thus gives rise to a varying concentration of localized states in the band-gap. Contrary to previous theoretical predictions, the substitution of oxygen for nitrogen is observed to extend over many monolayers for the open core dislocation. 1In recent years, GaN has developed into an important semiconductor for optical and electronic applications. However, due to a large lattice mismatch with the substrate, the material possesses an overall high density of threading dislocations. While efforts have been made to reduce dislocation density, the remaining dislocations still play an important role in device performance, one that is still not well understood. The previous work of Nakamura and others in fabricating GaN-based blue and green light emitting diodes (LED's) and commercializing nitride laser diodes [1,2] has proven functionality for GaN devices irrespective of impurities and dislocations, but an explanation of changes in device performance and efficiency over time is still pending. In fact, most purely intrinsic dislocations appear not to be related to device failure [3,4]. It therefore appears that the interaction of dislocations with impurities, and in particular, oxygen, may create impurity states in the band gap, act as traps for carriers, and could prove to be one of the key sources of device breakdown.Oxygen is an impurity that is known to be present in GaN thin films. However, as there exist only a few experimental studies of oxygen in GaN, the fundamental origin and role of the oxygen in determining the overall electronic characteristics of the films is poorly understood. For example, it has been suggested that oxygen in GaN may originate as an impurity in the NH 3 precursor for metal organic chemical vapor deposition A further complication to understanding the complex role of oxygen is how it interacts with the abundant dislocation cores in GaN, and whether the combination of impurity plus dislocation produces either a deleterious or benign effect. In this letter,we address the issue of impurity segregation to one of the three types of dislocations in GaN, the screw dislocation. More specifically, we provide direct experimental observations on the segregation of oxygen to three variants of screw dislocations: open core, filled core, and full core, and its effect on the electronic structure. These measurements provide evidence in favor of the interaction of oxygen with screw dislocations providing the origin of localized states at the cores.The experimental techniques used in this analysis are Z-contrast imaging and electron energy loss spectroscopy (EELS) performed in a JEOL 2010F 200kV scanning transmission electron microscope (STEM) [10]. In a Z-...

show abstract

supporting

confidence: 79%

Role of Oxygen at Screw Dislocations in GaN

2003

View full text Add to dashboard Cite

show abstract

“…The density of these defects was estimated to be in the range of 10 5 -10 7 cm -2 and their radii in the range 3-1500 nm. It was suggested (Liliental-Weber et al, 1997a;1997b) that these two types of defects are related to the presence of impurities in the material, supporting theoretical work by Elsner et al, (1998) who showed that O and O-related defect complexes can be formed on the walls of nanopipes in GaN. Cherns et al, (2000) suggested that nanopipes form under non-equilibrium conditions and are influenced by growth factors.…”

Section: Introductionsupporting

confidence: 49%

Screw Dislocations in GaN Grown by Different Methods

et al. 2004

Self Cite

View full text Add to dashboard Cite

A study of screw dislocations in Hydride-Vapor-Phase-Epitaxy (HVPE) template and Molecular-Beam-Epitaxy (MBE) over-layers was performed using Transmission Electron Microscopy (TEM) in plan-view and in cross-section. It was observed that screw dislocations in the HVPE layers were decorated by small voids arranged along the screw axis. However, no voids were observed along screw dislocations in MBE overlayers. This was true both for MBE samples grown under Ga-lean and Ga-rich conditions. Dislocation core structures have been studied in these samples in the plan-view configuration. These experiments were supported by image simulation using the most recent models. A direct reconstruction of the phase and amplitude of the scattered electron wave from a focal series of high-resolution images was applied. It was shown that the core structures of screw dislocations in the studied materials were filled. The filed dislocation cores in an MBE samples were stoichiometric. However, in HVPE materials, single atomic columns show substantial differences in intensities and might indicate the possibility of higher Ga concentration in the core than in the matrix. A much lower intensity of the atomic column at the tip of the void was observed. This might suggest presence of lighter elements, such as oxygen, responsible for their formation.

show abstract

“…2 Investigations have revealed many interesting features of epitaxial In x Ga 1Ϫx N films including compositional fluctuations, 3 chemical ordering, 4 surfactant behavior, 5 and the formation of a unique defect, the inverted hexagonal pyramid defect. [6][7][8][9][10] To understand and eventually gain control over these phenomena, which directly affect the optoelectronic properties of the material, it is essential to know how In interacts with the surface of the growing film. In this article we present theoretical studies to determine the behavior of In on GaN surfaces.…”

Section: Fritz-haber-institut Der Max-planck-gesellschaft Faradaywegmentioning

confidence: 99%