Inversion Domain Boundaries In GaN Research Articles

Towards simulation at picometer-scale resolution: Revisiting inversion domain boundaries in GaN

Motivated by recent high resolution results on the inversion domain boundaries (IDB) in gallium nitride, we refine by ab initio DFT calculations the well established atomic model ${\mathrm{IDB}}^{*}$ derived by Northrup et al. This allows us to recover these experimental results obtained by coherent x-ray diffraction and showing small additional shifts of the polarity domains, in particular 8 pm shift along the hexagonal direction. The influence of boundary conditions and electrostatic fields (IDB-IDB and IDB-surface interactions) on the results and the existence of metastable solutions is carefully discussed to stress the accuracy of the method. These results demonstrate a cross-talk between advanced characterization tools and state-of-the-art ab initio calculations that opens perspectives for the structural analysis of defects in the picometer range.

The structure of InAlGaN layers grown by metal organic vapour phase epitaxy: effects of threading dislocations and inversion domains from the GaN template.

Defects in quaternary InAlGaN barriers and their effects on crystalline quality and surface morphology have been studied. In addition to growth conditions, the quality of the GaN template may play an important role in the formation of defects in the barrier. Therefore, this work is focused on effects caused by threading dislocations (TDs) and inversion domains (IDs) originating from the underlying GaN. The effects are observed on the crystalline quality of the barrier and characteristic surface morphologies. Each type of TDs is shown to affect the surface morphology in a different way. Depending on the size of the corresponding hillock for a given pinhole, it was possible to determine the dislocation type. It is pointed out that the smallest pinholes are not connected to TDs whereas the large ones terminate either mixed type or edge type TDs. At sufficiently large layer thickness, the IDs originating from the GaN template lead to the formation of concentric trenches at the layer surface, and this is related to the change in growth kinetics on top and at the immediate surroundings of the ID.

Inversion Domain Boundaries in GaN Wires Revealed by Coherent Bragg Imaging.

Interfaces between polarity domains in nitride semiconductors, the so-called Inversion Domain Boundaries (IDB), have been widely described, both theoretically and experimentally, as perfect interfaces (without dislocations and vacancies). Although ideal planar IDBs are well documented, the understanding of their configurations and interactions inside crystals relies on perfect-interface assumptions. Here, we report on the microscopic configuration of IDBs inside n-doped gallium nitride wires revealed by coherent X-ray Bragg imaging. Complex IDB configurations are evidenced with 6 nm resolution and the absolute polarity of each domain is unambiguously identified. Picoscale displacements along and across the wire are directly extracted from several Bragg reflections using phase retrieval algorithms, revealing rigid relative displacements of the domains and the absence of microscopic strain away from the IDBs. More generally, this method offers an accurate inner view of the displacements and strain of interacting defects inside small crystals that may alter optoelectronic properties of semiconductor devices.

Pyramidal inversion domain boundaries revisited

The structure of pyramidal inversion domain boundaries in GaN:Mg was investigated by aberration corrected transmission electron microscopy. The analysis shows the upper (0001) boundary to consist of a single Mg layer inserted between polarity inverted GaN layers in an abcab stacking. The Mg bound in these defects is at least one order of magnitude lower than the chemical Mg concentration. Temperature dependent Hall effect measurements show that up to 27% of the Mg acceptors is electrically compensated.

Inversion domain boundaries in GaN studied by X‐ray microprobe

AbstractIn this study, we report on the application of synchrotron spectro‐microscopic techniques to the examination of inversion domain boundaries formed intentionally in a GaN‐based lateral polarity heterostructure. Using X‐ray sub‐microbeams, no evidence of field‐driven electrodiffusion effects has been observed on spatially separated inversion domain boundaries. In addition, XANES data around the Ga K‐edge strongly supported hexagonal Ga site configurations, suggesting high local order reconstruction. Based on inner‐shell excited luminescence on the micrometer scale, the uniform spectral distribution of the radiative centers was discussed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnesium incorporation at (0001) inversion domain boundaries in GaN

First-principles pseudopotential density functional calculations have been performed for Mg-rich inversion domain boundaries that form on (0001) planes in GaN. These types of boundaries separate inverted material from the host matrix in the pyramidal inversion domain defects reported to exist in heavily Mg-doped GaN. The model of the boundary proposed on the basis of these total energy calculations exhibits GaNMgNGa layers that are stacked in abcab registry, with at least 3/4 of the available c sites occupied by Mg atoms. An additional 1/4 monolayer of Mg can be incorporated in this layer provided additional compensating Mg acceptors are located nearby. A significant fraction of the Mg present in heavily doped material may reside in these boundaries.

Origin of the efficient light emission from inversion domain boundaries in GaN

Intentionally produced inversion domain boundaries in GaN have been reported to be highly efficient shallow recombination centers. This letter report a rationale for this phenomenon based on ab initio density-functional calculations. A model is also proposed, based on the existence of polarization in GaN, of the observation that a domain boundary acts as a rectifying junction under voltage applied between the two opposite-polarity surfaces.

Interaction Between Basal Stacking Faults and Prismatic Inversion Domain Boundaries in GaN

ABSTRACTThe interaction of growth intrinsic stacking faults with inversion domain boundaries in GaN epitaxial layers is studied by high resolution electron microscopy. It is observed that stacking faults may mediate a structural transformation of inversion domain boundaries, from the low energy types, known as IDB boundaries, to the high energy ones, known as Holt-type boundaries. Such interactions may be attributed to the different growth rates of adjacent domains of inverse polarity.