Inversion of wurtzite GaN(0001) by exposure to magnesium

Abstract

Magnesium incorporation during the molecular beam epitaxy growth of wurtzite GaN is found to invert the Ga-polar (0001) face to the N-polar face. The polarity is identified based on the two different sets of reconstructions seen on the film prior to and after about 1 monolayer Mg exposure. The inversion boundary is seen to lie on the (0001) plane from transmission electron microscopy images, and a structural model is presented for the inversion. On the Ga-polar face, Mg is also seen to stabilize growth in the N-rich regime.

Growth of p-type and n-type m-plane GaN by molecular beam epitaxy

“…1͑a͒, and are easily distinguishable from typical Ga-face 1 ϫ 1 and 2 ϫ 2 reconstructions. 7 It is possible to infer the presence of inversion domains from images of the sample surface taken ex situ with an atomic force microscope ͑AFM͒, especially if the sample has been exposed to an etchant that selectively etches N-face material. A typical example of this is shown in Fig.…”

“…7 These inversion domains are associated with sharp reduction in film conductivity. We have previously reported on our early measurements of p-type doping with Mg in PAMBE grown m-plane GaN, which show relatively high conductivity films compared to those realized by PAMBE growth of c-plane GaN.…”

Homoepitaxial growth of catalyst-free GaN wires on N-polar substrates

“…They were examined on a microscope operating at 300 12 This behavior tends to show that N-polar crystals favor the wire geometry formation with vertical sidewalls, while Ga-polar crystals present inclined facets that may limit the vertical extension and in some extent may lead to the formation of pyramidal geometry. The longitudinal change of polarity can not occur spontaneously during the crystal growth (except using heavily Mg-incorporation 15 ). Thus, the polarity of GaN crystal is probably imposed by the nucleation seeds, which are related to the surface state, i.e.…”

Molecular-beam epitaxy of p-type m-plane GaN

“…Plasma-assisted molecular-beam epitaxy ͑PAMBE͒-grown c-face GaN suffers from a second deleterious effect in that doping with the commonly used acceptor Mg at high concentrations or low III/V ratios often results in the formation of inversion domains that degrade the quality of the crystal. 5 Since the c axis is oriented in the growth plane, inversion should not occur for planar growth of an m-plane film. Nonpolar GaN, therefore, is an obvious choice for a route to high-quality relatively highly doped p GaN.…”