Modulation of Electrical Conductivity and Lattice Distortions in Bulk HVPE-Grown GaN

Abstract

The nature of self-organized three-dimensional structured architectures with spatially modulated electrical conductivity emerging in the process of hydride vapor phase epitaxial growth of single crystalline n-GaN wafers is revealed by photoelectrochemical etching. The amplitude of the carrier concentration modulation throughout the sample is derived from photoluminescence analysis and the localized heterogeneous piezoelectric response is demonstrated. The formation of such architectures is rationalized based on the generation of V-shaped pits and their subsequent overgrowth in variable direction. Detailed structure analysis with respect to X-ray diffraction and transmission electron microscopy gives striking evidence for inelastic strain to manifest in distortions of the P6 3 mc wurtzite-type structure. The deviation from hexagonal symmetry by angular distortions of the β angle between the basal plane and c-axis is found to be of around 1°. It is concluded that the lattice distortions are generated by the misfit strains originating during crystal growth, which are slightly relaxed upon photoelectrochemical etching.

Porous semiconductor compounds

“…As already mentioned in section 2, the fine modulation of the electrical and optical properties, both in-depth and in-plane directions, within extended areas, was found to be one of the peculiarities of HVPE growth of bulk GaN [136][137][138]. It was demonstrated by Kelvin Probe Force Microscopy and by SEM mapping after electrochemical etching [44], as well as by photoluminescence analysis [139], that this fine modulation of the electrical conductivity, determining the creation of self-organized 3D nanostructured architectures, including quasi-ordered concentric hexagonal structures, is related to the self-organized spatial distribution of impurities generated during the growth of single crystalline n-GaN substrates by HVPE. A model has been proposed to explain the formation of these self-organized spatial architectures on the basis of generation of V-pits and their subsequent overgrowth accompanied by the growth in variable direction.…”

Ultrafast Third-Order Nonlinear Optical Response Excited by fs Laser Pulses at 1550 nm in GaN Crystals

“…The density of threading dislocations is in the range of (1-2) × 10 7 cm −2 . Previous experiments revealed fine spatial modulation of the electrical conductivity in this crystal attributed to instability in the growth direction [38,39].…”