n-GaN pillar photoanodes are fabricated by dry etching of a planar GaN epilayer. The increased surface area results in a plateau photocurrent enhancement of 84%. However, surface damage is introduced during dry etching. In this work, the surface damage is controlled by the RF chuck power. The GaN pillars fabricated using the lowest RF power show a similar current onset potential and current-potential slope as the planar GaN. In addition, the damaged GaN surface of the pillars can be removed in NaOH solution, which leads to the plateau current enhancement of 100% and the onset potential shifts -60 mV with respect to planar GaN. A pair of anodic and cathodic peaks is found in the dark cyclic voltammogram of the damaged pillars, which indicates the charging and discharging of the deep-level traps existing at 0.6 eV below the CB edge.

Porous n-GaN has been fabricated using electrochemical anodic etching in a 0.5 M H2SO4 solution in the dark for different biases (5.5–18.0 V). The pore morphology of the porous GaN shows distinctive differences: from narrow branching pores to wide parallel pores for increasing applied bias. The pore formation process has been investigated using cyclic voltammetry and chronoamperometry. The photoelectrochemical properties of these porous n-GaN layers have been examined. For the porous GaN etched at 5.5–15.0 V, the plateau photocurrent increases over 4 times, and the potential difference between the current onset and the plateau is reduced by 0.24 V with respect to unetched, planar n-GaN.

•MgO was grown on high mobility GeSn and Ge by MBE.•We characterized the electrical properties of MOS capacitors.•Chemical and oxygen species effects prior to oxide deposition were studied.•Ozone treatment leads to low gate leakage.

GaN nanopillar arrays are fabricated by inductively-coupled-plasma dry etching of a GaN epitaxial layer, using self-assembled Ni clusters as mask. Pillars of 0.4-1.6 μm height were prepared and were investigated photoelectrochemically. After the roughening, the surface area increases up to 6 times and the plateau photocurrent increases by 84% with respect to the planar GaN. The enlarged GaN/electrolyte interface promotes charge transfer and photocarrier separation in the pillar array. The defect-mediated carrier recombination becomes more important after the dry etching process. The impact of surface damage is studied by the photoelectrochemical and photoluminescence measurements.

InxGa1−xN (InGaN) alloys are predominantly grown by heteroepitaxy on foreign substrates. Most often Al2O3, SiC and Si are used as substrates, however this complicates vertical conduction from the InGaN surface to the substrate backside. Therefore we investigate the heteroepitaxial growth of InGaN layers on Ge substrates. Single crystalline InGaN was obtained and domain formation was suppressed by using a thin GaN buffer layer. The InGaN shows compressive strain, which follows from the lattice mismatch with the GaN buffer layer. The In distribution is uniform throughout the InGaN layer, with no significant In segregation within the layer. Only at the surface, in a very thin layer of 20 nm, strong In segregation is observed with about 50% In. InGaN/GaN/Ge diodes show vertical current conduction of 1 A cm−2 at −2 V. InGaN grown on Ge is therefore promising for device applications with preferred vertical conduction.

The influence of nanostructuring on the photoelectrochemical (PEC) properties of GaN is investigated. GaN nanopillar arrays are fabricated by inductively-coupled-plasma dry etching of a GaN epitaxial layer, using a self-assembled Ni cluster mask. Pillars of 0.4-1.6 mu m in height were prepared and were investigated photoelectrochemically. After nanoroughening, the surface area increases up to 6 times and the plateau photocurrent increases by 84% with respect to planar GaN. The pillar structure provides abundant depletion area and therefore enhances the photocarrier separation. Surface recombination becomes more important after the dry etching process, as confirmed by the PEC and photoluminescence measurements. (C) 2013 The Electrochemical Society. All rights reserved.

In this work, we demonstrate the direct measurement of the strain state at the surface of nanostructures by in-plane X-ray diffraction. GaN tapered nanopillars have been fabricated by dry etching of a highly strained epilayer. The strain of the surface as function of pillar height shows an exponential relaxation which can be described by a single relaxation parameter. Additionally, we have simulated the strain relaxation and distribution of nanopillars. The impact of the pillar geometry on the strain relaxation has been discussed. In agreement with the measurements, an exponential relaxation of the strain is observed.