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Electron transport parallel to dislocation lines is not affected by the scattering at charged dislocation lines, according to research based on a model developed to analyze the low transverse mobility of GaN by scattering of electrons at charged dislocation lines. The repulsive band bending around dislocations and the directional dependence of the dislocation scattering prevent vertical devices being affected by the scattering of electrons at threading dislocation lines.

We experimentally demonstrate the formation of GaN nanotip pyramids by selective and anisotropic etching of N-polar GaN in KOH solution. For samples grown with adjacent Ga- and N-polar regions on the same wafer, the KOH solution was found to selectively etch only the N-polar surface while leaving the Ga-polar surface intact. An aggregation of hexagonal pyramids with well defined {10 &1macr; &1macr;} facets and very sharp tips with diameters less than ∼20 nm were formed. The density of the pyramids can be controlled by varying the KOH concentration, solution temperature or the etch duration. The GaN etching activation energy is estimated to be E[sub a] ≈ 0.587 eV. Dense GaN pyramids with sharp tips have applications in both electronic and photonic devices. [ABSTRACT FROM AUTHOR]

Intersubband optical absorption at λ ∼ 2.1 µm wavelength in doped 17.5 Å wide GaN quantum wells (QWs) with 51 Å wide intermediate AlN barriers is reported. A ∼600 nm thick GaN template and 15 QWs have been grown by molecular beam epitaxy on R-plane sapphire substrate and display pure A-plane orientation. QWs with A-plane orientation are essentially free from spontaneous polarisation, which is expected to greatly simplify the design of GaN/Al(Ga)N devices employing intersubband transitions. [ABSTRACT FROM AUTHOR]

Intersubband absorption in coupled GaN/AlGaN double quantum wells (DQWs) has been measured. The samples were grown by molecular-beam epitaxy on a sapphire substrate and with large (0.65 or 0.9) AlN-mole fraction in the barriers. Peak absorption wavelengths as short as 1.35 and 1.52 μm were measured for a symmetric DQW of 12 Å wide wells coupled by a 10 Å wide barrier, which also showed evidence of excited-state anticrossing. As expected, asymmetric DQWs displayed no such anticrossing, and the ground-state anticrossing energies were found to be much smaller, as a result of the comparatively large effective electron mass, than the energy broadening of individual transitions. Degenerate doping of the DQWs was used to establish a common reference energy at the Fermi level, which allows overcoming uncertainties related to intrinsic internal electric fields. The asymmetric DQWs displayed peak absorption wavelengths between 1.5 and 2.9 μm. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We investigate the optical properties of GaN grown over SiO[sub 2] on SiC substrates by electron cyclotron resonance assisted molecular beam epitaxy. The photoluminescence spectra and refractive index of GaN were compared for GaN/SiO[sub 2]/SiC and GaN/SiC. Strong band-edge luminescence was observed at 3.40 eV from the GaN on both SiO[sub 2]/SiC and on SiC. No defect-related yellow luminescence was observed. The refractive index of GaN at 1.96 eV (632.8 nm) was measured at 2.22 and 2.24 for GaN/SiO[sub 2]/SiC and GaN/SiC, respectively. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]