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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]

We report the experimental demonstration of second-harmonic generation in periodically poled GaN by first-order quasiphase matching. The periodically poled structure was grown by plasma-assisted molecular-beam epitaxy. We observed about 9 μW of second-harmonic power from a fundamental input laser wavelength of 1658.6 nm with a normalized conversion efficiency of 12.76% W[sup -1] cm[sup -2]. The ability to perform nonlinear wavelength conversion by periodic poling and the fact that GaN has a very wide window of transparency, pave the way for GaN to be used for nonlinear optical devices in telecommunications as well as a nonlinear light source for biochemical detection in the far infrared and deep ultraviolet. © 2003 American Institute of Physics. [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]

Focuses on an experiment which proposes that the model to explain the observed low transverse mobility in GaN, is the scattering of electrons at charged dislocation lines. What the photoluminescence (PL) investigations of GaN films; Information on scattering at filled traps on dislocation lines; Conclusion from experiment.

Intersubband optical absorption around 1.55 μm has been measured in GaN/AlGaN multiple quantum wells (MQWs) grown by molecular-beam epitaxy. First, peak absorption wavelengths as short as 1.41 μm are reported for ultranarrow, >=11 Å wide, well-doped MQWs with high, 85%, AlN mole-fraction barriers. Second, in order to enable modulation doping as well as the use of lower AlN mole-fraction barriers, we designed and fabricated QWs embedded in barriers consisting of a short period superlattice of narrow GaN QWs and only 65% AlN mole-fraction barriers. The resulting electron Bragg confinement allows peak absorption wavelengths as short as 1.52 μm. Furthermore, the structures can now be modulation doped through doping of the narrow superlattice wells and subsequent charge transfer into the active well. We observe a reduction of the absorption linewidth, from ∼200 to ∼130 meV, for these structures. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Intersubband optical absorption in narrow, 15-30 Å wide, GaN/AlGaN quantum wells has been measured. The samples were grown by molecular-beam epitaxy on sapphire substrate and the barrier AlN mole fraction was varied from 0.45 to 0.8. Peak absorption wavelengths ranged from 4.2 μm for 30 Å wide wells to 1.77 μm for a 15 Å wide well. Modeling shows that a large contribution to the considerable spectral width of the absorption of ∼150 meV likely results from monolayer fluctuations. In addition to the composition dependent band offset, the intrinsic electric fields in the wells and barriers are the determining factors for the shortest possible wavelength. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report absorption loss coefficients at 1550 nm of free-standing GaN grown by hydride vapor phase epitaxy. We measured propagation loss values at numerous locations of the facets and observed an average of 2.41 dB/cm and 1.85 dB/cm for transverse electric (TE) and transverse magnetic (TM) polarizations, respectively, in the low loss region of the sample. The minimum loss values in the sample were found to be 0.82 dB/cm (TE) and 0.61 dB/cm (TM). The ability to achieve such low propagation loss coefficients in GaN opens up the possibility of using this material in a variety of integrated optics and nonlinear optics applications. [ABSTRACT FROM AUTHOR]

GaN/SiC heterojunction diodes have been fabricated and characterized. Epitaxial n-type GaN films were grown using metalorganic chemical vapor deposition (MOCVD) and electron cyclotron resonance assisted molecular beam epitaxy (ECR-MBE) on p-type Si-face 6H-SiC wafers. The I–V characteristics have diode ideality factors and saturation currents as low as 1.2 and 10[sup -32] A/cm[sup 2], respectively. The built-in potential in the MOCVD- and ECR-MBE-grown n-p heterojunctions was determined from capacitance–voltage measurements at 2.90±0.08 eV and 2.82±0.08 eV, respectively. From the built-in potential the energy band offsets for GaN/SiC heterostructures are determined at ΔE[sub C]=0.11±0.10 eV and ΔE[sub V]=0.48±0.10 eV. © 1998 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]