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We report on the demonstration of low-loss, single-mode GaN-InAlN ridge waveguides (WGs) at fiber-optics telecommunication wavelengths. The structure grown by metal-organic vapor phase epitaxy contains AlInN cladding layers lattice-matched to GaN. For slab-like WGs propagation losses are below 3 dB/mm and independent of light polarization. For 2.6-mum-wide WGs the propagation losses in the 1.5- to 1.58-mum spectral region are as low as 1.8 and 4.9 dB/mm for transverse-electric- and transverse-magnetic-polarization, respectively. The losses are attributed to the sidewall roughness and can be further reduced by the optimization of the etching process.

The prospects of a control for a novel gallium nitride pseudo-halide vapor phase epitaxy (PHVPE) with HCN were thoroughly analyzed for hydrocarbons-NH3-Ga gas phase on the basis of quantum chemical investigation with DFT (B3LYP, B3LYP with D3 empirical correction on dispersion interaction) and ab-initio (CASSCF, coupled clusters, and multireference configuration interaction including MRCI+Q) methods. The computational screening of reactions for different hydrocarbons (CH4, C2H6, C3H8, C2H4, and C2H2) as readily available carbon precursors for HCN formation, potential chemical transport agents, and for controlled carbon doping of deposited GaN was carried out with the B3LYP method in conjunction with basis sets up to aug-cc-pVTZ. The gas phase intermediates for the reactions in the Ga-hydrocarbon systems were predicted at different theory levels. The located π-complexes Ga…C2H2 and Ga…C2H4 were studied to determine a probable catalytic activity in reactions with NH3. A limited influence of the carbon-containing atmosphere was exhibited for the carbon doping of GaN crystal in the conventional GaN chemical vapor deposition (CVD) process with hydrocarbons injected in the gas phase. Our results provide a basis for experimental studies of GaN crystal growth with C2H4 and C2H2 as auxiliary carbon reagents for the Ga-NH3 and Ga-C-NH3 CVD systems and prerequisites for reactor design to enhance and control the PHVPE process through the HCN synthesis.

In this article, we demonstrate closely spaced, monolithically integrated photodetectors in two largely different wavelength ranges. The epitaxial structure of the devices was grown by plasma-assisted molecular-beam epitaxy on an AlN-on- sapphire template; it consists of a Si-doped AlGaN thin film, and a nearly strain compensated 40 period AlN/GaN superlat- tice with 1.0 nm thick GaN quantum wells and 2.0 nm thick AlN barriers. The entire structure is covered with an AlGaN cap layer. The superlattice acts as active region for the infra- red detector, while the AlGaN buffer layer serves as active area for the ultraviolet detector. While the photovoltaic near- infrared detector has a center wavelength of 1.37 µm, the photoconductive ultraviolet detector has a long wavelength cutoff at 250 nm. The two detectors could be operated up to room temperature with reasonable sensitivities.

Closely spaced, monolithically integrated photodetectors in two largely different wavelengths ranges are demonstrated. The device structure was grown by plasma-assisted molecular-beam epitaxy on an AlNon-sapphire template, and it consists of a Si-doped AlGaN thin film, and a nearly strain compensated 40 period AlN/GaN superlattice with 1.0 nm-thick GaN quantum wells and 2.0 nm-thick AlN barriers. The entire structure is covered with an AlGaN cap. The superlattice constitutes the active region for the infrared detector, while the AlGaN buffer layer serves as active area for the ultraviolet detector. The photoconductive ultraviolet detector has a long wavelength cutoff at 250 nm, whereas the photovoltaic near-infrared detector has a centre wavelength of 1.37 mm. Multispectral cameras operating in entirely different wavelength ranges such as ultraviolet (UV), visible, or even the infrared (IR) are attracting increasing interest for applications in surveillance, failure analysis, and meteorology [1]. Up to now, such multispectral imaging systems have been fabricated by overlaying visible and UV pictures coming from two different image sensor arrays. Although this solution has the advantage of offering optimised performances for both wavelength ranges, it requires use of several bulky and rather expensive optical components. In addition, such a system is relatively sensitive for shocks or vibrations, and therefore not totally reliable for in-the-field applications. Systems being up to this challenge are therefore very expensive. A monolithic integration of two or even three operation wavelengths into a single camera chip could thus offer several advantages over existing solutions, notably in terms of price, robustness, and flexibility. Unfortunately, there are not many semiconductor materials which would allow a monolithic integration of all three wavelength ranges mentioned above. In addition, most semiconductors having sufficiently dissimilar bandgap energies suffer from large lattice mismatches, even within the same family [2]. For this reason, a different solution involving not only interband, but also intersubband transitions, must be pursued. One possible way which is presented in this Letter is the integration of a photoconductive UV interband detector based on an AlGaN thin film [3] and a photovoltaic near-IR intersubband detector based on an AlN/GaN superlattice [4– 6]. In a first demonstration, we show a UV/IR detector pair with only 350 mm separation between the UV and IR device. Both detectors exhibit spectrally narrow responsivity curves, which enlarges the UV-tovisible rejection ratio in the case of the UV device, and which improves the noise behaviour in the case of the IR detector.

We report on intersubband absorption of near infrared radiation in AlN/GaN superlattice structures grown by metal-organic vapor-phase epitaxy. A good correlation between well thickness and absorption peak energy was obtained. One sample shows a photovoltaic signal which overlaps well with the corresponding absorption curve at around 1.5 mu m (830 meV), a common wavelength in optical fiber telecommunication systems. This photovoltaic signal is strongest at temperatures around 75 K and persists up to room temperature. The frequency response of this sample was measured with a modulated 1.5 mu m laser diode. The amplitude of the response was highest for a frequency of 36 kHz.

We present measurements of the dynamics of photoexcited excitons inan ensemble of InAs/GaAs self-assembled quantum dots using a femtosec-ond spectral hole burning technique. We use this technique to examine theexciton spin relaxation and the line shape of optical transitions in the dots.PACS numbers: 73.21.La, 78.47.{p, 78.67.Hc