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Free-standing (0002)-oriented GaN substrates (φ = 2”) were coated with 200 nm of ZnO and used as templates for the growth of GaN thin films. SEM and AFM revealed that such GaN layers had a relatively homogenous surface morphology with an RMS roughness (5 μm x 5 μm) of less than 4nm. XRD studies revealed strained ZnO growth on the GaN substrate and the reproduction of the substrate rocking curve for the GaN overlayers after only a hundred nm of growth, thus indicating that the GaN films had superior crystallographic quality compared to those grown on sapphire or ZnO/sapphire substrates. Quarter-wafer areas of GaN were removed from the GaN substrate (by selective chemical etching away of the ZnO interlayer). The expensive GaN substrates were then reclaimed/reused (without the need for polishing) for a second cycle of ZnO and GaN growth, which gave similar XRD, SEM, CL and AFM results to the first cycle.

In the last decades, development of the (Al,Ga,In)N materials has led to new generations of opto- and micro-electronic devices. More recently, novel B(Al,Ga,In)N alloys have been proposed for optical applications in the UV range. Since material containing boron possesses unique properties, the B(Al,Ga,In)N materials system is expected to permit the design of improved and/or novel devices. To evaluate this potential, an improved knowledge of the physical properties of these new materials will be required, however. In this work, investigation of optical, structural, and compositional properties of low-boron content BGaN and BAlN ternary and BInGaN quaternary materials grown through Metalorganic Vapor Phase Epitaxy (MOVPE) are presented. It is shown that inclusion of a small amount of boron strongly affects the optical properties allowing the fabrication of BGaN-based Distributed Bragg Reflectors (DBRs) or Distributed Bragg Confinement layers (DBCs) with large refractive index contrast. Indeed, 1% of boron in BGaN/GaN multilayer structures gives a refractive index contrast of more than 0.1, which is equivalent to that of AlGaN/GaN containing 22% aluminum. The potential of boron-based material technology is illustrated for visible range solar cells applications through the example of BInGaN with good crystalline quality grown on ZnO buffered silicon substrates. It was found that through boron introduction, reduced lattice mismatch, and thus reduced tensile strain, could be obtained for high In contents.

We present a fiber based source of entangled photon-pairs in the 1550 nm telecom band that can be integrated into the existing fiber network and is well suited for quantum information processing. With this source we have demonstrated the generation, storage, and long-distance distribution of polarization entanglement in standard optical fiber. We have also investigated the origin of the large number of accidental coincidences in the experiments, which has been proved to be Raman scattering, and discussed how to suppress the Raman scattering to improve the quality of the fiber source.

We derive a CW theory for optical-fiber photon-pair sources, including the effect of non-zero response time of the fiber’s Kerr nonlinearity. We also include the effects of realistic transmission and detection losses. This theory predicts stronger photon-number correlations than seen experimentally with a pulsed pump, showing the need for development of a pulsed pump theory.