(In)GaN p-i-n structures were grown by MOVPE on both GaN- and ZnO-coated c-sapphire substrates. XRD studies of
the as-grown layers revealed that a strongly c-axis oriented wurtzite crystal structure was obtained on both templates and
that there was a slight compressive strain in the ZnO underlayer which increased after GaN overgrowth. The InGaN
peak position gave an estimate of 13.6at% for the indium content in the active layer. SEM and AFM revealed that the
top surface morphologies were similar for both substrates, with an RMS roughness (5 μm x 5 μm) of about 10 nm.
Granularity appeared slightly coarser (40nm for the device grown on ZnO vs 30nm for the device grown on the GaN
template) however. CL revealed a weaker GaN near band edge UV emission peak and a stronger broad defect-related
visible emission band for the structure grown on the GaN template. Only a strong ZnO NBE UV emission was observed
for the sample grown on the ZnO template. Quarter-wafer chemical lift-off (CLO) of the InGaN-based p-i-n structures
from the sapphire substrate was achieved by temporary-bonding the GaN surface to rigid glass support with wax and
then selectively dissolving the ZnO in 0.1M HCl. XRD studies revealed that the epitaxial nature and strong preferential
c-axis orientation of the layers had been maintained after lift-off. This demonstration of CLO scale-up, without
compromising the crystallographic integrity of the (In)GaN p-i-n structure opens up the perspective of transferring GaN
based devices off of sapphire substrates industrially.
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 present the design and construction of a high-speed telecom-band (1.5 μm) single-photon counting system based on an InGaAs/InP avalanche photodiode (APD) operating in the gated Geiger mode. The detector can be gated at high speeds (we examine its performance up to 25 MHz) to maximize the counting rate in long-distance, telecom-band, fiber-optic quantum communication applications. Narrow gate pulses (250 ps full width at half maximum) are used to reduce the dark-count and the after-pulse probability. In order to count the avalanche events, we employ a high-speed comparator to sample the unfiltered and unamplified avalanche photocurrent. The APD and all the associated electronics are integrated onto a printed circuit board with a computer interface. In addition, we cool the APD to -27°C to reduce the dark-count probability.
We review on-going progress in the development of fiber-based
telecom-band entanglement sources. Two different schemes (a
Sagnac-loop scheme and a counter-propagating scheme) for
generating polarization entanglement are reviewed and the pros and
cons of each are summarized. A new scheme, called the double-loop
scheme is proposed, which is theoretically shown to be capable of
combining the benefits and avoiding the pitfalls of each previous
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.