Enhancement of p-GaN conductivity using PECVD SiOx

A technique to enhance the hole concentration in activated Mg-doped p-type GaN epitaxial layers is described. The method consists of depositing a porous plasma-nhancedchemical vapor deposited SiOx layer on top of p-GaN after which the sample is heated to 950°C in nitrogen ambient for 1 min followed by the removal of the SiOx layer in a buffered HF solution. A significant improvement of the conductivity of the p-GaN layer has been obtained

A Mach-Zehnder interferometric switch with a 0.2 Vmm voltage length product

We have developed a 2*2 Mach Zehnder interferometric switch employing laterally contacted hetero n-i-p-i quantum wells for providing refractive index changes. We observe switching over a 4 pi range with an on/off ratio of 17:1. A differential switching voltage as low as 0.2 V.mm is observed in the push-pull configuration. It is the objective of the present paper to reduce the switching voltage-length product of a Mach-Zehnder interferometric switch by exploiting the advantages of a hetero n-i-p-i quantum well structure for providing refractive index changes in the arms of a Mach Zehnder interferometer switc

The impact of metallic contacts on propagation losses of an underlying photonic crystal waveguide

In view of an electrically pumped photonic crystal-based semiconductor optical amplifier (SOA), we investigate optical mode propagation in 2D PhC waveguides in the presence of metal contacts for carrier injection. Our photonic crystal (PhC) devices are manufactured in the InP/InGaAsP material system. For the loss measurements, we have fabricated contact strips as narrow as 300nm with a sub-50nm placing accuracy on top of W3 waveguides. We study the influence of their position and width on optical power transmission through passive waveguides with respect to viability for future active devices. Our experimental results are complemented by numerical studies (FDTD, plane-wave expansion method)

Fabrication of short GaAs wet-etched mirror lasers and their complex spectral behaviour

A versatile fabrication technique for GaAs-AlGaAs wet-etched mirror lasers is presented. This technique works independently of the Al concentration in the cladding layers up to a value of 70%, and it requires four photolithography steps. Ridge waveguide lasers have been successfully processed using a double heterostructure (DHS) as well as graded index separate confinement heterostructures (GRINSCH) having different quantum-well (QW) active layers. This technique is used to fabricate short-cavity lasers in GRINSCH structures having GaAs multiple-quantum-well (MQW) or bulk active layers. Laser operation was obtained in a 29-µm-long device using a 5-QW structure. Short lasers with QW active layers show a complex spectral behavior. These lasers operate at higher current densities (~20 kA/cm2) and emit light at more than one wavelength. This implies that higher order transitions are involved which is not the case when using a bulk GaAs active layer. Besides the two peaks corresponding to the n=1 and n=2 transitions, we found an intermediate peak which corresponds presumably to the forbidden transition E1-HH

Comparative study of Cl₂, Cl₂/O₂, and Cl₂/N₂ inductively coupled plasma processes for etching of high-aspect-ratio photonic-crystal holes in InP

An extensive investigation has been performed on inductively coupled plasmaetching of InP. An important motivation for this work is the fabrication of high-aspect-ratio holes for photonic crystals. The essential chemistry is based on Cl₂ with the addition of N₂ or O₂ for sidewall passivation. The influence of different process parameters such as gas flows, temperature,pressure, ion energy, and inductively coupled plasma power on the hole geometry is presented. It is concluded that photonic crystals can be etched with Cl₂ only; however, temperature and pressure control is critical. Adding passivation gases largely broadens the window in the parameter space for hole etching. Most importantly, etching of narrow holes can be carried out at higher temperatures where the etching is mass limited and spontaneous etching of InP by Cl₂ occurs.Part of this research is supported by NanoNed, a technology program of the Dutch Ministry of Economic Affairs

Novel integrated tunable laser using filtered feedback for simple and very fast tuning

We present a novel integrated tunable laser based on filtered feedback, which combines a simple tuning method with ns switching speed

High etch rate and smooth morphology using a novel chemistry in reactive ion etching of GaN

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Coplanar waveguides on AlN for AlGaN/GaN MMIC applications

In this paper we present results on the characterization of Coplanar Waveguides (CPW) on AlN substrates. These transmission lines will be used in matching networks for high power Al- GaN/GaN ampliers. The large currents that will flow inside these ampliers require a large crosssectional conductor area resulting in CPW lines with large signal-to-ground spacings and/or large center conductor widths. The Line-Reflect-Line (LRL) algorithm was used in combination with a capacitance measurement to determine the transmission line parameters. It will be shown that the CPW lines with large dimensions show non-quasi- TEM behavior presumably related to parallel plate modes which influence decreases with sample thickness. The CPW lines show dispersion in the lowfrequency