Ian McKerracher

Liquid crystal based nonlinear fishnet metamaterials

We study experimentally the nonlinear properties of fishnet metamaterials infiltrated with nematic liquid crystals and find that moderate laser powers result in significant changes of the optical transmission of the composite structures. We also show that the nonlinear response of our structure can be further tuned with a bias electric field, enabling the realization of electrically tunable nonlinear metamaterials.

Effects of rapid thermal annealing on device characteristics of InGaAs/GaAs quantum dot infrared photodetectors

In this work, rapid thermal annealing was performed on InGaAs∕GaAs quantum dot infrared photodetectors (QDIPs) at different temperatures. The photoluminescence showed a blueshifted spectrum in comparison with the as-grown sample when the annealing temperature was higher than 700°C, as a result of thermal interdiffusion of the quantum dots (QDs). Correspondingly, the spectral response from the annealed QDIP exhibited a redshift. At the higher annealing temperature of 800°C, in addition to the largely redshifted photoresponse peak of 7.4μm (compared with the 6.1μm of the as-grown QDIP), a high energy peak at 5.6μm (220meV) was also observed, leading to a broad spectrum linewidth of 40%. This is due to the large interdiffusion effect which could greatly vary the composition of the QDs and thus increase the relative optical absorption intensity at higher energy. The other important detector characteristics such as dark current, peak responsivity, and detectivity were also measured. It was found that the overa...

In-Plane Coupling of Light From InP-Based Photonic Crystal Band-Edge Lasers Into Single-Mode Waveguides

In this paper, we analyze the coupling of light from photonic-crystal band-edge lasers into single-mode waveguides. Both active and passive devices lie in the same plane and coupling of light is achieved by using parabolic and nanotapers in InP based epitaxial structures. Two- and three-dimensional finite-difference time-domain methods are employed to analyze these devices. Coupling efficiencies higher than 80% can be obtained with parabolic couplers. We also present laser configurations that can reduce multiwavelength coupling of light into single-mode waveguides, using structures that are similar to coupled cavity Fabry-Peacuterot lasers

Unexpected short- and medium-range atomic structure of sputtered amorphous silicon upon thermal annealing

We investigate the structure of magnetron-sputtered (MS) amorphous silicon (a-Si) prepared under standard deposition conditions and compare this to pure ion-implanted (II) a-Si. The structure of both films is characterized in their as-prepared and thermally annealed states. Significant differences are observed in short- and medium-range order following thermal annealing. Whereas II a-Si undergoes structural relaxation toward a continuous random network, MS a-Si exhibits little change. Cross-sectional transmission electron microscopy reveals the presence of nanopores in the MS film consistent with reduced mass-density. Therefore, the short- and medium-range order of annealed, MS a-Si is tentatively attributed to these pores.

The conduction band absorption spectrum of interdiffused InGaAs/GaAs quantum dot infrared photodetectors

Thanks are due to the Australian Research Council for the financial support of this research.

Integration of bandpass guided-mode resonance filters with mid-wavelength infrared photodetectors

Guided-mode resonances have been exploited to filter the normal-incidence transmission of mid-infrared wavelengths through a photonic crystal slab. A two-dimensionally periodic structure has been integrated with a quantum dot infrared photodetector to narrow its mid-wavelength infrared photoresponse spectrum. Finite-difference time-domain simulations were employed to extract the filter transmittance, which is dominated by a peak near 6 µm. The simulated resonance is linearly tunable with the air-hole radius but it is insensitive to small changes in the incidence angle. To realize this filter, a patterned Ge slab was fabricated on a CaF2 cladding layer, on the InGaAs/GaAs photodetector. Filters fabricated on a plain GaAs substrate were also characterized by Fourier-transform infrared spectroscopy. This transmittance was consistent with the corresponding simulation, however the resonance peak was degraded in comparison to the filtered photodetector and its associated simulations.

Selective Intermixing of InGaAs/GaAs Quantum Dot Infrared Photodetectors

Quantum dot infrared photodetectors have generated significant interest in recent years. They have the potential to outperform quantum well detectors in terms of normal-incidence responsivity and higher operating temperatures. Here, an InGaAs/GaAs dots-in-a-well detector grown by metal-organic chemical vapor deposition is spectrally tuned by rapid thermal annealing under dielectric layers. Four films are considered: SiO2 deposited by both plasma-enhanced chemical vapor deposition and sputter deposition, as well as TiO2 deposited by electron-beam evaporation and sputter deposition. The devices fabricated after these treatments are compared with an uncapped but annealed reference, and also with an as-grown device. The photoresponse peak in the latter occurs at 7.1 μm, whereas the peak responses of the annealed devices range from 7.4 to 11.0 μm. The films themselves were characterized and their properties related to the photoluminescence and spectral photoresponse of each detector. Peak responsivity, specific detectivity, and dark current were also measured for each device to compare their performance.

Intermixing of InGaAs/GaAs quantum wells and quantum dots using sputter-deposited silicon oxynitride capping layers

This work has been made possible with access to the ACT Node of the Australian National Fabrication Facility and through the financial support of the Australian Research Council.

Impurity-free vacancy disordering of quantum heterostructures with SiOxNy encapsulants deposited by magnetron sputtering

Post-growth techniques such as impurity-free vacancy disordering (IFVD) are simple and effective avenues to monolithic integration of optoelectonic components. Sputter deposition of encapsulant films can enhance quantum well intermixing through IFVD and an additional mechanism involving surface damage during the sputtering process. In this study, these two mechanisms were compared in a multi-quantum well structure. The compositions of different silicon oxy-nitride films were controlled by sputter deposition in different ambient gases. These different encapsulants were used to initiate IFVD in the same heterostructure and the observed intermixing is compared to the film properties.

Effect of GaP strain compensation layers on rapid thermally annealed InGaAs/GaAs quantum dot infrared photodetectors grown by metal-organic chemical-vapor deposition

The effect of GaP strain compensation layers was investigated on ten-layer InGaAs∕GaAs quantum dot infrared photodetectors (QDIPs) grown by metal-organic chemical-vapor deposition. Compared with the normal QDIP structure, the insertion of GaP has led to a narrowed spectral linewidth and slightly improved detector performance. A more significant influence of GaP was observed after the structure was annealed at various temperatures. While a similar amount of wavelength tuning was obtained, the GaP QDIPs exhibited much less degradation in device characteristics with increasing annealing temperature.