P. Van Dorpe

Low-Loss Singlemode PECVD Silicon Nitride Photonic Wire Waveguides for 532–900 nm Wavelength Window Fabricated Within a CMOS Pilot Line

PECVD silicon nitride photonic wire waveguides have been fabricated in a CMOS pilot line. Both clad and unclad single mode wire waveguides were measured at λ = 532, 780, and 900 nm, respectively. The dependence of loss on wire width, wavelength, and cladding is discussed in detail. Cladded multimode and singlemode waveguides show a loss well below 1 dB/cm in the 532-900 nm wavelength range. For singlemode unclad waveguides, losses 1 dB/cm were achieved at λ = 900 nm, whereas losses were measured in the range of 1-3 dB/cm for λ = 780 and 532 nm, respectively.

Very high spin polarization in GaAs by injection from a (Ga,Mn)As Zener diode

We demonstrate an electrically injected electron spin polarization in GaAs of 80% at 4.6 K by interband tunneling from the valence band of (Ga,Mn)As into an (Al,Ga)As light-emitting diode. The polarization is analyzed by the oblique Hanle effect and vanishes at 120 K, the Curie temperature of the (Ga,Mn)As injector. The temperature and the bias dependence of the polarization are explained in terms of the properties of the (Ga,Mn)As/GaAs diode.

Plasmon filters and resonators in metal-insulator-metal waveguides

We present the numerical and experimental demonstration of plasmonic Bragg filters and resonators inside metal-insulator-metal (MIM) waveguides. The presented filters and resonators are fabricated using standard top down lithography methods. The optical bandgap of the integrated Bragg filters is experimentally observed and its optical properties are investigated as a function of the grating pitch and the number of grating periods. Transmission filters based on a nanocavity resonance were measured, obtaining Q-factors above 30. Tuning of the cavity wavelength was experimentally achieved by varying the cavity length.

Oblique Hanle measurements of InAs/GaAs quantum dot spin-light emitting diodes

We report on studies of electrical spin injection from ferromagnetic Fe contacts into semiconductor light emitting diodes containing single layers of InAs∕GaAs self-assembled quantum dots (QDs). An oblique magnetic field is used to manipulate the spin of the injected electrons in the semiconductor. This approach allows us to measure the injected steady-state spin polarization in the QDs, Pspin as well as estimate the spin losses in the QD spin detector. After subtraction of magneto-optical effects not related to spin injection, we measured a Pspin of 7.5% at 15 K and estimated an injected spin polarization before QD recombination of around 20%.

Voltage-controlled spin injection in a (Ga,Mn)As/(Al,Ga)As Zener diode

The spin polarization of the electron current in a p-(Ga,Mn)As-n-(Al,Ga)As-Zener tunnel diode, which is embedded in a light-emitting diode, has been studied theoretically. A series of self-consistent simulations determines the charge distribution, the band bending, and the current-voltage characteristics for the entire structure. An empirical tight-binding model, together with the Landauer- Buttiker theory of coherent transport has been developed to study the current spin polarization. This dual approach allows to explain the experimentally observed high magnitude and strong bias dependence of the current spin polarization.

Spin Injection and Detection in Semiconductors—Electrical Issues and Device Aspects

Spin selectivity has already been demonstrated for both injection and (recently) detection contacts on semiconductors, but a clear demonstration of a magnetoresistance signal is still lacking. After outlining the various categories of device proposals and the associated choice of semiconductor material, we summarize the various injection contact technologies that have been reported and assess their potential for practical device applications in terms of electrical efficiency, bias dependence (both intrinsic and extrinsic), and performance in unipolar devices. We then focus on the design of an all-electrical injection-detection device in GaAs and demonstrate that a correct design of the semiconductor channel and contact regions is the key for preserving the spin sensitivity that is provided by the contacts

Efficient electrical spin injection in GaAs: A comparison between AlOx and Schottky injectors

We demonstrate electrical spin injection in GaAs from ferromagnetic metals through tunneling. We use and compare an AlOx insulating layer as well as the native Schottky barrier at the metal–semiconductor interface as tunnel barriers. The injected spin polarization has been measured by analyzing the electroluminescence polarization using the oblique Hanle effect technique. The observed bias dependence of the measured spin polarization is sensitive to both the type of injector and the doping profile in the semiconductor. Hot electron spin relaxation due to the D’yakonov–Perel spin relaxation mechanism has been identified as the cause of the different bias dependence in two AlOx-based injectors with different doping levels of the active region while a change in the electron transit times in the highly doped interfacial region has been found as the cause of the bias dependence in the Schottky-based injectors.

Detection of DNA Bases and Oligonucleotides in Plasmonic Nanoslits Using Fluidic SERS

Raman spectroscopy is a widely used vibrational spectroscopic technique to identify and study chemical compounds. The signal can be strongly enhanced in the presence of metal nanostructures resulting in so-called surface-enhanced Raman scattering (SERS). Here, we describe the use of SERS for the molecular characterization of DNA molecules inside a nanoslit across a thin, metal-coated membrane. Nanoslits with two different dimensions were examined. More specifically, relatively long nanoslits (over 700 nm) with a strong, broad plasmonic coupling mode as well as short nanoslits (100 nm) with a strong Fabry-Pérot resonance for a specific wavelength. Both geometries were fabricated using standard lithographic processes and were coated with gold to enable the excitation of surface plasmons, needed for SERS. Using electrophoresis to actuate the analytes across the nanoslits, we were able to record SERS spectra of a typical DNA base, namely adenine. Similarly, short DNA oligonucleotides were also successfully detected. It is expected that the nanoslit-based fluidic SERS will become a promising real-time detection tool, especially for DNA.

Design of the tunnel contacts and the transport region of all-electrical spin-injection-detection devices

The design of an all-electrical spin-injection-detection device is discussed. It is shown that the use and the design of tunnel barriers cannot simply be copied from the spin light-emitting diodes, where they have already been demonstrated. Using one-dimensional and two-dimensional self-consistent simulations, the doping levels of the tunnel contacts and the spin-transport region are engineered to obtain an optimal tunnel barrier resistance and an optimal current distribution in the spin-transport region.

Characterization of PECVD Silicon Nitride Photonic Components at 532 and 900 nm Wavelength

Low temperature PECVD silicon nitride photonic waveguides have been fabricated by both electron beam lithography and 200 mm DUV lithography. Propagation losses and bend losses were both measured at 532 and 900 nm wavelength, revealing sub 1dB/cm propagation losses for cladded waveguides at both wavelengths for single mode operation. Without cladding, propagation losses were measured to be in the 1-3 dB range for 532 nm and remain below 1 dB/cm for 900 nm for single mode waveguides. Bend losses were measured for 532 nm and were well below 0.1 dB per 90 degree bend for radii larger than 10 μm.