D. Starikov

Dual-band UV/IR optical sensors for fire and flame detection and target recognition

Several military and industrial applications require simultaneous or at least spatially synchronized detection of optical emissions in different spectral regions. The ability to grow III nitrides on Si wafers is considered to be key to the development of multi-color detectors ranging from the UV to IR wavelengths. GaN/InGaN p-n heterostructures grown on Si wafers indicated sensitivity in a wide spectral range from near UV to near IR. Employment of Schottky barrier photodiode structures based on AlGaN alloys allows extension of the spectral sensitivity further into the UV range beneficial for solar-blind sensing. An alternative way to combine sensitivities in separated IR (provided by silicon) and UV (featured by III nitrides) bands by employment of commercially available silicon-on sapphire (SOS) wafers is discussed.

FPGA implementation of a CDMA source coding and modulation subsystem for a multiband fluorometer with pattern recognition capabilities

We describe the design of a source coding and modulation circuit to be used in the front end of a multiband fluorometer device. The circuit uses a CDMA approach to minimize ambient and exogenous noise contamination and is implemented in a Xilinx Spartan 3 FPGA. The eight channel CDMA modulator and demodulator subsections use 1172 slices, or 61% of a XC3S200 FPGA, leaving ample room to embed a Microblaze IP core for spectral signature analysis and pattern recognition, and user interaction.

FIELD EMISSION FROM AS-GROWN AND SURFACE MODIFIED BN AND CN THIN FILMS

We have investigated the electron field emission characteristics of BN and CN on highly conductive silicon thin films deposited by End-Hall ion source and electron cyclotron resonance plasma source-assisted physical vapor deposition. The thermal processing and surface laser modification effects on the field emission properties were investigated. Current density-field emission characteristics Iη(E) were tested in a high vacuum environment. Mg-doped BN thin films on silicon exhibited a turn-on field as low as 25 V/μm and a current density higher than 1 A/cm2. The deposition of a thin BN layer on copper lithium (CuLi) metallic substrate yields surfaces with a 75 V/μm onset field and a current density 1000 times higher than that obtained from uncoated surfaces. Under high vacuum laser annealing BN coated CuLi showed no enhancement but more stable emission characteristics. Our results show also that pulsed ultraviolet laser irradiation of CN films in vacuum results in an increase of the field emission current ...

Metal–insulator–semiconductor Schottky barrier structures fabricated using interfacial BN layers grown on GaN and SiC for optoelectronic device applications

Metal–insulator–semiconductor Schottky barrier structures on GaN and 6H-SiC using highly stable interfacial BN layers have been investigated. As reported earlier, such structures fabricated with Ti contacts are capable of withstanding up to 350 and 600 °C when based on 6H-SiC and GaN, respectively. In this work we fabricated diode structures using interfacial BN layers and optically transparent Au contacts. Visible–blind photosensitive structures on GaN and 6H-SiC and prebreakdown light-emitting diode (LED) structures on 6H-SiC have been characterized. The radiant and spectral sensitivities of the photosensitive structures were measured in the range of 200–400 nm. The potential barrier heights determined from photoresponse measurements were 2.7 and 2.88 eV for GaN- and SiC-based samples, respectively. The spectrum of 6H-SiC and p-GaN-based prebreakdown LED structures measured through transparent Au electrodes extended to the ultraviolet region. The optical emission power of the 6H-SiC-based LED structures...

Molecular beam epitaxy growth of InGaN-GaN superlattices for optoelectronic devicesa)

In the absence of native substrates for InGaN films, the achievement of thick InGaN films of high structural quality remains a challenge. The investigation of InGaN-GaN superlattice (SL) structures is one potential way to increase optical absorption at energies below the GaN bandgap while reducing the formation of detrimental defects. In this article the authors evaluate the structural and optical properties of InGaN-GaN superlattices grown by plasma assisted molecular beam epitaxy with indium compositions of up to 38% and periods from 8 to 20 nm. Of primary concern was the degree of film relaxation as determined by x-ray diffraction (XRD) reciprocal space mapping as a function of indium content and thickness of the InGaN layers. Indium well fractions of up to 0.15 were found to exhibit little or no relaxation for the structures tested by x-ray diffraction. For indium well fractions near ∼0.2, relaxations of the superlattices were in the range of 35% depending on total layer thickness. The samples with in...

Photoenhanced reactive ion etching of III–V nitrides in BCl3/Cl2/Ar/N2 plasmas

Gallium nitride (GaN) and boron nitride (BN) are known as superior semiconductor materials for UV optoelectronic and high power, high temperature applications. As a result of their high molecular bond strength these materials are extremely difficult to etch. In this article, reactive ion etching (RIE) tests were performed on GaN and BN thin films using respectively BCl3/Cl2/Ar and Cl2/Ar chemistries. In order to improve the etch rates at lower rf powers and thus reduce ion bombardment-induced damage, a photoassisted RIE process was investigated. The same plasma chemistries in combination with a xenon arc lamp were utilized. In an attempt to minimize surface nitrogen depletion, N2 was used instead of Ar as dilution gas. Photoenhancement was observed for both GaN and BN etching. As expected, the etch rate increased with rf power for both unassisted and photoassisted etching conditions. The combination of illumination and N2 led to a nitrogen-rich surface for GaN. In the case of BN, photoassisted etching in ...

Comparison of the noise immunity of a LED-based multiband optoelectronic sensor when using FDMA and CDMA to code the excitation source

We compare the noise immunity of the LED-based optoelectronic front end of a multiband spectral detection and analysis device when using FDMA and CDMA coding for the excitation source. Our results are that the two coding schemes offer comparable performance at low signal-over-noise levels, but that the CDMA approach offers a much better noise immunity in noisy environments. It is thus a much better alternative to drive the excitation source than the more common synchronous modulation approach that underlines FDMA.

Integrated multi-wavelength fluorescence sensors

Significant efforts have been made to implement capabilities of a laboratory system into a compact portable fluorometer composed of solid-state components, such as light emitting diodes (LEDs) and photodiode (PDs). These devices, still use statistical sampling, lenses and glass filters, and do not meet the requirements addressed for multi-functional fluorescence sensors capable of performing in super-ambient environments. We have shown that UV/blue GaN/InGaN-based LEDs and optically filtered Si PDs can be employed in compact optoelectronic sensors capable of multi-functional operation in the absorption, scattering, and fluorescence mode. To take advantage of the high temperature and chemical stability of the III nitrides it would be beneficial to use these materials for the fabrication of all sensor components including the wavelength-selective features. In this work we fabricated a multi-wavelength fluorescence sensor prototype using III nitride-based components. This device was tested for measurements of fluorescein, chlorophyll, aromatic hydrocarbons, and E.coli bacteria expressing various fluorescence proteins. The new sensor prototype exhibited a lower detection limit and a larger dynamic range, than those achieved with previous prototypes. It has a compact size and a low fabrication cost.

Enhanced free carrier generation in boron nitride films by pulsed laser radiation

A transient laser photoconductivity (PC) technique is applied to the investigation of non-linear multi-photon excitation of mixed cBN/hBN films. A selection of sub-micron thickness films on sapphire substrates with different stoichiometries were synthesized using ion-assisted and ECR-plasma CVD techniques. Efficient free carrier generation in these thin films is demonstrated under nanosecond pulses excitation from VIS/UV harmonics of a Nd:YAG laser. The effect is shown to be influenced largely by the nitrogen deficiency and the carbon impurities present in the BN thin films. Both parameters are responsible for the existence of donor and acceptor levels in the material. A laser generated 400 mV electrical signal was realized when using 200 nm boron-rich hBN films. A method for further enhancing the carrier generation efficiency via post-growth X-ray irradiation of the films is demonstrated.

An Efficient SIMD Architecture with Parallel Memory for 2D Cosine Transforms of Video Coding

This paper proposes an efficient SIMD architecture with parallel memory for 2D cosine transforms of multiple video standards. A novel parallel memory scheme is employed to provide conflict-free parallel access in both horizontal and vertical directions with the successive or even/odd mode, as well as to eliminate data permutation and matrix transposition. Furthermore, application specific instructions are presented to accelerate the transform kernels, such as butterfly and rotate operations with scaling, rounding and clipping. The simulation results show that proposed architecture achieves significant performance improvement with low hardware cost of 3.2 K equivalent gate count for parallel memory subsystem (not including SRAMs) and 19.8 K for arithmetic units@250 MHz in 0.18 mum process.