UV Applications Research Articles

Physical Modeling and Design of Thin-Film SOI Lateral PIN Photodiodes

Lateral PIN diodes on thin-film silicon-on-insulator (SOI) substrates are photodetectors of prime interest for UV and fast IR applications. We present numerical simulations and a simple but accurate way to implement 1-D internal physical modeling of such devices. This modeling allows for the optimization of their external and macroscopic performances such as quantum efficiency and output current as a function of design parameters such as intrinsic length of the diode. Speed and dark current performances versus the intrinsic length are also addressed, and design tradeoffs are illustrated by concrete applications. For diodes with intrinsic lengths between 2 to 4 /spl mu/m, our results predict quantum efficiencies of 56% to 60% at a 400-nm wavelength, with bandwidth of 1 to 10 GHz and a dark current of around 1 pA for a total diode area of 75/spl times/75 /spl mu/m/sup 2/ in a 0.12 /spl mu/m partially depleted SOI technology.

Focus on Lasers and Optics

Focus on Lasers and Optics

Plasma-assisted molecular beam epitaxy of nitride-based photodetectors for UV and visible applications

Different growth modes have been identified in thick (⩾500 nm) AlGaN and InGaN layers grown by plasma-assisted molecular beam epitaxy as a function of parameters such as the growth temperature or the III–V ratio. Al mole fractions between 0% and 60% have been explored in AlGaN alloys, finding that a two-dimensional growth only occurs above a critical temperature under a metal-stable regime. This critical temperature increases with the Al content and depends strongly on the strain induced by the substrate and previous layers. A thermodynamical model is proposed to explain this behaviour. InGaN layers were also grown with In compositions in the 0–10% range. In this case, a metal-stable regime may induce In accumulation at the surface preventing the InGaN growth. Thus, slightly N-rich conditions are needed to reach an efficient In incorporation. To broaden the photodetection range of III-nitrides, photoconductors have been fabricated on both ternary alloys aiming to obtain high responsivity, solar-blind UV detectors (AlGaN) and narrow-band visible detectors (InGaN).

Size- and Surface-dependent Photoresistance in SnO2 Nanowires

AbstractNanostructured one-dimensional materials, such as nanowires, tubes and rods, are gaining increasing attention due to interesting properties and confinement effects, however controlled synthesis of these structures is still limited to a few methods. We present here the synthesis of SnO2 nanowires (Ø, 50 – 1000 nm) at moderate temperatures (550 – 900 °C) using a molecular source [Sn(OBut)4] with pre-existent Sn-O bonds. The growth occurs via a catalyst driven vapor-solid-solid mechanism. Size-selective synthesis of NWs in high areal density was achieved by choosing Au particles of appropriate size. HR-TEM analysis reveals the single crystalline behaviour of wires with a preferred growth direction [100]. Use of SnO2 nanowires as potential optical switches for UV applications was demonstrated by the photo-response measurements. Determination of band gap values confirmed the blue-shift of the main photo-response peak with shrinking radial dimensions of the wires. Furthermore, deposition of vanadium oxide onto SnO2 led to a red-shift of the main conduction value of the nanowires.

New Boron Nitride Whiskers: Showing Strong Ultraviolet and Visible Light Luminescence.

AbstractFor Abstract see ChemInform Abstract in Full Text.

New Boron Nitride Whiskers: Showing Strong Ultraviolet and Visible Light Luminescence

Boron nitride whiskers with a special structure have been synthesized by a thermal reaction process. The as-prepared BN whiskers have a length of tens of micrometers and a mean diameter of 500 nm. High-resolution TEM analysis shows that the as-prepared BN whiskers can be described as a nanofiber-interweaved network. Infrared and electron energy loss spectra reveal that the BN whiskers are composed of both sigma-sp2 and sigma-sp3 chemical bonds. The UV-vis absorption spectrum displays the energy band gap of the BN whiskers and multiple fine absorption peaks of the phonon-electron coupling. Both photoluminescence (PL) and cathodoluminescence (CL) measurements show the specially structured BN emits strong UV and visible luminescences, which is a promising material for deep-blue and UV applications.

Roughness evolution of some X-UV reflective materials induced by low energy (

Ion beam figuring (IBF) is an advanced technique that is been used for more than 10 years as a final step in the manufacturing of optical elements. It makes use of ion sputtering to correct shape defects but this process may eventually lead to the degradation of the surface roughness. In this study, the evolution of roughness for some optical materials subjected to the ion beam figuring process has been investigated by using optical profilometry and scanning electron microscopy. Emphasis has been made on electroplated nickel, PVD gold and CVD silicon carbide. These materials are often used for X-ray and UV applications but only limited data on their behavior under ion milling is currently available. Roughness measurements have been performed at different etching depths down to 5 μm which is representative of typical IBF treatments. The effects of using different inert gases (Ar, Kr and Xe) with ion energies ranging from 200 to 900 eV have been studied. The observed trends are an important increase of the roughness for electroplated nickel, a slight decrease for PVD gold and a slight increase for CVD silicon carbide. Results are discussed in relation to previous related works and within sputtering considerations.

Spectroscopic properties of Er3+ and Eu3+ doped acentric LaBO3 and GdBO3

This work studies the spectroscopic behavior of Eu3+-doped and Yb3+/Er3+-codoped single crystals of orthorhombic LaBO3 and rhombohedral GdBO3. Emissions from Er3+ at ∼1535 nm are shown to exhibit multiple narrow linewidth emissions. Luminescence from the D05→7F1, F27 transitions of Eu3+ is found to depend on the choice of LaBO3 or GdBO3 as a parent phase in a well-defined manner. Phonon sideband spectroscopy of the Eu3+ D25 excitation, corroborated using Raman spectroscopy, indicates that the highest energy phonon is less than 1400 cm−1 for the LaBO3 and less than 1010 cm−1 for the GdBO3. Further, absorption spectrum to 190 nm is provided for the GdBO3 clearly showing the I6 manifold, and the rarely seen D6 levels. Excitation of the D7/26 state at 250 nm in GdBO3 is shown to yield a strong ultraviolet emission centered at 314 nm. This work marks the lanthanide borates as candidate single crystals for active and nonlinear materials for UV, visible, and telecommunication band applications.

Simultaneous derivation of intensities and weighting functions in a general pseudo-spherical discrete ordinate radiative transfer treatment

The retrieval of atmospheric constituents from measurements of backscattered light requires a radiative transfer forward model that can simulate both intensities and weighting functions (partial derivatives of intensity with respect to atmospheric parameters being retrieved). The radiative transfer equation is solved in a multi-layer multiply-scattering atmosphere using the discrete ordinate method. In an earlier paper dealing with the upwelling top-of-the-atmosphere radiation field, it was shown that a full internal perturbation analysis of the plane-parallel discrete ordinate solution leads in a natural way to the simultaneous generation of analytically-derived weighting functions with respect to a wide range of atmospheric variables. In the present paper, a more direct approach is used to evaluate explicitly all partial derivatives of the intensity field. A generalization of the post-processing function is developed for the derivation of weighting functions at arbitrary optical depth and stream angles for both upwelling and downwelling directions. Further, a complete treatment is given for the pseudo-spherical approximation of the direct beam attenuation; this is an important extension to the range of viewing geometries encountered in practical radiative transfer applications. The numerical model LIDORT developed for this work is able to generate intensities and weighting functions for a wide range of retrieval scenarios, in addition to the passive remote sensing application from space. We present a number of examples in an atmosphere with O 3 absorption in the UV, for satellite (upwelling radiation) and ground-based (downwelling radiation) applications. In particular, we examine the effect of various pseudo-spherical parameterizations on backscatter intensities and weighting functions with respect to O 3 volume mixing ratio. In addition, the use of layer-integrated multiple scatter output from the model is shown to be important for satellite instruments with wide-angle off-nadir viewing geometries.

III-V nitrides for electronic and UV applications

Tremendous progress has been made in recent years in the growth, doping and processing technologies of the wide bandgap semiconductors. The principal driving force behind this activity is the potential use of, for example, the 1114 nitrides in high-power, high-temperature, high-frequency electronic and optical devices resistant to radiation damage. This article reports the current state of the art for producing some selected devices from the III-V nitrides.

4H-SiC visible blind UV avalanche photodiode

The first 4H-SiC avalanche photodiode for visible-blind UV applications has been designed and fabricated successfully. The device structure is described and the photo-responsivity characteristics presented. The observation of a positive temperature coefficient for an avalanche breakdown voltage up to 257/spl deg/C is also discussed.

Influence of hydrogen on the colour center formation in optical fibers induced by pulsed UV-laser radiation. Part 1: all silica fibers with high-OH undoped core

Creation of colour centers in fused silica fibers is the main problem during transmission of high-power UV-laser radiation, that leads to solarization and hence decreasing transmission. By loading commercial fused silica fibers with hydrogen, we found a way to improve the transmission properties through the reduction or suppression of solarization. The transmission behaviour of hydrogen loaded high-OH fibers for 266 nm pulsed laser radiation has been studied. Spectroscopic experiments explain many aspects of colour center creation and annealing and allow the determination of kinetic data for the underlying reactions. Based on this work it is possible to realize fiber optic beam delivery systems for frequency quadrupled Nd:YAG lasers and for other high power UV laser sources like excimer-lasers. These results may also be useful for the improvement of bulk fused silica for UV applications.

Borate Materials in Nonlinear Optics

What properties determine an effective nonlinear optical (NLO) material? These are reviewed and summarized for recently described borate compounds—materials that have proven to be superior to other commonly used NLO materials for UV applications. The Figure shows the arrangement of [B2O5] and [NbO6] groups within the unit cell of CsNbOB2O5.

Design and fabrication technology of thinned backside-excited CCD imagers and the family of the electron-bombarded CCD image tubes

The results of more than 10 years experience in design and manufacturing of thinned backside illuminated CCDs of different types are summed up. Based upon the EB CCDs created, the family of intensified electron-bombarded CCD image tubes has been designed, fabricated and tested. This family includes: the single-stage Gen I type EB CCD devices with the 532 × 580 and 780 × 580 pixels CCDs; the “hybrid” (the EB CCD tube plus Gen I image intensifier) devices; and the EB CCD tubes with the 40 mm photocathode and image demagnification factor 3:1. The results of tests of these devices are presented and discussed. Besides, the near future projects concerning EB CCD tubes with 80 mm photocathode and with image demagnification factor 5:1, the EB CCD tubes with solar blind photocathodes for the UV and EUV applications are briefly described.

Bilayer structure of PdAl 2O 3 for UV vidicon applications

A bilayer structure of PdAl 2O 3 was developed as a signal plate for vidicon TV tubes. The 20 Å thick Pd layer served as the conducting plate while the 30–50 Å thick Al 2O 3 coating functioned as the transparent protecting film. The obtained signla plates had a sheet resistance of 2.5 KΩ and a transmission coefficient of 71% at a wavelength of 250 nm. The main advantage of vidicons equipped with such signal plates is to have a dark current of less than 0.05 nA, which is suitable for UV applications. The PdAl 2O 3 bilayers were produced by a novel sputtering method.

Experimental characterization of the high-brightness electron photoinjector

Abstract Operational experience of the emittance compensated photoinjector at the Brookhaven Accelerator Test Facility (ATF) is presented in this paper. The photoinjector has demonstrated the stability and reliability required for UV and X-ray FEL applications. The RF gun has been routinely running at more than 100 MV/m peak acceleration field; the laser system of the photoinjector has achieved 2% peak to peak energy stability, 0,5% point stability and better than 2 ps timing jitter. The highest measured quantum efficiency of the Cu cathode is 0.05%. The electron beam bunch length was measured to be 10 ps using a linac RF phase scan. The normalized rms emittance for 0.5 nC charge was measured, to be from 1 to 2 mm rad, which agrees with PARMELA simulations.

Nonlinear optical materials based on MBe2BO3F2 (M=Na,K)

MBe2BO3F2 (M=Na,K) have been discovered to be nonlinear optical (NLO) materials for UV applications. They have relatively large NLO coefficients: deff is about 2.5 times as large as that of KH2PO4 (λ=1079 nm, Nd:YAP laser), the UV cutoff wavelengths are as short as 155 nm, and they have a moderate birefringence of nearly 0.10. Their structures are characterized by an infinite sheet which is formed by six-membered rings [Be2BO6F2] with Be-O and B-O edges in common. Such structures are favorable for good NLO properties. These NLO properties make MBe2BO3F2 promising candidates for vacuum UV NLO materials.

Anti‐reflective coating for deep UV lithography process enhancement

AbstractWe describe here performance enhancements provided by an anti‐reflective coating (ARC), developed for deep UV applications. The reduction in substrate reflections provided by the ARC layer results in significant increases in resolution capability and process latitude compared to single layer deep UV resist. Increased linewidth control and patterning capability for highly reflective, grainy, and topographical substrates is demonstrated.

T‐BOC blocked hydroxyphenyl‐methacrylates: On the way to quarter micron deep‐UV lithography

Abstractt‐Butyloxycarbonyl (t‐BOC) blocked compounds based on the protection of phenolic groups, e.g. poly‐4‐hydroxystyrene derivatives, Bisphenol A type dissolution inhibitors, or onium salt photoacid generators, have found widespread research interest for photoresist systems with excellent photosensitivity and high resolution power. We have made an extension of this approach using new phenol type polymers. This contribution presents first details on the chemistry of these systems and results of their lithographic evaluation as positive tone photoresists for deep UV applications.

Diamond-like carbon films for electroluminescent applications

Diamond-like carbon (DLC) films grown by plasma-enhanced chemical vapor deposition are employed for the first time as an active layer in an alternating current (a.c.) thin-film electroluminescent (ACTFEL) device configuration. The ACTFEL device configuration consists of the DLC active layer sandwiched between two insulating layers which are contacted by a reflecting and transparent electrode. A large a.c. waveform with a small duty cycle is applied with a sufficiently large amplitude so that the DLC layer electrically breaks down; the insulators prevent this breakdown from being catastrophic. Electroluminescence arises from radiative recombination of electrons and holes via bandtail-to-bandtail states. This type of luminescence is inherently very broad band and the electroluminescence appears white. We have been able to produce electroluminescent emission well into the UV region of the electromagnetic spectrum so that these devices are potentially useful for visible and UV applications. The brightness and efficiency of our devices are very low to date: 0.5 ft lambert and 0.002 lm W -1.