Electro-optical Characterization Research Articles

Distributed Bragg reflector lasers emitting between 696 and 712 nm

The authors report on design, fabrication, and electro-optical characterization of single-frequency diode lasers emitting around 696, 707, and 712 nm. This has been achieved by a variation of the periods of the 10th order surface Bragg gratings implemented on a single epitaxial wafer. Depending on the wavelength, the devices achieved an optical output power of up to 60 mW at a current of 150 mA and spectral linewidths of about 400 kHz (full width at half maximum (FWHM)) and 20 kHz (Lorentzian).

High Power Distributed Bragg Reflector Lasers at 689.45 nm for Quantum Technology Applications

Distributed Bragg Reflector semiconductor lasers are ideally suited for quantum technology applications due to their high efficiency, small footprint, and tunability in combination with the frequency stability provided by an integrated frequency selective element. Here we present the design, fabrication, and electro-optical characterization of DBR lasers optimized for strontium-based quantum technology applications at 689.449 nm. The devices achieved an optical output power of up to 88 mW, four times more than previously reported, as well as a spectral linewidth of 0.4 MHz.

Investigation of AlN/Si based heterogeneous Junction using inter-digitated electrodes for enhanced UV light detection

A 200 nm thick AlN layer is fabricated by Hydride Vapor Phase Epitaxial (HVPE) technique onto the n-type Silicon < 111 > wafer. After epitaxial growth the AlN is masked and 100 nm thick interdigitated electrodes of Silver are deposited by the atomistic scaled Physical Vapor Deposition (PVD) system. These interdigitated electrodes are further examined with five possible circuit configurations of AlN/Silicon under multiple biases and temperatures. Different electrical and electro-optical characterization such as Current-Voltage, Charge Deep Level Transient Spectroscopy and Kinetics of Dark and UV current; have been performed for each configuration. For all such cases the Ultra-Violet (UV) light has been sensed and found that the reversed biased silicon coupled with interdigitated AlN schemes may provide largest responsivity under both photovoltaic and photoconductive modes. Also, the photo-conversion gain (ratio of UV Current / Dark Current) of each case under different physical conditions have also been emulated and found that the same reverse biased configuration leads higher extent of photo-conversion gain. The charge based transient analysis using (Q-DLTS) have been performed for all said configurations and it is found that the same reverse biased scheme offers largest magnitude of capture cross section i.e. ~ 10−18 cm2, which may capture larger extent of free charge carriers in UV mode and could be opted for enhanced UV light detection.

Electro-optic characterization of synthesized infrared-visible light fields

The measurement and control of light field oscillations enable the study of ultrafast phenomena on sub-cycle time scales. Electro-optic sampling (EOS) is a powerful field characterization approach, in terms of both sensitivity and dynamic range, but it has not reached beyond infrared frequencies. Here, we show the synthesis of a sub-cycle infrared-visible pulse and subsequent complete electric field characterization using EOS. The sampled bandwidth spans from 700 nm to 2700 nm (428 to 110 THz). Tailored electric-field waveforms are generated with a two-channel field synthesizer in the infrared-visible range, with a full-width at half-maximum duration as short as 3.8 fs at a central wavelength of 1.7 µm (176 THz). EOS detection of the complete bandwidth of these waveforms extends it into the visible spectral range. To demonstrate the power of our approach, we use the sub-cycle transients to inject carriers in a thin quartz sample for nonlinear photoconductive field sampling with sub-femtosecond resolution.

A step beyond in steady-state and time-resolved electro-optical spectroscopy: Demonstration of a customized simple, compact, low-cost, fiber-based interferometer system.

Electro-optical spectroscopy is nowadays a routine approach for the analysis of light induced properties and dynamical processes in matter, whose understanding is particularly crucial for the intelligent design of novel synthetic materials and the engineering and optimization of high-impact optoelectronic devices. Currently, within this field, it is the common choice to rely on multiple commercial setups, often costly and complex, which can rarely combine multiple functions at the same time with the required sensitivity, resolution, and spectral tunability (in both excitation and detection). Here, we present an innovative, compact, and low-cost system based on “three in one” components for the simultaneous electro-optical material and device characterization. It relies on compact fiber-coupled Fourier transform spectroscopy, the core of the system, enabling a fast spectral analysis to acquire simultaneously wavelength and time resolved photoluminescence (PL) maps (as a function of the time and wavelength), PL quantum yield, and electroluminescence signal. Our system bypasses conventional ones, proposing a new solution for a compact, low-cost, and user-friendly tool, while maintaining high levels of resolution and sensitivity.

Synthesis of GaSb-VDS thin film by electron beam physical vapour deposition and its electro-optical characterization as prerequisite for p-n device construction

III–V materials owing to have low effective masses, high mobilities and a direct band gap, exhibit suitability for both optoelectronic as well as tunnelling devices. Gallium Antimonide (GaSb), a III–V semiconducting compound, shows narrow band gap and high carrier mobility apposite for high-performance optoelectronics in the mid-IR range.The vertical directional solidification (VDS) is a crystal growth technique employed for the growth of high quality (>6N)bulk crystals, without the seed, without contact to the ampoule wall, without coating and without external pressure.Bulk crystalline GaSb was grown by VDS and then its fractured form is harnessed as source material for synthesis of thin film. GaSb-VDS thin semiconducting film of uniform thickness1.8μm was synthesized at 350°C by electron beam physical vapour deposition method.This thin film is p-type and will be implanted by group VI n-dopant(Telluriumions)impurities to form a junction. For same reason it is characterized for optical, electrical and morphological properties prior to support its claim as a device construction substrate. XRD, EDAX Raman, AFM, four probe and FTIR techniques were employed for the confirmation of crystalline, compositional, morphological, resistivity and optical band gap respectively.XRD of film reveals peaks close to 25°and42° corresponding to [111] and [220] crystal planes are in agreement as reported for crystalline GaSb. Raman spectra also confirm the GaSb crystalline film formation. SEM and EDAX of synthesized film found to be polycrystalline and agree the weight%of35.36and64.64 for GaandSb respectively. Four-probe technique yields the sheet resistance of 5.6Ωpersquare and optical band gap 0.728eV was obtained by FTIR. Optical band gap of the semiconducting film is obtained as 0.728eV and a Sheet resistance of5.6Ωpersquare. Uniform monolayer with low defect density is confirmed by Atomic force microscopy.It establishes formation of a p-type GaSb VDS thin film that is good for n-type implantation and show rectification tendency.

Characterization and correction of serial deferred charge in LSST camera ITL CCDs

Electro-optical testing and characterization of the Vera C. Rubin Observatory Legacy Survey of Space and Time Camera has shown that the focal plane charge-coupled devices developed by Imaging Technology Laboratory exhibit serial deferred charge signal in excess of the expected proportional deferred charge loss from global charge transfer inefficiency. We model the additional deferred charge as resulting from localized charge trapping in the serial register and from a signal-dependent electronic offset effect. A physically motivated forward deferred charge simulation algorithm and a reverse deferred charge correction algorithm were developed in order to correct for deferred charge during data reduction and reduce the possible impacts on Rubin Observatory project science goals. We apply the correction algorithm to calibration data and demonstrate the ability to reduce deferred charge signal measured in the overscan pixel regions and remove the serial pixel correlations resulting from the redistribution of charge between pixel neighbors during readout.

Carbon Nanotubes Blended Nematic Liquid Crystal for Display and Electro-Optical Applications

In this paper, we investigate a commercial nematic liquid crystal (LC) mixture namely E7 dispersed with small concentrations of multi-walled carbon nanotubes (MWCNTs). The dielectric and electro-optical characterizations have been carried out in the homogeneously and vertically aligned LC cells. The electro-optical response of LC molecules has been enhanced by 60% after the addition of MWCNTs, which is attributed to the reduced rotational viscosity in the composites. MWCNTs act like barricades for ionic impurities by reducing them up to ∼34.3% within the dispersion limit of 0.05 wt%. The nematic–isotropic phase transition temperature (TNI) of the E7 LC has also been shifted towards the higher temperature, resulting in a more ordered nematic phase. The enhanced birefringence and orientational order parameter in the LC-MWCNTs are attributed to π-π electron stacking between the LC molecules and the MWCNTs. The outlined merits of the LC-MWCNTs composites evince their suitability for ultrafast nematic-based electro-optical devices.

Advanced Packaging Technology for Novel 1-dimensional and 2-dimensional VCSEL Arrays

Abstract In this paper we present an optimized manufacturing technique for special long-wavelength 1-dimensional and 2-dimensional Vertical Cavity Surface Emitting Laser Diode (VCSEL) arrays with focus on die bonding and a special wire bonding process as well as additional possibilities to make the manufacturing more productive and to increase the product quality, reliability, and life time. VCSEL arrays have a very broad application potential. Objective of this paper is the development of an assembly technology for long-wavelength VCSEL arrays with high positioning accuracy for automated production with high total yield, using gold-based conductive glue (because silver migration is a concern) securing high yield and extremely high reliability and lifetime. Due to special customer requirements, a final thickness of the conductive glue of 35 micron with low standard deviation is necessary. For highest reliability, gold wire bonding of the top side contact of the VCSEL to a silicon substrate with gold metallization has been a customer requirement. With the described technique we develop and produce customer specific products with dedicated wavelength, performance, and packaging options. Bases on our findings, very flexible and scalable solutions are possible, matching many different applications. Finally, we will present an overview of our results on the physical and electro-optical characterization of the VCSEL devices. This yielded a very productive manufacturing technique, meeting the requirements mentioned above. Special design features of the VCSEL ensure that the relatively high thermal resistance of the cured conductive glue layer does not impair the electro-optical properties or the lifetime of the VCSELs. For the interconnection of the top side contact we used gold wire with 20 microns diameter, using ball-wedge, Stand-Off Stich Bond process with special loop geometry, required by the customer. Due to the properties of the semiconductor material of the VCSELs a low bonding temperature is required, enabled by our special wire bonding process. Gold wire bonding delivered excellent results, by far exceeding the customer specification. The optical spectrum of the VCSELs and other measurements indicate that the assembly processes do not harm the laser diodes or their electro-optical properties. All customer requirements for the 1-dimensional and 2-dimensional VCSEL arrays have been met. The electro-optical and burn-in data furnished proof of the quality of the engineered assembly technology. The technologies developed for low current as well as high current laser arrays will enable new devices for a huge amount of new applications because of the novel manufacturing processes as well as innovative packaging of the VCSEL arrays.

Modeling and characterization of photovoltaic and photoconductive effects in insulated-gate field effect transistors under optical excitation

Under optical illumination of metal–insulator-semiconductor field effect transistors with insulated gate structure (MISFETs including MOSFETs and TFTs), photo-generated electron-hole pairs (ehp’s) cause the photovoltaic effect (PVE) and the photoconductive effect (PCE) in the electrical characteristics of MISFETs. In the modeling and characterization of MISFETs under optical excitation for both optical sensing and/or electro-optical characterization of traps through photonic C-V and I-V responses, it is necessary to separate the PVE from the PCE in MISFETs. In this letter, we report the modeling and separate characterization of the PVE from the PCE in MISFETs applicable to MOSFETs and TFTs. We confirmed the proposed model and the technique through experimental results adopting the different substrate contact configurations and optical power of the device under characterization. As a result, the effective surface potential change for the PCE (VPCE) and the effective substrate potential change for the PVE (VPVE) could be quantitatively extracted.

Fast Switching Dual-Frequency Nematic Liquid Crystal Tunable Filters.

We develop tunable optical filters with dual-frequency nematic liquid crystal optical retarders to enable fast switching between the passed wavelengths. The filters are composed of a series of two liquid crystal optical retarders. We select the specific thicknesses of the liquid crystal retarders and use individual biasing schemes to continuously tune the wavelength and bandwidth of the filter. This enables fine-tuned filter switching speeds of filter operation in the ms regime. We present theoretical predictions and experimental results for the electro-optical filter characterization as well as an example application for our filter in total internal reflection fluorescence microscopy. We find that our filter switching speeds can be as short as a few ms, an order of magnitude improvement over typical mechanical filter wheel switching speeds. The quality of our fluorescence images is similar to those obtained by conventional filters.

Electro-optical performance characterization of charge coupled device for directional polarimetric camera

The directional polarimetric camera (DPC) is a space-borne polarimetric sensor which has the characteristics of ultra-wide angle and low-distortion imaging. The charge coupled device (CCD) detector is the core component of the photoelectric conversation for DPC which is used to obtain multi-angle, multi-spectrum polarization information, so it is necessary to measure its electric-optical performance comprehensively before installed in the DPC. Instrumentation is proposed and developed with the aim to evaluate the electro-optical performance of array CCD. The instrument mainly consists of light source subsystem, detector imaging subsystem and detector refrigeration subsystem with the structure of optical-mechanical-electric integration. The photoelectric response performance and the spectral characteristics of the detector are comprehensively and quantitatively tested and analyzed. The key parameters, such as quantum efficiency, dark current, full well capacity and system gain are measured; the spectrum response of the detector is measured from 400 nm to 940 nm with the spectral resolution around 1 nm. The experimental results show that the CCD used for DPC has no defective pixels, the system gain is 0.0245DN/e−, the full well charge is 138.8ke−/pixel, the dark current is 990.5e−/pixel/s when the detector works at 6 °C. The photo response non-uniformity under different wavelengths is better than 3% and the linearity error under different wavelengths is less than 1%. The quantum efficiency has a strong dependence on temperature in the near-infrared band, the maximum fluctuation of QE in 865 nm and 910 nm is 5.84% and 6.65%, respectively, in the temperature range from 0 °C to 20 °C. The Instrumentation can be used in the screening and testing the electro-optical performance of scientific grade CCD.

Electro-optical characterization of a weakly polar liquid crystalline compound influenced polyvinyl pyrrolidone capped gold nanoparticles

Dielectric and electro-optic properties of a weakly polar nematic liquid crystals (NLCs) based on polyvinyl pyrrolidone capped gold nanoparticles doping has been reported. The dielectric spectra of these composites with a concentration of 0.25 wt%, 0.5 wt%, and 1.0 wt% are recorded in the frequency range of 42 Hz to 5.5 MHz. Dielectric permittivity and dielectric loss in these samples have been analyzed for both homogeneously-aligned and vertically-aligned liquid crystal (LC) cells. It has been observed that GNPs doping significantly reduce the threshold voltage (~27%) for LC reorientation which is explained by increased dielectric anisotropy and decreased splay elastic constant of doping LC cells. Nearly 57% faster fall time is also observed as a consequence of a remarkable reduction in the relaxation time (about short molecular axis) thus rotational viscosity of the doping LC cells. GNPs doping has an auspicious application to the fields of LC devices and displays. The present work shows that the composite under investigation performs far better than the pure LC cell in the display as well as photonic applications.

P-Oligophenylene-based polymeric fluorescent nanofilms. Synthesis, electrooptical characterization and application in aqueous phase nitroaromatic detection

Model compounds and new polymeric materials bearing p -terphenylene and p -quaterphenylene units tethered by their para-positions were synthesized. PTF , with terphenylene groups tethered with C(CF 3 ) 2 groups, reached the higher polymerization degrees. All these materials, except PTF , show variable amounts of local ordering in the form of J- and H-aggregates. The insensibility of the fluorescence response of PTF films to casting conditions or the excitation wavelength makes it a good candidate for thin-film chemosensory applications. Thus, thin films of PTF and its biphenylene homolog PBF were used as fluorescent active layers for sensitive detection of nitroaromatics in water media. PTF films are quite sensitive to nanomolar concentrations of TNT, the quenching being a combination of PET and IFE contributions. PBF presents a weaker response to TNT that arises from hindered TNT diffusion into the polymeric film. On the contrary, PBF is very sensitive towards picric acid, PA. The sensing configuration polymeric film/aqueous solution studied here demonstrated promising potential for the direct sensing of nitroaromatics in water bodies of industrial and city areas. • Synthesis of terphenylene and quaterphenylene macromolecular materials. • PTF , with p -terphenylene tethered by C(CF3)2 groups, was soluble and amorphous. • All materials, except PTF , present local ordering as H- and J-aggregates. • Fluorescence response of PTF films is independent of casting conditions or λexc • The fluorescence of PTF and PBF films is responsive to nanomolar solutions of TNT and PA.

Impact of seed layer annealing on the optoelectronic properties of double-step CBD grown n-ZnO nanowires/p-Si heterojunctions

In the current work, n-ZnO nanowires are grown by employing double-step chemical bath deposition (CBD) technique on p-Si substrate for the fabrication of n-ZnO nanowires/p-Si heterojunction diodes. The as-deposited ZnO seed layer is furnace annealed at 400 °C and 600 °C for 30 min in argon ambient for studying comparative changes of their optoelectronic properties. The systematic change of surface morphology, chemical compositions, crystallite structure, oxidation states, defect levels and photodetecting properties due to annealing of the seed layer has been investigated. Annealing the seed layer at 400 °C exhibits a nanosphere-like structure and provides superior nucleation sites for vertical growth of the nanowires in comparison to the as-deposited and 600 °C -annealed samples. The electrical, electro-optical and physical characterization results suggest the nanowires grown on 400 °C -annealed ZnO seeds to provide superior performance.

Design of High-Efficiency SPADs for LiDAR Applications in 110nm CIS Technology

Single photon avalanche diodes (SPADs) featuring a high detection rate of near-IR photons are much desired for outdoor LiDAR based on direct time-of-flight (ToF). This article presents the complete design flow of a SPAD detector for LiDAR. First, the selection of the emitter wavelength is discussed, considering the maximum allowed power underlying eye safety regulations, solar irradiance, and reflected signal power. Then, the choice of the SPAD structure is discussed based on the TCAD simulation of quantum efficiency and crosstalk. Next, the proposed P-well/ Deep N-well SPAD is explained. The electro-optical characterization of the detectors is presented as well. The performance of the time-of-flight image sensors is determined by the characteristics of the individual SPADs. To fully characterize this technology, devices with various sizes, shapes, and guard ring widths have been fabricated and tested. The measured mean breakdown voltage is 18 V. The proposed structure has a 0.4 Hz/μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> dark count rate and 0.5% afterpulsing. The FWHM (total) jitter and photon detection probability at 850nm wavelength are of 92 ps and 10%. All figures have been measured at 3 V excess voltage. Finally, the performance of the SPAD detector is analyzed by evaluating the signal-to-noise ratio at different acquisition times. Distance ranging measurements have been performed, achieving a depth resolution of 1 cm up to 6.3 m range.

Directly addressable GaN-based nano-LED arrays: fabrication and electro-optical characterization

The rapid development of display technologies has raised interest in arrays of self-emitting, individually controlled light sources atthe microscale. Gallium nitride (GaN) micro-light-emitting diode (LED) technology meets this demand. However, the current technology is not suitable for the fabrication of arrays of submicron light sources that can be controlled individually. Our approach is based on nanoLED arrays that can directly address each array element and a self-pitch with dimensions below the wavelength of light. The design and fabrication processes are explained in detail and possess two geometries: a 6 × 6 array with 400 nm LEDs and a 2 × 32 line array with 200 nm LEDs. These nanoLEDs are developed as core elements of a novel on-chip super-resolution microscope. GaN technology, based on its physical properties, is an ideal platform for such nanoLEDs.

Effect of oil palm leaf-based carbon quantum dot on nematic liquid crystal and its electro-optical effects

ABSTRACT The present study discloses electro-optical characterisation of oil palm leaf-based carbon quantum dots (CQDs size range 4–6 nm) dispersed in nematic liquid crystal E 48 at different concentrations (0.1 wt/wt. %, 0.2 wt/wt. % and 0.3 wt/wt.% named as MIX 1, MIX 2 and MIX 3). Thevolatile memory has been evident from the dielectric and electro-optical measurement with the application of dc bias voltage. Electro-optical results demonstrate that the total response time reduces to ~ 20% for MIX 1 and it increases to ~ 24% for MIX 2 and ~ 42% for MIX 3 respectively, hence MIX 2 and MIX 3 exhibits slower response compared to pure nematic. The birefringence has been found to be around 0.22 for pure nematic, 0.25 for MIX 1, 0.19 for MIX 2 and 0.16 for MIX 3 at 40°C temperature. The figure-of-merit parameter has been found to be almost 27 µm2/sec for pure nematic E 48, 43 µm2/sec for MIX 1, 16 µm2/sec for MIX 2 and 11 µm2/sec for MIX 3. This study finds its applicability in, phase shifters, security system and memory devices etc.

Electro-Optical Performance Study of 4H-SiC/Pd Schottky UV Photodetector Array for Space Applications

4H-SiC Schottky photodetector array was fabricated by pulsed dc sputter deposition of palladium thin film as UV semitransparent Schottky contact on active pixel. Results of electro-optical characterization of these devices as a function of temperature varying from 33 to 393 K are presented. A peak spectral responsivity of 122 mAW−1 at 280 nm is observed. Further, spatial response uniformity for a 4 mm $\times4$ mm detector, scanned by UV spot of $100~\mu \text{m}$ diameter, is within ±5%, whereas the crosstalk between the pixels in $4\times 2$ detector array with a pixel size of $850\,\,\mu \text{m}\,\,\times 850\,\,\mu \text{m}$ is within 1.3%. Capacitance at near zero bias is around 11 pF and 4.79 pF at a reverse bias of 30 V. From the ${I}$ – ${V}$ characteristics, the calculated Schottky barrier height is 1.37 eV for 70 A thick palladium metal film on 4H-SiC as against the theoretical value of 1.96 eV. Operating temperature studies on detector UV response at 300 nm have shown that the photo-current response at 113 K falls to half of its peak value at ambient. The responsivity of the detectors at 248-nm wavelength is almost constant over a wide temperature range of 33 to 393 K.

Electro-Optical and Thermophysical Characterization of Poly (Tripropylene Glycol Di-Acrylate)/Liquid Crystal Composite Materials Prepared by Polymerization Induced Phase Separation

This work examines the development and characterization of tripropylene glycol di-acrylate/liquid crystal E7 (TPGDA/LC E7) PDLCs composite materials (polymer-dispersed-liquid-crystals). These systems were produced by UV irradiation photopolymerization (PIPS) of a mixture of the monomer tripropylene glycol di-acrylate (TPGDA) and the liquid crystal E7 (LC E7, a mixture of three cyano-biphenyl and one cyano-terphenyl LCs), in the presence of 2 wt% (of the acrylate/E7 mixture) of a photoinitiator. Electro-optical, thermal and optical characterization was used to understand the effect of the LC concentration on the electro-optical and thermo-physical properties of these materials. Polarizing optical microscopy (POM) and differential scanning calorimetry (DSC) studies were performed to observe the system morphology and to determine the transition temperatures of these materials, both as a function of their composition. The findings showed a slight variation of the nematic-isotropic transition temperature, TNI, of the LC E7 and of the glass transition temperature, Tg, of the TPGDA polymeric matrix as a function of the mass percentage of the LC E7. A very good electro-optical response for the composition 30/70 wt % TPGDA/LC E7 was obtained.