Photodetectors

Some of these demonstrations were implemented for wearable applications by exploiting the material's exceptional robustness and flexibility. [5,6] However, there remain major obstacles that hinder the industrial adoption of MoS 2 and other 2D TMDC materials. The most challenging obstacle has been finding an industrially compatible method that enables the production of these materials on a mass scale. We have recently demonstrated that electrodeposition is a potentially viable method for solving this challenge. [7,8] Electrodeposition offers important advantages in 2D material production over other methods such as chemical vapor deposition (CVD), [9,10] sputtering, [11] or atomic layer deposition (ALD). [12] Electrodeposition is not a lineof-sight deposition method as material growth occurs at electrical contacts and is controlled by electrical potential or current. [13] It can hence be utilized to deposit materials over 3D surfaces including patterned nanostructures of high aspect ratios. [14-17] In addition, electrodeposition is usually performed at room temperature, avoiding harsh environments such as plasma or extremely high temperatures, which can damage pre-existing materials on the substrate, such as graphene electrodes. [7] However, there is an important limitation with electrodeposition that needs to be overcome. This method requires an electrically conductive surface from which materials are traditionally grown vertically. [18] Depositing a semiconductor material on a conductor provides a low resistance current path in planar (opto-) electronic devices such as transistors and photodetectors, thus limiting the use of electrodeposition traditionally to certain vertical device structures or metal interconnects (through the dual damascene process). [19] Prior to the work described herein, this limitation has been a drawback, specifically for developing 2D material based devices where planar structures that exploit the unique 2D properties of the material are the "natural" route forward. [20-23] Creating innovative techniques to electrodeposit planar 2D materials over non-conducting surfaces would solve this limitation and open new routes where the insulator base can be utilized, such as in transistor gating. In the early 1990s, Nishizawa et al. described the electrochemical growth of poly(pyrrole)

Photo-conducting CdS films were coated on glass at 450 °C using cadmium chloride and thiourea as Cd and S sources, respectively, with different concentrations. The sprayed CdS films are crystallized in the hexagonal structure and orienting along (0 0 2) plane with good adherence. All the films have high optical absorption in the visible region showing optical bandgap values in the range of 2.39-2.43 eV. The variation of precursor alters the surface morphology of the films. The formed grains are uniformly spread over the substrate and highly agglomerated at 0.15 M concentration. Band to band emission and defect-related emission are reported using photoluminescence (PL) measurements. The CdS device shows relatively high photosensitivity of 0.4 A/W, detectivity of 8.46 × 10 10 Jones, external quantum efficiency (EQE of 140%) with a rise time about 0.2 s and decay time about 0.3 s. These results propose that the CdS thin films are potential candidates for the visible photo-detector applications prepared using an easy and low-cost fabrication method.

The light detection efficiency of Photon detecting components is very much dependent on the operating temperature. Rise in operating temperature reduces their ability of photon detection and reduced output signal. This effect becomes prominent in the cases where very weak signals are needed to be detected. There are various methods which can be applied to cater for the situation of changing ambient temperature or the temperature of the component itself. This study present a method which tracks the temperature changes as seen by the device and hence adjusts the bias voltage being supplied to it. The bias voltage mainly depends upon the temperature coefficient of the component and hence adjusts itself. Design and testing method of bias power supply are presented along with the graphical presentation of result. Streszczenie. Pomiar światła przy wykorzystaniu fotodiody bardzo zależy od temperatury-szczególnie w przypadku małego sygnału wyjściowego. W zaproponowanym układzie zasilania zmienia się napięcie w zależności od temperaury. Obwód zasilania fotodiody z kompensacją temperatury Introduction Temperature compensation becomes necessary in situations where the ambient temperatures keep varying or the components itself are prone to temperature changes as their operation goes along[1]. The situation effects the overall operation of electronic circuitry in terms that required output keep changing drastically. In this regard several approaches have been adopted by researchers, these pertain to use of Zener diodes, Peltier elements and N-JFETs [2] as reference for compensation. Nishida etal also presented a temperature compensation model to work with avalanche photodiodes [3], whereas,Webb et al [4] claimed a quantum efficiency of up to 100% after carrying out temperature compensation for an RAPD. Tajammal and Nagi [5] presented a temperature compensation solution for laser diodes.

Two-dimensional transition metal dichalcogenides have attracted much attention in the field of optoelectronics due to their tunable bandgaps, strong interaction with light and tremendous capability for developing diverse van der Waals heterostructures with other nanomaterials.

A new optical technique for microwave single sideband modulation is reported. It uses metal-semiconductor-metal Schottky photodiodes formed in a GaAs/Al0.3Ga0.7As materials system to detect microwave in-phase and quadrature signals on optical carriers. Modulation of the photodetector bias voltages results in a single sideband modulation of the microwave signal, rf and undesired-sideband suppression of 36 dB and 27 dB, respectively, were achieved. The optical wavelength was 850 nm, and the bandwidth of the photodetectors is greater than or equal to 29 GHz.

A new optical technique for microwave single sideband modulation is reported. It uses metal-semiconductor-metal Schottky photodiodes formed in a GaAs/Al0.3Ga0.7As materials system to detect microwave in-phase and quadrature signals on optical carriers. Modulation of the photodetector bias voltages results in a single sideband modulation of the microwave signal, rf and undesired-sideband suppression of 36 dB and 27 dB, respectively, were achieved. The optical wavelength was 850 nm, and the bandwidth of the photodetectors is greater than or equal to 29 GHz.

—To date, the photodiode still the first choice component is used in optical communication, especially for visible light communication (VLC) system. It has advantages of speed, energy consumption, and sensitivity, compared to other devices (e.g. image sensor). There are many practical implementations of high-speed VLC which uses photodiode. Commercially available photodiode typically have specific characteristics, so that it needs some consideration to be used as optimal receiver devices in VLC system. In this paper, analysis of received power characteristics of the photodiode in indoor line-of-sight (LoS) channel of VLC system is discussed. MATLAB® simulation is used as approach model (student version). The experiments are done by changing several parameters such as the semi-angle half power of the transmitter, distance from the transmitter to receiver, room size, field-of-view (FOV), lens index and optical filter gain. From the results, it can be known that distance, room size, FOV and LED power factor to have linear characteristic against the received power of commercial photodiode. Also in LoS channel model, the gain of optical filter and lens index plays an important role in defining the characteristics of received power.

We present a self-powered, high-performance graphene-enhanced ultraviolet silicon Schottky photodetector. Different from traditional transparent electrodes, such as indium tin oxides or ultra-thin metals, the unique ultraviolet absorption property of graphene leads to long carrier life time of hot electrons that can contribute to the photocurrent or potential carrier-multiplication. Our proposed structure boosts the internal quantum efficiency over 100%, approaching the upper-limit of silicon-based ultraviolet photodetector. In the near-ultraviolet and mid-ultraviolet spectral region, the proposed ultraviolet photodetector exhibits high performance at zero-biasing (self-powered) mode, including high photo-responsivity (0.2 A W−1), fast time response (5 ns), high specific detectivity (1.6 × 1013 Jones), and internal quantum efficiency greater than 100%. Further, the photo-responsivity is larger than 0.14 A W−1 in wavelength range from 200 to 400 nm, comparable to that of state-of-the-art Si, GaN, SiC Schottky photodetectors. The photodetectors exhibit stable operations in the ambient condition even 2 years after fabrication, showing great potential in practical applications, such as wearable devices, communication, and “dissipation-less” remote sensor networks.

Two of the key challenges in the realisation of focal plane arrays based on type-II InAs/GaSb superlattices (T2SL) are the difficulty in achieving a good sidewall profile and the increased dominance of surface leakage current as the device dimensions shrink. We report the electrical and morphological results of test pixels for mid-wave infrared T2SL photodiodes etched using a Cl2/Ar based inductively coupled plasma reactive ion etching (ICP-RIE) process and passivated using SU-8 epoxy photoresist. The etch rate and sidewall surface morphology of GaSb, InAs, and InAs/GaSb T2SL materials are compared after dry etching under the same conditions, leading to the determination of an optimal etch rate. The effect of surface treatment using selected wet chemical etchants before passivation on the surface leakage current is presented. Limitations of the dry etching recipe and further improvement of the sidewall verticality and smoothness are also discussed. Good sidewall profiles and bulk-limited dark currents are demonstrated for T2SL photodiodes etched to depths between 1.5 and 3.5 μm with a pitch size down to 12 μm.

Asymmetric twin-waveguide (ATG) technology has been shown to be a versatile and high-performance platform for the integration of a wide range of photonic integrated circuits. Following the conceptual and theoretical description in the preceding paper, here we discuss several archetype ATG-based photonic integrated devices and circuits. We present results on the three basic device classes that span the entire range of photonic component needs: light emitters, detectors, and light transporting devices (e.g., waveguides) that have been realized using the twin waveguide platform. Specifically, we discuss Fabry-Pe´rot and wavelength-tunable lasers, high-bandwidth p-i-n photodiodes, a polarization-insensitive arrayed waveguide grating receiver with integrated p-i-n photodiodes, as well as combinations of functions including integrated electroabsorption-modulated lasers, and a semiconductor optical amplifier integrated with a p-i-n photodiode. Finally, we address potential integration challenges and novel applications of the ATG scheme, and avenues for improvement.

Pristine and neodymium-doped (3, 6, and 9 wt.%) ZnO nanostructured thin films were deposited on glass sub-strates using the chemical bath technique. The changes in structural, topographical, photoluminescence, and UV detection properties have been studied. XRD studies confirmed the ZnO phase with a hexagonal structure with a strong prevalence of (002) peak. Nd-doping reduces the bandgap value of the grown material from 3.33 to 3.18 eV. The photoluminescence studies of grown nanowires exhibited the presence of luminescence centers at 387, 412, 438, 452, 477, and 525 nm, respectively. The photocurrent value is increased from 5.37 × 10 − 7 to 3.77 × 10 − 6 A on increasing the Nd doping content from 0 to 6%. The Responsivity, External quantum efficiency, and Detectivity of pristine and doped samples were also studied. We found that the 6% Nd-doped sample shows improved values of optoelectronic parameters which indicate that it is a potential candidate for photodetector applications.

The main aim of this work is to investigate the real CMOS imaging possibilities of standard (not CMOS imaging enhanced) 0.5µm and 0.35µm CMOS processes available for in-house fabrication at the Fraunhofer IMS by performing an extensive study of standard available photodetector structures, mainly based on reverse biased p-n junctions and/or metal-oxide-semiconductor capacitors (MOS-C). Moreover, novel concepts of photodetector pixel structures and readout circuits are proposed, modelled, simulated, fabricated, and characterised, that should achieve an improvement in performance as well as new application developments in the area of CMOS imaging systems. The latter, undergoing as a small amount of changes (extra masks, thermal steps, ion implantations, etc.) as possible within the standard CMOS processes mentioned. In this sense, in Chapter 1 a brief review of the fundamentals of silicon oriented photodetection and electronic devices physics is given, some of the basic postulates of w...

The performance of three types of InGaAs/InP avalanche photodiodes is investigated for photon counting at 1550 nm in the temperature range of thermoelectric cooling. The best one yields a dark count probability of $% 2.8\cdot 10^{-5}$ per gate (2.4 ns) at a detection efficiency of 10% and a temperature of -60C. The afterpulse probability and the timing jitter are also studied. The results obtained are compared with those of other papers and applied to the simulation of a quantum key distribution system. An error rate of 10% would be obtained after 54 kilometers.

Layered semiconductors of the IIIA-VIA group have attracted considerable attention in (opto)electronic applications thanks to their atomically thin structures and their thickness-dependent optical and electronic properties, which promise ultrafast response and high sensitivity. In particular, 2D indium selenide (InSe) has emerged as a promising candidate for the realization of thin-film field effect transistors and phototransistors due to its high intrinsic mobility (>10 2 cm 2 V −1 s −1) and the direct optical transitions in an energy range suitable for visible and near-infrared light detection. A key requirement for the exploitation of large-scale (opto)electronic applications relies on the development of low-cost and industrially relevant 2D material production processes, such as liquid phase exfoliation, combined with the availability of high-throughput device fabrication methods. Here, a β polymorph of indium selenide (β-InSe) is exfoliated in isopropanol and spray-coated InSe-based photodetectors are demonstrated, exhibiting high responsivity to visible light (maximum value of 274 A W −1 under blue excitation 455 nm) and fast response time (15 ms). The devices show a gate-dependent conduction with an n-channel transistor behavior. Overall, this study establishes that liquid phase exfoliated β-InSe is a valid candidate for printed high-performance photodetectors, which is critical for the development of industrial-scale 2D material-based optoelectronic devices.