HgCdTe Research Articles

HgCdTe surface passivation with low-temperature plasma-enhanced atomic layer deposited HfO2

Mercury cadmium telluride (Hg1−xCdxTe) is widely utilized for infrared detection applications. However, the quality of the surface and the presence of interface defects significantly impact device performance, so further improvements in surface passivation are still necessary. In this study, we explore the use of plasma-enhanced atomic layer deposition (PE-ALD) to deposit HfO2 as a passivation layer for HgCdTe in the temperature range of 80–160 °C. The insulating film, semiconductor surface, and their interface are characterized using spectral ellipsometry, X-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (EELS), atomic force microscopy (AFM), electron microscopy, and capacitance–voltage (C–V) methods. XPS analysis reveals that the fraction of impurities in the HfO2 films significantly decreases at higher deposition temperatures. Simultaneously, changes in the surface composition of HgCdTe become more pronounced. The bandgap width of HfO2 and the insulator–semiconductor interfacial band discontinuity are estimated using EELS and XPS. The surface morphology of the deposited coatings closely resembles that of the underlying HgCdTe. The permittivity of the insulator and the effective fixed charge strongly depend on the deposition temperature. Our findings demonstrate that low-temperature PE-ALD HfO2 effectively passivates the HgCdTe surface, and we propose an optimal deposition temperature for the further development of HgCdTe-based devices.

Native Oxidation of HgCdTe Compound Semiconductors and Its Impact on Infrared Detectors Performances

The development of high-operating temperature (HOT) infrared imaging systems is motivated by the growing demand to reduce the size, weight, power consumption, and total cost of infrared detectors. HgCdTe photodiodes have unique material properties, making them one of the most promising candidates to produce infrared detectors with background-limited performances at room temperature, as predicted by the "Law 19" photodiode performance metric [1]. However, in state-of-the-art devices, the fraction of anomalous pixel responses increases alongside the detectors' operating temperature and cut-off wavelength. Numerous studies have already identified surface states induced by manufacturing processes as one of the main sources of this issue. As a result, the assessment and understanding of HgCdTe surface chemistry will be critical for future technological advancements.HgCdTe surface processing and its exposition to the environment promotes the formation of surface oxides reported to influence the interface electrical behavior and the global material electronic properties [2]. Nonetheless, the complexity of the HgCdTe surface chemistry makes it challenging to characterize the nature of the surface states caused by the presence of native oxide. As a result, there is no consensus in the literature on the effect of the alloy composition on the formed surface native oxide and its subsequent effects on the passivation quality.The purpose of this work is to investigate the mechanisms underlying the formation of HgCdTe native oxides and discuss their impact on the devices’ electrical performances. Therefore, X-ray Photoelectron Spectroscopy (XPS) and Spectroscopic Ellipsometry (SE) studies were performed in an attempt to understand HgCdTe oxidation as a function of its nominal bulk composition.The samples used in this study were epitaxial Hg(1-x)Cd(x)Te layers grown on CdZnTe substrate with multiple cadmium molar fractions (x ≃ 0.2 to 0.7). A technologically relevant standard wet etching procedure was used to achieve clean, oxide-free surfaces. Freshly etched samples were transported to the XPS in an inert atmosphere using a transfer vessel to representative surfaces and prevent alterations. The surfaces showed no oxides identifiable by XPS, thus showing the effectiveness of the transfer procedure. Furthermore, it was found that the HgCdTe components of these surfaces were not stoichiometric. Particularly, the surfaces were enriched in tellurium regardless of the alloy composition under study. These differences from the nominal composition are induced by the preferred etching of the alloy's components (Cd > Hg >> Te).Dynamic SE measurements were used to monitor native oxide formation in real-time, with scans taken every few seconds for the first hour after exposure to a clean-room environment. Furthermore, the long-term evolution of the surfaces was assessed by taking further measurements over several days. SE trends revealed a two-stage formation of native HgCdTe oxides, with an initial fast oxide growth (<1 hour) followed by a slower oxidation. The findings were supported by XPS measurements on additional samples exposed to air and kept in an airtight plastic box to obtain surface oxides of different thicknesses. Regardless of the alloy composition, the excess surface tellurium is oxidized during early oxide formation. While lengthier environment exposures resulted in oxide thicknesses correlated to the alloy cadmium molar fraction. Therefore, indicating for the first time a clear experimental demonstration of the cadmium contribution to further oxidize the material.Consequently, the combination of surface characterization techniques used in this work allowed us to investigate the formation mechanisms surrounding the native oxide of wet-etched HgCdTe surfaces and to discuss the effect of their formation on the device's performance. Acknowledgements :This work, carried out on the Platform for Nanocharacterisation (PFNC), was supported by the “Recherche Technologique de Base” and "France 2030 - ANR-22-PEEL-0014" programs of the French National Research Agency (ANR) References :[1] M. Kopytko and A. Rogalski, New Insights into the Ultimate Performance of HgCdTe Photodiodes, Sensors Actuators A Phys. 339, 113511 (2022).[2] E. R. Zakirov, V. G. Kesler, G. Y. Sidorov, and A. P. Kovchavtsev, Effect of HgCdTe Native Oxide on the Electro-Physical Properties of Metal-Insulator-Semiconductor Structures with Atomic Layer Deposited Al2O3, Semicond. Sci. Technol. 35, 0 (2020).

Nano-Tomography Iinvestigation of Residual Damages in p-Type Doped HgCdTe Semiconductor

Mercury cadmium telluride, Hg1−xCdxTe (MCT), is a semiconductor widely used as an active material for high-end infrared imaging systems. For this semiconductor, state-of-the-art performances are obtained for p-on-n photodiode architectures [1, 2]. The fabrication process of these photodiodes involves the use of ion implantation for the incorporation of dopants. As this process induces irradiation damage, a specific annealing is used to remove most of it. In previous work, we showed by scanning transmission electron microscopy (STEM) that residual defects such as nano-voids and nano-crystals can still be observed despite of the use of damage correction annealing [3].As the crystal quality of the active layer is critical to ensure the best device performances [4, 5], a better understanding of how this process induces defects is needed to limit their occurrences. However, the small size and low density of these defects make their study difficult.In this work, we used FIB-SEM nano-tomography to better understand these residual damages. Indeed, this characterization technique is well suited to our problem as it allows the visualization of large volumes of interest with a resolution down to a few nanometers.MCT epitaxial layers were grown on CdZnTe lattice-matched substrates. These crystals were then implanted with arsenic ions in a random off-axis direction at an energy of 360 keV. The same standard annealing procedure was applied to all samples. In each case, FIB-SEM nano-tomography allows us to extract the defect density as well as the size and depth profiles of the observed defects. These results are confronted with the depth profiles of the dopants concentration from secondary ion mass spectrometry (SIMS).This procedure was applied to equivalent samples with various fluences of implanted arsenic ions and various molar fractions of cadmium in the semiconductor alloy. These variants allow for insight into defect formation mechanisms in light of the solubility of the dopant in the alloy.[1] W. E. Tennant, “Interpreting mid-wave infrared MWIR HgCdTe photodetectors,” Prog. Quantum Electron., vol. 36, no. 2–3, pp. 273–292, 2012, doi: 10.1016/j.pquantelec.2012.05.001.[2] N. Baier, O. Gravrand, C. Lobre, O. Boulade, A. Kerlain, and N. Péré-Laperne, “HgCdTe Diode Dark Current Modeling: Rule 07 Revisited for LW and VLW,” J. Electron. Mater., vol. 48, no. 8, pp. 5233–5240, Aug. 2019, doi: 10.1007/s11664-019-07299-z. [3] C. Lobre, P.-H. Jouneau, L. Mollard, and P. Ballet, “Characterization of the Microstructure of HgCdTe with p-Type Doping,” J. Electron. Mater., vol. 43, no. 8, pp. 2908–2914, Apr. 2014, doi: 10.1007/s11664-014-3147-9.[4] T. Broult, A. Kerlain, V. Destefanis, P. Guinedor, E. Le Bourhis, and G. Patriarche, “Controlled Dislocations Injection in N/P Hg1−xCdxTe Photodiodes by Indentations,” J. Electron. Mater., vol. 48, no. 10, pp. 6108–6112, Oct. 2019, doi: 10.1007/s11664-019-07139-0.[5] K. Jóźwikowski, A. Jóźwikowska, M. Kopytko, A. Rogalski, and L. R. Jaroszewicz, “Simplified model of dislocations as a SRH recombination channel in the HgCdTe heterostructures,” Infrared Phys. Technol., vol. 55, no. 1, pp. 98–107, 2012, doi: 10.1016/j.infrared.2011.10.003.

Optoelectronic performance prediction of HgCdTe homojunction photodetector in long wave infrared spectral region using traditional simulations and machine learning models

This research explores the design of an infrared (IR) photodetector using mercury cadmium telluride (Hg1–xCdxTe). It proposes two- and three-dimensional homojunction models based on p+-Hg0.7783Cd0.2217Te/n–-Hg0.7783Cd0.2217Te, focusing on applications in the long-wavelength infrared range. The photodetector’s performance is analyzed using Silvaco ATLAS TCAD software and compared with analytical calculations based on drift-diffusion, tunneling, and Chu’s approximation techniques. Optimized for operation at 10.6 μm wavelength under liquid nitrogen temperature, the proposed photodetector demonstrates promising optoelectronic characteristics including the dark current density of 0.20 mA/cm2, photocurrent density of 4.98 A/cm2, and photocurrent density-to-dark current density ratio of 2.46 × 104, a 3-dB cut-off frequency of 104 GHz, a rise time of 0.8 ps, quantum efficiency of 58.30 %, peak photocurrent responsivity of 4.98 A/W, specific detectivity of 3.96 × 1011 cmHz1/2/W, and noise equivalent power of 2.52 × 10–16 W/Hz1/2 indicating its potential for low-noise, high-frequency and fast-switching applications. The study also incorporates machine learning regression models to validate simulation results and provide a predictive framework for performance optimization, evaluating these models using various statistical metrics. This comprehensive approach demonstrates the synergy between advanced materials science and computational techniques in developing next-generation optoelectronic devices. By combining theoretical modeling, simulation, and machine learning, the research highlights the potential to accelerate progress in IR detection technology and enhance device performance and efficiency. This multidisciplinary methodology could serve as a model for future studies in optoelectronics, illustrating how advanced materials and computational methods can be utilized to enhance device capabilities.

Native Oxidation of HgCdTe Compound Semiconductors and Its Impact on Infrared Detectors Performances

HgCdTe surface processing and exposition to the atmospheric environment promote the formation of surface oxides, which have been reported to influence the electrical behavior of devices. This work investigates the formation of HgCdTe of air native oxides on epitaxial Hg(1-x)Cd(x)Te layers after a standard wet etching procedure (x ≃ 0.2 to 0.7). Real-Time Spectroscopic Ellipsometry (RTSE) studies were performed to monitor initial native oxide formation in a clean-room environment and revealed a two-stage kinetic of oxide formation. X-ray Photoelectron Spectroscopy (XPS) was used to assess the evolution of the surface chemistry. After etching, the surfaces exhibited an excess of tellurium that oxidized during early oxide formation (< 45min). Longer air exposures resulted in oxide thicknesses correlated to the alloy composition, indicating a cadmium contribution to further oxidize the material. The combination of techniques allowed the investigation of the formation mechanisms surrounding the native oxide of wet-etched HgCdTe surfaces.

Plasmon‐Enhanced Fluorescence of NIR‐Emitting CdxHg1‐xTe Quantum Dots by Ag Nanoprisms

AbstractNear‐infrared (NIR)‐emitting colloidal semiconductor nanocrystals (NCs) draw a lot of attention due to various fields of their potential application, such as bio‐imaging, photovoltaics, photodetectors, light‐emitting diodes, and optical amplifiers for telecommunication. Since they typically suffer from the partial loss of their fluorescence in a solid state, strategies to increase their quantum yields are of outstanding importance. One of the means to improve it is their coupling with structures exhibiting localized surface plasmon resonance (LSPR). As demonstrated for the visible range of light, plasmon‐exciton interactions can enhance the photoluminescence (PL) of CdSe and CdTe NCs. In this work, the influence of the electromagnetic field of plasmonic silver NCs on the PL of CdxHg1–xTe NCs in the NIR region with a special emphasis on tuning the distance between these particle species is studied. In a series of samples prepared by a layer‐by‐layer deposition through polyelectrolytes, a 1.4‐fold PL enhancement at a distance of 9–11 nm between the two layers is observed, while at any other separation emission quenching is a dominating effect. These findings corroborate well with theoretical predictions of an emission increase at these specific distances and can be applied to other types of plasmonic and emitting materials.

Advancing LWIR FSO communication through high-speed multilevel signals and directly modulated quantum cascade lasers.

This study investigates the potential of long-wave infrared (LWIR) free-space optical (FSO) transmission using multilevel signals to achieve high spectral efficiency. The FSO transmission system includes a directly modulated-quantum cascade laser (DM-QCL) operating at 9.1 µm and a mercury cadmium telluride (MCT) detector. The laser operated at the temperature settings of 15°C and 20°C. The experiment was conducted over a distance of 1 m and in a lab as a controlled environment. We conduct small-signal characterization of the system, including the DM-QCL chip and MCT detector, evaluating the end-to-end response of both components and all associated electrical elements. For large-signal characterization, we employ a range of modulation formats, including non-return-to-zero on-off keying (NRZ-OOK), 4-level pulse amplitude modulation (PAM4), and 6-level PAM (PAM6), with the objective of optimizing both the bit rate and spectral efficiency of the FSO transmission by applying pre- and post-processing equalization. At 15°C, the studied LWIR FSO system achieves net bitrates of 15 Gbps with an NRZ-OOK signal and 16.9 Gbps with PAM4, both below the 6.25% overhead hard decision-forward error correction (6.25%-OH HD-FEC) limit, and 10 Gbps NRZ-OOK below the 2.7% overhead Reed-Solomon RS(528,514) pre-FEC (KR-FEC limit). At 20°C, we obtained net bitrates of 14.1 Gbps with NRZ-OOK, 16.9 Gbps with PAM4, and 16.4 Gbps with PAM6. Furthermore, we evaluate the BER performance as a function of the decision feedback equalization (DFE) tap number to explore the role of equalization in enhancing signal fidelity and reducing errors in FSO transmission. Our findings accentuate the competitive potential of DM-QCL and MCT detector-based FSO transceivers with digital equalization for the next generation of FSO communication systems.

Detector size selection for long-range targeting performance in the extended shortwave infrared band

Interest in the eSWIR band is growing due to focal plane array technology advancements with mercury cadmium telluride and type-II superlattice materials. As design and fabrication processes improve, eSWIR detector size, weight, and power can now be optimized. For some applications, it is desirable to have a smaller detector size. Reduced solar illumination in the 2 to 2.5 μm spectral range creates a fundamental limit to passive imaging performance in the eSWIR band where the resolution benefit of small detectors cannot out-compete the reduced SNR in photon-starved environments. This research explores the underlying theory using signal-to-noise ratio radiometry and modeled target discrimination performance to assess the optimal detector size for eSWIR dependent upon illumination conditions. Finally, we model continuous-wave laser illumination in the eSWIR band to compare the effect of detector size on active and passive imaging for long-range object discrimination.

Optoelectronic Material Characterization Platform using RF Topological Edge States

AbstractEfficient characterization of optoelectronic material properties represents a crucial step in the development of next‐generation infrared (IR) materials and devices. For the first time, a sensitive, contact‐free optoelectronic material characterization platform is demonstrated that exploits the unique properties of radio frequency (RF) topological edge states implemented in a topological microstrip waveguide. The topological device is compatible with standard printed circuit board (PCB) processes with no additional materials, stubs, or resonators. The waveguide and topological properties computationally are designed and then experimentally the results are validated with S‐parameter and near‐field measurements. Finally, as a proof of principle, the room temperature spectral response of a micron‐scale thick mid‐wave infrared (MWIR) mercury cadmium telluride (Hg0.70Cd0.30Te) is measured using the topological microstrip and a five‐fold and 20‐fold increase is demonstrated in response when compared to a plain microstrip and trivial bandgap device, respectively. These results open the door to straightforward, low‐cost characterization of optoelectronic films.

All-dielectric grating-assisted absorption enhancement in a subwavelength mercury cadmium telluride layer for infrared photodetectors

Light absorption enhancement in a 1.5 μm thick mercury–cadmium–telluride (Hg0.762Cd0.238Te, MCT) layer at room temperature utilizing 1D dielectric grating at mid-wave infrared (MWIR) wavelengths (3–5 μm) has been theoretically investigated. The optimized dielectric grating facilitates light diffraction and scattering into the MCT-absorbing waveguiding layer resulting in an increased lateral optical path. The light absorption was improved from ∼37.5% to ∼71% (TE) and ∼70% (TM) at normal incidence. With enhanced absorption, the photocarrier generation rate in the thin layer would be comparable to a bulk 5 μm thick MCT layer. A ∼3× reduction in the MCT layer thickness without compromising absorption has the potential for realizing infrared photodetectors with improved sensitivity at conventional operating temperatures and/or elevated operating temperatures.

In situ Ellipsometric Control of Growth Processes of ZnTe and CdTe Buffer Layers in Technology of Molecular Beam Epitaxy of Mercury Cadmium Telluride

In situ Ellipsometric Control of Growth Processes of ZnTe and CdTe Buffer Layers in Technology of Molecular Beam Epitaxy of Mercury Cadmium Telluride

Boosting infrared absorption through surface plasmon resonance enhanced HgCdTe microcavity

As one of the most widely used infrared (IR) detectors, a mercury cadmium telluride (MCT) detector usually requires liquid nitrogen refrigeration to suppress thermally activated noise mechanisms that are inherent to its narrow bandgap, which limits its practical applications. Therefore, it is essential to develop strategies to suppress dark current with reduced cooling demand. In this work, a surface plasmon resonance (SPR) enhanced MCT microcavity was proposed to intensify optical absorption across a broadband while diminishing the thickness of the MCT layer to reduce intrinsic dark current proportional to the volume of the absorber. The microcavity is formed by sandwiching the MCT layer between a top well-designed hybrid golden-cross antenna array and a bottom golden reflector. The microcavity is employed to trap the incident light to amplify the absorption, and the golden-cross antenna array is introduced to not only significantly enhance the incident light field through the SPR effect but also to broaden the microcavity resonant mode. Numerical calculation indicated that an absorptance exceeding 95.3% can be attained at 3.4 μm with the full width at half maxima (FWHM) extending beyond 1.38 μm, which almost covers the absorption band of MCT in mid-wavelength IR (MWIR), all while the MCT layer is only 530 nm. Moreover, the prototype device unit was fabricated and tested. Measured peak absorption reached 98.7% @ 3.6 μm and FWHM was as broad as 1.12 μm. These results demonstrate that the high and wideband absorption in an ultrathin MCT layer is achieved based on the synergistic effects of SPR and microcavity resonance.

DEVELOPMENT OF METHANE CARBON ISOTOPE BASED ON MID-INFRARED ABSORPTION SPECTRUM TECHNOLOGY APPLIED IN LOGGING PLATFORM

To meet the requirements of rapid measurement of oil and gas methane isotopes in offshore logging platforms, a methane carbon isotope measurement system based on mid-infrared TDLAS technology was proposed in this paper. The measuring system adopted a mid-infrared compact-linear optical structure, including an interband cascade laser (central wavelength at 2963.25 cm-1), long optical path multi-pass cell (effective optical path is 24 m) and mercury cadmium telluride detector (response wavelength is from 2 μm to 5 μm). Combining two 13CH4/12CH4 absorption lines, 2963.25 cm-1 and 2963.34 cm-1, with a high precision temperature control system using an integral separation PID control method, a temperature fluctuation within 100 mK can be achieved. In the experiment, CH4 gases with five different concentrations were configured to calibrate the measurement system, and the response linearity was more than 99%. When the integration time is 121s, the precision of isotope measurement was as low as 0.83 ‰. The average isotopic abundance of methane gas measured by the system was -10.2 ‰, and the error fluctuation was about ±0.5 ‰. It was verified that the system can rapidly measure oil and gas methane isotopes.

Computational Imaging at the Infrared Beamline of the Australian Synchrotron Using the Lucy–Richardson–Rosen Algorithm

The Fourier transform infrared microspectroscopy (FTIRm) system of the Australian Synchrotron has a unique optical configuration with a peculiar beam profile consisting of two parallel lines. The beam is tightly focused using a 36× Schwarzschild objective to a point on the sample and the sample is scanned pixel by pixel to record an image of a single plane using a single pixel mercury cadmium telluride detector. A computational stitching procedure is used to obtain a 2D image of the sample. However, if the imaging condition is not satisfied, then the recorded object’s information is distorted. Unlike commonly observed blurring, the case with a Schwarzschild objective is unique, with a donut like intensity distribution with three distinct lobes. Consequently, commonly used deblurring methods are not efficient for image reconstruction. In this study, we have applied a recently developed computational reconstruction method called the Lucy–Richardson–Rosen algorithm (LRRA) in the online FTIRm system for the first time. The method involves two steps: training step and imaging step. In the training step, the point spread function (PSF) library is recorded by temporal summation of intensity patterns obtained by scanning the pinhole in the x-y directions across the path of the beam using the single pixel detector along the z direction. In the imaging step, the process is repeated for a complicated object along only a single plane. This new technique is named coded aperture scanning holography. Different types of samples, such as two pinholes; a number 3 USAF object; a cross shaped object on a barium fluoride substrate; and a silk sample are used for the demonstration of both image recovery and 3D imaging applications.

A novel radiometric calibration of an infrared thermometer

A new temperature calibration scheme was proposed and implemented on the National Physical Laboratory infrared radiometer Absolute Measurements of Blackbody Emitted Radiance (AMBER) operating in the wavelength range from 9 µm to 11 µm and equipped with a cryogenically cooled mercury cadmium telluride detector. The scheme involves measurements of the relative spectral responsivity of the filter radiometer including the spectral transmittance of the window and lens. It requires calibration at two reference temperatures, but does not involve measurement of the zero-radiance signal. The scheme uses a Ga-point blackbody as one reference point, and a variable temperature blackbody source at close to −30 °C with its temperature measured with a standard platinum resistance thermometer as the other. The measured temperature was compared using the variable temperature blackbody as the source against the temperature measured by the standard platinum resistance thermometer and agreement within the uncertainties was confirmed at intermediate temperatures. The scheme has the advantage that it makes full use of the small uncertainty realised by the fixed-point blackbody. The scheme was successfully implemented in an international comparison of sea surface temperature measuring radiometers where AMBER served to provide the reference.

High Spectral Efficiency Long-Wave Infrared Free-Space Optical Transmission With Multilevel Signals

This study explores the potential of long-wave infrared free-space optical (FSO) transmission that leverages multilevel signals to attain high spectral efficiency. The FSO transmission system consists of a directly modulated-quantum cascade laser (DM-QCL) operating at 9.15 μm and a mercury cadmium telluride (MCT) detector. To fully understand the system, we conduct measurements on the DM-QCL chip and MCT detector and assess the overall amplitude response of the DM-QCL, MCT detector, and all electrical components. We apply various signals, including on-off keying (OOK), 4-level pulse amplitude modulation (PAM4), 6-level PAM (PAM6), and 8-level PAM (PAM8) to maximize the bit rate and spectral efficiency of the FSO transmission. Through a two-dimensional sweeping of the laser bias current and MCT detector photovoltage, we optimize the transmission performance. At the optimal operation point, the FSO system achieved impressive results which are up to 6 Gbaud OOK, 3.5 Gbaud PAM4, 3 Gbaud PAM6, and 2.7 Gbaud PAM8 signal transmissions, with a bit error rate performance below 6.25% overhead hard decision-forward error correction limit when the DM-QCL operates at 10°C. We also evaluate the eye diagrams and stability of the system to showcase its remarkable transmission performance. Our findings suggest that the DM-QCL and MCT detector-based FSO transceivers offer a highly competitive solution for the next generation of optical wireless communication systems.

Modeling of dark current in semispherical quantum dot structures for infrared photodetection

Due to its tunable heterojunction bandgap and great sensitivity to normal incident illumination, the Quantum Dot Infrared Photodetectors (QDIPs) have received a lot of attention for the purpose of infrared sensing. It could be a very promising replacement for conventional infrared photodetectors made with established technology, including mercury cadmium telluride and quantum well infrared photodetectors. In this work, a model for the dark current in semispherical QDIP has been developed, resolves the primary semiconductor Poisson's and continuity equations, where the wave function and the bound states effects are investigated. In this study, Boltzmann transport equation in the photodetector active layer with embedded QDs is solved using the finite difference time domain method to determine the photodetector carrier mobility and its degradation due the quantum dot scattering. The outcomes of the presented have been contrasted with truncated conical QDIPs showing that smaller volume QDs had less noisy dark current. Investigations have been done into how the semispherical QDIP's dark current characteristics are affected by the QD volume, density, and operating temperature.

Optimizing the Charge Carrier Dynamics of Thermal Evaporated TexSe1‐x Films for High‐Performance Short‐Wavelength Infrared Photodetection

AbstractShort‐wavelength infrared photo‐sensing materials are dominated by germanium, indium gallium arsenide, indium antimonide, and mercury cadmium telluride. However, the complex fabrication process and high production cost hinder their widespread applications. Recently, TexSe1‐x has shown great potential for infrared photodetection, but TexSe1‐x‐based devices are still suffering from extremely high dark current and poor device performance. In this work, high‐quality TexSe1‐x films are fabricated by thermal evaporation and low‐temperature annealing. The optoelectronic properties of the TexSe1‐x thin films are systematically investigated and optimized. The absorption spectrum is carefully tuned to cover the broad range from 300 to 1600 nm by modulating the ratio of Te and Se. Photodiodes based on the optimized TexSe1‐x thin films are also fabricated, and achieve high responsivity, reduced dark and low noise current density, and a fast response time of &lt;850 ns. Then, prototypical devices based on Te0.65Se0.35 thin films are demonstrated for optical communications, indicating the great potential for next‐generation, low‐cost short‐wavelength infrared photodetection.

Carrier Decay Lifetimes in the Narrow-gap Hg1–xCdxTe at the Interband and Intraband Excitations

The lifetimes of photoconductive decay carriers under interband and intraband excitations are studied in epitaxial layers of narrow-gap Hg1−xCdxTe (x ∼0.2). Samples with large distances (&gt;3 mm) between small-area electrical contacts and small distances (∼10 μm) with largearea contacts (THz antennas) are studied. The lifetimes of decay carriers for intraband and interband excitations are measured and compared. It has been established that, in samples with n-type conductivity, the lifetimes are comparable (in the interval of 40 ns) for both methods of excitation. At the same time, in samples with a small distance between contacts and a large area (bow-tie antennas), contacts make the main contribution to recombination. The elimination of recombination at the contacts leads to a lifetime of ∼10−6 s.

Recovery of Tellurium from Waste Anode Slime Containing High Copper and High Tellurium of Copper Refineries

Tellurium is used in cadmium tellurium-based solar cells. Mercury cadmium telluride is used as a sensing material for thermal imaging devices. High-purity tellurium is used in alloys for electronic applications. It is one of the important raw materials for solar energy applications. It is used as an alloying element in the production of low-carbon steel and copper alloys. Tellurium catalysts are used chiefly for the oxidation of organic compounds and as vulcanizing/accelerating agents in the processing of rubber compounds. Even though several researchers tried to recover tellurium from different raw materials, there is no attempt to develop a process flow sheet to recover tellurium from waste anode slime having a high tellurium concentration. In this study, optimum conditions were developed to recover Te and Cu from anode slime with the composition Cu: 31.8%, Te: 24.7%, and As: 0.96%. The unit operations involved are leaching, purification, and electro winning. The optimum conditions for producing Te at a recovery of 90% are found to be roasting of anode slime at 450 °C without the addition of soda ash followed by leaching in 1 M NaOH at 10% pulp density for 2 h. The purity of Te metal achieved was up to 99.99%, which could provide a sustainable energy future. The major impurities of the tellurium are observed to be in the order: Se &gt; Sb &gt; As &gt; Cu.