Dark Current Components Research Articles

Low-frequency noise and impedance measurements in Auger suppressed LWIR N+p(π)P+n+ HgCdTe detector

The paper reports on the electrical performances of LWIR N+p(π)P+n+ HgCdTe photodiodes optimized for λcut-off(50%) ≈ 10.6 μm at T = 230 K. Presented work mainly focuses on the region where negative resistance is observed due to Auger suppression effect. Previous reports showed that for such detectors it is usually observed at temperature conditions above ∼120 K for devices designed to operate in HOT conditions. The studies were carried out over a wide temperature range using few measurement methods: dark current, low-frequency noise, and impedance components. The results were also investigated as a function of the applied bias. A detailed analysis of the results were presented to show the influence of operating conditions when the detector works in negative resistance region. In these regions, we observed a dynamic change of the complex impedance from both parallel capacitance and resistance. The low-frequency noise measurements showed that in the negative resistance region, the noise spectral density is still rising with the reverse bias voltage despite reduction of the dark current by Auger suppression and the noise-current related intensity coefficient α is also still tends to rise. For temperatures above 160 K the noise-bias voltage interdependence near Si ∼ V2 was noticed. Moreover, the studies showed that the noise-temperature behaviour depends on the applied bias. The results obtained in experiments were discussed based on the current knowledge of these devices to verify and explain the behaviours of the dark current, noise and impedance-related parameters.

Dark Current Components of nB(SL)n Structures Based on HgCdTe for a Wide Range of Bias Voltages

Dark Current Components of nB(SL)n Structures Based on HgCdTe for a Wide Range of Bias Voltages

Design and Fabrication of High Performance InGaAs near Infrared Photodetector

InGaAs photodiodes have a wide range of important applications; for example, NIR imaging, fiber optical communication, and spectroscopy. In this paper, we studied InGaAs photodiodes with different doping concentration absorber layers. The simulated results suggested that, by reducing the absorber doping concentration from 1 × 1016 to 1 × 1015 cm−3, the maximum quantum efficiency of the devices can rise by 1.2%, to 58%. The simulation also showed that, by increasing the doping concentration of the absorber layer within a certain range, the dark current of the device can be slightly reduced. A PIN structure was grown and fabricated, and CV measurements suggested a low doping concentration of about 1.2 × 1015 cm−3. Although the thermal activation energy of the dark current suggested a distinct component of shunt dark current at a high temperature range, a dark current of ~6 × 10−4 A/cm2 (−0.5 V) was measured at room temperature. The peak quantum efficiency of the InGaAs device was characterized as 54.7% without antireflection coating and 80.2% with antireflection coating.

Electromagnetically induced transparency based quantum well infrared photodetectors

The characteristics of quantum well infrared photodetectors (QWIPs) which utilizing electromagnetically induced transparency (EIT) have been presented in this communication. Instead of direct absorption and creation of photoelectrons by the long wavelength infrared signal, the absorption properties of a short wavelength probe is modified by the infrared signal which subsequently creates photoelectrons. Owing to the indirect creation of photocurrent, the component of dark current which is due to thermionic emission is eliminated, thereby decreasing total dark current appreciably. The value of photocurrent depends on infrared signal power, bias voltage, probe detuning, and Rabi frequency of the control field. Results of this investigation may find potential applications in the development of terahertz infrared quantum well photodetectors under room temperature operation.

Al0.3InAsSb/Al0.7InAsSb Digital Alloy nBn Photodetectors

We report Al0.3InAsSb/Al0.7InAsSb digital alloy n-barrier-n (nBn) photodetectors that operate in the 2-μm wavelength window. The AlxIn1-xAsySb1-y digital alloy material system exhibits near-zero valence-band offset, which is beneficial for nBn photodetectors. At 300 K these Al0.3InAsSb/Al0.7InAsSb nBn photodetectors have achieved specific detectivities of 1.7 × 10 10 and 3.0 × 10 10 Jones under 2-μm and 1.8-μm illumination, respectively. The dark current density at -0.5 V bias decreases from 3.1 × 10 -3 A/cm 2 at 300 K to 1.6 × 10 -10 A/cm 2 at 120 K, where the dominant dark current component is tunneling. The area-dependence of key performance parameters show that for mesa diameter ≤ 250 μm, surface defects assume a dominant role in the total noise.

High-performance HgCdTe avalanche photodetector enabled with suppression of band-to-band tunneling effect in mid-wavelength infrared

HgCdTe avalanche photodiodes promise various fascinating applications due to the outstanding capability of detecting weak signals or even single photon. However, the underlying transport mechanisms of diverse dark current components are still unresolved at high reverse bias, thus limiting the development of high-performance devices. Here, we establish an accurate model to demonstrate the competitive mechanism between band-to-band and avalanche dark currents in positive-intrinsic-negative structures. Based on the high consistency between the simulated and measured results, we find that both components jointly dominate overall dark current but with a larger avalanche current. This breaks the conventional cognition that band-to-band dark current contributes the majority. With the guidance, we reconstruct an optimized device and achieve gain 1876 (6153) and dark current 10−10 (10−9) A at bias −10 (−10.5) V, respectively. Comparisons of dark current and gain with reported single-element devices further confirm the outstanding performance of our device.

The Study of Dark Currents in HgCdTe Heterostructure Photodiodes

Dark current is the main factor that influences photodiode performance. It should be minimal to reduce noise and ensure a high level of photoelectric parameters. In order to identify the predominant causes of generation–recombination in photodiodes based on a mercury–cadmium–tellurium (MCT) ternary compound in the given voltage range, a calculation model is proposed for dark currents caused by fundamental and other current mechanisms. The components of dark current in photodiodes based on MCT heterostructures grown by molecular beam epitaxy (MBE) and liquid-phase epitaxy (LPE) methods are determined in the reverse bias voltages range from 0 to 40 mV. In the range from 0 to 20 mV, these characteristics are reduced to the diffusion component. When the reverse bias voltage exceeds 30 mV, an increase in the Shockley–Read–Hall (SRH) generation–recombination current and tunneling current through trap levels in the band gap is observed.

Electrode material and modification dependent performances of lateral photodetectors based on MAPbI3 single crystal

Abstract As new-type optoelectronic materials, organometallic halide perovskites (MAPbX3, X = I, Br, Cl) is an emerging solution-processable material with excellent optoelectronic performances that can be used for photodetectors and solar cells. Here, the effects of electrode materials (Au, Ag and Cu) on MAPbI3 single crystal photodetectors are investigated. Among the three MSCPs, the one with Au electrode exhibits the lowest dark current of 0.01 μA, which indicate that the electron drift current is the dominant component of dark current in MAPbI3 single crystals. While for the 650 nm wavelength illumination, the one with Ag electrode has largest R of 24.5 A/W and highest external quantum efficiency (EQE) of 4676% due to lower electron injection energy barrier at the contact. More importantly, the C60 layer and CuPc:C60 bulk heterojunction layer were used to modify the Au electrode respectively, a large R of 174 A/W and EQE of 33,354% is obtained by C60:CuPc-MSCP and C60-MSCP exhibits the largest PDR of 15,952 and D* of 4.5 × 1013 Jones. These results suggest that lateral photodetectors based on MAPbI3 single crystal modified by heterojunction buffer layer will obtain better optical performance.

Sensitivity Calculations of High-Speed Optical Receivers Based on Electron-APDs

Sensitivity of high-speed optical receivers is heavily influenced by the performance of the optical detectors used in the receivers, the data rate, and the target bit-error-rate (BER). A simulation model for sensitivity of optical receivers based on electron-avalanche photodiodes (e-APDs) is presented. It allows for the optimization of avalanche width and operating voltage to achieve the optimum receiver sensitivity for given bit rate and target BER. The effects modelled include inter-symbol interference (ISI), various dark current components (tunnelling, diffusion, and generation), current impulse duration, avalanche gain, and amplifier's noise. The model was demonstrated through simulations of Indium Arsenide (InAs) e-APDs. For $10^{-12}$ target BER, the receiver's sensitivities were found to be −30.6, −22.7, −19.2, and −16.6 dBm, for 10, 25, 40, and 50 Gb/s data rate, respectively. Desirable avalanche properties of InAs e-APDs are counteracted by detrimental effects of high dark currents. Hence InAs e-APDs with lower dark currents are required to be more competitive with other optical detector technologies for high-speed optical receivers. The data reported in this article is available from the ORDA digital repository (DOI: 10.15131/shef.data.9959468).

Design and Demonstration of High-Efficiency Quantum Well Solar Cells Employing Thin Strained Superlattices

Nanostructured quantum well and quantum dot III–V solar cells provide a pathway to implement advanced single-junction photovoltaic device designs that can capture energy typically lost in traditional solar cells. To realize such high-efficiency single-junction devices, nanostructured device designs must be developed that maximize the open circuit voltage by minimizing both non-radiative and radiative components of the diode dark current. In this work, a study of the impact of barrier thickness in strained multiple quantum well solar cell structures suggests that apparent radiative efficiency is suppressed, and the collection efficiency is enhanced, at a quantum well barrier thickness of 4 nm or less. The observed changes in measured infrared external quantum efficiency and relative luminescence intensity in these thin barrier structures is attributed to increased wavefunction coupling and enhanced carrier transport across the quantum well region typically associated with the formation of a superlattice under a built-in field. In describing these effects, a high efficiency (>26% AM1.5) single-junction quantum well solar cell is demonstrated in a device structure employing both a strained superlattice and a heterojunction emitter.

Analysis of Current–Voltage Characteristics in UV AlGaN Heterostructure FPAs

UV visible-blind and solar-blind 320 × 256 photodiode arrays based on AlxGa1 – xN heteroepitaxial structures (AlGaN HES) and sensitive in the near-ultraviolet range of 0.2–0.4 μm have been created and studied. The AlGaN HES were grown by organometallic vapor deposition (MOCVD) and molecular beam epitaxy (MBE) on sapphire substrates. To reduce structural defects, the state of the surface and the surface layer of epipolished sapphire substrates was investigated, and a finishing technology was developed. UV FPAs in the AlGaN HES were produced by ion etching. The dark current components for AlGaN photodiodes were simulated. The main dark current components, such as generation–recombination, shunting leakage, hopping conductivity, and Poole–Frenkel components, are calculated. The possibility of achieving photoelectric parameters on the level of the best foreign counterparts is demonstrated.

Effects of multiplication layers on dark current components of InGaAs/InP avalanche photodiodes.

Based on results from the Silvaco Atlas device simulation software, a separate absorption grading charge multiplication InGaAs/InP avalanche photodiode has been modeled. The Shockley-Read-Hall current, avalanche amplification current, trap-assisted tunneling current, and band-to-band direct tunneling current are combined and considered as the dark current. Individual components of the dark current have been obtained separately through numerical simulation. Due to the multiplication effect, the influence of the multiplication layer on the dark current components has been studied. The simulation results are analyzed based on semiconductor physics knowledge. The conclusions presented provide some theoretical guidance for the optimum design of avalanche photodiodes.

Analysis of temperature-dependent dark current transport mechanism for GaAs-based blocked-impurity-band (BIB) detectors

Temperature-dependent dark current transport mechanism has been analyzed for GaAs-based blocked-impurity-band detectors. Device structure, processing steps and physical models are described in detail. In this work, the analysis of dark current transport mechanism has been greatly simplified by electron drift current related discussion based on the assumption that the diffusion current and the generation–recombination current as two dominating components of dark current in the absorbing layer can be equivalent to the electron drift current in the blocking layer. After confirming this assumption, our discussion focuses on why dark current is a monotonically increasing function of operation temperature for a fixed anode bias. Our results reveal that from dark current suppression point of view, low donor doping level and low operation temperature are preferred.

Improved algorithm for determining the Visible Infrared Imaging Radiometer Suite Day/Night Band high-gain stage dark offset free from light contamination

Dark offset is one of the key parameters for Visible Infrared Imaging Radiometer Suite (VIIRS) Day/Night Band (DNB) high-gain stage (HGS) radiometric calibration, whose accuracy strongly impacts applications of DNB low-light detection for Earth observation at nighttime. Currently, DNB observation of the VIIRS onboard calibrator blackbody (OBCBB) view, together with its observation of deep space during the spacecraft pitch maneuver performed early in the mission, has been used to compute the HGS dark offset continuously. However, the relationship between the DNB OBCBB data and the Earth view (EV) data is unclear due to electronic timing differences between these two views. It is questionable whether the DNB OBCBB data can monitor the EV HGS dark offset change. Through comprehensive analysis of the DNB OBCBB data and EV data acquired from the monthly special acquisitions known as the VIIRS recommended operating procedures (VROPs), we have shown that the OBCBB data can only track the dark current component of the DNB HGS EV dark offset, instead of the total dark offset. The DNB observation of deep space during the spacecraft pitch maneuver was also contaminated by starlight. With such background, in this paper we propose an improved algorithm for determining the DNB HGS dark offset. By combined use of the DNB OBCBB data and the DNB VROP data, the generated DNB HGS dark offset is both free from light contamination and capable of tracking continuous drift. The improved algorithm could potentially improve the DNB radiometric performance at low radiance level. Our results provide a solid theoretical basis for dark offset calibration of the VIIRS DNB onboard Suomi National Polar-Orbiting Partnership satellite and the following Joint Polar Satellite System satellites.

InGaAs nBn SWIR detector design with lattice-matched InAlGaAs barrier

Dark current optimization with band gap engineering has been numerically studied for InGaAs nBn type infrared photodetectors. Undoped InAlGaAs grading layers are utilized in constructing the barrier and dipole delta-doped layers are placed in both sides of the graded layers for eliminating valence band offset. As a result, the high band gap barrier layer blocks the majority carriers and allows minority carrier flow while minimizing various dark current components, as expected from an nBn detector. Substantial improvement has been shown in the dark current level without compromising any photoresponse compared to the conventional pn junction and recently proposed all InGaAs nBn type photodetectors.

Optimization of in-device depleted passivation layer for InGaAs photodetectors

Lattice matched InGaAs/InP photodetector structure with an InP layer for in-device passivation purposes has been analyzed numerically, an optimized design for mesa type devices has been proposed and experimental verification has been shown. Structural and electrical parameters such as thickness and doping concentration of InP layer have been studied in order to avoid any hole barrier possible in the valence band and to achieve a high photo-current with pixel isolation while reducing the surface leakage dark current component substantially. The passivation effect has been quantified for a variety of surface instability levels in comparison with the traditional InGaAs/InP hetero-junction structure and fully depleted InP layer has shown to be able to isolate pixels successfully and provide passivation that can help reduce the total dark current more than one order of magnitude. Photo-response in the proposed structure has been observed to be enhanced as well due to the increased collection efficiency.

Influencing Sources for Dark Current Transport and Avalanche Mechanisms in Planar and Mesa HgCdTe p-i-n Electron-Avalanche Photodiodes

In this paper, both planar and mesa homojunction p-i-n HgCdTe electron-avalanche photodiodes (e-APDs) are fabricated and investigated to better understand the dark current transport and electron-avalanche mechanisms of the devices and optimize the structures. The experiment results are agreed well by simulated ${I}$ – ${V}$ characteristics based on established numerical models. Our results show that the multiplication region fabrication process leads to enormous characteristic difference between planar and mesa diodes. Shockley–Read–Hall and trap-assisted tunneling current are the main components of dark current for the planar/mesa junction under low bias voltage, and dark current is mainly influenced by band-to-band tunneling and avalanche current when higher reverse bias is added. In addition, we found that the difference between the uniformity of the electric field distributions in multiplication regions is the primary reason for the differences of the dark current. It was also proved that the dark current of planar e-APDs is dramatically affected by the junction corners, and mesa e-APDs dark current is found to be greatly dependent on the multiplication region thickness. Our work provides a great deal of theoretical basis for dark current formation and the avalanche mechanism of HgCdTe e-APDs.

Analysis of dark current considering trap-assisted tunneling mechanism for InGaAs PIN photodetectors

In0.53Ga0.47As PIN photodetectors were fabricated and their dark currents were measured. Based on the analysis of different mechanisms, a complete dark current model considering trap-assisted tunneling (TAT) mechanism under low and intermediate reverse bias is constructed by studying the electric fields and carrier generation-recombination rates. The obtained current–voltage experimental results under dark conditions are in good agreement with our simulation using this complete model. The contribution of each mechanism is investigated, and to evaluate the dominant factor deriving from Shockley–Read–Hall generation or TAT, a critical voltage ( $$V_{cri}$$ ) where $$I_{TAT} = I_{SRH} \approx 0.5I_{dark}$$ is proposed. In addition, the effects of thickness and doping concentration of absorption layer on $$V_{cri}$$ are discussed in detail, from which we demonstrate that $$I_{TAT}$$ is the dominant component of dark current for those photodetectors operating under the reverse bias of 5 V if the thickness of absorption layer is less than 1 μm when the doping concentration is 1 × 1015 cm−3, or the doping concentration of absorption layer is more than 7 × 1015 cm−3 when the thickness is 2 μm. The effect of temperature on dark current due to TAT is also analyzed.

Dark current investigation in thin P-i-N InGaAs photodiodes for nano-resonators

We investigated the dark current components of thin planar InGaAs photodiodes grown by metalorganic vapor-phase epitaxy for optical nano-resonators. Owing to their high electric field enhancement, nano-resonators make it possible to substantially reduce the thickness of the active region to about 100 nm all the while maintaining high quantum efficiency. In the present study, to cover a broad spectral band, we combined several resonance peaks induced by guided-mode resonances in a given spectral range. This type of geometry allowed us to introduce InAlAs at the edge of a thin InGaAs active region in order to drastically reduce both the diffusion current and the generation/recombination current. We found that, in such devices, tunneling dark current components increase as the thickness of the active layer is reduced and dominate the reverse dark current. By optimizing the epitaxial stack, while keeping its total thickness constant (the optical properties of the nano-resonator remained unchanged), we showed that we are already able to achieve a specific detectivity of up to 1×1013 cmHz W−1 for λ=1.55 μm.

Type-II InAs/GaSb photodiode array pixel isolation by femto-second laser anneal

A 775nm, 150fs laser anneal technique for increased inter-pixel isolation in type-II InAs/GaSb superlattice photodiode arrays (5.5μm cutoff wavelength) without mesa etch, is presented. With only p+ inter-pixel etch and fs laser anneal, a greater than two fold improvement in the inter-pixel isolation is observed at 70K. A similar reduction in the dark current of p+ etched+fs laser annealed p-i-n photodiodes is observed at 70K over un-passivated mesa etched photodiodes of 400μm pixel sizes, whereas in 55μm pixels a seven fold reduction in the surface component of dark current over un-passivated mesa etched diodes is achieved. An increased band gap of the inter-pixel region (∼10meV) due to fs annealed intermixing has been calculated to be a possible reason for the improved inter-pixel isolation.