Temperature Dependence Of Dark Current Research Articles

Predictable quantum efficient detector for low optical flux measurements

The predictable quantum efficient detector (PQED) is a primary standard of optical power, which utilizes two custom-made induced-junction photodiodes that are mounted in a wedged trap configuration for the reduction of reflectance losses. PQED photodiodes of p-type and n-type were characterized for their dark current dependence on reverse bias voltage at room temperature. As simulations predict that the dark current will decrease exponentially with temperature, the temperature dependence of dark current for the n-type photodiodes was also measured. Two n-type induced-junction photodiodes were assembled inside a liquid nitrogen cryostat. The results from the dark current measurements indicate that the cooled n-type photodiodes are suitable for measuring optical fluxes in the few photon regime. A photon flux of approximately 7,000,000 photons per second was measured using the PQED at a cryogenic temperature with a relative standard uncertainty of 0.15%. The results support the utilization of the PQED as a primary standard of optical power in single and few photon applications.

Room temperature operation of mid-infrared InAs081Sb019 based photovoltaic detectors with an In02Al08Sb barrier layer grown on GaAs substrates

In this paper, InAs0.81Sb0.19-based hetero-junction photovoltaic detector (HJPD) with an In0.2Al0.8Sb barrier layer was grown on GaAs substrates. By using technology computer aided design (TCAD), a design of a barrier layer that can achieve nearly zero valance band offsets was accomplished. A high quality InAs0.81Sb0.19 epitaxial layer was obtained with relatively low threading dislocation density (TDD), calculated from a high-resolution X-ray diffraction (XRD) measurement. This layer showed a Hall mobility of 15,000 cm2/V⋅s, which is the highest mobility among InAsSb layers with an Sb composition of around 20% grown on GaAs substrates. Temperature dependence of dark current, photocurrent response and responsivity were measured and analyzed for fabricated HJPD. HJPD showed the clear photocurrent response having a long cutoff wavelength of 5.35 μm at room temperature. It was observed that the dark current of HJPDs is dominated by the diffusion limited current at temperatures ranging from 200K to room temperature from the dark current analysis. Peak responsivity of HJPDs exhibited the 1.18 A/W and 15 mA/W for 83K and a room temperature under zero bias condition even without anti-reflection coating (ARC). From these results, we believe that HJPDs could be an appropriate PD device for future compact and low power dissipation mid-infrared on-chip sensors and imaging devices.

InGaAs/InP quantum well infrared photodetector integrated on Si substrate by Mo/Au metal-assisted wafer bonding

Integration of an InGaAs/InP quantum well infrared photodetector (QWIP) onto a Si substrate was successfully demonstrated via a metal-assisted wafer bonding (MWB) using a Mo/Au metal scheme. The Mo/Au/Mo layer, situated between the QWIP structure and the Si, has shown a well-ordered lamination. It provides a smooth surface with a roughness of about 0.8 nm, as measured by a scanning electron microscope (SEM) and atomic force microscopy (AFM). The results on crystalline quality evaluated by Raman spectroscopy and X-ray diffraction (XRD) imply that the MWB could be achieved without any measurable material degradation and residual strain. Temperature dependence of dark current revealed that there is no noticeable change in the dark current properties of the QWIP after bonding on Si, despite that the quantum wells are only 200 nm away from the bonding interface.

Electronic defects in the halide antiperovskite semiconductor Hg3Se2I2

Halide perovskites have emerged as a potential photoconducting material for photovoltaics and hard radiation detection. We investigate the nature of charge transport in the semi-insulating chalcohalide ${\mathrm{Hg}}_{3}{\mathrm{Se}}_{2}{\mathrm{I}}_{2}$ compound using the temperature dependence of dark current, thermally stimulated current (TSC) spectroscopy, and photoconductivity measurements as well as first-principles density functional theory (DFT) calculations. Dark conductivity measurements and TSC spectroscopy indicate the presence of multiple shallow and deep level traps that have relatively low concentrations of the order of ${10}^{13}\ensuremath{-}{10}^{15}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}3}$ and capture cross sections of $\ensuremath{\sim}{10}^{\ensuremath{-}16}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}$. A distinct persistent photoconductivity is observed at both low temperatures ($l170\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) and high temperatures ($g230$ K), with major implications for room-temperature compound semiconductor radiation detection. From preliminary DFT calculations, the origin of the traps is attributed to intrinsic vacancy defects (${V}_{\mathrm{Hg}}, {V}_{\mathrm{Se}}$, and ${V}_{\mathrm{I}}$) and interstitials (${\mathrm{Se}}_{\mathrm{int}}$) or other extrinsic impurities. The results point the way for future improvements in crystal quality and detector performance.

Predictable quantum efficient detector based on n-type silicon photodiodes

The predictable quantum efficient detector (PQED) consists of two custom-made induced junction photodiodes that are mounted in a wedged trap configuration for the reduction of reflectance losses. Until now, all manufactured PQED photodiodes have been based on a structure where a SiO2 layer is thermally grown on top of p-type silicon substrate. In this paper, we present the design, manufacturing, modelling and characterization of a new type of PQED, where the photodiodes have an Al2O3 layer on top of n-type silicon substrate. Atomic layer deposition is used to deposit the layer to the desired thickness. Two sets of photodiodes with varying oxide thicknesses and substrate doping concentrations were fabricated. In order to predict recombination losses of charge carriers, a 3D model of the photodiode was built into Cogenda Genius semiconductor simulation software. It is important to note that a novel experimental method was developed to obtain values for the 3D model parameters. This makes the prediction of the PQED responsivity a completely autonomous process. Detectors were characterized for temperature dependence of dark current, spatial uniformity of responsivity, reflectance, linearity and absolute responsivity at the wavelengths of 488 nm and 532 nm. For both sets of photodiodes, the modelled and measured responsivities were generally in agreement within the measurement and modelling uncertainties of around 100 parts per million (ppm). There is, however, an indication that the modelled internal quantum deficiency may be underestimated by a similar amount. Moreover, the responsivities of the detectors were spatially uniform within 30 ppm peak-to-peak variation. The results obtained in this research indicate that the n-type induced junction photodiode is a very promising alternative to the existing p-type detectors, and thus give additional credibility to the concept of modelled quantum detector serving as a primary standard. Furthermore, the manufacturing of PQEDs is no longer dependent on the availability of a certain type of very lightly doped p-type silicon wafers.

Temperature Dependence Study of Mesa-Type InGaAs/InAlAs Avalanche Photodiode Characteristics

Avalanche photodiodes (APDs) are key optical receivers due to their performance advantages of high speed, high sensitivity, and low noise. The most critical device parameters of APD include the avalanche breakdown voltage and dark current. In this work, we study the temperature dependence of the breakdown voltage and dark current of the mesa-type APD over a wide temperature range of 20–145°C. We institute an empirical model based on impact ionization processes to account for the experimental data. It is shown that highly stable breakdown characteristics of mesa-type APD can be attained with the optimization of the multiplication layer design. We have achieved excellent stability of avalanche breakdown voltage with a temperature coefficient of 0.017 V/°C. The temperature dependence of dark current is attributed to generation-recombination mechanism. The bandgap energy is estimated to be about 0.71 eV based on the temperature variation of dark current, in good agreement with the value for InGaAs.

Photocurrent response of B12As2 crystals to blue light, and its temperature- dependent electrical characterizations

With the global shortage of 3He gas, researchers worldwide are looking for alternative materials for detecting neutrons. Among the candidate materials, semiconductors are attractive because of their light weight and ease in handling. Currently, we are looking into the suitability of boron arsenide (B12As2) for this specific application. As the first step in evaluating the material qualitatively, the photo-response of B12As2 bulk crystals to light with different wavelengths was examined. The crystals showed photocurrent response to a band of 407- and 470- nm blue light. The maximum measured photoresponsivity and the photocurrent density at 0.7 V for 470 nm blue light at room temperature were 0.25 A ⋅ W−1 and 2.47 mA ⋅ cm−2, respectively. In addition to photo current measurements, the electrical properties as a function of temperature (range: 50-320 K) were measured. Reliable data were obtained for the low-temperature I-V characteristics, the temperature dependence of dark current and its density, and the resistivity variations with temperature in B12As2 bulk crystals. The experiments showed an exponential dependence on temperature for the dark current, current density, and resistivity; these three electrical parameters, respectively, had a variation of a few nA to μA, 1-100 μA ⋅ cm−2 and 7.6x105-7.7x103 Ω ⋅ cm, for temperature increasing from 50 K to 320 K. The results from this study reported the first photoresponse and demonstrated that B12As2 is a potential candidate for thermal-neutron detectors.

Extraction of activation energies from temperature dependence of dark currents of SiPM

Despite several advantages of Silicon Photomultipliers (SiPM) over Photomultiplier Tubes (PMT) like the increased photon detection efficiency (PDE), the compact design and the insensitivity to magnetic fields, the dark count rate (DCR) of SiPM is still a large drawback. Decreasing of the SiPM dark count rate has become a modern task, which could lead to an enormous enhancement of the application range of this promising photo-detector. The main goal of this work is to gain initial information on the dark generation and identify the dominating contributions to dark currents. The chosen approach to fulfill this task is to extract characteristic activation energies of the contributing mechanisms from temperature dependent investigations of dark currents and DCR. Since conventional methods are not suited for a precise analysis of activation energies, a new method has to be developed. In this paper, first steps towards the development of a reliable method for the analysis of dark currents and dark events are presented.

Electro-Optical Characteristics of P+n In0.53Ga0.47As Hetero-Junction Photodiodes in Large Format Dense Focal Plane Arrays

This paper is concerned with focal plane array (FPA) data and use of analytical and three-dimensional numerical simulation methods to determine the physical effects and processes limiting performance. For shallow homojunction P+n designs the temperature dependence of dark current for T < 300 K depends on the intrinsic carrier concentration of the In0.53Ga0.47As material, implying that the dominant dark currents are generation and recombination (G–R) currents originating in the depletion regions of the double layer planar heterostructure (DLPH) photodiode. In the analytical model differences from bulk G–R behavior are modeled with a G–R like perimeter-dependent shunt current conjectured to originate at the InP/InGaAs interface. In this description the fitting property is the effective conductivity, σeff(T), in mho cm−1. Variation in the data suggests σeff (300 K) values of 1.2 × 10−11–4.6 × 10−11 mho cm−1). Substrate removal extends the quantum efficiency (QE) spectral band into the visible region. However, dead-layer effects limit the QE to 10% at a wavelength of 0.5 μm. For starlight–no moon illumination conditions, the signal-to-noise ratio is estimated to be 50 at an operating temperature of 300 K. A major result of the 3D numerical simulation of the device is the prediction of a perimeter G–R current not associated with the properties of the metallurgical interface. Another is the prediction that for a junction positioned in the larger band gap InP cap layer the QE is bias-dependent and that a relatively large reverse bias ≥0.9 V is needed for the QE to saturate to the shallow homojunction value. At this higher bias the dark current is larger than the shallow homojunction value. The 3D numerical model and the analytical model agree in predicting and explaining the measured radiatively limited diffusion current originating at the n-side of the junction. The calculations of the area-dependent G–R current for the condition studied are also in agreement. Unique advantages of the 3D numerical simulation are the ability to mimic real device structures, achieve deeper understanding of the real physical effects associated with the various methods of junction formation, and predict how device designs will function.

GaSb-based infrared detectors utilizing InAsPSb absorbers

InPSb and InAsPSb have been investigated for use as absorber materials in GaSb-based n-type/barrier/n-type (nBn) detectors with cutoff wavelengths shorter than 4.2 μm. The growth temperature window for high-quality InPSb lattice-matched to GaSb by molecular beam epitaxy is approximately 440–460 °C. InPSb films with thicknesses greater than approximately 1 μm or films grown outside this temperature window have high densities of large defects, with films grown at lower temperatures exhibiting evidence of significant phase separation. In contrast, InAsPSb films can be grown with excellent surface morphologies and no apparent phase separation over a wide temperature range. InAsPSb samples with low-temperature photoluminescence between 3.0 and 3.4 μm and lattice mismatch of less than 1 × 10−3 have been grown, although both photoluminescence and x-ray diffraction data exhibit peak splitting indicative of compositional nonuniformity. AlAsSb-barrier nBn detectors with InPSb and InAsPSb absorbers have been fabricated. At 160 K, InPSb-absorber devices have a photocurrent responsivity edge at approximately 2.8 μm and a dark current of approximately 1.4 × 10−7 A/cm2, and InAsPSb devices with responsivity edges of 3.1–3.2 μm have a dark current of 2.3 × 10−8 A/cm2. Both InPSb and InAsPSb devices require significant reverse bias for full photocurrent collection at low temperature, suggesting the existence of an undesirable valence band energy discontinuity. The temperature dependence of dark current indicates that it is dominated by a mechanism other than generation in the undepleted absorber region.

AlAsSb Avalanche Photodiodes With a Sub-mV/K Temperature Coefficient of Breakdown Voltage

The temperature dependence of dark current and avalanche gain were measured on AlAsSb p-i-n diodes with avalanche region widths of 80 and 230 nm. Measurements at temperatures ranging from 77 to 295 K showed that the dark current decreases rapidly with reducing temperature while avalanche gain exhibits a weak temperature dependence. No measurable band to band tunneling current was observed in the thinner diodes at an electric field of 1.07 MV/cm, corresponding to a bias of 95% of the breakdown voltage. Temperature coefficients of breakdown voltage of 0.95 and 1.47 mV/K were obtained from 80 and 230 nm diodes, respectively. These are significantly lower than a range of semiconductor materials with similar avalanche region widths. Our results demonstrated the potential of using thin AlAsSb avalanche regions to achieve low temperature coefficient of breakdown voltage without suffering from high band to band tunneling current.

Amorphous HgCdTe infrared photoconductive detector with high detectivity above 200 K

Temperature dependence of dark current (Id) and photocurrent (Iph) is reported for Si-based amorphous HgCdTe (a-MCT) infrared photoconductive detector at 80-300 K. It is indicated that an uncooled a-MCT infrared detector can be fabricated based on the Si-based a-MCT. To describe the transport process, the Mott and Davis model [Davis and Mott, Philos. Mag. 22, 903 (1970)] is proposed as the conducting model originally developed for amorphous silicon. A possible mechanism of the carrier transports is shown in the a-MCT materials. The transport transition between the localized and extended carriers leads to the maximal Iph/Id above 200 K.

Low Dark Count Rate and High Single-Photon Detection Efficiency Avalanche Photodiode in Geiger-Mode Operation

An In0.53Ga0.47As-InP avalanche photodiode with very low dark current (0.15 pA at 95% breakdown voltage, 200 K) has been characterized in gated mode for single-photon detection. The temperature dependence of dark current and dark count yields activation energy of ~0.4 eV from 240 K to 297 K. High single-photon detection efficiency (SPDE) at telecom wavelengths with very low dark count rate (DCR) (e.g., DCR =12 kHz at SPDE =45% at 1.31 mum and 200 K) was achieved

Circuit model for quantum-well infrared photodetectors and its comparison with experiments

This paper presents a PSPICE model for quantum-well infrared photodetectors (QWIP). Bias dependence of the dark current and photocurrent is accurately described by the model with the aid of analogue behaviour modelling (ABM) technique in PSPICE. The model can be easily integrated with the readout electronics for circuit optimisation. In addition, we have also incorporated the temperature dependence of dark current into the model for analysing the effects of operating temperature on the performance. The various design parameters of the QWIP can be fed into the model as user-defined inputs to simulate the detector performance. Experimental data of different QWIP structures were compared with the simulated results and their good agreement verifies the accuracy of the PSPICE model.

Photoconductivity, optical and electrical properties of GaSe 0.95S 0.05 : Na mixed crystals

To identify sodium-related and intrinsic structural defect levels in GaSe 0.95S 0.05 : Na mixed crystals; photoconductivity (PC), electrical conductivity (EC), current–voltage characteristics (CVC) and optical absorption spectrum (OA) were investigated. It was observed that these mixed crystals exhibit impurity PC bands at 1.81, 1.55 and 1.37 eV.These bands can be attributed to optical transitions from the localized acceptor levels located at energies of about 0.225, 0.48 and 0.67 eV to the indirect conduction band. Optical absorption spectrum at 300 K exhibits indirect band gap of 2.035 eV. Furthermore, it was found that photocurrent increases monotonically with increasing temperature from 300 K up to T cr=357 K and decreases for T> T cr. Moreover, the photocurrent–light intensity dependence in these crystals obeys the power law I ph∝ F γ with γ between 0.8 and 1. This indicates the continuous distribution of localized states in the band gap. It was also found that, temperature dependence of dark current in Ohmic and space-charge-limited current (SCLC) regions exhibits the same single thermal activation energy 0.151±0.004 eV. This reflects the presence of single set of discrete hole trapping level at E t=0.151±0.004 eV. The acceptor level at 0.225 eV from PC spectrum was also detected from temperature dependence of EC. These localized levels confirm the extrinsic nature of EC and PC in these mixed crystals. In the light of the experimental results; an energy band diagram can be suggested.

Microstructural Aspects Related to Carriers Transport Properties of Nanocrystalline Porous Silicon Films

A microstructural investigation of porous silicon films, related with a study of carriers transport, is presented. Scanning electron microscopy and conventional transmission electron microscopy with selected area electron diffraction were performed. The films show a double scale porosity: the macroporosity forms an alveolar structure at a micrometric scale and the nanoporosity forms a silicon nanowires network in the alveolar walls and at their surface. Current‐voltage characteristics in the −5 to +5 V range and the temperature dependence of dark current in the 150‐330 K interval at low voltage were measured. The transport properties are explained by means of a simplified quantum confinement model. Two symmetries of the nanowires, cylindrical and square, are investigated and the differences between them are shown to be insignificant. © 1999 The Electrochemical Society. All rights reserved.

Investigation of localized levels in Na-intercalated GaSe single crystal

To identify sodium related and intrinsic structural defect levels in Na-intercalated GaSe single crystal; photoconductivity (PC), current–voltage characteristics (CVC) and electrical conductivity (EC) were investigated. Spectral distribution of PC reveals two bands; the main peak of the first band which lies at 2.052 eV is ascribed to indirect excitonic transitions whereas the weak peak of the second band which lies at 1.90 eV is attributed to optical transitions from the acceptor level A 1 of sodium related defects with ionization energy 0.152±0.002 eV to the indirect conduction band. Temperature dependence of dark current in space-charge limited current (SCLC) and Ohmic regions indicates the presence of a single discrete trapping level A 1 located at energy E t=0.153±0.002 eV above the valence band, this value is in good agreement with that obtained from the temperature dependence of the trapping factor θ; with E t=0.154 eV and N t=3×10 10 cm −3. This trapping level which acts as hole traps originates from sodium related defect acceptor level A 1. Furthermore, electrical conductivity measurement reveals two additional acceptor levels A 2 and A 3 with activation energies 0.322 and 0.560 eV, indicating that conduction in GaSe is extrinsic. In the light of the experimental results an energy diagram of the forbidden gap of Na-intercalculated GaSe has been proposed.

Electrical behaviour of fresh and stored porous silicon films

We have measured I–V and C–V characteristics, the temperature dependence of dark currents, and thermally stimulated depolarisation currents on fresh and stored samples of photoluminescent porous silicon. By storage in ambient, the low rectifying I–V curves become strong rectifying, and C–V curves become MIS-like. I–T characteristics for fresh samples have only one activation energy, in the 0.49–0.55 eV range. After storage, a slightly modified value, of about 0.50–0.60 eV is observed at low temperatures only. At about 280 K, the activation energy suddenly changes to 1.20–1.80 eV. Also, both the number and the positions of maxima in thermally stimulated depolarisation currents change by storage. The annealing at about 50°C induces small reversible changes in I–T characteristics and strong irreversible ones in thermally stimulated depolarisation currents, both for fresh and stored samples. A simplified quantum confinement model is proposed to explain the main aspects of the electrical behaviour of porous silicon films. The surface and/or interface contributions are observed especially in thermally stimulated depolarisation currents. The changes induced by storage are attributed to the oxidation process of the internal surface of porous silicon films.

Design and performance of InAlGaAs/InAlAs superlattice avalanche photodiodes

InAlGaAs-InAlAs superlattice avalanche photodiodes (SL-APD's) have been designed and experimentally analyzed. The layer structures and the electric field profiles were designed for 10 Gb/s applications. The mesa-structure SL-APD's exhibited a gain-bandwidth product of 120-150 GHz, a top bandwidth of 15 GHz, and a multiplied dark current of 15-20 nA for a mesa-diameter of 30 /spl mu/m. Other characteristics, such as temperature dependence of dark current and dynamic ranges, were also analyzed. Furthermore, an estimated life-time of longer than 10/sup 5/ h was achieved for the first time. The obtained characteristics, especially their high-speed characteristics with their low dark current, indicate potential for 2.5-10 Gb/s high-sensitivity and small optical receiver applications.

セレン化カドミウムをポリマーでカプセル化した複合体の光導電特性

Cadmium selenide (CdSe) was encapsulated in polymethylmethacrylate (PMMA) or polystyrene (PSt) by the encapsulating polymerization process. The behavior of CdSe in the encapsulating polymerization, and the photoconductivities and the photosensitive mechanism of the resulted composite materials were investigated. The polymerization was carried out by use of the initiators giving positive and negative charges to the molecular ends of the produced polymer. In both cases of the initiator, it was observed that a large part of the polymer existed in the form of stable latex polymer in the aqueous phase. The encapsulating polymer on the CdSe particles resisted to the Soxhlet extraction. The dark current, the photocurrent and the relative sensitivity of the CdSe encapsulated in PMMA were found to be enhanced as compared with CdSe and CdSe-dispersed PMMA. These values tended to increase with the increase of the encapsulating ratio. In addition, the voltage-current characteristics, temperature dependence of dark current, the light intensity dependence and the initial rising rate of photocurrent were investigated, it was concluded that the photoconductive mechanism of the CdSe encapsulated in PMMA was caused by the carrier trap.