Zero-bias Resistance-area Product Research Articles

Modelization of electrical and optical characteristics of short-wave infrared type I InGaAsBi/InGaAs/InP quantum wells p-i-n detector

In the present work, we will exhibit a theoretical analysis and optimization of electrical and optical characteristics of a short-wave infrared p-i-n detector closely lattice matched to conventional (001) InP substrate by the use of quaternary dilute bismide alloy InxGa1−xAs1−yBiy/InxGa1−xAs quantum wells as an active layer. The content of about 6% of Bismuth has been responsible of red-shift of the 50% cut-off wavelength from 2.2 towards 2.8 μm at room temperature, resulting in a band gap reduction of nearly 305 meV caused by the bismuth incorporation. The temperature dependence of zero-bias resistance area product (R 0 A) and bias dependent dynamic resistance of the designed structure have been investigated thoroughly to analyses the dark current contributions mechanisms that might limit the electrical performance of the considered structure. It was revealed that the R 0 A product of the detector is limited by thermal diffusion currents when temperatures are elevated whereas the ohmic shunt resistance contribution limits it when temperatures are low. The modeled heterostructure, reveals a comforting dark current of 1.25 × 10−8 A at bias voltage of −10 mV at 300 K. The present work demonstrates that the p-i-n detector based on compressively strained InxGa1−xAs1−yBiy quantum well is a potential candidate for achieving a short-wave infrared detection.

Performance analysis of an N-structure type-II superlattice photodetector for long wavelength infrared applications

We propose a high performance N-structure type-II superlattice (T2SL) photodetector for long wavelength infrared (LWIR) applications. Theoretical study on the electrical and optical properties of the N-structure T2SL LWIR detector with different carrier concentration and different thicknesses in the p-region is carried out. We obtain the relationship of material parameters and performance parameters. With the increasing of the thickness of p-region, quantum efficiency (QE) gradually improves. In contrast, zero-bias resistance area (R0A) product decreases. QE will significantly decreases when the carrier concentration of p-region is too high, while R0A first increases, then decreases. The results show that the performance of the N-structure T2SL LWIR detector can be state of the art by optimizing the carrier concentration and material thickness during the structure growth and device fabrication.

Surface leakage current in 12.5 μm long-wavelength HgCdTe infrared photodiode arrays.

Long-wavelength (especially >12 μm) focal plane array (FPA) infrared detection is the cutting edge technique for third-generation infrared remote sensing. However, dark currents, which are very sensitive to the growth of small Cd composition HgCdTe, strongly limits the performance of long wavelength HgCdTe photodiode arrays in FPAs. In this Letter, 12.5 μm long-wavelength Hg1-xCdxTe (x≈0.219) infrared photodiode arrays are reported. The variable-area and variable-temperature electrical characteristics of the long-wavelength infrared photodiodes are measured. The characteristics of the extracted zero-bias resistance-area product (l/R0A) varying with the perimeter-to-area (P/A) ratio clearly show that surface leakage current mechanisms severely limit the overall device performance. A sophisticated model has been developed for investigating the leakage current mechanism in the photodiodes. Modeling of temperature-dependent I-V characteristic indicates that the trap-assisted tunneling effect dominates the dark current at 50 K resulting in nonuniformities in the arrays. The extracted trap density, approximately 1013-1014 cm-3, with an ionized energy of 30 meV is determined by simulation. The work described in this Letter provides the basic mechanisms for a better understanding of the leakage current mechanism for long-wavelength (>12 μm) HgCdTe infrared photodiode arrays.

Investigation of dark current and differential resistance contributing mechanisms in type-II InAs/GaSb superlattice

The zero-bias resistance area (R0A) product is a primary figure-of-merit of infrared detector. The contributions of different dark current to R0A have been analyzed based on a long wavelength infrared type-II InAs/GaSb superlattice p-i-n photodiode. A dark current of 2.052 × 10−4 A cm−2 and a differential resistance-area of 32.314 Ω cm2 at zero bias voltage are achieved with a 100 % cutoff of 12.5 μm at 77 K. The temperature-dependence and bias-dependence of the dark currents are studied experimentally and correlated to the theory. At 77 K, by modeling the different reduced carrier concentration, the dominant mechanism of R0A can be varied from generation-recombination to tunneling.

The Influence of Surface Passivation on Dark Current Contributing Mechanisms of the InAs/GaSb Superlattice

We report on the investigation of the dark current contributing mechanism by an effective SiO2 passivated layer deposited at low temperatures. In comparison with the unpassivated photodiodes, at 77 K, the dark current density is reduced by one order of magnitude and a maximum zero-bias resistance area product (R0A) of 567 Ω cm2 is achieved by introducing SiO2-passivated layer deposition technology at a lower temperature of 75°C. The temperature-dependence and bias-dependence of the dark current are studied experimentally and correlated to the theory, and then the fitting with experimental results shows good agreement between theory and experiment. The contribution of each dark current mechanism is also identified.

A bandgap-engineered HgCdTe PBπn long-wavelength infrared detector

In this paper, the HgCdTe PBπn (π represents p-type absorption layer) long-wavelength infrared detector based on bandgap-engineering is designed and validated by the preliminary experiments. Numerical simulation was applied to calculate the current-voltage (I-V) characteristic and zero-bias resistance-area product (R0A) for PBπn detectors and traditional pn photodiodes. The results show that the performance of PBπn detector was significantly improved compared with that of conventional pn photodiodes. The design of PBπn barrier structure can essentially reduce the dark current, while significantly improving the responsivity. In addition, when reverse biased, optimized PBπn device can also suppress Auger processes in the absorption layer under the high temperature up to 215 K. The proposed HgCdTe long wavelength infrared detectors based on vertical PBπn structure pave the way for development of high performance and high operation temperature infrared sensor applications.

Direct band gap InxGa1−xAs/Ge type II strained quantum wells for short-wave infrared p–i–n photodetector

We theoretically investigate GaAs/Ge/InGaAs as a quantum wells for the design of short-wave infrared p–i–n photodetectors in which the quantum well Ge/InGaAs is the active region. At room temperature, strained Ge/InxGa1−xAs becomes a direct band gap when In composition x is lower than 2.5% and 5% respectively. We have calculated the electronic band parameters for the heterointerface Ge/InxGa1−xAs. Then, a type-II strain GaAs/Ge/In0.35Ga0.65As/GaAs quantum wells heterostructure optimized in terms of compositions and thicknesses is studied by solving Schrödinger equation as well as the absorption coefficient (>1.5×104cm−1). These computations have been used for the study of p–i–n infrared photodetectors operating at room temperature in the range 1.3–1.55μm. The electron transport in the GaAs/Ge/In0.35Ga0.65As/GaAs multi-quantum wells-based p–i–n structure was analyzed and numerically simulated taking into account tunneling process and thermally activated transfer through the barriers mainly. The temperature dependence of dark current mechanisms and zero-bias resistance area product (R0A) have been analyzed. Extracted from current–voltage characteristics, R0A products above 3.6⋅106Ωcm2 at 77K were calculated, and the quantitative analysis of the J–V curves showed that the dark current density of Ge/In0.35Ga0.65As photodetector is dominated by generation–recombination processes. The suitability of the modeled photodetector is approved by its feasibility of achieving good device performance near room temperature operating at 1.55μm. Quantum efficiency of ∼90% and responsivity ∼0.6A/W, have been achieved.

State-of-the-Art HgCdTe at Raytheon Vision Systems

Dark current density data recorded over the past 14 years at Raytheon Vision Systems on short-wavelength infrared (SWIR) and medium-wavelength infrared (MWIR) devices were examined. This included HgCdTe detector arrays grown by liquid-phase epitaxy on CdZnTe and molecular beam epitaxy on both silicon and CdZnTe substrates. This study analyzed zero-bias resistance–area product and current–voltage measurements from test structure assemblies included on every detector wafer. The data span cutoff wavelengths from 1.7 μm to 7.5 μm and operating temperatures from 40 K to 300 K. A basis is derived for a simple manufacturing trend model for a wide range of cutoffs and temperatures. This model uses a function similar to Tennant’s Rule’07 but includes a generation–recombination (GR) term. Dark current densities below the test set limit are extrapolated assuming GR-limited performance. Model assumptions are tested using sensor chip assembly (SCA) median dark current density values at the same inverse cutoff–temperature products. This model allows probabilistic determination of array manufacturability and prediction of yield, and provides a statistical basis for Raytheon’s state-of-the-art performance.

Dark current mechanisms investigation of surface passivation InAs/GaSb photodiodes at low temperatures

The dark current mechanisms were investigated at low temperatures (4–77K). By optimizing the diodes fabrication processes and introducing SiO2 dielectric layer, the surface leakage was effectively suppressed even in smaller diameter (50μm) with 607Ωcm2 zero-bias resistance area product (R0A) at 77K, which was 6 times higher than the R0A of unpassivated diode. In lower temperatures, the diffusion and generation–recombination (GR) current were not dominant contributing mechanisms to the total dark current. Qualitatively current density–voltage (J–V) modeling showed trap-assisted tunneling dominated behavior of dark current at temperatures lower than 50K.

Modeling of electrical and optical characteristics of near room-temperature CdS/ZnSe based NIR photodetectors

Results of modeled photodetector characteristics in (CdS/ZnSe)/BeTe multi-well diode with p–i–n polarity are reported. The dark current density (J–V) characteristics, the temperature dependence of zero-bias resistance area product (R0A), the dynamic resistance as well as bias dependent dynamic resistance (Rd) and have been analyzed to investigate the mechanisms limiting the electrical performance of the modeled photodetectors. The quantum efficiency, the responsivity and the detectivity have been also studied as function of the operating wavelength. The suitability of the modeled photodetector is demonstrated by its feasibility of achieving good device performance near room temperature operating at 1.55μm wavelength required for photodetection in optical communication. Quantum efficiency of ∼95%, responsivity ∼0.6A/W and D*∼5.7×1010cmHz1/2/W have been achieved at 300K in X BeTe conduction band minimum.

Modelling of the Quantum Transport in Strained Si/SiGe/Si Superlattices Based P-i-n Infrared Photodetectors for 1.3 - 1.55 μm Optical Communication

In this paper, a p-i-n heterojunction based on strain-compensated Si/Si1-xGex/Si multiple quantum wells on relaxed Si1-yGey is proposed for photodetection applications. The Si1-yGey/Si/Si1-xGex/Si/Si1-yGey stack consists in a W-like potential profile strain-compensated in the two low absorption windows of silica fibers infrared (IR) photodetectors. These computations have been used for the study of p-i-n infrared photodetectors operating at room temperature (RT) in the range 1.3 - 1.55 μm. The electron transport in the Si/Si1-xGex/Si multi-quantum wells-based p-i-n structure was analyzed and numerically simulated taking into account tunneling process and thermally activated transfer through the barriers mainly. These processes were modeled with a system of Schrodinger and kinetic equations self-consistently resolved with the Poisson equation. Temperature dependence of zero-bias resistance area product (RoA) and bias-dependent dynamic resistance of the diode have been analyzed in details to investigate the contribution of dark current mechanisms which reduce the electrical performances of the diode.

Photodiode properties of molecular beam epitaxial InSb on a heavily doped substrate

Photodiodes of InSb were fabricated on an epitaxial layer grown using molecular beam epitaxy (MBE). Thermal cleaning of the InSb (001) substrate surface, 2° towards the (111) B plane, was performed to remove the oxide. Photodiode properties of МВЕ-formed epitaxial InSb were demonstrated. Zero-bias resistance area product (R0A) measurements were taken at 80K under room temperature background for a pixel size of 100μm×100μm. Values were as high as 4.36×104Ω/cm2, and the average value of R0A was 1.66×104Ω/cm2. The peak response was 2.44(A/W). The epitaxial InSb photodiodes were fabricated using the same process as bulk crystal InSb diodes with the exception of the junction formation method. These values are comparable to the properties of bulk crystal InSb photodiodes.

Analysis of electrical and optical characteristics of InGaSb PIN photodiodes

This study represents an analysis of electrical and optical characteristics of InGaSb PIN photodiodes. The electrical characteristics are analysed by depicting a model of zero-bias resistance–area product (R0A) of such photodiodes. The effects of dislocation and temperature on R0A are also included in the model. Different optoelectronic properties of the material are extracted by fitting the obtained models with experimental data. The extracted dislocation density is 6.67×108 cm−2, which is close to the measured value of 2.4(±0.2)×108 cm−2. Through the dislocation and temperature-dependent modelling, maximum R0A is found to be 1.85 Ω cm2 at 139 K. Experimental data obtained at 300 and 363 K are fitted with theoretical model. The optical properties are analysed by the modelling of responsivity, quantum efficiency and detectivity. Cutoff wavelength is found to be 2271 nm, which is within ±5 nm of the experimentally obtained data. The present analysis gives a photodiode responsivity is 0.47 A/W, quantum efficiency is 28.86% and detectivity is 1.53×109 cm Hz1/2/W1 at a particular wavelength of λ=2.0 µm, which are agreeable to the experimentally obtained data.

Si/Si1−xGex/Si-based quantum wells infrared photodetector operating at 1.55 μm

A quantum well infrared photodetector consisting of self-assembled type II SiGe/Si based quantum wells operating around 1.55μm at room temperature has been investigated. The Si1−yGey/Si/Si1−xGex/Si/Si1−yGey stack results in a ‘W’ like profiles of the conduction and valence bands strain-compensated in the two low absorption windows of silica fibers infrared photodetectors have been proposed. Such computations have been used for the study of the p-i-n infrared photodetectors operating, around (1.3–1.55μm) at room temperature. The quantum transport properties of electrons and holes were approved with Schrödinger and kinetic equations resolved self-consistently with the Poisson equation. The theoretical performances of the photodetector were carried out such as the dark current mechanisms, the temperature dependence of normalized dark current and the zero-bias resistance area product (R0A).

Dark Current and Noise Measurements of an InAs/GaSb Superlattice Photodiode Operating in the Midwave Infrared Domain

A midwave infrared pin photodiode based on a type II InAs/GaSb superlattice (SL) was fabricated, and electrical measurements under dark conditions were performed as a function of temperature. The SL structure exhibits photoluminescence emission at 4.55 μm at 77 K. Deduced from current density–voltage (J–V) measurements, a zero-bias resistance–area product R0A greater than 1 × 106 Ω cm2 at 77 K was measured. Additional noise measurements show no presence of intrinsic 1/f noise above 20 Hz, and the photodiode presents Schottky-limited behavior below −600 mV. All these results confirm the potential for such SL InAs/GaSb superlattice pin photodiodes operating in the midwave infrared domain.

Passivation of infrared photodiodes with alcoholic sulfide solution

The effect of passivation with the solution of sodium sulfide (Na2S) in isopropyl alcohol on the room-temperature performance of the GaInAsSb/GaAlAsSb and InAs/InAsSbP photodiodes is investigated. After such a treatment the dark current density of the GaInAsSb/GaAlAsSb photodiodes at a reverse bias of 0.1 V is reduced from 5.5 × 10−2 to 2.1 × 10−3 A/cm2 and a zero-bias resistance-area product (R 0 A) is improved from 1.0 to 25.6 Ω cm2. For the InAs/InAsSbP photodiodes, the dark current density at U = −0.1 V is decreased from 1.34 to 8.1 × 10−1 A/cm2, while the R 0 A value increases from 4.4 × 10−2 to 7.3 × 10−2 Ω cm2. The method offers long-term stability of the photodiode performance.

Noise Characterization of Midwave Infrared InAs/GaSb Superlattice pin Photodiode

We report on noise characterization of a midwave infrared (MWIR) InAs/GaSb superlattice (SL) single detector. The SL structure was made of eight InAs monolayers (MLs) and eight GaSb MLs, with a total thickness of 2 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$</tex></formula> (440 SL periods). This structure exhibits a cut-off wavelength of 4.8 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$</tex></formula> at 77 K. Extracted from current–voltage characteristics, zero-bias resistance area product <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${R} _{0}{A}$</tex> </formula> above <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$5\times 10 ^{5} ~\Omega \cdot \hbox{cm}^{2}$</tex></formula> at 80 K was measured. Noise measurements were also performed under dark conditions. The measurements reveal the absence of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$ 1/{f}$</tex></formula> noise above 30 Hz. Moreover, the detector under test remains Schottky noise-limited up to a bias voltage of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$-$</tex></formula> 200 mV typically, which confirms the quality of the MWIR SL pin photodiode.

Suppression of leakage currents in InAsSb MWIR photodiodes by chemical treatment and illumination

Novel surface treatments for an InAs0.91Sb0.09 p–n junction grown on GaSb by MOCVD are proposed and demonstrated. Exposure of the p–n junction to argon ion plasma followed by etching with tartaric acid reduces the dark currents by five orders of magnitude. An additional reduction by two orders of magnitude in the dark current is achieved by illuminating the sample with white light. A mid-wavelength infrared photodetector based on the so treated p–n junction exhibits a high zero-bias resistance–area product (R0A) of 2.7 × 107 Ω cm2 and an internal quantum efficiency of 70% at 77 K. The measured BLIP temperature is 170 K and a high detectivity value (D* BLIP) of 4.03 × 1011 cm Hz1/2 W−1 is observed at 3.7 µm. The surface treatment results indicate that the device performance is limited by bulk material properties.

Computer modeling of MWIR single heterojunction photodetector based on mercury cadmium telluride

In the present paper, an abrupt heterojunction photodetector based on Hg 1 − x Cd x Te (MCT) has been simulated theoretically for mid-infrared applications. A semi-analytical simulation of the device has been carried out in order to study the performance ratings of the photodetector for operation at room temperature. The energy band diagram, carrier concentration, electric field profile, dark current, resistance–area product, quantum efficiency and detectivity have been calculated and optimized as a function of different parameters such as device thickness, applied reverse voltage and operating wavelength. The effect of energy band offsets in conduction and valance band on the transportation of minority carriers has been studied. The influences of doping concentration, electron affinity gradient and the p– n junction position within heterostructure on potential barrier have been analyzed. The optical characterization has been carried out in respect of quantum efficiency, and detectivity of the heterojunction photodetector. In present model the Johnson–Nyquist and shot noise has been considered in calculation of detectivity. The simulated results has been compared and contrasted with the available experimental results. Results of our analytical-cum-simulation study reveal that under suitable biasing condition, the photodetector offers a dark current, I D ≈ 6.5 × 10 −12 A, a zero-bias resistance–area product, R 0 A ≈ 11.3 Ω m 2, quantum efficiency, η ≈ 78%, NEP = 2 × 10 −12 W Hz 1/2 and detectivity D ∗ ≈ 4.7 × 10 10 mHz 1/2/W.

Electrical Characterization of Different Passivation Treatments for Long-Wave Infrared InAs/GaSb Strained Layer Superlattice Photodiodes

Silicon dioxide (SiO2), silicon nitride (SixNy), and zinc sulfide (ZnS) with ammonium sulfide [(NH4)2S] as a prepassivation surface treatment were compared as passivants for InAs/GaSb strained layer superlattice detectors with a 0% cutoff wavelength of ∼10 μm. SiO2 did not show significant improvement and the zero-bias resistance-area product (R0A) was 0.72 Ω-cm2 at 77 K. SixNy passivation showed a nominal improvement with an R0A value of 4.1 Ω-cm2 at 77 K. ZnS with (NH4)2S treatment outperformed others significantly, improving the R0A value to 492 Ω-cm2 at 77 K. Variable-area diode measurements indicated a bulk-limited R0A value of 722 Ω-cm2. ZnS-passivated diodes exhibited maximum surface resistivity with a value of 2500 Ω-cm.