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EN
A method for defects extraction for a mercury cadmium telluride (MCT) multilayer low-bandgap heterostructure is presented. The N⁺/T/p/T/P⁺/n⁺ epitaxial layer was deposited on a GaAs substrate by a metal-organic chemical vapour deposition (MOCVD). The absorber was optimized for a cut-off wavelength of 𝜆𝑐=6 μm at 230 K. Deep-level transient spectroscopy (DLTS) measurements were conducted for the isolated junctions of the N⁺/T/p/T/P⁺/n⁺ heterostructure. Three localised point defects were extracted within the p-type active layer. Two of them were identified as electron traps and one as a hole trap, respectively.
EN
The performance of long-wave infrared (LWIR) x = 0.22 HgCdTe avalanche photodiodes (APDs) was presented. The dark currentvoltage characteristics at temperatures 200 K, 230 K, and 300 K were measured and numerically simulated. Theoretical modeling was performed by the numerical Apsys platform (Crosslight). The effects of the tunneling currents and impact ionization in HgCdTe APDs were calculated. Dark currents exhibit peculiar features which were observed experimentally. The proper agreement between the theoretical and experimental characteristics allowed the determination that the material parameters of the absorber were reached. The effect of the multiplication layer profile on the detector characteristics was observed but was found to be insignificant.
EN
The dual-band avalanche photodiode (APD) detector based on a HgCdTe material system was designed and analysed in detail numerically. A theoretical analysis of the two-colour APD intended for the mid wavelength infrared (MWIR) and long wavelength infrared (LWIR) ranges was conducted. The main purpose of the work was to indicate an approach to select APD structure parameters to achieve the best performance at high operating temperatures (HOT). The numerical simulations were performed by Crosslight numerical APSYS platform which is designed to simulate semiconductor optoelectronic devices. The current-voltage characteristics, current gain, and excess noise analysis at temperature T = 230 K vs. applied voltage for MWIR (U = 15 V) and LWIR (U = –6 V) ranges were performed. The influence of low and high doping in both active layers and barrier on the current gain and excess noise is shown. It was presented that an increase of the APD active layer doping leads to an increase in the photocurrent gain in the LWIR detector and a decrease in the MWIR device. The dark current and photocurrent gains were compared. Photocurrent gain is higher in both spectral ranges.
EN
This paper presents examples of infrared detectors with mercury cadmium telluride elaborated at the Institute of Applied Physics, Military University of Technology and VIGO Photonics S.A. Fully doped HgCdTe epilayers were grown with the metal organic chemical vapour deposition technique which provides a wide range of material composition covering the entire infrared range from 1.5 μm to 14 μm. Fundamental issues concerning the design of individual areas of the heterostructure including: the absorber, contacts, and transient layers with respect to their thickness, doping and composition were discussed. An example of determining the gain is also given pointing to the potential application of the obtained devices in avalanche photodiode detectors that can amplify weak optical signals. Selected examples of the analysis of current-voltage and spectral characteristics are shown. Multiple detectors based on a connection in series of small individual structures are also presented as a solution to overcome inherent problems of low resistance of LWIR photodiodes. The HgCdTe detectors were compared with detectors from III-V materials. The detectors based on InAs/InAsSb superlattice materials achieve very comparable parameters and, in some respects, they are even superior to those with mercury cadmium telluride.
EN
Short-period 10 monolayers InAs/10ML GaSb type-II superlattices have been deposited on a highly lattice-mismatched GaAs (001), 2° offcut towards <110> substrates by molecular beam epitaxy. This superlattice was designed for detection in the mid-wave infrared spectral region (cut-off wavelength, λcut-off = 5.4 μm at 300 K). The growth was performed at relatively low temperatures. The InAs/GaSb superlattices were grown on a GaSb buffer layer by an interfacial misfit array in order to relieve the strain due to the ~7.6% lattice-mismatch between the GaAs substrate and type-II superlattices. The X-ray characterisation reveals a good crystalline quality exhibiting full width at half maximum ~100 arcsec of the zero-order peak. Besides, the grown samples have been found to exhibit a change in the conductivity.
EN
The temperature dependence of photoluminescence spectra has been studied for the HgCdTe epilayer. At low temperatures, the signal has plenty of band-tail states and shallow/deep defects which makes it difficult to evaluate the material bandgap. In most of the published reports, the photoluminescence spectrum containing multiple peaks is analyzed using a Gaussian fit to a particular peak. However, the determination of the peak position deviates from the energy gap value. Consequently, it may seem that a blue shift with increasing temperature becomes apparent. In our approach, the main peak was fitted with the expression proportional to the product of the joint density of states and the Boltzmann distribution function. The energy gap determined on this basis coincides in the entire temperature range with the theoretical Hansen dependence for the assumed Cd molar composition of the active layer. In addition, the result coincides well with the bandgap energy determined on the basis of the cut-off wavelength at which the detector response drops to 50% of the peak value.
EN
A theoretical analysis of the mid-wavelength infrared range detectors based on the HgCdTe materials for high operating temperatures is presented. Numerical calculations were compared with the experimental data for HgCdTe heterostructures grown by the MOCVD on the GaAs substrates. Theoretical modelling was performed by the commercial platform SimuAPSYS (Crosslight). SimuAPSYS fully supports numerical simulations and helps understand the mechanisms occurring in the detector structures. Theoretical estimates were compared with the dark current density experimental data at the selected characteristic temperatures: 230 K and 300 K. The proper agreement between theoretical and experimental data was reached by changing Auger-1 and Auger-7 recombination rates and Shockley-Read-Hall carrier lifetime. The level of the match was confirmed by a theoretical evaluation of the current responsivity and zero-bias dynamic resistance area product (R0A) of the tested detectors.
EN
Numerical analysis of the dark current (Id) in the type-II superlattice (T2SL) barrier (nBn) detector operated at high temperatures was presented. Theoretical calculations were compared with the experimental results for the nBn detector with the absorber and contact layers in an InAs/InAsSb superlattice separated AlAsSb barrier. Detector structure was grown using MBE technique on a GaAs substrate. The k·p model was used to determine the first electron band and the first heavy and light hole bands in T2SL, as well as to calculate the absorption coefficient. The paper presents the effect of the additional hole barrier on electrical and optical parameters of the nBn structure. According to the principle of the nBn detector operation, the electrons barrier is to prevent the current flow from the contact layer to the absorber, while the holes barrier should be low enough to ensure the flow of optically generated carriers. The barrier height in the valence band (VB) was adjusted by changing the electron affinity of a ternary AlAsSb material. Results of numerical calculations similar to the experimental data were obtained, assuming the presence of a high barrier in VB which, at the same time, lowered the detector current responsivity.
EN
The semiempirical rule, “Rule 07” specified in 2007 for P-on-n HgCdTe photodiodes has become widely popular within infrared community as a reference for other technologies, notably for III-V barrier photodetectors and type-II superlattice photodiodes. However, in the last decade in several papers it has been shown that the measured dark current density of HgCdTe photodiodes is considerably lower than predicted by benchmark Rule 07. Our theoretical estimates carried out in this paper support experimental data. Graphene and other 2D materials, due to their extraordinary and unusual electronic and optical properties, are promising candidates for high-operating temperature infrared photodetectors. In the paper their room-temperature performance is compared with that estimated for depleted P i-N HgCdTe photodiodes. Two important conclusions result from our considerations: the first one, the performance of 2D materials is lower in comparison with traditional detectors existing on global market (InGaAs, HgCdTe and type- II superlattices), and the second one, the presented estimates provide further encouragement for achieving low-cost and high performance HgCdTe focal plane arrays operating in high-operating temperature conditions.
EN
Graphene applications in electronic and optoelectronic devices have been thoroughly and intensively studied since graphene discovery. Thanks to the exceptional electronic and optical properties of graphene and other two-dimensional (2D) materials, they can become promising candidates for infrared and terahertz photodetectors. Quantity of the published papers devoted to 2D materials as sensors is huge. However, authors of these papers address them mainly to researches involved in investigations of 2D materials. In the present paper this topic is treated comprehensively with including both theoretical estimations and many experimental data. At the beginning fundamental properties and performance of graphene-based, as well as alternative 2D materials have been shortly described. Next, the position of 2D material detectors is considered in confrontation with the present stage of infrared and terahertz detectors offered on global market. A new benchmark, so-called “Law 19”, used for prediction of background limited HgCdTe photodiodes operated at near room temperature, is introduced. This law is next treated as the reference for alternative 2D material technologies. The performance comparison concerns the detector responsivity, detectivity and response time. Place of 2D material-based detectors in the near future in a wide infrared detector family is predicted in the final conclusions.
EN
The paper reports on the barrier mid-wave infrared InAs/InAsSb (xSb = 0.4) type-II superlattice detector operating below thermoelectrical cooling. AlAsSb with Sb composition, xSb = 0.97; barrier doping, ND < 2×10¹⁶ cm⁻³ leading to valence band offset below 100 meV in relation to the active layer doping, ND = 5×10¹⁵ cm⁻³ was proved to be proper material not introducing extra barrier in valence band in the analyzed temperature range in XBn architectures. The detectivity of the simulated structure was assessed at the level of ∼ 1011 Jones at T ∼ 100K assuming absorber thickness, d = 3 μm. The detector’s architecture for high frequency response operation, τs = 420 ps (T ∼ 77K) was presented with a reduced active layer of d = 1 μm.
EN
A revision of the standard approach to characterization of thin-semiconductor-layer Hall samples has been proposed. Our results show that simple checking of I(V) curve linearity at room temperature might be insufficient for correct determination of bias conditions of a sample before measurements of Hall effect. It is caused by the nonlinear behaviour of electrical contact layers, which should be treated together with the tested layer a priori as a metal-semiconductor-metal (MSM) structure. Our approach was examined with a Be-doped p-type InAs epitaxial layer, with four gold contacts. Despite using full high-quality photolithography a significant asymmetry in maximum differential resistance (Rd) values and positions relative to zero voltage (or current) value was observed for different contacts. This suggests that such characterization should be performed before each high-precision magneto-transport measurement in order to optimize the bias conditions.
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