nBn Structure Research Articles

Exploring the optical property of InAs1−xSbx-based nBn structures for high-temperature mid-wave infrared detection

InAs0.9Sb0.1-based nBn structures for mid-wave infrared detection are designed and prepared by molecular beam epitaxy. The structural, electrical, and optical properties are characterized, based on which the density-functional theory calculation is carried out by combining with the hybrid HSE06 exchange-correlation function. The results demonstrate that (i) the calculated bandgap for InAs0.9Sb0.1 is well consistent with that of optical spectroscopies (∼266 meV, or a cutoff wavelength of ∼4.66 μm), suggesting the practical effectivity of the theoretical model; (ii) the valence band offset of the unbiased InAs0.9Sb0.1/AlAs0.1Sb0.9 nBn structure is determined as ∼105 meV, with ignorable influence on the hole transport of the devices by considering the rather low dark current when working at a high temperature of ∼150 K; and (iii) the conduction band offset of InAs0.9Sb0.1/GaSb is roughly ∼0.6 eV. This work not only provides a strategy for effectively evaluating the InAs1−xSbx bandgap both theoretically and experimentally but also offers a more reliable basis for fabricating high-performance mid-infrared detectors with high operating temperatures.

NbN-based tunnel-type π-junctions for low-power half-flux-quantum circuits

We have developed half-flux-quantum (HFQ) circuits using all-π-junctions formed from an NbN/AlN/PdNi/NbN (SIFS) structure. The circuits were fabricated using a novel process that incorporated a ground plane on top of the chip, enabling the epitaxial growth of NbN-based junctions from the substrate. The π-state of the junctions was demonstrated through a HFQ shift. Notably, these π-junctions exhibited self-overdamped current-voltage characteristics, enabling them to function as switching components without the need for shunt resistors. The elimination of shunt resistors and the high sheet inductance of NbN are expected to enhance the density of HFQ circuits. To evaluate the performance and power consumption of the all-π-junctions HFQ circuits, we designed and fabricated an HFQ toggle flip-flop (HFQ-TFF) circuit utilizing π-π-π SQUIDs as the fundamental components. Our findings reveal that the NbN-based HFQ-TFF circuit correctly operates as a frequency divider while consuming only around 30% of the power compared to single-flux-quantum TFF (SFQ-TFF) circuits. These results suggest that the HFQ circuit using SIFS-π-junctions has promising potential for integrated circuits requiring low-power consumption at cryogenic temperatures, such as qubit control.

Growth and characterization of nBn structures based on CdxHg1–xTe for photodetectors in the 3–5 µm spectral range

Growth and characterization of nBn structures based on Cd_xHg_1–xTe for photodetectors in the 3–5 µm spectral range

Design and performance of dual-band MWIR/LWIR focal plane arrays based on a type-II superlattice nBn structure

Design and performance of dual-band MWIR/LWIR focal plane arrays based on a type-II superlattice nBn structure

Direct observation on argon tagging nitrobenzene radical anion in gas phase: Infrared photodissociation spectroscopy and theoretical calculation.

The infrared photodissociation spectroscopy was applied to characterize nitrobenzene radical anion (NB-). NB- tagged by argon [NB(Ar)-] was prepared by a mixture of nitrobenzene/Ar through a supersonic ion source and then selected by a time-of-flight mass spectrometer. Eight strong peaks observed at 977.9, 999.6, 1059.8, 1275.7, 1309.7, 1339.7, 1367.6 and 1581.7cm-1 in the fingerprint region were assigned to NB(Ar)-, corresponding to CC bending, CC stretching, CC bending+symmetric O-N stretching vibration, antisymmetric O-N and CC stretching vibration, antisymmetric O-N stretching and CH rocking vibration, CC stretching+antisymmetric O-N stretching vibration, C-N stretching vibration, and symmetric CC stretching vibration. Most interestingly, the distinguishable CH stretching vibrations were observed at 3006.5, 3048.6 and 3084.5cm-1 absorptions. Combined with density functional theoretical (DFT) calculation, five tagging argon NB- isomers were optimized and analyzed with no imaginary frequency. The results indicated that most bond lengths in NB- become longer than those of neutral NB, except for the C1-C2/C4-C5 bonds, which are only slightly shorter than those of neutral NB, and the C-N bond, which is 0.085 A shorter in the anion. The NB- tagged by argon located on the nitro group had no change on bond parameters with Ar-tagging or not theoretically. Natural population analysis (NPA) show that the negative natural charges are mainly distributed on both oxygen atoms. And the one electron resonates between the nitro group and benzene ring. N-O bonds in NB- become much more polar than those of the neutral NB. This paper proved the usefulness to characterize NB(Ar)- and further explore the structures of NBn- (n>1) clusters by infrared photodissociation spectroscopy combining with the time-of-flight mass spectrometer.

Mid-wave infrared optical receiver based on an InAsSb-nBn photodetector using the barrier doping engineering technique for low-power satellite optical wireless communication.

This paper proposes a new nBn photodetector (nBn-PD) based on InAsSb with a barrier doping engineering technique [core-shell doped barrier (CSD-B) nBn-PD] for utilization as a low-power receiver in satellite optical wireless communication (Sat-OWC) systems. In the proposed structure, the absorber layer is selected from an I n A s 1-x S b x (x=0.17) ternary compound semiconductor. The difference between this structure and other nBn structures is the placement of the top and bottom contacts in the form of a PN junction, which increases the efficiency of the proposed device through the creation of a built-in electric field. Also, a barrier layer is placed from the AlSb binary compound. The presence of the CSD-B layer with the high conduction band offset and very low valence band offset improves the performance of the proposed device compared to conventional PN and avalanche photodiode detectors. By applying -0.1V bias at 125K, the dark current is demonstrated at 4.31×10-5 A/c m 2 by assuming high-level traps and defect conditions. Examining the figure of merit parameters under back-side illumination with a 50% cutoff wavelength of 4.6µm shows that at 150K, the responsivity of the CSD-B nBn-PD device reaches about 1.8A/W under 0.05W/c m 2 light intensity. Regarding the great importance of using low-noise receivers in Sat-OWC systems, the results indicate that the noise, noise equivalent power, and noise equivalent irradiance are calculated as 9.98×10-15 A H z -1/2, 9.21×10-15 W H z 1/2, and 1.02×10-9 W/c m 2, respectively, at -0.5V bias voltage and 4µm laser illumination with the influence of shot-thermal noise. Also, D ∗ obtains 3.26×1011 c m H z 1/2/W without using the anti-reflection coating layer. In addition, since the bit error rate (BER) plays an essential role in the Sat-OWC systems, the effect of different modulations on the BER sensitivity of the proposed receiver is investigated. The results represent that the pulse position modulation and return zero on-off keying modulations create the lowest BER. Attenuation is also investigated as a factor that significantly affects BER sensitivity. The results clearly express that the proposed detector provides the knowledge to achieve a high-quality Sat-OWC system.

Structure and thermal stability investigations of (1-x)CaBi2Nb2O9- xNa0.5Bi2.5Nb2O9 ceramics

In this paper, (1-x)CaBi2Nb2O9-xNa0.5Bi2.5Nb2O9 [(1-x)CBN-xNBN; x = 0, 0.1, 0.3, 0.5 and 0.7] ceramics were prepared by the traditional solid-state method. The structure and properties of CBN and NBN are very close to each other, and XRD shows that Na/Bi ions have entered the lattice of CBN. By adjusting the content of NBN in (1-x)CBN-xNBN ceramics, the crystal structure of the ceramics undergoes a pseudo-tetragonal distortion that can significantly improve thermal stability. Analysis of the data of XRD refinement confirms there is pseudo-tetragonal phase at x = 0.1 to 0.5. Moreover, the remnant polarization Pr is obviously improved due to the reduction of grain size and pseudo-tetragonal distortion. Although the Curie temperature of the CBN-NBN piezoelectric ceramics decreases, the tanδ at high temperatures is significantly reduced and the DC resistivity is increased. The 0.5CBN-0.5NBN ceramic shows excellent comprehensive properties: d33 of 13.8 pC/N, Tc of 873 °C, tanδ of 2.1% at 500 °C, and Pr of 8.92 μC/cm2, especially the d33 maintains 94.9% of the initial d33 after depolarization at 850 °C, which has competitiveness in the high-temperature piezoelectric materials.

Assessment of surface recombination in mid-wave infrared InAsSb nBn detectors using transient microwave reflectance

Investigation of surface recombination is an important area for infrared detectors as the demand for smaller pixels increases. In this study, we use transient microwave reflectance to characterize the minority carrier lifetime of InAsSb nBn structures under three conditions: As-Grown, blanket Barrier-Etched, and SU-8 Passivated blanket barrier-etched. A qualitative comparison of these three samples shows that the minority carrier lifetime decreases for the Barrier-Etched sample compared to the As-Grown sample, indicating that the minority carrier lifetime is sensitive to changes in the sample surface, specifically the introduction of surface states. We compare these samples quantitatively using a polynomial fit (A−1 + Bn + Cn2). We find for the As-Grown sample A = 1.22 ± 0.45 µs, B = 2.5 ± 0.2 × 10−12 cm3/s, and C = 5.004 ± 4.996 × 10−31 cm6/s, for the Barrier-Etched sample A = 1.17 ± 0.40 µs, B = 9.9 ± 0.2 × 10−12 cm3/s, and C = 9.502 ± 9.498 × 10−30 cm6/s, and for the Passivated sample A = 1.34 ± 0.45 µs, B = 5.3 ± 0.5 × 10−12 cm3/s, and C = 5.500 ± 4.500 × 10−33 cm6/s.

Energy band offsets and charge transport process in an InAsSb based nBn structure: A numerical simulation

We report on the valence energy band offset (ΔEvC-A) between the InAsSb contact (C) and the InAsSb absorber (A) layers, in the C–InAsSb/B–AlAsSb/A-InAsSb nBn structure. ΔEv(C-A) is analyzed, numerically, for different thicknesses of the AlAsSb barrier (B) layer and different doping levels of the barrier and the contact layers, under equilibrium and at room temperature. A value of ΔEv(C-A) around 0,331 meV, corresponding to a near flat band situation, was obtained with donor's concentration of about 1016 cm−3 in the contact. First, simulations were carried at room temperature, under reverse bias, and for a 50 nm and a 100 nm barrier's thicknesses. The temperature dependence of ΔEv(C-A), under reverse bias, was analyzed between 150 K and 300 K. Finally, the reverse current-voltage characteristics of the structure were simulated in the dark and under illumination. Our results are compared to experimental results encountered in the literature and for the same system.

Bulk InAsSb-based upside-down pCBn photodetectors with greater than 5 µm cut-off wavelength

The InAsSb-based photodetectors covering the whole mid-infrared wavelength at 150 K have been modeled, successfully fabricated, and characterized. In this work, we increased the Sb composition in InAs1−xSbx to extend the cut-off wavelength; simultaneously, the novel upside-down structure was adopted to decrease the dark current to ensure good performance of the device at high operating temperature. The growth sequence of the upside-down InAs0.81Sb0.19/AlAsSb material system was reversed to the conventional nBn structure, and the AlSb/AlAs0.08Sb0.92 electron compound barrier was grown before the InAs0.81Sb0.19 active layer. At 150 K and 0.8 V forward bias, the fabricated photodetector demonstrates a dark current density around 3.46 × 10−4 A/cm2, a peak responsivity up to 1.89 A/W, and a quantum efficiency up to 56% at 4.2 µm, corresponding to 1.23 × 1011 cm Hz1/2/W detectivity.

Dual-band InGaAs nBn photodetectors at 2 μm

An nBn type InGaAs photodetector structure operating at 2 μm with dual-band operation capability has been numerically designed and experimentally characterized. A compositionally graded and unintentionally doped InGaAlAs layer with a delta-doped nano-layer behaves as the barrier for majority carrier flow. The pixels fabricated with a 20 μm pitch mesa process yielded peak quantum efficiencies of 67% and 53% without anti-reflective coating for the e-SWIR and SWIR sides, respectively. Dark current measurements on a large area pixel yield 3.40 mA/cm2 at 300 K and 0.61 μA/cm2 at 200 K for the e-SWIR side, while 8.05 μA/cm2 at 300 K and 1.09 nA/cm2 at 200 K are obtained for the SWIR side. I–V characteristics analysis performed with pixels having different areas shows that the designed nBn structure has no surface leakage current presenting a potential benefit for dual-band applications requiring mesa structures that usually suffer from surface states for the InGaAs material system. Temperature dependent dark current characterization confirms this result and implies diffusion current dominated dark current.

Investigation of the surface leakage current of the nBn InGaAsSb infrared photodetector by using photoreflectance spectroscopy

The surface leakage current of the nBn infrared detector based on InGaAsSb/AlGaSb heterostructure was studied by using photoreflectance spectroscopy (PR). The Franz-Keldysh oscillations (FKOs) in PR spectra showed that the minority carriers (electrons) mainly affect the surface electric field in the nbn structures. The results show that the electric field increases due to the photovoltaic effect as the temperature increases. However, the increased ratio of the electric field at low temperature is lower than that of high temperature. At low temperatures, when the temperature drops, the generation-recombination (G-R) associated with dark current is eliminated, and the surface electric field variation becomes lower. By increasing the temperature and dark current, the electric field changes more. In addition, the unipolar barrier photodiode exhibits no surface leakage current at low temperatures without blocking the bulk currents.

Admittance of barrier nanostructures based on MBE HgCdTe

Mid- and long-wave infrared nBn structures based on HgCdTe grown by molecular beam epitaxy (MBE) on GaAs (013) substrates were fabricated. For mid-wave nBn structures, the composition in the absorbing layer was 0.29, and for long-wave nBn structures, this composition was 0.21. The composition in the MBE HgCdTe barrier layers ranged from 0.61 to 0.67. Based on the fabricated HgCdTe nBn structures, test metal–insulator–semiconductor (MIS) devices were created by applying a dielectric Al2O3 film with the thickness of about 90 nm. The admittance of test MIS devices was investigated over a wide range of frequencies and temperatures. An equivalent circuit of MIS device based on MBE HgCdTe nBn structure is proposed, which includes the dielectric capacitance, the capacitance and resistance of the barrier layer, and the series resistance of the absorbing layer bulk. It is shown that the values of the equivalent circuit elements are easy to determine from the experimental frequency dependences of admittance in accumulation mode. Comparison of element values for MIS devices based on mid-wave and long-wave nBn structures is carried out.

Aдмиттанс МДП-структур на основе nBn-систем из эпитаксиального HgCdTe, разработанных для детектирования в спектральном диапазоне 3-5 μm

The admittance of test MIS devices based on nBn structures from Hg1-xCdxTe grown by molecular beam epitaxy (MBE) is investigated. The composition x in the absorbing layer was 0.29, and the composition in the barrier layer was 0.60. An equivalent circuit of a MIS device based on an nBn structure is proposed and the values of the elements of this circuit are found under various conditions. Comparison of the temperature dependence of the barrier resistance with the Rule07 model indicates the possibility of creating efficient nBn detectors based on MBE HgCdTe for the spectral range of 3–5 μm.

Темновые токи униполярных барьерных структур на основе теллурида кадмия и ртути для длинноволновых инфракрасных детекторов

Two types of long-wave infrared nBn structures based on mercury cadmium telluride grown by molecular beam epitaxy on GaAs (013) substrates have been fabricated. For each type of device, the side walls of the mesa structures were passivated with an Al2O3 dielectric film or left without passivation. The CdTe content in the absorbing layers was 0.20 and 0.21, and in the barrier layers, 0.61 and 0.63. The dark currents of the manufactured devices were studied in a wide range of voltages and temperatures. The values of the surface leakage component are found under various conditions. It has been shown that the surface leakage current density decreases upon passivation with an Al2O3 film. It was found that at room temperature in the fabricated nBn structures with reverse biases, the surface leakage component dominates, and with forward biases, the dark current is determined by the combined effect of the surface leakage component and the bulk current component. From the Arrhenius plots, the values of the activation energies of the surface leakage current component were found, which at small reverse biases are in the range from 0.05 to 0.10 eV. At small reverse biases, upon cooling the samples, the role of the bulk component of the dark current increases, which at 180 K is approximately 0.81 A/cm2. In the temperature range 200-300 K, the values of the dark current density exceed the values calculated according to the empirical Rule07 model by a factor of 10-100, which indicates the possibility of creating long-wave infrared barrier detectors with a decrease in the values of the surface leakage component.

Surface leakage current reduction of InAsSb nBn MWIR HOT detector via hydrogen peroxide treatment

InAsSb nBn structure plays a key role in realizing high operating temperature (HOT) MWIR detectors. However, the AlAsSb layer, functioning as a barrier layer, can be rapidly oxidized during the pixel isolation process, forming undesirable oxides that can contribute to increase the surface leakage current. In this work, electrical and optical analysis were performed to investigate the role of the post-treatment process after pixel isolation step in reducing the oxidation and inhibiting the formation of unfavorable oxides closely related to the surface leakage currents. Our study shows that H2O2 post-treatment after the dry pixel isolation process can effectively reduce the barrier oxidation and suppress the formation of Sb2O5, greatly reducing the surface leakage current. Using the proposed post-treatment process, the dark current density of less than 1 × 10−6 A/cm2 was obtained at an applied bias of −0.3 V and 150 K, which is one order of magnitude lower than that of the InAsSb nBn device recently reported.

Study on structural, mechanical, electronic properties and Debye temperature of four NbN structures

A new structure of NbN (P62m-NbN) is predicted by first-principles density functional theory calculations. For the new structure and P6m2, Pm3m and P63mmc-NbN, they are stable according to elastic, dynamic, thermodynamic and chemical stability, under 0 GPa, 20 GPa, 40 GPa, 60 GPa, 80 GPa, and 100 GPa pressure. Their physical properties are calculated, under 0 GPa, 20 GPa, 40 GPa, 60 GPa, 80 GPa, and 100 GPa pressure. For P6m2, Pm3m and P63mmc-NbN under 0GPa pressure, the calculated physical properties are in excellent agreement with the early ones, indicating the reliability of the approach. To the best of our knowledge, the physical properties of four NbN phases under 20GPa to 100GPa pressure are the first attempt to explore and compare. P6m2-NbN is harder to compress and P62m-NbN is easier to compress. The P6m2-NbN is the stiffest material and P62m-NbN is the softest material at 0 GPa pressure. Pm3m-NbN is the stiffest material at 100 GPa pressure. The P6m2-NbN is close to shear isotropy. The Debye temperatures are 760 K, 735 K, 707 K and 684 K for P6m2, Pm3m, P63mmc and P62m-NbN, respectively, at 0 GPa. The Debye temperature of P62m-NbN is the minimum in four NbN phases, from 0GPa to 100GPa. The Debye temperature of Pm3m-NbN is the maximum in four NbN phases, from 20GPa to 100GPa. Four NbN structures are conductors both at 0GPa and 100GPa pressure.

Resonant Cavity Enhanced Photodiodes in the Short-Wave Infrared for Spectroscopic Detection

The design, fabrication and characterization of resonant cavity enhanced photodiodes for the short-wave infrared has been investigated. An InGaAsSb absorber and AlGaSb barrier were used in an nBn structure, within a Fabry-Perot cavity bounded by AlAsSb/GaSb DBR mirrors. The resonant cavity design produced a narrow response at 2.25 μm, with a FWHM of ~ 26 nm and peak responsivity of 0.9 A/W. The photodiodes exhibited high specific detectivities and low leakage currents at 300 K - 5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> cmHz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> W <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and 0.2 mAcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> respectively, with an applied bias voltage of -100 mV. A maximum specific detectivity of 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> cmHz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> W <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> was achieved at 275 K and the detector continued to perform well at high temperatures - at 350 K the peak specific detectivity was 3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> cmHz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> W <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . The narrow resonant response of these detectors make them suitable for spectroscopic sensing, demonstrated by measurements of glucose concentrations in water. Concentrations as low as 1 % were discriminated, limited only by the associated electronic systems.

Impedance of MIS Devices Based on nBn Structures from Mercury Cadmium Telluride

Three types of nBn structures based on mercury cadmium telluride grown by molecular beam epitaxy have been fabricated. As barrier layers in nBn structures, Hg1–xCdxTe at x = 0.67 and 0.84 and the 18 period Hg0.20Cd0.80Te (9 nm) – HgTe (2 nm) superlattice were used. To study the properties of barrier layers based on nBn structures, MIS devices were created using dielectric Al2O3 films. The impedance of the created devices was investigated over wide ranges of voltages, frequencies, and temperatures. Equivalent circuits of MIS devices based on nBn structures in the accumulation mode are proposed. It is shown that measurements of the frequency dependences of the impedance make it possible to determine the values of the differential resistance of the barrier layer in a wide range of conditions. It was found that the values of the differential resistance are determined only by the bulk component of the dark current, and the surface leakage component does not affect the measured impedance of MIS devices. The dependences of the values of the equivalent circuit elements on the area of structures, voltage, and temperature are determined. It is shown that in the temperature range 210–300 K, the values of the differential resistance of the barrier layer based on Hg0.33Cd0.67Te are determined by the diffusion-limited flow of holes from the contact and absorbing layers, at the forward and reverse biases, respectively. The values of the product of the differential resistance and the area are determined for nBn structures with various parameters of the barrier layers. The possibilities of using the measurements of impedance of MIS devices based on nBn structures to study the homogeneity of properties of various layers are demonstrated..

Admittance of Barrier Structures Based on Mercury Cadmium Telluride

The results of studying the admittance of unipolar barrier structures based on HgCdTe grown by molecular beam epitaxy (MBE) on GaAs (013) substrates are presented. Using passivation with an Al2O3 insulator, device nBn structures based on HgCdTe were fabricated. The layer parameters in the created structures provided the possibility of detection in the spectral range of 3–5 μm. Based on the analysis of the frequency dependences of the admittance, an equivalent circuit of nBn structures at small biases is proposed. The dependences of the equivalent circuit parameters on the area of the mesa structure and temperature are determined. The properties of high-temperature maxima in the voltage dependences of the capacitance and conductance of nBn structures, which are presumably related to the recharging of surface states at the heterointerface between the barrier and absorbing layers, are studied. It is found that in a wide range of frequencies and temperatures, the capacitance – voltage characteristics of nBn structures based on HgCdTe at reverse biases can be used to determine the concentration of donor impurities in the absorbing layer. It is shown that the admittance of test MIS devices in a mesa configuration, formed on the basis of the MBE HgCdTe nBn structures, is determined by the combined influence of electronic processes in the contact, barrier, and absorbing layers.