HgCdTe Quantum Research Articles

Quantifying non-threshold Auger-recombination processes in mid-wavelength infrared range HgCdTe quantum wells

We study photoluminescence temperature quenching in HgTe/CdHgTe quantum wells (QWs) emitting at 3–4 μm wavelengths and recover temperature-dependent interband recombination rates. Recombination coefficients are determined for the process that we identify as a non-threshold ehh Auger process involving valence band continuum states in barriers. With the effective Auger coefficient CA reaching ∼10−13 cm4/s under resonant conditions, such a process is shown to determine stimulated emission thresholds in a wide temperature interval, while the contribution of conventional, activated Auger processes is presumably rather limited. Thus, threshold energy considerations should be used with caution for the optimization of HgCdTe QW lasers operating around 3 μm, and relatively low-barrier QWs may provide better performance than the high-barrier ones despite lower energy thresholds for thermally activated eeh-Auger recombination. It holds as long as the conduction band offset is detuned from the bandgap energy to avoid additional non-threshold eeh-processes and sufficient hole localization at elevated temperatures is maintained.

Generation of Long-Wavelength Stimulated Emission in HgCdTe Quantum Wells with an Increased Auger Recombination Threshold

Generation of Long-Wavelength Stimulated Emission in HgCdTe Quantum Wells with an Increased Auger Recombination Threshold

Energy Position of the Size Quantization Levels in Multiple HgCdTe Quantum Wells

Energy Position of the Size Quantization Levels in Multiple HgCdTe Quantum Wells

Interference Transport in a Two-Dimensional Topological Insulator in a CdHgTe Quantum Well

Interference transport in mesoscopic samples of a two-dimensional topological insulator in CdHgTe quantum wells is studied for the first time. It is established that quasi-ballistic edge transport in such an insulator exists at lengths up to 10 µm. In this transport regime, almost periodic Aharonov–Bohm oscillations caused by the formation of closed loops with a characteristic size of about 200 nm by edge states are found. The phase coherence length in the two-dimensional topological insulator is determined for the first time from the measured temperature dependence of their amplitude.

Stimulated emission in 24–31 μ m range and «Reststrahlen» waveguide in HgCdTe structures grown on GaAs

Long-wavelength stimulated emission (SE) is studied in optically pumped HgCdTe quantum well heterostructures with dielectric waveguides. Continuous temperature tuning of the wavelength from 27 to 18 μm is achieved in structures with optimized waveguides. Above 27 μm, SE clamps at 31 μm wavelength, where mode leaking is reduced due to the Reststrahlen effect in the GaAs substrate. The operating temperature is mainly limited by the activation of Auger recombination in quasi-equilibrium conditions, while at low temperatures, we expect that lowering initial carrier heating would enhance the gain considerably. We conclude that exploiting the Reststrahlen effect should allow one to achieve continuous wavelength tuning around 30 μm and operating wavelengths up to 40 μm with technologically attainable epistructure thickness.

Rashba Spin Splitting in HgCdTe Quantum Wells with Inverted and Normal Band Structures.

In quantum wells (QWs) formed in HgCdTe/CdHgTe heterosystems with a variable composition of Cd(Hg), Shubnikov-de-Haas (SdH) oscillations are investigated to characterize the Rashba-type spin-orbit coupling in QWs with both a normal and inverted band structure. Several methods of extracting the Rashba spin-splitting at zero magnetic field and their magnetic field dependences from the beatings of SdH oscillations are used for greater reliability. The large and similar Rashba splitting (25–27 meV) is found for different kinds of spectrum, explained by a significant fraction of the p-type wave functions, in both the E1 subband of the sample with a normal spectrum and the H1 subband for the sample with an inverted one.

Edge and Bulk Transport in a Two-Dimensional Topological Insulator Based on a CdHgTe Quantum Well

The transport response of a CdHgTe quantum well with a thickness of 11.5 nm is investigated. The behavior of the local and nonlocal resistance in the temperature range from 0.1 to 20 K is examined. It is shown that the system under study is a two-dimensional topological insulator. In comparison with traditional two-dimensional topological insulators implemented in 8-nm-thick HgTe quantum wells, the investigated one is characterized by a significantly smaller energy gap and, at the same time, a higher carrier mobility. The data are analyzed using computer simulations taking into account the actual geometry of the sample, as well as scattering between edge and bulk carrier states. It is shown that the backscattering probability of topological electrons within the edge states is nearly independent of temperature. In contrast, the probability of scattering from the edge channels into the bulk depends exponentially on the temperature, and fitting this dependence with a standard activation formula is the most accurate way to determine the mobility gap in the system under study. Even at the highest temperature, the probability of scattering between the counter-propagating states of the same edge exceeds the probability of scattering into the bulk by an order of magnitude. Therefore, this mechanism is dominant and determines the mean free path of edge electrons.

Influence of quantum well parameters on the spectrum of two-dimensional plasmons in HgTe/CdHgTe heterostructures

Influence of parameters of a quantum well and electronic polarizability spatial dispersion on the dependence of two-dimensional plasmon energy on wave vector in narrow-gap CdHgTe quantum wells (band gap 35 meV) is studied theoretically. It is shown that at energies above 20 meV, the dispersion law of two-dimensional plasmons is close to linear. Taking into account the finite width of the quantum well decreases the plasmon phase velocity. This effect increases with an increase in the fraction of cadmium in the QW while maintaining the band gap and with a decrease in the concentration of charge carriers in it. Keywords: two-dimensional plasmon, narrow-gap HgTe.

Toward Peltier-cooled mid-infrared HgCdTe lasers: Analyzing the temperature quenching of stimulated emission at ∼6 μm wavelength from HgCdTe quantum wells

Despite the ultimate performance of the existing cascade lasers, simple interband emitters in the mid-infrared (IR) can still be of interest as a cheaper and widely tunable alternative for some applications. In this work, we show mid-infrared stimulated emission (SE) at 5–6 μm wavelength from an optically pumped mercury–cadmium–telluride quantum well (QW) heterostructures at temperatures up to 200 K. At lower temperatures, the SE threshold appears to be mostly determined by conventional eeh Auger recombination, while the contribution of alternative QW-specific ehh Auger processes is limited. At higher temperatures, we establish heating of the electron gas by pumping radiation as a primary factor responsible for the thermal quenching of the SE. Consequently, both pumping scheme and QW designs should be carefully revised to minimize carrier heating in order to realize near-to-mid-IR optical converters operating close to ambient temperature. We suggest using low-barrier QWs to minimize excessive heat introduced in the QW upon carrier capture and also to eliminate eeh Auger processes involving excited QW subbands. Thus, mid-infrared HgCdTe lasers are expected to reach operating temperatures readily attainable under thermoelectric cooling.

Coherent Emission in the Vicinity of 10 THz due to Auger-Suppressed Recombination of Dirac Fermions in HgCdTe Quantum Wells

The discovery of Dirac fermions in a number of 2D and 3D materials boosted the solid-state research in an unprecedented way. Among the many hopes of using their exceptional physical properties, it ...

All-electrically tunable networks of Majorana bound states

Second-order topological superconductors (SOTSs) host localized Majorana fermions and provide a new platform for topological quantum computation. We propose a remarkable and feasible way to realize networks based on SOTSs which allow to nucleate and braid Majorana bound states (MBSs) in an all-electrical manner without fine-tuning. The proposed setups are scalable in a straightforward way and can accommodate any even number of MBSs. Moreover, the MBSs in the networks allow defining qubits whose states can be initialized and read out by measuring Josephson currents flowing between SOTS islands. Our proposal can be implemented in monolayers of $\text{FeTe}{}_{1-x}\text{Se}_{x}$, monolayers of 1T'-WTe$_2$, and inverted Hg(Cd)Te quantum wells in proximity to conventional superconductors.

Ternary alloyed HgCdTe nanocrystals for short-wave and mid-wave infrared region optoelectronic applications

Semiconductor quantum dots (QDs) are emerging as the forefront alternative for the conventional imaging technology, particularly in infrared region from near infrared (0.75–1.4 μm) to long-wave infrared (8–14 μm) region. A handful of materials are explored for mid infrared imaging QDs and they are all invariably binary semiconductor compounds. Ternary alloyed quantum dots in many previous cases have shown properties that are unique and better than parent binary compounds. In this work, we have synthesized ternary alloyed HgCdTe quantum dots and studied their photophysical properties. Previously studied ternary alloyed HgCdTe CQDs absorb and emit in regions limited upto near-infrared region. We have tuned the excitonic absorption of HgCdTe QDs in the range of 2.2–5 μm, where addition of cadmium clearly showed blueshift in excitonic peak as compared to that of HgTe QDs. Structural properties are studied by TEM, XRD & XPS techniques. Electrical behaviour is studied by measuring I-V, I-V-T curves. Photodetectors are fabricated in photoconductive geometry showing promising photo-response under visible (532 nm) and NIR (810 nm, 1550 nm) excitation. Responsivity of the devices is in the order of 1 mA W−1 at 1 V bias and show good linearity over irradiance range of 0.025 and 2.5 W cm−2. These results pave the way for development of next generation cost-effective short-wave and mid-wave infrared region optoelectronic devices based on narrow bandgap HgCdTe nanocrystals.

Group II–VI semiconductor quantum dot heterojunction photodiode for mid wave infrared detection

In this article we report the development of 10×10 photodiode array by realizing heterojunction between mercury cadmium telluride (HgCdTe) quantum dot (diameter ∼14 nm) and silicon responsive in mid wave infrared (MWIR) range (λ=3–5 µm) at room temperature. Performance of this optical sensor has been evaluated experimentally and Detectivity of $$1.6 \times {10^8}{\rm{cm}}\sqrt {{\rm{Hz}}} /{\rm{W}}$$ has been achieved at spectral wavelength of 3.5 µm at 300 K. This work ascertains the compatibility of chemically synthesized HgCdTe quantum dots with commercially available direct injection type readout integrated circuits (ROIC) for the development of low cost large format MWIR focal plane array (FPA).

HgCdTe Quantum Dot Over Interdigitated Electrode for Mid-Wave Infrared Photon Detection and Its Noise Characterization

In this paper, we report the development of mid-wave infrared (MWIR) photon sensor using solution-processed mercury cadmium telluride (Hg[Formula: see text]CdxTe) semiconductor colloidal quantum dots (CQDs) coated over interdigitated metallic electrode structure, having significant response in the MWIR spectral band range ([Formula: see text]–5.0[Formula: see text][Formula: see text]m) at room temperature. HgCdTe CQD has been chemically synthesized. We have characterized the optical and [Formula: see text] noise performances of the developed sensor to understand its behaviors at different operating biases as an introductory step toward development of large-format MWIR focal-plane arrays having similar pixel structure. The optimum biasing conditions have been experimentally evaluated at room temperature. We have achieved a noise equivalent power (NEP) of 2.5[Formula: see text]pW at 1.5-V bias voltage which corresponds to detectivity ([Formula: see text]) in the order of 108. This work highlights the development of low-cost colloidal HgCdTe quantum dot photodetectors and their utility in the monolithic infrared focal-plane arrays.

Terahertz Photoluminescence of Double Acceptors in Bulky Epitaxial HgCdTe Layers and HgTe/CdHgTe Structures with Quantum Wells

The photoluminescence of bulky films and heterostructures with HgCdTe quantum wells is studied in the far IR range upon interband optical excitation. Photoluminescence lines are found whose position is independent of temperature, and intensity nonmonotonically changes with increasing temperature. These lines are shown to be related to the radiative recombination of holes by singly ionized mercury vacancies. A drastic increase in the equilibrium recombination of such centers involved in the formation of the photoluminescence signal with the temperature change from 40 to 70 K leads to the nonmonotonic temperature dependence of the photoluminescence intensity.

Effect of Features of the Band Spectrum on the Characteristics of Stimulated Emission in Narrow-Gap Heterostructures with HgCdTe Quantum Wells

Effect of Features of the Band Spectrum on the Characteristics of Stimulated Emission in Narrow-Gap Heterostructures with HgCdTe Quantum Wells

Recombination of CdHgTe Quantum Dot and “Dextran - Magnetic Layered Double Hydroxide - Fluorouracil” System for Cell Imaging

In this paper, we synthesized a CdHgTe type water-soluble quantum dots, combined in the next time with the drug delivery system "dextran - magnetic layered double hydroxide - fluorouracil" (DMF), built a new nanostructures platform QD@DMF for blending the fluorescent probe function of quantum dot together with the magnetic targeting curative effect of the DMF system. The Fluorescence spectrophotometer, Ultraviolet spectrophotometer, TEM and XRD were used to characterize the luminescent properties, particle morphology and phase characteristics of the QD@DMF samples. The experiments on cell imaging were carried out by laser con-focal scan microscopy technique. Results showed that the CdHgTe QDs could be successfully grafted onto the surface of the DMF system through electrostatic coupling, forming a special structure based on magnetic layered double hydroxide with a near-infrared emission wavelength in 575~780 nm. Compared with QDs, the QD@DMF composite could significantly improve the cell imaging effect, the label intensity increased with the magnetic field intensity and obeyed the linear relationship Dmean = 1.760+0.013B. The fluorescent magnetic nanoparticles maintained not only the super-paramagnetic of DMF but also the photoluminescence properties of the QDs, implicating that the QD@DMF composite may be an effective multifunction tool for optical bio-imaging and magnetic targeted therapy.

Влияние особенностей зонного спектра на характеристики стимулированного излучения в узкозонных гетероструктурах с квантовыми ямами на основе HgCdTe

AbstractWe report on the stimulated emission obtained in the wavelength range of 20.3–17.4 μm on the interband transitions at T = 8–50 K in HgCdTe quantum wells placed in a dielectric waveguide formed from wide-gap CdHgTe solid solution. Heterostructures with HgCdTe quantum wells are interesting for designing long-wavelength lasers operating in the wavelength range of 25–60 μm, which is not covered by currently available quantum cascade lasers. It is shown that the maximum temperature of stimulated emission is determined by the position of lateral maxima in the dispersion dependences in the first valence subband of the quantum well. Methods for suppressing nonradiative recombination in the structures with HgCdTe quantum wells are discussed.

Stimulated emission from HgCdTe quantum well heterostructures at wavelengths up to 19.5 μm

We report on stimulated emission at wavelengths up to 19.5 μm from HgTe/HgCdTe quantum well heterostructures with wide-gap HgCdTe dielectric waveguide, grown by molecular beam epitaxy on GaAs(013) substrates. The mitigation of Auger processes in structures under study is exemplified, and the promising routes towards the 20–50 μm wavelength range, where HgCdTe lasers may be competitive to the prominent emitters, are discussed.

Sodium Chloride Protected CdHgTe Quantum Dot Based Solid-State Near-Infrared Luminophore for Light-Emitting Devices and Luminescence Thermometry

Solid-state luminophores operating in the near-infrared (NIR) region may have applications in sensing, communication, and medicine. We report environmentally protected solid-state NIR-emitting luminophores fabricated by embedding CdHgTe colloidal quantum dots (QDs) into a NaCl matrix, with remarkable photo- and thermal stability and a photoluminescence quantum yield of 31% in the solid state, which is among the highest reported for solid-state NIR luminophores so far. We employed this luminophore as a down-conversion layer in a NIR-light-emitting device with a stable emission at 940 nm. Carrier recombination dynamics of the CdHgTe QDs@NaCl powders are examined as a function of temperature using steady-state and transient photoluminescence spectroscopy, and characteristic parameters such as the band gap, the temperature coefficient, the Debye temperature, the activation energy of thermal quenching, and radiative and nonradiative recombination rates are derived. Temperature-dependent changes of the spectral...