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We propose and investigate a novel coherent laser array design based on laterally coupled photonic crystal surface-emitting lasers (PCSELs). As a new type of semiconductor laser technology, PCSELs have field confinement in a planar cavity and laser beam emission in the surface normal direction. By engineering lateral couplings between PCSELs with heterostructure photonic crystal designs, we can achieve coherent operations from an array of PCSELs. In this paper, we demonstrate coherent operation from a passively coupled PCSEL array design. We fabricated PCSEL array devices on a GaAs-based quantum well heterostructure at a target wavelength of 1040 nm. Experimental results show that the 2-by-2 PCSEL arrays have spectral linewidth of 0.14–0.22 nm. Beam combining performance was characterized by self-interference experiments. Similar coherency between the PCSEL array and single PCSEL device was observed. Our compact PCSEL array designs by passive lateral coupling have potential applications in fields of on-chip photonic computing, quantum, and information processing. [ABSTRACT FROM AUTHOR]

The effect of inserting a nm-scale layer of Zn(Si,Ge)N2 into an AlGaN quantum well structure designed for light emission in the wavelength range from 255 to 305 nm is investigated here. The enhanced confinement of the hole within the quantum well results in an enhancement of the overlap of the hole and electron wave functions, resulting in an enhancement of the radiative recombination rate. In this theoretical calculation, for emission at a 270 nm wavelength, the enhancement in the wavefunction overlap can reach a factor of 7 when compared to an AlGaN quantum well device specifically engineered for optimal emission at the identical wavelength. Increases of almost an order of magnitude in both the peak spontaneous emission intensity and the radiative recombination rate are predicted. The peak emission wavelength can be tuned from 255 to 305 nm by adjusting the width and/or the composition of the inserted layer. The proposed structures provide a route to higher efficiency ultraviolet practical light emitting diodes and lasers. [ABSTRACT FROM AUTHOR]

We discuss the electrical properties of molecular beam epitaxy (MBE) grown, modulation doped, Ge1− x Sn x quantum well devices. A consequence of the epitaxial growth process is that electronic disorder is introduced even in modulation doped quantum well structures and electrical transport properties that are characteristic of a high level of disorder are apparent. MBE growth of this material also results in the surface segregation of elemental β -Sn in the way that has been observed utilizing other epitaxial growth methods. A thermally activated, p-type mobility is a clear feature of the electrical properties with generally temperature independent hole densities ∼1012 cm−2 from the measured Hall effect and coming from the modulation doping. We present a discussion of Hall effect measurements in this disordered regime. The percolation carrier density in MBE modulation doped GeSn is in the region of ∼1 × 1012 cm−2 although Hall measurements in this regime are difficult to quantify when the resistivity >(h / e 2). In this notation h is Planck's constant and e is the unit of charge. Conductivities (σ) as low as ∼0.028 × (e 2/ h) × square can be measured in the four-contact ac configuration and the temperature dependence indicates a mobility edge in these p-type devices below ∼2 × 1012 cm−2. At lower temperatures (<∼1 K) the presence of a Coulomb gap can be determined using dc transport, constant voltage measurements where small ac current excitation is not available experimentally. This two-contact configuration can determine σ down to ∼10−6 × (e 2/ h), deep into the localization regime, revealing a hopping conductivity dominated system. We discuss the relevance of these electrical properties for MBE grown GeSn devices. [ABSTRACT FROM AUTHOR]

GaAs is often used as a multijunction subcell due to its high material quality on GaAs substrates, despite having a non-optimal bandgap. The bandgap can be beneficially reduced using many layers of thin, strain-balanced GaInAs in a superlattice or quantum well device, but achieving excellent carrier collection without increased recombination has proven challenging. Here, we develop and demonstrate high performance, optically thick GaInAs/GaAsP strain-balanced solar cells. Excellent material quality is achieved in thick superlattices by using growth conditions that limit progressive thickness and composition fluctuations. Bandgap-voltage offsets as low as 0.31 V are shown in superlattice cells using thin, highly strained GaP barriers. Optically thick superlattice cells with over 2500 nm of total GaInAs in the depletion region are developed, enabling 3.8 mA/cm2 of extra photocurrent beyond the GaAs band edge under the AM0 space spectrum. Optimized superlattice solar cells are incorporated into two-junction devices that achieve 29.2% efficiency under the AM0 space spectrum due to their improved bandgap combination and high subcell voltages. [ABSTRACT FROM AUTHOR]

Herein, methods for the fabrication of monolithic diamond integrated photonic devices via Faraday cage‐angled etching of functional epitaxial diamond layers are presented. Optimal waveguide width is determined via simulation and the fabrication of nitrogen vacancy (NV) center‐doped microring resonators is demonstrated. The performance of the devices is verified via microphotoluminescence as well as cathodoluminescence scans of the in‐grown NV centers, revealing clearly visible cavity lines. The scalable fabrication method allows for the realization of large numbers of lateral waveguide structures as needed for future applications in integrated quantum sensing devices as well as novel spin‐based quantum computers. [ABSTRACT FROM AUTHOR]

The ByAlxGa1-x–yN system validates promise as a suitable option for fabricating opto-electronic devices like light-emitting-diodes (LEDs) and laser diodes. This study conducts a comparative analysis between two types of LEDs: one with a single quantum well composed of AlGaN and another with BAlGaN, containing 1% boron, 22% aluminum, and a 3 nm thickness. These LEDs are designed as AlGaN-based quantum well (LED1) and BAlGaN-based quantum well devices (LED2). Technology computer-aided design (TCAD) Silvaco physical simulator is used to perform simulations and comparisons in terms of both optical and electrical characteristics. The simulations includes anode current with respect to anode voltage, luminous power and wall-plug efficiency relative to injection current, and power spectral density concerning wavelength. Remarkably, even with a mere 1% boron content within the quantum well, the LED's performance displays a 5% enhancement in power spectral density and a 7% boost in wall-plug efficiency. [ABSTRACT FROM AUTHOR]

Quantum algorithms for simulating quantum systems provide a clear and provable advantage over classical algorithms in fault-tolerant settings. There is also interest in quantum algorithms and their implementation in Noisy Intermediate Scale Quantum (NISQ) settings. In these settings, various noise sources and errors must be accounted for when executing any experiments. Recently, NISQ devices have been verified as versatile testbeds for simulating open quantum systems and have been used to simulate simple quantum channels. Our goal is to solve the more complicated problem of simulating convex mixtures of single qubit Pauli channels on NISQ devices. We consider two specific cases: mixtures of Markovian channels that result in a non-Markovian channel (M + M = nM) and mixtures of non-Markovian channels that result in a Markovian channel (nM + nM = M). For the first case, we consider mixtures of Markovian single qubit Pauli channels; for the second case, we consider mixtures of Non-Markovian single qubit depolarising channels, which is a special case of the single qubit Pauli channel. We show that efficient circuits, which account for the topology of currently available devices and current levels of decoherence, can be constructed by heuristic approaches that reduce the number of CNOT gates used in our circuit. We also present a strategy for regularising the process matrix so that the process tomography yields a completely positive and trace-preserving (CPTP) channel. Key points This work simulates the convex mixtures of single qubit Markovian and non-Markovian quantum channels on NISQ devices provided by the IMBQE. The circuits used to implement the channels take into account the topolgy of the quantum device used as well as the number of CNOT gates used. We present a strategy for regularising the process matrix to ensure the quantum process tomography yields a CPTP channel. Something that is not correctly implemented in Qiskit. A method is outlined for finding mixtures of non-Markovian depolarising channels that yield a Markovian depolarising channel. It is also shown that, one cannot convexly mix two Markovian depolarising channels that leads to a non-Markovian depolarising channel. [ABSTRACT FROM AUTHOR]

The realization of intrinsic magnetic topological insulators offers an ideal platform to investigate high-temperature quantum anomalous Hall effect as well as quantum devices. The family of MnBi2Te4(Bi2Te3)n has been confirmed that it belongs to this system. However, whether there is a bandgap in the surface states remains controversial. In this work, the ferromagnetism in Sb-doped MnBi4Te7 is confirmed by magnetic transport. Utilizing angle-resolved photoemission spectroscopy, we demonstrate the nontrivial topology in Mn(Bi0.7Sb0.3)4Te7 with an energy gap on the MnBi2Te4 termination. As well, we detect distinct topological surface states on two different terminations. Our results provide spectral evidence of an energy gap in the topological surface states. [ABSTRACT FROM AUTHOR]

The realization of intrinsic magnetic topological insulators offers an ideal platform to investigate high-temperature quantum anomalous Hall effect as well as quantum devices. The family of MnBi2Te4(Bi2Te3)n has been confirmed that it belongs to this system. However, whether there is a bandgap in the surface states remains controversial. In this work, the ferromagnetism in Sb-doped MnBi4Te7 is confirmed by magnetic transport. Utilizing angle-resolved photoemission spectroscopy, we demonstrate the nontrivial topology in Mn(Bi0.7Sb0.3)4Te7 with an energy gap on the MnBi2Te4 termination. As well, we detect distinct topological surface states on two different terminations. Our results provide spectral evidence of an energy gap in the topological surface states. [ABSTRACT FROM AUTHOR]

Theoretical investigation of electro-absorption modulators in the mid-infrared range (>∼2 μm) is performed using asymmetric intra-step quantum wells based on Ge1−η1Snη1/Ge1−η2Snη2 heterostructures with SiGeSn outer barriers. After exploring the parameter space of the Sn content difference and width ratio of the intra-layers, a linear and much larger Stark shift is realized, compared to that of a square quantum well, without an increase of the total structure width. A modulator based on an optimized intra-step quantum well structure with a total well width of 12 nm is theoretically predicted to have both a larger peak shift per unit applied field and a larger absorption change than a 12 nm square quantum well device. By analyzing the device performance based on the two figures of merit: (1) absorption change per applied field and (2) absorption change per applied field squared, and taking 10 dB extinction ratio, a 44% higher bandwidth per volt and 46% lower power consumption per bit are achieved in intra-step than in a square well. Although the swing voltage for a square quantum well can be reduced by using a larger on-set applied field and performance could be improved, we found that the intra-step quantum well using zero on-set still retains its advantages when compared to the square quantum well which uses a 0.5 V on-set voltage. [ABSTRACT FROM AUTHOR]

The exploration of functional light-emitting devices and numerous optoelectronic applications can be accomplished on an elegant platform provided by rapidly developing transition metal dichalcogenides (TMDCs). However, TMDCs-based light emitting devices encounter certain serious difficulties, such as high resistance losses from ohmic contacts or the need for complex heterostructures, which restricts the device applications. Despite the fact that AC-driven light emitting devices have developed ways to overcome these challenges, there is still a significant demand for multiple wavelength emission from a single device, which is necessary for full color light emitting devices. Here, we developed a dual-color AC-driven light-emitting device by integrating the WSe2 monolayer and AlGaInP–GaInP multiple quantum well (MQW) structures in the form of capacitor structure using AlOx insulating layer between the two emitters. In order to comprehend the characteristics of the hybrid device under various driving circumstances, we investigate the frequency-dependent EL intensity of the hybrid device using an equivalent RC circuit model. The time-resolved electroluminescence (TREL) characteristics of the hybrid device were analyzed in details to elucidate the underlying physical mechanisms governing its performance under varying applied frequencies. This dual-color hybrid light-emitting device enables the use of 2-D TMDC-based light emitters in a wider range of applications, including broad-band LEDs, quantum display systems, and chip-scale optoelectronic integrated systems. [ABSTRACT FROM AUTHOR]

We show the importance of using a thermodynamically consistent flux discretization when describing drift–diffusion processes within light emitting diode simulations. Using the classical Scharfetter–Gummel scheme with Fermi–Dirac statistics is an example of such an inconsistent scheme. In this case, for an (In,Ga)N multi quantum well device, the Fermi levels show an unphysical hump within the quantum well regions. This result originates from neglecting diffusion enhancement associated with Fermi–Dirac statistics in the numerical flux approximation. For a thermodynamically consistent scheme, such as the SEDAN scheme, the humps in the Fermi levels disappear. We show that thermodynamic inconsistency has far reaching implications on the current–voltage curves and recombination rates. [ABSTRACT FROM AUTHOR]

We have fabricated a device which includes two lateral p–n junctions on an n-type GaAs/Al0.33Ga0.67As heterostructure. A section of the n-type material has been converted to p-type by removing dopants and applying a voltage to a gate placed in this region. Controlled electroluminescence from both of the p–n junctions has been demonstrated by varying the applied bias voltages. An emission peak with a width of ∼ 8 nm is observed around 812 nm. The electroluminescence seen from both junctions is considered to originate from the GaAs quantum well layer in the device. The lithographic techniques that we have developed are compatible for further integration of gated quantum devices such as single-electron pumps to build on-demand single-photon sources. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) hexagonal boron nitride (h-BN) is one of the few materials showing great promise for light emission in the far ultraviolet (UV)-C wavelength, which is more effective and safer in containing the transmission of microbial diseases than traditional UV light. In this report, we observed that h-BN, despite having an indirect energy bandgap, exhibits a remarkably high room-temperature quantum efficiency (∼60%), which is orders of magnitude higher than that of other indirect bandgap material, and is enabled by strong excitonic effects and efficient exciton-phonon interactions. This study offers a new approach for the design and development of far UV-C optoelectronic devices as well as quantum photonic devices employing 2D semiconductor active regions. [ABSTRACT FROM AUTHOR]

In this paper, we theoretically investigate intersubband absorption in La-doped BaSnO3/BaO perovskite-oxide double and triple symmetrical quantum wells. The goal is to assess the emerging possibilities offered by perovskite heterostructures for realization of oxide-based quantum well optoelectronic devices. Properties such as small electron effective mass, very high room-temperature mobility of BaSnO3, large conduction band offset between the two materials, are all promising for technological applications. Some of the possible applications include active n-channel materials in p-n junctions, field-effect transistors, ferroelectric field-effect transistors, sensitive UV photoconductors, and electron transport layers in perovskite solar cells. We are interested in tuning of the absorption spectra via quantum well width modulation, changing of doping density and variation of external electric field along the growth direction which is important for application in electro-optical light modulators. The electronic structure is calculated self-consistently by solving the Schrödinger–Poisson system of equations where the exchange correlation effects are also taken into the account. [ABSTRACT FROM AUTHOR]

Perovskite colloidal quantum wells (QWs) are promising to realize narrow deep‐blue emission, but the poor optical performance and stability suppress their practical application. Here, we creatively propose a water‐driven synthesis strategy to obtain size‐homogenized and strongly confined deep‐blue CsPbBr3 QWs, corresponding to three monolayers, which emit at the deep‐blue wavelength of 456 nm. The water controls the orientation and distribution of the ligands on the surface of the nanocrystals, thus inducing orientated growth through the Ostwald ripening process by phagocytizing unstable nanocrystals to form well‐crystallized QWs. These QWs present remarkable stability and high photoluminescence quantum yield of 94 %. Furthermore, we have prepared light‐emitting diodes based on the QWs via the all‐solution fabrication strategy, achieving an external quantum efficiency of 1 % and luminance of 2946 cd m−2, demonstrating state‐of‐the‐art brightness for perovskite QW‐based LEDs. [ABSTRACT FROM AUTHOR]

To meet the increasing demand of short-wavelength red lasers for laser display technology and medical applications, we propose a new short-wavelength red semiconductor laser structure. The laser uses Ge/SiGe as the substrate and GaInP, AlInP and other group III-V materials as the main structural layers. The composition of Ge is adjusted to change the lattice constant of the SiGe layer according to the needs of GaInP strain quantum well design to achieve a short-wavelength red laser. A semiconductor laser with a wavelength of 620 nm is used as an example, and the effect of both the interfacial state and the GaInP-strained quantum well on the device characteristics is discussed through simulation. It is found that the laser structure has the optimal output characteristics when the quantum well is subjected to 0.32% compressive strain under the conditions of the interfacial state, which indicates the feasibility of this laser structure design scheme. [ABSTRACT FROM AUTHOR]

The second-harmonic generation susceptibility is theoretically investigated based on the compact density-matrix formalism in two- and three-level AlGaN/GaN systems. The electronic states and their related wave functions were calculated by solving self-consistently the Schrödinger–Poisson equations within the effective mass and Hartree approximations. The presence of spontaneous and piezoelectric polarizations is taken into account in the modeling part. It was revealed from the relevant results that (i) the second-order susceptibility shows a multiple peak structure due to intersubband and their corresponding virtual transitions, (ii) the use of a back doping as well as the optimization of the layer widths in delta-doped AlGaN/GaN asymmetric quantum wells improved considerably the second-harmonic susceptibility, and (iii) the three-level AlGaN/GaN system is the most efficient structure, which generates the second-harmonic with a significant intensity up to 4.36 × 10−5 mV−1. Numerical results of the present work could lay the basis for research in AlGaN-related optoelectronic device applications. [ABSTRACT FROM AUTHOR]

In this paper, we discuss the design of photovoltaic quantum well infrared photodetectors (QWIPs) based on polar GaN/AlGaN multiquantum wells (MQWs). Getting a reasonable escape probability of the excited electron requires adjusting the bound-to-quasibound intersubband transition in the absorbing quantum well and engineering the polarization-related internal electric field in the barriers. This can be achieved with a MQW period that consists of 3 layers, namely, the active quantum well, an extraction barrier, and an injection barrier, the latter being thin enough to allow tunneling transport. Following this design scheme, we demonstrate bound-to-quasibound GaN/AlGaN QWIPs with peak photocurrent response at 2.3 μm, operating at room temperature in both photovoltaic and photoconductive modes. Based on high-resolution x-ray diffraction measurements, the entire detector structure, which included a 40-period MQW with 30 nm-thick barriers, along with top and bottom contact layers of combined thickness above 900 nm, was grown pseudomorphically on an AlGaN-on-sapphire template. A room-temperature responsivity of 88 μA/W was measured at zero bias, increasing up to 302 μA/W at −1.0 V bias. The responsivity reached its maximum at 150–200 K, where it was approximately a factor of 2 higher than at room temperature. Ideas for a new device structure to improve the QWIP response in the photovoltaic mode are proposed. [ABSTRACT FROM AUTHOR]

The infrared technology is entering widespread use as it starts fulfilling a growing number of emerging applications, such as smart buildings and automotive sectors. Majority of infrared photodetectors are based on interband transition, which is the energy gap between the valence band and the conduction band. As a result, infrared materials are mainly limited to semi-metal or ternary alloys with narrow-bandgap bulk semiconductors, whose fabrication is complex and expensive. Different from interband transition, intraband transition utilizing the energy gap inside the band allows for a wider choice of materials. In this paper, we mainly discuss the recent developments on intraband infrared photodetectors, including 'bottom to up' devices such as quantum well devices based on the molecular beam epitaxial approach, as well as 'up to bottom' devices such as colloidal quantum dot devices based on the chemical synthesis. [ABSTRACT FROM AUTHOR]

The article provides an overview of scanning microwave impedance microscopy (sMIM), a near-field technique for probing electrical properties of materials with nanoscale lateral resolution. Topics include advantages include imaging floating dielectrics and sub-surface features without the need for sample grounding; and principles of operation of sMIM, gives an overview of the low-temperature configuration including use in semiconductor failure analysis, and quantum computing research.

Extensive high resolution transmission and scanning transmission electron microscopy observations were performed in In(Ga)N/GaN multi-quantum well short period superlattices comprising two-dimensional quantum wells (QWs) of nominal thicknesses 1, 2, and 4 monolayers (MLs) in order to obtain a correlation between their average composition, geometry, and strain. The high angle annular dark field Z-contrast observations were quantified for such layers, regarding the indium content of the QWs, and were correlated to their strain state using peak finding and geometrical phase analysis. Image simulations taking into thorough account the experimental imaging conditions were employed in order to associate the observed Z-contrast to the indium content. Energetically relaxed supercells calculated with a Tersoff empirical interatomic potential were used as the input for such simulations. We found a deviation from the tetragonal distortion prescribed by continuum elasticity for thin films, i.e., the strain in the relaxed cells was lower than expected for the case of 1 ML QWs. In all samples, the QW thickness and strain were confined in up to 2 ML with possible indium enrichment of the immediately abutting MLs. The average composition of the QWs was quantified in the form of alloy content. [ABSTRACT FROM AUTHOR]

In this work, by sandwiching a p-AlGaN layer into the n-AlGaN layer, we generate an energy barrier in the n-AlGaN layer to improve the current spreading effect of AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs). The abrupt energy barrier can balance the resistivity in the n-AlGaN layer, and this leads to the better lateral current distribution in the p-type hole injection layer. Numerical and experimental results show that the homogenized current distribution enables the enhanced external quantum efficiency (EQE) for the proposed DUV LED. In addition, the better conductivity modulation arising from the more homogenized current distribution decreases the forward voltage and suppresses the self-heating effect. [ABSTRACT FROM AUTHOR]

We report on 3-D FDTD simulation of waveguide-integrated plasmonic Ge/SiGe MQWs photodetectors. Despite several significant works on Ge/SiGe MQW optical modulators, Ge/SiGe MQW photodetectors still show improvable performance, limiting the potential to employ them for both optical modulation and detection. In this paper, we investigate the use of plasmonic concept to enhance electromagnetic field confinement inside the Ge/SiGe MQWs absorbing region with a view to having a compact and low-voltage waveguide-integrated Ge/SiGe MQWs photodetectors. Optical responsivities in term of applied electric fields, device dimensions of width and length, optical bandwidth, fabrication misalignment, and number of QWs periods are taken into account. The investigation shows that using plasmonic enhancement, a waveguide-integrated Ge/SiGe MQWs photodetector that is as short as 5 μm could be obtained with comparable responsivity and bias voltage values to some of the state-of-the-art bulk Ge-based devices, increasing the potential usage of Ge/SiGe MQWs for both optical modulation and detection in low-energy optical interconnects. [ABSTRACT FROM AUTHOR]

The variational quantum eigensolver (VQE) is one of the most promising algorithms to find eigenstates of a given Hamiltonian on noisy intermediate-scale quantum devices (NISQ). The practical realization is limited by the complexity of quantum circuits. Here we present an approach to reduce quantum circuit complexity in VQE for electronic structure calculations. Our ClusterVQE algorithm splits the initial qubit space into clusters which are further distributed on individual (shallower) quantum circuits. The clusters are obtained based on mutual information reflecting maximal entanglement between qubits, whereas inter-cluster correlation is taken into account via a new "dressed" Hamiltonian. ClusterVQE therefore allows exact simulation of the problem by using fewer qubits and shallower circuit depth at the cost of additional classical resources, making it a potential leader for quantum chemistry simulations on NISQ devices. Proof-of-principle demonstrations are presented for several molecular systems based on quantum simulators as well as IBM quantum devices. [ABSTRACT FROM AUTHOR]

In this study, Pre-diagnosis of degraded aluminum indium gallium phosphide (AlInGaP) light-emitting diodes (LEDs) that were soaked in liquid nitrogen (LN2) was performed. To visualize the early deterioration of LED emission, a combination of material, electrical, optical, and computer-aided machine-vision analysis of LED failure spots on the surface was examined. Results indicate that several small failure spots, which can be identified by the MATLAB processed emission images and surface roughness variation, can be found. Furthermore, LN2 soaking induced some local damages inside the device that penetrate the multiple-quantum well. The decrease of current and luminescence intensity also reflects the gradual degradation of the device after being soaked in LN2. This integrated analysis and Pre-diagnosis of the degraded device provided early screening of LED failure spots and real-time inspection during operations. [ABSTRACT FROM AUTHOR]

We demonstrated high-brightness InGaN/GaN green light emitting diodes (LEDs) with ex-situ sputtered stress-manipulated AlNO buffer on 4-inch patterned sapphire substrates. The lattice constant of the AlNO buffer was adjusted by oxygen flow. As a result, the dislocation density and the in-plane compressive stress caused by lattice mismatch were greatly reduced, while the interface quality of the InGaN/GaN multiple quantum wells and the uniformity of the indium composition were greatly improved. At 20A/cm2, the external quantum efficiency and wall plug efficiency of the 526.4-nm-green LEDs grown on the sputtered AlNO buffer reached 46.1% and 41.9%, which were both higher than reported values. [ABSTRACT FROM AUTHOR]

To promote the modulation bandwidth of GaN-based blue micro-light emitting diodes ($\mu $ -LEDs) for visible light communication, the multiple quantum well active region has been improved via approaches based on low-temperature (LT) GaN insertion layer in barriers. $\mu $ -LED arrays with 10 $\times $ 10 pixels have been fabricated. The device using LT-GaN interlayer has an output power of 2.14 mW and a modulation bandwidth of 220 MHz, with an enhancement factor of 2.5 and 1.7, respectively, as compared with the device without LT-GaN interlayer. It is believed that these improvements are a result of the suppression of strain-related quantum-confined Stark effect and defects/dislocations by LT-GaN interlayer based optimization. The LT-GaN interlayer not only facilitates a tensile strain in barriers, making it more lattice-compatible with InGaN well to reduce the strain there, but also has an effect on blocking the propagation of threading dislocation into upper layers. Our work provides an effective approach to enhance the modulation bandwidth of III-nitride $\mu $ -LEDs using LT interlayer. [ABSTRACT FROM AUTHOR]

In this work, whole metal oxide-based p-NiO/i-Ga2O3-i-Al2O3:Ga2O3 multiple quantum wells (MQWs)/n-HfO2:Ga2O3 deep ultraviolet light-emitting diodes (DUV-LEDs) were manufactured and studied. To investigate the improved luminance of the MQWs, single i-Ga2O3 active layer was utilized to replace MQWs in the DUV-LEDs. The vapor cooling condensation system was used to deposit n-HfO2:Ga2O3, i-Ga2O3, and i-Al2O3:Ga2O3 films on sapphire substrate. Besides, the radio frequency magnetron sputtering system was used to deposit p-NiO film onto the MQWs. As the measurement of electroluminescence spectra, the peak emission wavelength of both the devices with MQWs and i-Ga2O3 active layer was approximately 243 nm. Compared with the utilization of single i-Ga2O3 active layer, the peak luminance intensity of the DUV-LEDs with MQWs was enhanced due to the effective carrier recombination in the i-Ga2O3 well caused by the effective carrier block of the i-Al2O3:Ga2O3 barrier in the MQWs. [ABSTRACT FROM AUTHOR]

An AlGaInAs multiple-quantum-well (MQW) polarization mode controller (PMC) using a stepped height ridge waveguide is presented, which is monolithically integrated with a sidewall grating distributed feedback laser using quantum well intermixing (QWI). QWI is used to create a 100 nm blueshift in the PMC and to partially eliminate the anisotropy and birefringence of the MQW structure. The PMC structure is modelled and optimized using a 3D full-vectorial Finite-Element Method package. The maximum polarization conversion efficiency (PCE) is around 96% for a 537-μm-long PMC operating at a wavelength of 1550 nm. To maintain a PCE of ≥90%, the fabrication tolerances of the dry-etch corner and ridge waveguide widths are ± 0.05 μm and ± 0.03 μm respectively. The main advantages of the proposed design are that only a single step of MOPVE and two steps of dry etching are required for the whole integrated device, significantly reducing complexity and cost. [ABSTRACT FROM AUTHOR]

The variation of the internal quantum efficiency (IQE) of single InGaN quantum well structures emitting from blue to red is studied as a function of the excitation power density and the temperature. By changing the well width, the indium content, and adding a strain compensation AlGaN layer, we could tune the intrinsic radiative recombination rate by changing the quantum confined Stark effect, and we could modify the carrier localization. Strong quantum confined Stark effect and carrier localization induce an increase in the carrier density and then favor Auger non-radiative recombination in the high excitation range. In such high excitation conditions with efficient Auger recombination, the variation of the IQE with the photo-excitation density P is ruled by a universal power law independent of the design: IQE=IQEMAX – a log10P with a close to 1/3. The temperature dependences of the different recombination mechanisms are determined. At low temperature, both quantum confined Stark effect and carrier localization trigger electron-electron repulsions and therefore the onset of the Auger effect. The increase in the value of coefficient C with changing temperature reveals indirect Auger recombination that relates to the interactions of the carriers with other phonons than the longitudinal optical one. [ABSTRACT FROM AUTHOR]

In this work, we compare the luminescence results obtained on InGaN/GaN multiple quantum well (QW) structures with different numbers of QWs. Structures are designed for scintillating applications, where large QW number covering particle penetration depth is necessary, and fast luminescence response is required. Special attention is devoted to increase the intensity of fast excitonic QW emission and to decrease the luminescence of the QW defect band, which has slower luminescence response and is undesired for fast scintillator applications. We found that increasing the In content in QWs suppresses the defect band luminescence and decreasing the QW growth rate increases the photoluminescence (PL) intensity of excitonic luminescence. We also show that increasing the number of InGaN further improves the PL properties of InGaN QWs. The photoluminescence and cathodoluminescence characteristics are compared and discussed. [ABSTRACT FROM AUTHOR]

The focused ion beam milling tool was used to convert a GaSb-based broad area gain-guided quantum well laser device with a standard Fabry-Pérot cavity into one with an unstable resonator cavity. A cylindrical mirror was formed at the back facet of the broad area device emitting near 2 μm. Compared to the Fabry-Pérot cavity device, where the coherency of the beam is severely disrupted by filamentation, the unstable resonator cavity device exhibits an ~2× diffraction limited beam. The relatively small penalty in slope efficiency demonstrates that a much higher brightness can be reached in this class of broad area devices. [ABSTRACT FROM AUTHOR]

In this study, we investigated the combined effects of structure parameters such as size and geometry, as well as hydrostatic pressure, temperature, and magnetic field on the electronic and optical properties of a double inverse parabolic quantum well within the framework of the effective mass and parabolic band approximations. It is very important to consider the effects of temperature and hydrostatic pressure, especially in practical applications involving quantum wells such as semiconductor devices and optoelectronics. The results obtained are in good agreement with the literature. Understanding how these factors affect the electronic and optical properties of semiconductor heterostructures helps to optimize the performance and stability of devices operating under different environmental conditions. [ABSTRACT FROM AUTHOR]

Infrared cameras with narrow-band detection capability are widely used for SF6 gas detection, which is an essential part of power equipment inspection. Narrow-band detection is usually achieved by a combination of quantum well infrared photodetectors (QWIPs) and narrow-band filters. Improving the quantum efficiency of QWIPs and reducing the detection bandwidth are important ways to improve camera performance. In this study, a back-incident-type device of quantum well micropillar array targeting at a 10.5 μm central wavelength is designed and studied by three-dimensional simulation. The operating mechanism of the device was determined by investigating the effect of the device geometry on the quantum efficiency. The enhanced absorption capability of the device mainly comes from the Fabry–Pérot resonance and the antireflection effect. The final device exhibits a remarkable peak quantum efficiency of 83% at 10.5 μm and an ultra-narrow spectral bandwidth of 0.2 μm. These excellent properties are achieved without an antireflective film and narrow-band filter, which can significantly improve the narrow-band capability and integration of the system; the dark current reduces to be 0.2762 times due to the low-duty cycle. These properties indicate that the structure of the quantum well micropillar array is of great significance to the development of QWIPs used in gas detection. [ABSTRACT FROM AUTHOR]

In this work, we present a GaN-based blue LED construction utilizing bottom tunnel junction (TJ) grown by plasma-assisted molecular beam epitaxy. The setup allows for N-polar-like built-in field alignment while being grown on a Ga-polar substrate. In this study, we present an efficient bottom TJ LED in which the distance between the quantum well and device surface is only 25 nm. This is achieved by the utilization of an n-type current spreading layer consisting of 20 nm thick In0.02Ga0.98N with a Ge doping concentration of 7 × 1019 cm−3. Heavily Ge and Mg doped bottom TJs allowed achieving a low LED turn-on voltage of 2.75 V at 20 A/cm2 and a differential resistivity of 4.7 × 10−4 Ω cm2 at 1 kA/cm2. The device maintained high crystal quality and smooth morphology, which allows for its use as a light emitting platform for further integration. Although the p-up reference LED exhibits lower resistivity at high current, its luminous efficiency is lower than for bottom TJ LEDs. [ABSTRACT FROM AUTHOR]

We developed a semiconductor regrowth scheme for InP photonic integrated circuits (PICs) with optical-gain sections. Unlike conventional semiconductor regrowth schemes, a limited area corresponding to a 200-μm waveguide of an original epitaxial wafer is replaced with an optical-gain material, which improves the flexibility of a PIC process design. In this paper, we describe the partial regrowth (PRG) procedure using a window regrowth mask that defines the regrowth area. A minimum window in terms of semiconductor quality assurance is determined by observing the micro-photoluminescence intensities of the replaced regions. We also show basic performances of optical semiconductor amplifiers (SOAs) obtained by the PRG including amplification of in-phase/quadrature modulation optical signals. Furthermore, practical InP PIC applications of the PRG are also depicted: an SOA-integrated Mach-Zehnder modulator and an electrooptically tunable laser with an arrayed gain. [ABSTRACT FROM AUTHOR]

The dilute-As InGaNAs-based quantum well (QW) active region and the corresponding large-overlap design is analyzed by using a self-consistent 6-band $k\cdot p$ method. Our study evaluates the optical transition energy, ground state electron-hole wavefunction overlap, and optical gain characteristics of a dilute-As InGaNAs QW consisting of a 3.3 nm thick In0.19Ga0.81N0.94As0.06 well and 10 nm thick GaN barriers. The calculation suggests that the In0.19Ga0.81N0.94As0.06 QW may result in a transition wavelength and optical gain comparable to a conventional 3.3 nm thick In0.35Ga0.65N QW, while preserving low In-content (~19%). In addition, a staggered dilute-As InGaNAs QW design with a modulated As-doping profile in the InGaNAs QW is presented, and the calculation results in a significantly enhanced wavefunction overlap and optical gain. This study reveals the excellent potential of the dilute-As InGaNAs semiconductor for application as a high efficiency active region material for future long wavelength emitters. [ABSTRACT FROM AUTHOR]

Silicon (Si)-based mid-infrared (MIR) photonics has promising potential for realizing next-generation ultra-compact spectroscopic systems for various applications such as label-free and damage-free gas sensing, medical diagnosis, and defense. The epitaxial growth of ${\rm Ge}_{\rm 1-x}{\rm Sn}_{\rm x}$ alloy on Si substrate provides the promising technique to extend the cut-off wavelength of Si photonics to MIR range by Sn alloying. Here, we present the theory and simulation of heterojunction p-i-n MIR photodetectors (PDs) with ${\rm Ge}_{0.87}{\rm Sn}_{0.13}/{\rm Ge}_{0.92}{\rm Sn}_{0.08}$ quantum-wells with an additional Ge0.91Sn0.09 layer to elongate the photoabsorption path in the MIR spectrum. The incorporation of QW pairs (N) enables the light-matter interaction due to the carrier and optical confinement in the active region. As a result, the spectral response of the device is enhanced in the MIR range. Devices with varying N were compared in terms of various figure-of merits including dark-current, a photocurrent-to-dark current ratio, detectivity, spectral responsivity, and noise equivalent power (NEP). Additionally, parasitic capacitance-dependent RC and 3dB bandwidth were also studied using a small-signal equivalent circuit model. The proposed device exhibited the extended photodetection wavelength at ${\sim }3370\,{\mathrm {nm}}$ and $I_{\rm ph} \mathord {\left /\right. } I_{\rm dark}$ up to ${\sim }7.3\times {10}^{3}$ with a dark current of ${\sim }56.3\,{\mathrm {nA}}$ for ${\mathrm {N}}=8$ at 300 K. At a bias of −3V, the proposed device achieved the spectral responsivity of 0.86 A/W at 2870 nm and 0.55 A/W at 3300 nm, detectivity more than $2.5\times 10^{9}$ Jones and a NEP less than $2.1\times 10^{-13}\,{\mathrm {W}}{\rm Hz}^{-0.5}$ for ${\mathrm {N}}=8$ at 3250 nm. The calculated 3dB bandwidth of 47.8 GHz, the signal-to-noise ratio (SNR), and linear dynamic range (LDR) of 93 dB and 74 dB were achieved at 3300 nm for ${\mathrm {N}}=8$. Thus, these results indicate that the proposed GeSn-based QW p-i-n PDs pave the pathway towards the realization of new and high-performance detectors for sensing in the MIR regime. [ABSTRACT FROM AUTHOR]

This paper evaluates the propagation delay of a four-state/two-bit spatial wavefunction-switched field-effect transistors (SWS) FET-based inverter. The SWS-FET has two or more vertically stacked quantum-well or quantum dot (QD) layers where the magnitude of the gate voltage determines the location of carriers in the upper or lower channel. A calibration method based on an analytical propagation delay model expanded for the SWS-FET based inverter to account for the multiple quantum wells within the device. Cadence iterative simulations are used for calibrating the SWS inverter size to reach a symmetrical propagation delay for the four logic transitions. The SWS transfer characteristic and the inverter circuit time specifications are obtained by integrating the BSIM (Berkeley Short-channel IGFET Model) and the Analog Behavioral Model (ABM). Calibration and adjustment of the contributing parameters of the model leads to the improvement of the device accuracy for circuit designs based on SWS-FET technology. [ABSTRACT FROM AUTHOR]

In this paper, a multifunctional ultraviolet-C (UVC) micro-LED with monolithically integrated photodetector (PD) based on AlGaN multiple quantum wells (MQWs) was fabricated. We designed and integrated UVC LED with sizes of 40 and 300  $\mu$ m emitted at 277 nm on a single chip which also serve functions as PDs and further studied the performance of on-chip real-time photodetection. The photocurrent generated from one LED can well reflect the light output power of the adjacent LED. Furthermore, both 40  $\mu$ m UVC micro-LED and 300  $\mu$ m UVC LED play important roles in high speed UVC communication with record bandwidths of 497.58 MHz for 40  $\mu$ m micro-LED and 467.38 MHz for 300  $\mu$ m LED, offering each other as backup light source in high speed UVC communication. And the data transmission rates of 1.6 Gbps for 40  $\mu$ m micro-LED and 1.21 Gbps for 300  $\mu$ m LED over 1 m link based on the 16-ary quadrature amplitude modulation orthogonal frequency division multiplexing (16-QAM-OFDM) with pre-equalization were achieved. The multifunctional UVC micro-LED monolithically integrated PD, without the need for an external PD to monitor the fluctuations in the luminescence, providing high stability for diverse applications, such as spatial wireless communication for 6 G communication. [ABSTRACT FROM AUTHOR]

Since the luminance of Micro-LEDs is highly dependent on the injected current density, inevitable voltage fluctuations will lead to luminance fluctuations and weak luminance robustness. In this work, Micro-LED chips working in non-electrical contact and non-carrier injection (NEC and NCI) mode is proposed, which is totally different from the current-injected mode. The luminance of NEC and NCI Micro-LEDs first increases with the increase of the voltage, and the saturation luminance can be obtained during a relatively large voltage range, which is defined as an operating voltage window. Then the luminance decreases when the voltage is further increased. It is demonstrated that the operating voltage windows can enhance luminance robustness. Finally, the insulating layer that is crucial for the operating voltage windows is optimized. And the working mechanisms related to the existence of operating voltage windows are discussed. [ABSTRACT FROM AUTHOR]

The recombination rates in an In0.25Ga0.75N/Al0.48Ga0.52N/GaN multiple quantum well (MQW) structure are measured to identify the cause of low efficiencies in high In-content InGaN quantum wells. The MQWs emit from 640 to 565 nm and are grown using metal-organic chemical vapor deposition (MOCVD). The addition of AlGaN interlayers within the MQW provides strain balancing and suppresses defect formation in high In-content InGaN quantum wells. The rates are found by transforming the optically measured radiative efficiency, differential carrier lifetimes, and optical absorption. Both components of non-radiative recombination rates, Shockley-Read-Hall (SRH) and Auger recombination, are found to be similar to the values of blue-emitting InGaN MQWs. The low SRH recombination rate is attributed to the use of the AlGaN interlayer. The radiative recombination rate, however, is more than an order of magnitude lower compared to blue emitting (lower In-content) InGaN-based MQWs. While this large reduction in radiative rate can be attributed to differences in carrier overlap and transition energy, it may also include effects of variations in thickness and compositional inhomogeneities. [ABSTRACT FROM AUTHOR]

3D hybrid integration based on III-V/Si waveguides by selective undercut wet etching (SUWE) of the lower Si layer has been demonstrated on a silicon-on-insulator (SOI) template. The process was performed on an adhesive-bonding material structure, defined by the upper InP/InAlGaAs (InAlGaAs quantum well) p-i-n heterostructure and the lower 220 nm SOI. After the top p-i-n III-V tapered waveguide was first fabricated and covered by Si3N4, KOH was then used for SUWE of Si layer from SiO2 and Si3N4, forming the bottom SOI single-mode waveguide. In comparison to monolithic III-V waveguide structure (InP based material), the simulated confinement factor of active region shows an enhancement from 10.3% to 16.7%. SOA/EAM devices were also processed and integrated in III-V layer, showing 7.2 dB optical gain at 70 mA injection current in SOA and 21.7 dB extinction ratio within 0~−2 V swing voltage in EAM. The strong quantum confined Stark effect (QCSE) in MQW confirms the improved confinement factor. It suggests a vertical self-alignment scheme could be used for realizing compact and submicron scale heterogeneous integration in a Si photonics template. [ABSTRACT FROM AUTHOR]

Compressively strained Ge quantum well devices have a spin-splitting in applied magnetic field that is entirely consistent with a Zeeman effect in the heavy hole valence band. The spin orientation is determined by the biaxial strain in the quantum well with the relaxed SiGe buffer layers and is quantized in the growth direction perpendicular to the conducting channel. The measured spin-splitting in the resistivity ρxx agrees with the predictions of the Zeeman Hamiltonian where the Shubnikov-deHaas effect exhibits a loss of even filling factor minima in the resistivity ρxx with hole depletion from a gate field, increasing disorder or increasing temperature. There is no measurable Rashba spin-orbit coupling irrespective of the structural inversion asymmetry of the confining potential in low p-doped or undoped Ge quantum wells from a density of 6 × 1010 cm-2 in depletion mode to 1.7 × 1011 cm-2 in enhancement. [ABSTRACT FROM AUTHOR]

In this paper, we compare and contrast the experimental data and the theoretical predictions of the low temperature optical properties of polar and nonpolar InGaN/GaN quantum well structures. In both types of structure, the optical properties at low temperatures are governed by the effects of carrier localisation. In polar structures, the effect of the in-built electric field leads to electrons being mainly localised at well width fluctuations, whereas holes are localised at regions within the quantum wells, where the random In distribution leads to local minima in potential energy. This leads to a system of independently localised electrons and holes. In nonpolar quantum wells, the nature of the hole localisation is essentially the same as the polar case but the electrons are now coulombically bound to the holes forming localised excitons. These localisation mechanisms are compatible with the large photoluminescence linewidths of the polar and nonpolar quantum wells as well as the different time scales and form of the radiative recombination decay curves. [ABSTRACT FROM AUTHOR]

The effect of charge carrier localization resulting in "S-shaped" temperature dependence of the photoluminescence peak energy of InAsxP1–x/InP quantum wells (QWs) is distinctly revealed by the temperature dependent surface photo voltage (SPV) and photoconductivity (PC) processes. It is observed that the escape efficiency of carriers from QWs depends on the localization energy, where the carriers are unable to contribute in SPV/PC signal below a critical temperature. Below the critical temperature, carriers are strongly trapped in the localized states and are therefore unable to escape from the QW. Further, the critical temperature increases with the magnitude of localization energy of carriers. Carrier localization thus plays a pivotal role in defining the operating temperature range of InAsxP1–x/InP QW detectors. [ABSTRACT FROM AUTHOR]