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Quasi-2D Dion–Jacobson (DJ) halide perovskites with large exciton binding energy, self-assembled quantum wells, and high quantum yield attract growing attention in light-emitting diodes and solar devices. DJ-layered perovskites have the eliminated van der Waals gap and show improved photophysical features. However, there are a variety of defects and complex phase distributions produced during the solution procedure and the fast crystal development. In this paper, we reveal the effect of phase distribution and defect passivation on amplified spontaneous emission of quasi-2D perovskite (PDMA)(MA)2Pb3Br10 thin films through solvent engineering and additive methods, by establishing the correlation between the precursor compositions and the photophysical performance of the layered DJ perovskites. The energy transfer rate and the photoluminescence quantum yield increase due to the spatially homogeneous domain distribution and the reduced defect density after the addition of KBr in the DMSO:DMF. More importantly, we realize green amplified spontaneous emission and single-mode vertical-cavity surface-emitting lasing with low thresholds of 8.8 and 10.5 μJ cm−2, respectively. This work provides a guideline to achieve low-threshold multicolor lasers based on DJ perovskites. [ABSTRACT FROM AUTHOR]

Rapid electron transport triggers many novel physical phenomena and becomes a critical point for high-speed electronics. Two-dimensional electron gas (2DEG) has drawn great attention due to its high electron mobility, and this has been observed in different materials, such as semiconductor, oxide interfaces, and 2D materials. In this paper, we report, for the first time, the existence and electrical manipulation of 2DEG in the Schottky quantum well, which was formed in the titanium oxide thin films. We take the asymmetry interface electron scattering effect into consideration when studying the electrical transport properties of our multilayer thin films. We found electrons would be transferred from the low-mobility semiconducting and metallic conductive channels to the high-mobility 2DEG conductive channel with an in-plane applied electric field. Therefore, electron concentration and mobility of the 2DEG formed in the Schottky quantum well could be tuned, and the nano-devices exhibited non-linear voltage–current curves. The differential resistivity of the nano-devices could decrease by two orders with increasing electric field at room temperature. Weak electron localization of electrons was experimentally observed in our nano-devices at low temperature, which further demonstrated the existence of 2DEG in the Schottky quantum well. Our work will provide us new physics about the rapid electron transport in the multilayer thin films and bring novel functional devices for the modern microelectronic industry. [ABSTRACT FROM AUTHOR]

The integration of narrow-band and spectral detection capabilities on pixel-level detectors is widely expected for compact infrared gas detection. This imposes great challenges on the detector performance, as the device response must precisely match with the gas absorption spectrum while also collecting enough signals in a limited spectral range to maintain high detection sensitivity. In this paper, a pixel-level narrow-band high quantum efficiency metal microcavity quantum well infrared photodetector (MC-QWIP) working around 10.6 μm is designed and fabricated. The device shows good narrow-band characteristics (200–550 nm) and high peak responsivity (at least eight times stronger than the reference device with 45° edge facet). The results of experiments and numerical simulations show that several different resonance modes with peak wavelengths close to the intrinsic detection wavelength can be obtained by changing the width of the microcavity. The response bandwidth of the device can be controlled by changing resonance modes, while the resonant wavelength can be fine-tuned by the width of the microcavity. This indicates that the MC-QWIP device has good prospects in narrow-band gas detection and narrow-band differential detection. [ABSTRACT FROM AUTHOR]

Direct integration of III–V semiconductor light sources on silicon is an essential step toward the development of portable, on-chip infrared sensor systems. Driven by the presence of characteristic molecular fingerprints in the mid-infrared (MIR) spectral region, such systems may have a wide range of applications in infrared imaging, gas sensing, and medical diagnostics. This paper reports on the integration of an InAs virtual substrate and high crystalline quality InAs/InAsSb multi-quantum wells on Si using a three-stage InAs/GaSb/Si buffer layer. It is shown that the InAs/GaSb interface demonstrates a strong dislocation filtering effect. A series of strained AlSb/InAs dislocation filter superlattices was also used, resulting in a low surface dislocation density of approximately 4 × 107 cm−2. The InAs/InAsSb wells exhibited a strong photoluminescence signal at elevated temperatures. Analysis of these results indicates that radiative recombination is the dominant recombination mechanism, making this structure promising for fabricating MIR Si-based sensor systems. [ABSTRACT FROM AUTHOR]

In this paper, we reported our design and experimental results of a two-stage long wavelength interband cascade infrared photodetector (ICIP). A 3 × 3 multiple quantum well relaxation region was proposed for long wavelength ICIP. The 50% cutoff wavelength was 11.6 μm at 80 K. The quantum efficiency (QE) of the ICIP was measured to be 24.5% at 8.5 μm. The dark current density at −0.05 V bias of the ICIP was measured to be 3.32 × 10−4 A/cm2 at 55 K, which is approximately 1/3 of a PBπBN superlattice detector. The peak detectivity of ICIP was measured to be 4.6 × 1010 cm·Hz1/2/W at 80 K and further raised to 3.6 × 1011cm·Hz1/2/W when the temperature decreased to 55 K. In comparing with the PBπBN superlattice device, the ICIP shows smaller shunt currents and tunneling currents at low temperatures. [ABSTRACT FROM AUTHOR]

In this paper, we perform a comprehensive study on energy band engineering of InGaN multi-quantum-well (MQW) solar cells using AlGaN electron- and hole-blocking layers. InGaN MQW solar cells with AlGaN layers were grown by metalorganic chemical vapor deposition, and high crystal quality was confirmed by high resolution X-ray diffraction measurements. Time-resolved photoluminescence results showed that the carrier lifetime on the solar cells with AlGaN layers increased by more than 40% compared to that on the reference samples, indicating greatly improved carrier collections. The illuminated current-density (J–V) measurements further confirmed that the short-circuit current density (Jsc) of the solar cells also benefited from the AlGaN layer design and increased 46%. At room temperature, the InGaN solar cells with AlGaN layers showed much higher power conversion efficiency (PCE), by up to two-fold, compared to reference devices. At high temperatures, these solar cells with AlGaN layers also delivered superior photovoltaic (PV) performance such as PCE, Jsc, and fill factor than the reference devices. These results indicate that band engineering with AlGaN layers in the InGaN MQW solar cell structures can effectively enhance the carrier collection process and is a promising design for high efficiency InGaN solar cells for both room temperature and high temperature PV applications. [ABSTRACT FROM AUTHOR]

In this paper, N-polar GaN films with different V/III ratios were grown on vicinal C-face SiC substrates by metalorganic chemical vapor deposition. During the growth of N-polar GaN film, the V/III ratio was controlled by adjusting the molar flow rate of ammonia while keeping the trimethylgallium flow rate unchanged. The influence of the V/III ratio on the surface morphology of N-polar GaN film has been studied. We find that the surface root mean square roughness of N-polar GaN film over an area of 20 × 20 μm2 can be reduced from 8.13 to 2.78 nm by optimization of the V/III ratio. Then, using the same growth conditions, N-polar InGaN/GaN multiple quantum wells (MQWs) light-emitting diodes (LEDs) were grown on the rough and the smooth N-polar GaN templates, respectively. Compared with the LED grown on the rough N-polar GaN template, dramatically improved interface sharpness and luminescence uniformity of the InGaN/GaN MQWs are achieved for the LED grown on the smooth N-polar GaN template. [ABSTRACT FROM AUTHOR]

This paper reports on the predicted increase in the Rashba interaction due to the incorporation of Bi in GaAs/AlGaAs heterostructures. Band structure parameters obtained from the band anti-crossing theory have been used in combination with self-consistent Schrödinger-Poisson calculations and k.p models to determine the electron spin-splitting caused by structural inversion asymmetry and increased spin-orbit interaction. A near linear seven fold increase in the strength of the Rashba interaction is predicted for a 10% concentration of Bi in a GaAsBi/AlGaAs quantum well heterostructure. [ABSTRACT FROM AUTHOR]

In this paper, we report on the effects of including Si-doped (In)GaN prelayers on the low temperature optical properties of a blue-light emitting InGaN/GaN single quantum well. We observed a large blue shift of the photoluminescence peak emission energy and significant increases in the radiative recombination rate for the quantum well structures that incorporated Si-doped prelayers. Simulations of the variation of the conduction and valence band energies show that a strong modification of the band profile occurs for the quantum wells on Si-doped prelayers due to an increase in strength of the surface polarization field. The enhanced surface polarization field opposes the built-in field across the quantum well and thus reduces this built-in electric field. This reduction of the electric field across the quantum well reduces the Quantum Confined Stark Effect and is responsible for the observed blue shift and the change in the recombination dynamics. [ABSTRACT FROM AUTHOR]

In this paper, we report our experimental investigation on the influence of electron barrier (eB) in mid-infrared interband cascade photodetectors. Even though earlier theoretical projection indicates that an eB with 2-pairs GaSb/AlSb quantum wells (QWs) is sufficient to block electrons direct tunneling between stages, our experimental results show that a thicker (with 6-pairs of GaSb/AlSb QWs) electron barrier could significantly reduce the device dark current, with little influence on the optical performance. The 5-stage devices have demonstrated a dark current density of 1.10 × 10-7 A/cm2 (at -5 mV) and a Johnson-limited D* of 1.81 × 1011 cmHz1/2/W (at 3.8 μm) at 150 K, respectively. [ABSTRACT FROM AUTHOR]

In this paper, we report a Hall mobility of one million in a germanium two-dimensional hole gas. The extremely high hole mobility of 1.1?×?106 cm² V-1 s-1 at a carrier sheet density of 3?×?1011?cm-2 was observed at 12?K. This mobility is nearly an order of magnitude higher than any previously reported. From the structural analysis of the material and mobility modeling based on the relaxation time approximation, we attribute this result to the combination of a high purity Ge channel and a very low background impurity level that is achieved from the reduced-pressure chemical vapor deposition growth method. [ABSTRACT FROM AUTHOR]

In this paper, we present our study of the maximum electron density, nmax, accessible via low-temperature transport experiments in enhancement-mode Si/Si1-xGex heterostructure field-effect transistors. Experimentally, we find that nmax is much higher than the value obtained from self-consistent Schrödinger-Poisson simulations and that nmax can be changed only by changing the Ge concentration in the Si1-xGex barrier layer, not by varying the barrier layer thickness. The discrepancy between experiments and simulations is explained by a non-thermal-equilibrium tunneling-limited model. [ABSTRACT FROM AUTHOR]

In this paper, we present experimental results related to tunable dual wavelength passive mode locking of two independent ground state sub-bands in a multi section InAs/InGaAs quantum dot laser. The emission of these sub-bands is related to gain suppression at the center of the ground state emission, whereas their wavelength separation is tunable with injection current. Through the mechanism of passive mode locking two independent pulses were obtained, with typical pulse width in the order of 17 ps. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the polarization selection rules of wurtzite InGaN/GaN quantum wells using the k·p perturbation method. It was found that the symmetry properties of the valence subbands’ wavefunctions at kt≠0 are quite different with those at kt=0. These symmetry properties of valence subbands’ wavefunctions influence the momentum matrix element for TE and TM modes, leading to a different polarization selection rules from the ones at kt=0 and the absence of spectra peak shift between TE and TM modes. It is suggested that the polarization selection rule at kt≠0 should be considered in the main transition process for wurtzite III-V semiconductors. [ABSTRACT FROM AUTHOR]

In this paper we report on the optical properties of a series of GaN/AlGaN multiple quantum well structures grown on a-plane (1120) GaN, which had been deposited on r-plane (1102) sapphire substrates, compared to a reference GaN template of the same orientation. The low temperature photoluminescence spectrum of the template layer is dominated by two emission bands, which we attribute to recombination involving excitons in the bulk of the layer and electrons and holes trapped at basal-plane stacking faults, designated X1 and X2, respectively. The photoluminescence spectra from the quantum well structures show similar emission bands except that both X1 and X2 shift to higher energy with decreasing quantum well thickness. The shift to higher energy is due to the effects of quantum confinement on carriers trapped at the stacking faults that intersect the quantum wells, as well as those excitons that are localized within the quantum wells. This assignment is based partly on excitation spectroscopy that reveals exciton transitions associated with electrons from the n=1 and n=2 quantum well confined states. [ABSTRACT FROM AUTHOR]

In this paper, we examine the wavelength tuning limitations of type-II antimonide lasers containing InAs/InGaSb/InAs quantum wells. Wavelength tuning is accomplished by varying the thickness of the InAs electron wells while keeping all else fixed. In principle, these wells can be tuned from λ≈2.5 μm out to far IR wavelengths by increasing the thickness of the InAs layers. However, a practical upper limit of λ≈9.5 μm is set due to the high waveguide losses awg and the diminishing modal overlap with the gain at longer wavelengths. The waveguide losses grow as awg∝λ3.44 and are attributable to free carrier absorbance. In order for the long-IR laser devices to achieve threshold, they must continually band fill, spectrally tuning to shorter wavelengths, until the laser gain exceeds the losses, which occurs near 9.5 μm. [ABSTRACT FROM AUTHOR]

In this paper, the carrier transport in (Al)InGaN based test structures with In-rich quantum wells on c-plane substrates is investigated under high current operation. To get access to the injection efficiency, the devices are processed as ridge waveguide lasers and examined above threshold. The slope efficiency reveals a slight decrease as a function of current even under pulsed operation that can be related to a reduction of the injection efficiency based on carrier leakage. As the test structure contains an InGaN detection layer on the n-side, it is possible to verify hole overflow across the active region. Moreover, by analysing the current dependence of the radiative recombination in the detection layer, the reduction of slope efficiency can be correlated to increasing hole leakage. [ABSTRACT FROM AUTHOR]

Recombination and trapping effect in quantum dots are large barriers to efficient photon-generated carrier extraction. In this paper, Infrared (IR)-assisted carrier extraction in a Si/SiO2 multiple quantum well is demonstrated. Operated at reverse bias, enhanced photoresponse from 300 to 700 nm is observed. External quantum efficiency nearly 200% is obtained when both visible light and IR are added. The enhancement is attributed to potential modulation by photo-illumination. A theoretical model including three processes is presented to explain this conclusion. The secondary light source IR could excite trapped carriers from the defects at the Si/SiO2 interface, improving extraction efficiency. [ABSTRACT FROM AUTHOR]

Responds to a commentary on the paper 'Energy level schemes for far-infrared quantum well lasers,' published in the journal 'Applied Physics Letters.' Design of optically pumped far-infrared intersubband lasers; Optimization of the lifetime of the radiative state.

Responds to a commentary on the paper 'Noise gain and detectivity in n-type GaAs/AlAs/AlGaAs quantum well infrared photodetectors,' published in the 'Applied Physics Letters.' Decreases in detectivity with increasing carrier capture probability; Comparable to detectivities of other detectors.

Comments on the paper 'Noise gain and detectivity in n-type GaAs/AlAs/AlGaAs quantum well infrared photodetectors,' published in the 'Applied Physics Letters.' Maximization of photoconductivity.