Robust design of mid-infrared GaSb-based single-mode laser diode fabricated by standard photolithography with socketed ridge-waveguide modulation.

In this paper, we put up a robust design of a stable single-mode-operated GaSb-based laser diode emitting around 1950nm. This novel design structure with socketed ridge-waveguide enables a simple fabrication and batch production of mid-infrared laser diodes on account of the mere usage of standard photolithography. By introducing micron-level index perturbations distributed along the ridge waveguide, the threshold gains of different FP modes are modulated. Four geometrical parameters of the perturbations are systematically optimized by analyzing the reflection spectrum to get a robust single-mode characteristic. Based on the optimized geometrical parameters, 1-mm long uncoated lasers are carried out and exhibit a stable single longitudinal mode from 10 °C to 40 °C with a maximum output power of more than 10 mW. Thus, we prove the feasibility of the standard photolithography to manufacture the monolithic single-mode infrared laser source without regrowth process or nanoscale lithography.

High-performance infrared photodetectors based on InAs/InAsSb/AlAsSb superlattice for 3.5†µm cutoff wavelength spectra.

High-performance infrared p-i-n photodetectors based on InAs/InAsSb/AlAsSb superlattices on GaSb substrate have been demonstrated at 300K. These photodetectors exhibit 50% and 100% cut-off wavelength of ∼3.2 µm and ∼3.5 µm, respectively. Under -130 mV bias voltage, the device exhibits a peak responsivity of 0.56 A/W, corresponding to a quantum efficiency (QE) of 28%. The dark current density at 0 mV and -130 mV bias voltage are 8.17 × 10-2 A/cm2 and 5.02 × 10-1 A/cm2, respectively. The device exhibits a saturated dark current shot noise limited specific detectivity (D*) of 3.43 × 109 cm·Hz1/2/W (at a peak responsivity of 2.5 µm) under -130 mV of applied bias.

A review on III-V compound semiconductor short wave infrared avalanche photodiodes.

The on-chip avalanche photodiodes (APDs) are crucial component of a fully integrated photonics system. Specifically, III-V compound APD has become one of the main applications of optical fiber communication reception due to adaptable bandgap and low noise characteristics. The advancement of structural design and material choice has emerged as a means to improve the performance of APDs.Therefore, it is inevitable to review the evolution and recent developments on III-V compound APDs to understand the current progress in this field. To begin with, the basic working principle of APDs are presented. Next, the structure development of APDs is briefly reviewed, and the subsequent progression of III-V compound APDs (InGaAs APDs, AlxIn1-xAsySb1-y APDs) is introduced. Finally, we also discuss the key issues and prospects of AlxIn1-xAsySb1-y digital alloy avalanche APDs that need to be addressed for the future development of ≥2µm optical communication field.

A review on III-V compound semiconductor short wave infrared avalanche photodiodes.

The on-chip avalanche photodiodes (APDs) are crucial component of a fully integrated photonics system. Specifically, III-V compound APD has become one of the main applications of optical fiber communication reception due to adaptable bandgap and low noise characteristics. The advancement of structural design and material choice has emerged as a means to improve the performance of APDs. Therefore, it is inevitable to review the evolution and recent developments on III-V compound APDs to understand the current progress in this field. To begin with, the basic working principle of APDs are presented. Next, the structure development of APDs is briefly reviewed, and the subsequent progression of III-V compound APDs (InGaAs APDs, AlxIn1-xAsySb1-yAPDs) is introduced. Finally, we also discuss the key issues and prospects of AlxIn1-xAsySb1-ydigital alloy avalanche APDs that need to be addressed for the future development of ≥2µm optical communication field.

Fine modulation of the energy band strategy to control the carrier confinement capability of digital alloys.

In this paper, a strategy to finely modulate the energy band structure to control the carrier confinement capability of digital alloys (DA) is proposed. Strain analysis shows that As and Sb atoms are exchanged within the AlAsSb DA. The bottom of the corrected potential well is low on the left and high on the right in the growth direction, resulting in a higher band offset of the AlSb potential barrier layer on the left side of the potential well than on the right side. The modulation of the band leads to a higher probability of electron tunneling in DA under the action of an electric field opposite to the growth direction. Conversely, it is difficult for the electrons to tunnel into the lower energy level potential wells. TheI-Vcurve of DA shows that the current value under positive bias is significantly smaller than the value under negative bias when the voltage is higher. The measured results correspond perfectly with the modified energy band model, which verifies the feasibility of energy band modulation. This is important for the structural design of DA and the reduction of dark current in optoelectronic devices.

High spectral purity GaSb-based blazed grating external cavity laser with tunable single-mode operation around 1940nm.

In this article, we present a tunable GaSb-based blazed grating external cavity laser (BG-ECL) with high spectral purity and high output power single-mode operation around 1940nm. The drastic increase in spectral selectivity and optical power results from the employment of a single-transverse-mode operating narrow ridge waveguide laser diode with an optimized AR coating on the front facet. The stable fundamental spatial mode output beam from the laser diode enables efficient collimation and high coupling efficiency with the blazed grating, leading to stronger wavelength-selective feedback. The AR coating with proper low reflectivity on the straight waveguide effectively suppresses the internal cavity mode lasing without causing extra optical loss. As a result, the BG-ECL device exhibits excellent comprehensive performance with a side mode suppression ratio (SMSR) over 50 dB with optical power exceeding 30 mW within a 70 nm tuning range. A maximum SMSR of 56.26 dB with 35.12 mW output power was observed in continuous-wave operation. By increasing the working temperature of the diode laser, the tuning range can be further extended to over 100 nm without noticeable degradation in spectral and output power performance.

Heterointerface-Driven Band Alignment Engineering and its Impact on Macro-Performance in Semiconductor Multilayer Nanostructures.

Interfaces in semiconductor heterostructures is of continuously greater significance in the trend of scaling materials down to the atomic limit. Since atoms tend to behave more irregularly around interfaces than in internal materials, accurate energy band alignment becomes a major challenge, which determines the ultimate performance of devices. Therefore, a comprehensive understanding of the interplay between heterointerface, energy band, and macro-performance is desiderated. Here, such interplay is explored by investigating asymmetric heterointerfaces with identical fabrication parameters in multiple-quantum-well lasers. The unexpected asymmetry derives from the atomic discrepancy around heterointerfaces, which ultimately improves the optical property through altered valence band offsets. Strain and charge distribution around heterointerfaces are characterized via geometric phase analysis and in situ bias electron holography, respectively. Combining experiments with theories, arsenic-enrichment at one of the interfaces is considered the origin of asymmetry. To reveal actual band alignment, valence band model is modified focusing on the transition around heterojunctions. The enhanced photoluminescence intensity reflects the alleviation of hole confinement insufficiency and the enlargement of valence band offset. The results help to advance the understanding of the general problem of interface in nanostructures and provide guidance applicable to various scenarios for micro-macro correlation.

Investigation of regime switching from mode locking to Q-switching in a 2 µm InGaSb/AlGaAsSb quantum well laser.

A two-section InGaSb/AlGaAsSb single quantum well (SQW) laser emitting at 2 µm is presented. By varying the absorber bias voltage with a fixed gain current at 130 mA, passive mode locking at ~18.40 GHz, Q-switched mode locking, and passive Q-switching are observed in this laser. In the Q-switched mode locking regimes, the Q-switched RF signal and mode locked RF signal coexist, and the Q-switched lasing and mode-locked lasing happen at different wavelengths. This is the first observation of these three pulsed working regimes in a GaSb-based diode laser. An analysis of the regime switching mechanism is given based on the interplay between the gain saturation and the saturable absorption.

WOX11 and 12 are involved in the first-step cell fate transition during de novo root organogenesis in Arabidopsis.

De novo organogenesis is a process through which wounded or detached plant tissues or organs regenerate adventitious roots and shoots. Plant hormones play key roles in de novo organogenesis, whereas the mechanism by which hormonal actions result in the first-step cell fate transition in the whole process is unknown. Using leaf explants of Arabidopsis thaliana, we show that the homeobox genes WUSCHEL RELATED HOMEOBOX11 (WOX11) and WOX12 are involved in de novo root organogenesis. WOX11 directly responds to a wounding-induced auxin maximum in and surrounding the procambium and acts redundantly with its homolog WOX12 to upregulate LATERAL ORGAN BOUNDARIES DOMAIN16 (LBD16) and LBD29, resulting in the first-step cell fate transition from a leaf procambium or its nearby parenchyma cell to a root founder cell. In addition, our results suggest that de novo root organogenesis and callus formation share a similar mechanism at initiation.

Low lateral divergence 2 µm InGaSb/ AlGaAsSb broad-area quantum well lasers.

High power and high brightness mid-infrared GaSb based lasers are desired for many applications, however, the high lateral divergence is still the influence factor for practical application. In this paper, a simple and effective approach based on the fishbone-shape microstructure was proposed, the effective improvement on both the lateral divergence and output power of 2 µm GaSb based broad-area lasers was demonstrated. The lateral divergence is reduced averagely by 55% and 15.8° for 95% power content is realized. The continuous-wave emission power is increased about 19% with the decreased threshold current. The other merits for this microstructure are the unchanged intrinsic characteristic of broad-area lasers and the low cost fabrication.

Watt-level continuous-wave antimonide laser diodes with high carrier-confined active region above 2.5 µm.

Thanks to high performance above room temperature, antimonide laser diodes have shown great potential for broad application in the mid-infrared spectral region. However, the laser`s performance noticeably deteriorates due to the reduction of carrier confinement with increased emission wavelength. In this paper, a novel active region with higher carrier confinements both of electron and hole, by the usage of an indirect bandgap material of Al0.5GaAs0.04Sb as the quantum barrier, was put up to address the poor carrier confinement of GaSb-based type-I multi-quantum-well (MQW) diode lasers emission wavelength above 2.5 µm. The carrier confinement and the differential gain in the designed active region are enhanced as a result of the first proposed usage of an indirect-gap semiconductor as the quantum barrier with larger band offsets in conduction and valence bands, leading to high internal quantum efficiency and low threshold current density of our lasers. More importantly, the watt-level output optical power is obtained at a low injection current compared to the state of the art. Our work demonstrates a direct and cost-effective solution to address the poor carrier confinement of the GaSb-based MQW lasers, thereby achieving high-power mid-infrared lasers.

Annealing-Modulated Surface Reconstruction for Self-Assembly of High-Density Uniform InAs/GaAs Quantum Dots on Large Wafers Substrate.

In this work, we developed pre-grown annealing to form ß2 reconstruction sites among ß or α (2 × 4) reconstruction phase to promote nucleation for high-density, size/wafer-uniform, photoluminescence (PL)-optimal InAs quantum dot (QD) growth on a large GaAs wafer. Using this, the QD density reached 580 (860) µm-2 at a room-temperature (T) spectral FWHM of 34 (41) meV at the wafer center (and surrounding) (high-rate low-T growth). The smallest FWHM reached 23.6 (24.9) meV at a density of 190 (260) µm-2 (low-rate high-T). The mediate rate formed uniform QDs in the traditional ß phase, at a density of 320 (400) µm-2 and a spectral FWHM of 28 (34) meV, while size-diverse QDs formed in ß2 at a spectral FWHM of 92 (68) meV and a density of 370 (440) µm-2. From atomic-force-microscope QD height distribution and T-dependent PL spectroscopy, it is found that compared to the dense QDs grown in ß phase (mediate rate, 320 µm-2) with the most large dots (240 µm-2), the dense QDs grown in ß2 phase (580 µm-2) show many small dots with inter-dot coupling in favor of unsaturated filling and high injection to large dots for PL. The controllable annealing (T, duration) forms ß2 or ß2-mixed α or ß phase in favor of a wafer-uniform dot island and the faster T change enables optimal T for QD growth.

OBERON3 and SUPPRESSOR OF MAX2 1-LIKE proteins form a regulatory module driving phloem development.

Spatial specificity of cell fate decisions is central for organismal development. The phloem tissue mediates long-distance transport of energy metabolites along plant bodies and is characterized by an exceptional degree of cellular specialization. How a phloem-specific developmental program is implemented is, however, unknown. Here we reveal that the ubiquitously expressed PHD-finger protein OBE3 forms a central module with the phloem-specific SMXL5 protein for establishing the phloem developmental program in Arabidopsis thaliana. By protein interaction studies and phloem-specific ATAC-seq analyses, we show that OBE3 and SMXL5 proteins form a complex in nuclei of phloem stem cells where they promote a phloem-specific chromatin profile. This profile allows expression of OPS, BRX, BAM3, and CVP2 genes acting as mediators of phloem differentiation. Our findings demonstrate that OBE3/SMXL5 protein complexes establish nuclear features essential for determining phloem cell fate and highlight how a combination of ubiquitous and local regulators generate specificity of developmental decisions in plants.

Investigation on Residual Strength and Failure Mechanism of the Ceramic/UHMWPE Armors after Ballistic Tests.

In this paper, the ballistic damage mechanism and residual bearing capacity of ceramic/backing plate armor were investigated. First, a series of lightweight armors were prepared, consisting of ceramic and ultra-high molecular weight polyethylene fiber-reinforced resin matrix composite (UHMWPE) plates, and were wrapped in a high-strength fabric. Then, the ceramic/UHMWPE armors were hit by one or two bullets, and finally subjected to compression testing. The results showed that the main failure mode of integral ceramic/UHMWPE armors was ceramic brittle fracture. Many zigzag patterns on the compression curve indicated that the specimens had undergone the stages of crack propagation, ceramic fragment reorganization, plastic deformation of UHMWPE backing plate, interlaminar tearing, and overall fracture. The failure of spliced ceramic/UHMWPE armors was mainly due to the dislocation between ceramic sheets; the smooth compression curves indicated that there was no recombination of ceramic fragments and obvious interlayer debonding during the compression. Under the maximum load, each ceramic/UHMWPE armor with ballistic damage did not suddenly break and fail. The structure and thickness of ceramic plates all had an impact on residual strength: under the same structure, the greater the thickness, the greater the residual strength, but the relationship between them was not linear; under the same thickness, the residual strength of the spliced ceramic/UHMWPE armor was higher. The residual strength was also related to the number of shots: after two bullets hit, its value was only one-third of that after one bullet hit.

Promotion of Specific Single-Transverse-Mode Beam Characteristics for GaSb-Based Narrow Ridge Waveguide Lasers via Customized Parameter Design.

GaSb-based single-transverse-mode narrow ridge waveguide (RW) lasers with high power and simultaneous good beam quality have broad application prospects in the mid-infrared wavelength region. Yet its design and formation have not been investigated systematically, while the beam characteristics that affect their suitability for specific applications remain rarely analyzed and optimized. The present work addresses these issues by theoretically establishing a waveguide parameter domain that generalizes the overall possible combinations of ridge widths and etch depths that support single-transverse-mode operation for GaSb-based RW lasers. These results are applied to develop two distinct and representative waveguide designs derived from two proposed major optimization routes of model gain expansion and index-guiding enhancement. The designs were evaluated experimentally based on prototype 1-mm cavity-length RW lasers in the 1950 nm wavelength range, which were fabricated with waveguides having perpendicular ridge and smooth side-walls realized through optimized dry etching conditions. The model gain expanded RW laser design with a relatively shallow-etched (i.e., 1.55 [Formula: see text]m) and wide ridge (i.e., 7 [Formula: see text]m) yielded the highest single-transverse-mode power to date of 258 mW with a narrow lateral divergence angle of 11.1[Formula: see text] full width at half maximum at 800 mA under room-temperature continuous-wave operation, which offers promising prospects in pumping and coupling applications. Meanwhile, the index-guiding enhanced RW laser design with a relatively deeply etched (i.e., 2.05 [Formula: see text]m) and narrow ridge (i.e., 4 [Formula: see text]m) provided a highly stable and nearly astigmatism-free fundamental mode emission with an excellent beam quality of M[Formula: see text] factor around 1.5 over the entire operating current range, which is preferable for seeding external cavity applications and complex optical systems.

Insights into Growth-Oriented Interfacial Modulation within Semiconductor Multilayers.

Interfacial engineering plays a crucial role in regulating the quality and property of heterogeneous structures, especially for nanometer-scaled devices. However, traditional methods for interfacial modulation (IFM) generally treat all the interfaces uniformly, neglecting the inherent disparities of interfaces like their growth sequence. Herein, it is found that the growth-oriented characteristic of IFM strongly determines the main regions where the modulation takes effect. Specifically, in a semiconductor quantum well structure, the arsenic atoms modulated at the well-on-barrier (WoB) interface tend to diffuse into and thus affect the next-grown well layer. In contrast, the arsenic atoms introduced at the barrier-on-well (BoW) interface mainly take effect within the next-grown barrier layer. According to theoretical simulations and electron holography (EH) experiments, the depth of quantum wells and the height of potential barriers are extended by introducing arsenic atoms at WoB and BoW interfaces, respectively. Resultantly, while modulating at the BoW interface has little impact on the photoluminescence (PL) spectrum, applying IFM at the WoB interface could dramatically improve the luminescent intensity (about 30%), which demonstrates the impact of the growth-oriented characteristic. Furthermore, in situ bias EH results indicate that IFM at the WoB interface helps to suppress the quantum-confined Stark effect.

Control of electron tunnelling by fine band engineering of semiconductor potential barriers.

Quantum tunnelling (QTN) devices show a promising future for energy saving and ultrafast operation thanks to the unprecedented development of two-dimensional materials. However, the immature techniques for device fabrication hamper severely their further progress and application. To overcome such a challenge, the abundant processing technology used in semiconductor electronics is worth considering. Herein, a device prototype is fabricated based on band engineering to enable flexible control of QTN probability (TP) within a III-V semiconductor multilayer. While the initial heights of all barriers are set to obtain similar TPs under no bias, the conduction band slopes of InGaSb and AlSb barriers are modulated to a state where their TPs vary reversely under electric fields. On this basis, revealed by in situ bias electron holography, a unidirectional accumulation of electrons has been realized inside the multilayer structure. Moreover, the inevitable element segregation/diffusion during device growth plays a key role in band structure optimization, which is confirmed by strain analysis. The feasibility of the above modulation strategy is also confirmed by theoretical simulations. Our findings might provide a new perspective on the innovation of semiconductor devices and the application of QTN effect.

A new method for evaluating the normal rake angle and inclination angle on medical needles.

Hollow needles are the most frequently used medical equipment. The design of a hollow needle that best enables medical procedures requires a better understanding of needle tip geometry. Calculating the cutting angles of a needle for a complex surface topology is difficult. This article proposes a new method based on non-Euclidean geometry for the analysis of biopsy needle tip. The method can be used to calculate the cutting angles on any pipe needle. To verify the validity of this method, the normal rake angle and inclination angle on four types of needles (bias bevel needle, cylinder surface needle, curved surface needle and Cournand-type needle) were investigated. It was found that calculation of the cutting angles was simple and convenient using this method, especially for the curved surface needles. Images of the cutting angles from the Cournand-type needles revealed that the smaller bevel angle [Formula: see text] resulted in a higher normal rake angle [Formula: see text] and inclination angle [Formula: see text]. As [Formula: see text] increased, the range of the normal rake angle [Formula: see text] became larger at first and then became smaller.

Elimination of Bimodal Size in InAs/GaAs Quantum Dots for Preparation of 1.3-µm Quantum Dot Lasers.

The device characteristics of semiconductor quantum dot lasers have been improved with progress in active layer structures. Self-assembly formed InAs quantum dots grown on GaAs had been intensively promoted in order to achieve quantum dot lasers with superior device performances. In the process of growing high-density InAs/GaAs quantum dots, bimodal size occurs due to large mismatch and other factors. The bimodal size in the InAs/GaAs quantum dot system is eliminated by the method of high-temperature annealing and optimized the in situ annealing temperature. The annealing temperature is taken as the key optimization parameters, and the optimal annealing temperature of 680 °C was obtained. In this process, quantum dot growth temperature, InAs deposition, and arsenic (As) pressure are optimized to improve quantum dot quality and emission wavelength. A 1.3-µm high-performance F-P quantum dot laser with a threshold current density of 110 A/cm2 was demonstrated.

Quantum efficiency optimization by maximizing wave function overlap in type-II superlattice photodetectors.

Quantum efficiency (QE) is a crucial parameter that determines the final performance of photodetector devices. Herein, by fitting the charge distribution fluctuation under a series of bias voltages, revealed by groups of in situ electron holography experiments, a simple model based on modulus square of wave function (MSWF) is qualitatively built to shed new light on the relationship between QE and wave function overlap (WFO). It is found that there exists a competition of WFO between the potential well regions and the interface regions, and a peak value of the overall WFO can be obtained under an appropriate voltage. On combining such competition with the measured QE results from actual infrared photodetectors, the positive correlation between QE and WFO is manifested, and the QE can be boosted to 51% from 34%. Our results offer a new perspective to the understanding of the carrier transportation within superlattice (SL) structures and the design on photoelectric devices with enhanced performance.