Optoelectronic properties of single-crystalline GaInAsSb quaternary alloy nanowires

Bandgap engineering of semiconductor nanomaterials is critical for their applications in nanoelectronics, optoelectronics, and photonics. Here we report, for the first time, the growth of single-crystalline quaternary alloyed Ga_(0.75)In_(0.25)As_(0.49)Sb_(0.51) nanowires via a chemical-vapor-deposition method. The synthesized nanowires have a uniform composition distribution along the growth direction, with a zinc-blende structure. In the photoluminescence investigation,these quaternary alloyed semiconductor nanowires show a strong band edge light emission at 1950 nm(0.636 e V). Photodetectors based on these alloy nanowires show a strong light response in the near-infrared region(980 nm) with the external quantum efficiency of 2.0 × 10~4% and the responsivity of 158 A/W. These novel near-infrared photodetectors may find promising applications in integrated infrared photodetection, information communication, and processing.     

Exciton luminescence and many-body effect of monolayer WS2 at room temperature

Monolayer transition metal dichalcogenides favor the formation of a variety of excitonic quasiparticles, and can serve as an ideal material for exploring room-temperature many-body effects in two-dimensional systems. Here, using mechanically exfoliated monolayer WS₂ and photoluminescence (PL) spectroscopy, exciton emission peaks are confirmed through temperature-dependent and electric-field-tuned PL spectroscopy. The dependence of exciton concentration on the excitation power density at room temperature is quantitatively analyzed. Exciton concentrations covering four orders of magnitude are divided into three stages. Within the low carrier concentration stage, the system is dominated by excitons, with a small fraction of trions and localized excitons. At the high carrier concentration stage, the localized exciton emission from defects coincides with the emission peak position of trions, resulting in broad spectral characteristics at room temperature.     

Band gap engineering of atomically thin two-dimensional semiconductors

Atomically thin two-dimensional(2D) layered materials have potential applications in nanoelectronics, nanophotonics, and integrated optoelectronics. Band gap engineering of these 2D semiconductors is critical for their broad applications in high-performance integrated devices, such as broad-band photodetectors, multi-color light emitting diodes(LEDs), and high-efficiency photovoltaic devices. In this review, we will summarize the recent progress on the controlled growth of composition modulated atomically thin 2D semiconductor alloys with band gaps tuned in a wide range, as well as their induced applications in broadly tunable optoelectronic components. The band gap engineered 2D semiconductors could open up an exciting opportunity for probing their fundamental physical properties in 2D systems and may find diverse applications in functional electronic/optoelectronic devices.     

High performance photodetectors based on high quality InP nanowires

In this paper,small diameter InP nanowires with high crystal quality were synthesized through a chemical vapor deposition method.Benefitting from the high crystallinity and large specific surface area of InP nanowires,the simply constructed photodetector demonstrates a high responsivity of up to 1170 A·W ~(-1) and an external quantum efficiency of2.8 × 10~5% with a fast rise time of 110 ms and a fall time of 130 ms,even at low bias of 0.1 V.The effect of back-gate voltage on photoresponse of the device was systematically investigated,confirming that the photocurrent dominates over thermionic and tunneling currents in the whole operation.A mechanism based on energy band theory at the junction between metal and semiconductor was proposed to explain the back-gate voltage dependent performance of the photodetectors.These convincing results indicate that fine InP nanowires will have a brilliant future in smart optoelectronics.     

数学解题教学需要寻找根源

数学解题教学的高效和有效是教师教学最核心的教学内容.在新课程理念引入到教学之后,我们常常看到各种层出不穷的全新教学方式、方法,有很多教学模式围绕学生进行了设计和尝试,是非常值得我们学习和探索的,比如,以积极建构为主的数学新知类教学模式、以马登变式理论构建的变式教学复习模式、以APOS理论进行的知识探索类教学模式等,都有较大的借鉴意义.随着新课程理念的不断深入,在高三复习解题教学中,我们对新课程如何更好更妙地实施教学高效性和有效性,在认识方面并不足够.笔者常常出去观摩高三解