Photodetectors based on small-molecule organic semiconductor crystals

Small-molecule organic semiconductor crystals(SMOSCs) combine broadband light absorption(ultraviolet–visible–near infrared) with long exciton diffusion length and high charge carrier mobility. Therefore, they are promising candidates for realizing high-performance photodetectors. Here, after a brief resume of photodetector performance parameters and operation mechanisms, we review the recent advancements in application of SMOSCs as photodetectors, including photoconductors, phototransistors, and photodiodes. More importantly, the SMOSC-based photodetectors are further categorized according to their detection regions that cover a wide range from ultraviolet to near infrared. Finally, challenges and outlooks of SMOSC-based photodetectors are provided.

Controlled 2D growth of organic semiconductor crystals by suppressing “coffee-ring” effect

Owing to enhanced charge transport efficiency arising from the ultrathin nature,two-dimensional(2D)organic semiconductor single crystals(OSSCs)are emerging as a fascinating platform for high-performance organic field-effect transistors(OFETs).However,ucoffee-ring"effect induced by an evaporation-induced convective flow near the contact line hinders the large-area growth of 2D OSSCs through a solution process.Here,we develop a new strategy of suppressing the"coffee-ring"effect by using an organic semiconductor:polymer blend solution.With the high-viscosity polymer in the organic solution,the evaporation-induced flow is remarkably weakened,ensuring the uniform molecule spreading for the 2D growth of the OSSCs.As an example,wafer-scale growth of crystalline film consisting of few-layered 2,7-didecylbenzothienobenzothiophene(C10-BTBT)crystals was successfully accomplished via blade coating.OFETs based on the crystalline film exhibited a maximum hole mobility up to 12.6 cm^2·V^-1·s^-1,along with an average hole mobility as high as 8.2 cm^2·V^-1·s^-1.Our work provides a promising strategy for the large-area growth of 2D OSSCs toward high-performance organic electronics.

Pressure-controlled terahertz filter based on 1D photonic crystal with a defective semiconductor

The tunable terahertz(THz) filter has been designed and studied, which is composed of 1D photonic crystal(PC) containing a defect layer of semiconductor Ga As. The analytical solution of 1D defective PC(1DDPC) is deduced based on the transfer matrix method, and the electromagnetic plane wave numerical simulation of this 1DDPC is performed by using the finite element method. The calculated and simulated results have confirmed that the filtering transmittance of this 1DDPC in symmetric structure of air/(Si/SiO_2)~N/GaAs/(SiO_2/Si)~N/air is far higher than in asymmetric structure of air/(Si/SiO_2)~N/GaAs/(Si/SiO_2)~N/air, where the filtering frequency can be tuned by the external pressure. It can provide a feasible route to design the external pressure-controlled THz filter based on 1DPC with a defective semiconductor.

Semiconductor photonic crystal laser

By combing artificial micro–nano structures, photonic crystals(PCs), with traditional semiconductor laser material to realize the dynamic collaborative control of photonic states and confined electrons, the band engineering of the PC has been confirmed. This brings new development space for the semiconductor laser, such as for low threshold and high efficiency.Based on a series of works by Zheng's group, this paper has reviewed kinds of PC lasers including electrical injection PC vertical cavity and lateral cavity surface-emitting lasers, and PC high beam quality lasers, to show that the PC is vital for promoting the continuous improvement of semiconductor laser performance at present and in the future.

Application of Photonic Crystals in Semiconductor Lasers

Photonic crystals(PCs) have attracted much considerable research attention in the past two decades. They are artificially fabricated periodic dielectric structures. The periodic dielectric structures have photonic band gap(PBG) and are referred to as photonic band gap materials. This paper mainly introduces one-dimensional (1-D) and 2D PCs applied in the semiconductor lasers.

GaSb单晶研究进展

近年来,锑化物红外技术发展迅速,成为半导体技术的重要发展方向之一。锑化镓(GaSb)作为典型的Ⅲ-Ⅴ族化合物半导体,凭借优异的性能成为锑化物红外光电器件的关键衬底材料。随着锑化物红外技术逐步成熟和应用逐渐开展,人们对GaSb单晶片的需求日益剧增的同时也对其质量提出更高的要求。GaSb单晶片质量直接影响着外延材料和器件性能,这就要求GaSb单晶片具有大尺寸、更低的缺陷密度、更好的表面质量和一致性。本文就GaSb晶体材料的性质、制备方法、国内外机构的研究进展及其应用情况进行了综述,并对其发展前景和趋势进行了展望。

VGF法磷化铟单晶炉加热器对炉内热场分布影响的研究

磷化铟(InP)是一种重要的化合物半导体,在通信、航空航天和人工智能等领域具有广泛的应用。InP单晶生长质量的优劣取决于其生长炉内热场的稳定与温控。InP晶体工业生产中广泛采用的垂直梯度凝固(VGF)法是在磷化铟单晶生长炉中构建高温、封闭、稳定及可控的热场,但因炉内缺乏直接观测和完整的参数监测手段,利用计算机数值仿真对炉内晶体生长的温度场进行科学分析,以获取最佳的生长温控条件,俨然成为有效且重要的方法。本文基于ANSYS有限元软件及炉内元件实测参数,建立了InP单晶生长系统热场三维物理和数学模型,基于磷化铟单晶生长过程中的温度离散数据,对所建模型对比和验证,获得了与实际生产温度数据吻合良好的效果(温度偏差控制在3%以内),验证了所建模型的有效性。基于此模型,本文对生产条件下四段加热器温度波动对热场分布影响进行了探讨,并对炉内四段加热器的温度波动对炉内低温区、高温区及料管中心温度影响规律进行了研究,所得结论对揭示工业生产过程中InP单晶炉热场的分布规律及调节方法具有一定的指导意义。

基于溶液法制备卤化铅钙钛矿的直接型辐射探测器研究进展

X射线和γ射线探测在医学成像、安防检查、国土安全、无损检测等各个领域得到广泛应用,钙钛矿材料具有高辐射吸收系数、高载流子迁移率-寿命乘积、特殊的缺陷容忍特性而成为辐射探测器件优异的候选材料。溶液法在制备钙钛矿材料方面具有显著的优势,溶液法的成本较低,能在低温或环境条件下制备,更易推行工业化生产,是未来优化材料体系,制备高质量、大尺寸晶体材料的关键技术。本文从溶液法制备卤化铅钙钛矿材料的角度出发,分析晶体生长及材料组成对辐射探测性能的影响,重点介绍从优化晶体生长质量和器件结构设计等方面提升辐射探测性能,最后总结钙钛矿材料在辐射探测领域面临的挑战,并展望了未来研究的发展方向,期望为钙钛矿材料在辐射探测领域走向工业化提供参考。

1,1’-磺酰基双(2-甲基-1H-咪唑)对宽带隙钙钛矿太阳电池性能的影响

对倒置结构,带隙为1.68 eV的钙钛矿太阳电池光吸收层掺杂1,1’-磺酰基双(2-甲基-1H-咪唑),以改善钙钛矿薄膜质量,提高太阳电池性能。空间电荷限制电流(SCLC)测试结果表明,掺杂后的钙钛矿薄膜的缺陷密度明显降低;稳态光致发光光谱(PL)结果表明,掺杂后的钙钛矿薄膜的非辐射复合被显著抑制;最终太阳电池的开路电压达到1.17 V,光电转换效率达到21.42%,在氮气环境下储存1000 h后,未封装的太阳电池仍能保持初始效率的96%,稳定性显著提高。

顶部籽晶溶液法生长碳化硅单晶及其关键问题研究进展

因其优异的物理特性,第三代半导体碳化硅(SiC)材料在高温、高频、高压及大功率电力电子器件和射频微波器件领域具有非常明确的应用前景。受限于自身技术特点,利用传统的物理气相输运(PVT)法制备SiC晶体仍面临许多技术挑战,难以满足当前电子器件对大尺寸、高质量和低成本SiC单晶衬底的迫切需求。顶部籽晶溶液(TSSG)法可以在更低的温度和近热力学平衡条件下实现SiC晶体制备,能够显著弥补PVT法的不足,正逐渐成为极具竞争力的低成本、高质量SiC单晶衬底创新技术之一。本文首先阐述了TSSG法生长SiC晶体的理论依据,并给出了各工艺环节要点,然后归纳了TSSG法生长SiC晶体的主要技术优势,梳理了国内外在该技术领域的研究现状并重点讨论了TSSG法生长SiC晶体关键技术问题、产生机制,以及可能的解决途径等。最后,对TSSG法生长SiC晶体的未来发展做出展望。

Characterization and chemical surface texturization of bulk ZnTe crystals grown by temperature gradient solution growth

Using tellurium as a solvent, we grew ZnT e ingots of 30 mm in diameter and 70 mm in length by a temperature gradient solution growth method. Hall tests conducted at 300 K indicated that the as-grown ZnT e exhibits p-type conductivity, with a carrier concentration of approximately 1014 cm-3, a mobility of approximately 300 cm2·V-1·s-1, and a resistivity of approximately 102 ·cm. A simple and effective method was proposed for chemical surface texturization of ZnT e using an HF:H2O2:H2O etchant. Textures with the sizes of approximately 1 μm were produced on {100}, {110}, and {111}Zn surfaces after etching. The etchant is also very promising in crystal characterization because of its strong anisotropic character and Te-phase selectivity.

Recent Developments in Functional Crystals in China

Functional crystals are the basic materials for the development of modern science and technology and are playing key roles in the modern information era. In this paper, we review functional crystals in China, including research history, significant achievements, and important applications by highlighting the most recent progress in research. Challenges for the development of functional materials are discussed and possible directions for development are proposed by focusing on potential strengths of these materials.

Modification of the spontaneous emission of quantum dots near the surface of a three-dimensional colloidal photonic crystal

This paper demonstrates experimentally and numerically that a significant modification of spontaneous emission rate can be achieved near the surface of a three-dimensional photonic crystal.In experiments,semiconductor core-shell quantum dots are intentionally confined in a thin polymer film on which a three-dimensional colloidal photonic crystal is fabricated.The spontaneous emission rate of quantum dots is characterised by conventional and time-resolved photoluminescence (PL) measurements.The modification of the spontaneous emission rate,which is reflected in the change of spectral shape and PL lifetime,is clearly observed.While an obvious increase in the PL lifetime is found at most wavelengths in the band gap,a significant reduction in the PL lifetime by one order of magnitude is observed at the short-wavelength band edge.Numerical simulation reveals a periodic modulation of spontaneous emission rate with decreasing modulation strength when an emitter is moved away from the surface of the photonic crystal.It is supported by the fact that the modification of spontaneous emission rate is not pronounced for quantum dots distributed in a thick polymer film where both enhancement and suppression are present simultaneously.This finding provides a simple and effective way for improving the performance of light emitting devices.

Synthesis, Crystal Structure and Property of Cu Pb_2(OH)_2Cl_3

A new copper(I)-lead(II) oxyhalide, Cu Pb2(OH)2Cl3, has been prepared by hydrothermal reaction and structurally characterized by single-crystal X-ray analysis. The compound crystallizes in tetragonal, space group I4(1)/acd with a = b = 13.77(1), c = 15.38(1) , V = 2916.2(2), Z = 4, Mr = 618.29, Dc = 5.633 g/cm3, μ = 49.97(2) mm-1, F(000) = 4192, the final R = 0.0204 and w R = 0.0452 for 757 observed reflections with I > 2σ(I). The structure of Cu Pb2(OH)2Cl3 contains one-dimensional helical chains built by Cu Cl4 tetrahedra with corner-sharing along the c-axis, in which the Pb2+ and OH- ions are located at the voids between chains. Optical reflectance spectrum measurements indicate that it is a semiconductor with a band-gap of 3.23 e V.

p-Type CaFe_2O_4 semiconductor nanorods controllably synthesized by molten salt method

Pure phase, regular shape and well crystallized nanorods of p-type semiconductor CaFe_2O_4 have been fabricated for the first time by a facile molten salt assisted method, as confirmed by XRD, TEM, SEM and HRTEM. UV-vis diffuse reflectance spectra and Mott–Schottky plots show that the band structure of the CaFe_2O_4 nanorods is narrower than that of the CaFe_2O_4 nanoparticles synthesized by conventional method. The enhancement of the visible-light absorption is due to narrowness of the band gap in CaFe_2O_4 nanorods. The appropriate ratio between the molten salt and the CaFe_2O_4 precursors plays an important role in inhibiting the growth of the crystals along the(201) plane to give the desired nanorod morphology. This work not only demonstrates that highly pure p-type CaFe_2O_4 semiconductor with tunable band structure and morphology could be obtained using the molten salt strategy, but also affirms that the bandgap of a semiconductor may be tunable by monitoring the growth of a particular crystal plane.Furthermore, the facile eutectic molten salt method developed in this work may be further extended to fabricate some other semiconductor nanomaterials with a diversity of morphologies.

Al-induced Lateral Crystallization of Amorphous Si Thin Films by Microwave Annealing

Al-induced lateral crystallization of amorphous silicon thin films by microwave annealing is investigated.The crystallized Si films are examined by optical microscopy,Raman spectroscopy,transmission electron microscopy and transmission electron diffraction micrography.After microwave annealing at 480 ℃ for 50 min,the amorphous Si is completely crystallized with large grains of main (111) orientation.The rate of lateral crystallization is 0.04μm/min.This process,labeled MILC-MA,not only lowers the temperature but also reduces the time of crystallization.The crystallization mechanism during microwave annealing and the electrical properties of polycrystalline Si thin films are analyzed. This MILC-MA process has potential applications in large area electronics.

Transport Properties of AgInSe₂Crystals

AgInSe2 crystals were grown by Bridgman technique. The crystals were identified structurally by X-ray diffraction technique. Measurements of electrical conductivity and Hall effect were performed in the temperature range (138 K - 434 K) and (220 K - 488 K) for thermoelectric power measurements. From these measurements, many physical parameters were determined. The energy gap was calculated to be 1.24 eV. The conductivity type was found to be n-type. Crystallite size (D) of the obtained AgInSe2 crystals was calculated to be 70 nm. The lattice parameters for the prepared crystals were a = 6.0938 ? and c = 11.7775 ?.