量子级联波长上转换系统红外响应特性研究

通过对波长上转换红外探测过程的分步测试和理论计算,对量子级联波长上转换器件与系统的红外响应特性进行了深入的研究。结果表明:量子级联波长上转换红外探测器件可以在较低的本底发光下实现较强的红外响应。上转换器件的响应度在平带偏压附近迅速增加,且红外光转换为上转换器件电流的线性度良好。对于波长上转换器件的近红外发光过程,文中应用ABC模型,获得了与测试结果非常一致的系统响应电流与电流转换效率,并合理地解释了波长上转换红外探测系统的非线性响应特征。     

甚长波量子阱红外探测器中的双激发态工作机理

通过对甚长波量子阱红外探测器的变温变偏压光谱实验,发现了光电流谱峰值响应波长与半高宽随偏置电压和温度变化均会发生变化,尤其以小偏压下峰值移动明显.结合器件能带结构计算的结果,提出了甚长波量子阱红外探测器中双激发态工作模型,并阐明了其中束缚态-准束缚态跃迁模式中准束缚态的物理特性,包括隧穿特性和热离化特性,以及不同工作条件下这两种物理过程在形成光电流时的主导性.同时,验证了甚长波量子阱红外探测器件的第一激发态随外界工作条件的变化会呈现出准束缚到准连续的变化特性.最后,揭示了在甚长波量子阱红外探测器工作中束缚态-准束缚态跃迁工作模式对于降低器件暗电流、提升器件工作温度、提高器件探测率的有效性.     

局域光场增强的量子阱红外探测器（特邀）

量子阱红外探测器是继碲镉汞红外探测器之后又一重要的可以在中、长波段和甚长波段工作的红外探测器件。它在长波红外探测、多色探测及其焦平面技术方面表现出比碲镉汞红外探测器更具特色的优势,对量子阱红外探测器的研究将在很大程度上推动我国红外探测器技术的发展。这一探测器的突出优势是其材料均匀性好,制备技术成熟。但是由于量子效率偏低,且无法直接吸收垂直入射红外光,所以需要针对不同的红外探测波段,设计和制备各类光栅或微腔结构来进行光耦合及局域光场增强以有效提升探测器性能。如何更有效提升量子阱红外探测器的光耦合效率,降低暗电流,提高器件工作温度是仍然是目前研究的重点。文中着重介绍和总结了近5年来研究的局域光场增强的新型量子阱红外探测器,从提高探测器光耦合效率、降低器件暗电流和提高工作温度等方面重点讨论各种量子阱红外探测器的新结构和新机理,同时展望了这一探测器的未来发展方向。     

可见光通信感知一体化芯片及关键技术

通信感知一体化是6G关键技术之一。氮化镓量子阱二极管的发射光谱和光探测谱存在重叠区,量子阱二极管光探测器能够吸收具有相同量子阱结构的光发射器件发出的短波长光子,生成光电流。该文基于该物理现象,研制同质集成光发射光接收器件的氮化镓光电子芯片,由于单个量子阱二极管芯片器件自身发光干扰导致感知外界光信号弱,但是收发分离芯片又存在效率低、紧凑性弱、鲁棒性差等问题,将具有相同量子阱结构的量子阱二极管器件制备在同一块芯片上,分别作为发光和接收器件,构建自由空间逆向光通信系统,探索可见光通信感知一体化芯片及关键技术。     

GaAs/AlGaAs多量子阱红外探测器外延材料PL谱研究

结合薛定谔方程和泊松方程,模拟计算得到GaAs/AlGaAs多量子阱红外探测器外延材料能带图,并对该材料进行光致荧光谱(PL)测量.结合理论计算,由材料吸收峰位置得到势垒高度以及势阱基态位置,采用传输矩阵法得到价带与导带基态能量,并由此推算出相应的红外探测响应波长.以傅里叶变换红外光谱仪对GaAs/AlGaAs多量子阱红外探测器器件进行光谱测量,测量结果表明,所采用的计算方法得出的理论结果与器件的光电流谱吻合较好,利用光荧光谱对外延材料进行测量,可以在器件工艺前,快速确定器件的探测波长,从而更加有效地开展器件的研究.     

用PCS提高QWIP-LED光提取效率的仿真研究

量子阱红外探测器发光二极管(Quantum Well Infrared Photodetector Light Emitting Diode,QWIP-LED)是一种新型红外上转换器件,配合电荷耦合器件(Charge Coupled Device,CCD)能够实现中波红外成像探测。与常规红外成像器件相比,QWIP-LED最大的优势在于成本低。然而,QWIP-LED较低的光提取效率(约2%)严重制约了该器件的广泛应用。以提高QWIP-LED的光提取效率为目标,在LED表面引入二维光子晶体薄膜(Photonic Crystal Slab,PCS)结构,采用时域有限差分法(Finite-Difference Time-Domain,FDTD)计算了其对光提取效率的改善效果,并对PCS的结构参数进行了优化。仿真结果表明,优化的PCS可以使QWIP-LED的光提取效率提高2.32倍。最后,基于PCS的能带理论以及等效介质理论,对PCS结构提高器件光提取效率的机理进行了分析。     

半导体量子点集成有机发光二极管的光光转换器进展

介绍的光光转换器是新型红外光-可见光转换器件,红外光产生的光生载流子直接注入有机发光二极管产生可见光。以半导体红外探测与有机发光器件单片集成的光光转换器,直接实现了红外光到可见光的集成转换,在红外凝视技术中有极大的应用潜力。综述了无机红外探测与有机发光的光-光转换器的研究进展。     

基于温度变化的量子阱红外探测器研究

量子阱红外探测器受到温度、压强等多种因素的影响,本文主要从温度方面进行了研究.在文献[2]的基础上,进一步推导了超晶格中热应变与温度的关系;结合量子阱红外探测器的能级公式以及波长与能级差的关系式,定量地分析了温度变化对量子阱红外探测器探测峰值波长的影响.     

移去电子阻挡层对双蓝光波长LED性能的影响

采用数值分析方法进行模拟分析In Ga N/Ga N混合多量子阱中移去p-Al Ga N电子阻挡层对Ga N基双蓝光波长发光二极管(LED)性能的影响。结果发现,与传统的具有p-Al Ga N电子阻挡层的双蓝光波长LED相比,移去电子阻挡层能有效地改善电子和空穴在混合多量子阱活性层中的分布均匀性,实现电子空穴在各个量子阱中的均衡辐射。在小电流驱动时,移去电子阻挡层器件的发光功率要明显优于具有电子阻挡层的器件;而在大电流驱动时,电子阻挡层能有效地减少电子溢流,改善器件的发光效率。     

GaN基绿光LED材料蓝带发光对器件特性的影响

分析比较了在不同外延生长条件下GaN基高In组分绿光LED材料室温和低温10K下光致发光谱中蓝带发光峰,研究了外延结构中p型层蓝带峰发光特性对材料晶体质量和器件电光转换效率的影响.结果表明:通过优化p型层的外延生长条件,可有效降低和消除其蓝带发光峰较之多量子阱主峰的相对强度,有利于提高LED器件特别是高In组分绿光LED器件在同等注入电流条件下的发光功率.     

红外上转换油墨光转换特性共焦光学检测

研制了一种红外上转换材料的微型共焦光学检测器并提出改进措施,用改进前后的共焦光学系统对掺杂有Yb和Er的氟氧化物复合红外上转换材料油墨进行检测,分析了改进后的优点,讨论了离焦量对样品激发光能的影响,给出了不同质量混合比油墨的检测可靠性数据。对其在隐形条码方面的应用进行了初步研究。     

Spatial modulation characteristics of single-photon frequency up-conversion systems pumped by Gaussian laser beam

In a Gaussian laser beam pumped single-photon frequency up-conversion system, the spatial distribution of the conversion efficiency is calculated, which strongly depends on the intensity distribution of the pump beam and leads to a spatial modulation of the output single photons. As a result, by simply varying the Gaussian pump beam intensity and the beam size, the converted photons could be modulated spatially and exhibit a programmable distribution. This will be meaningful for the researches on quantum communication and quantum manipulation based on frequency up-conversion system.     

Highly Efficient Top-Emitting Infrared-to-Visible Up-Conversion Device Enabled by Microcavity Effect

Infrared (IR)-to-visible up-conversion device allows a low-cost, pixel-free IR imaging over the conventional expensive compound semiconductor-based IR image sensors. However, the external quantum efficiency has been low due to the integration of an IR photodetector and a light-emitting diode (LED). Herein, by inducing a strong micro-cavity effect, a highly efficient top-emitting IR-to-visible up-conversion device is demonstrated where PbS quantum dots IR-absorbing layer is integrated with a phosphorescent organic LED. By optimizing the optical cavity length between indium tin oxide (ITO)/thin Ag/ITO anode and semi-transparent Mg:Ag top cathode, the up-conversion device yields 15.7% of photon-to-photon conversion efficiency from the top-emission. The high efficiency can be achieved under a low IR transmission through the semi-reflective anode. Finally, pixel-free IR imaging is demonstrated using the up-conversion device, boosting the effect of micro-cavity on the brightness and the contrast of an IR image.     

Limitations and optimization of (near) two-photon-resonant frequency up-converters

This paper considers the limitations of (near) two-photon-resonant frequency up-conversion due to quadratic Kerr effect, two-photon absorption, and Raman scattering. These processes, which are intimately tied to the four-wave mixing process, limit the efficiency and/or the pulse length due to breaking of phase-matching, attenuation, and (de)focusing. General expressions are derived for the limits on the efficiency and the pulse length resulting from these processes. The results of the theoretical analysis are applied to three examples of great practical interest; i.e., tripling of the CO2laser in liquid CO, mixing of IR photons using vibrational nonlinearities, and IR image up-conversion in alkali metal vapors. Several new, important properties of these systems are derived.     

Effect of localized tail states in InGaN on the efficiency droop in GaN light-emitting diodes with increasing current density

The mechanism of the internal quantum efficiency droop in InGaN/GaN structures with multiple quantum wells at current densities of up to 40 A cm^?2 in high-power light-emitting diodes is analyzed. It is shown that there exists a correlation between the efficiency droop and the broadening of the high-energy edge of the emission spectrum with increasing current density. It is also demonstrated that the efficiency is a spectrum-dependent quantity and the emission of higher energy photons starts to decrease at higher current densities. The effect of tunneling and thermally activated mechanisms of thermalization of carriers captured into shallow band-tail states in the energy gap of InGaN on the efficiency and the emission spectrum??s shape is considered. Analysis of the results obtained suggests that the efficiency droop occurs at high current densities because of the relative rise in the contribution from nonradiative recombination via defect states as a result of the increasing occupancy of deep band-tail states in InGaN. It is shown that power efficiency close to the theoretical limit can be obtained in the case of low-voltage tunnel injection into localized band-tail states in the InGaN active region.     

（英）组分过冲对InP基InAlAs递变缓冲层的影响

通过在InP基InxAl1-xAs 递变缓冲层上生长In0.78Ga0.22As/In0.78Al0.22As量子阱和In0.84Ga0.16As探测器结构,研究了缓冲层中组分过冲对材料特性的影响。原子力显微镜结果表明,在InAlAs缓冲层中采用组分过冲可以使量子阱及探测器样品表面粗糙度都得到降低。对于相对较薄的量子阱结构,X射线衍射倒易空间扫描图和光致发光谱的测量表明,使用组分过冲可以增加弛豫度、减小剩余应力并改善光学性质。而对于较厚的探测器结构,X射线衍射和光致发光谱测试发现使用组分过冲后的材料性质没有明显的变化。量子阱和探测器结构的这些不同特性需要在器件设计应用中加以考虑。     

A multi-color CdS/ZnSe quantum well photodetector for mid- and long-wavelength infrared detection

In this paper, we report on the design and characterization of a quantum well based infrared photodetectors covering simultaneously infrared radiation within mid- and long-infrared spectral regions. The proposed infrared photodetectors rely on intersubband transitions in asymmetric ZnSe/CdS double quantum wells. The three-energy-level and the wavelengths of the intersubband transitions in the asymmetric double quantum wells are obtained by solving the Schrödinger and Poisson equations self consistently, the influence of the right well width on the absorption coefficient is studied. The peak positions of intersubband absorption coefficients in the structure are found at 3.31, 4.4 and 13.5 µm for a 1 nm right well width while the absorption peak positions are located at 3.33, 6.43 and 6.95 µm for a 1.4 nm right well thickness. Then, the electro-optic performances of the infrared photodetector are evaluated; the dark current dependence with the applied voltage and temperature is discussed. This work demonstrates the possibility of detection of widely separated wavelength bands using intersubband transitions in quantum wells with a low dark current.     

Threshold characteristics of an IR laser based on deep InAsSb/AlSb quantum well

The basic threshold characteristics of a semiconductor IR laser based on a heterostructure with deep InAs_0.84Sb_0.16/AlSb quantum wells (QWs) have been studied. The threshold carrier densities and threshold current densities of radiative and Auger recombination (AR) were found. It is shown that at certain QW parameters the AR rate is strongly (by several orders of magnitude) suppressed. In this case, the emission wavelength falls within the interval 2–3.5 μm, which corresponds to the mid-IR spectral range. The internal quantum efficiency of emission at the lasing threshold was calculated and its dependence on the QW width within the AR suppression range was demonstrated. The laser structure was optimized with respect to the number of QWs.     

Sub-bandgap photon harvesting for organic solar cells via integrating up-conversion nanophosphors

Lanthanide-doped up-conversion nanophosphors were employed as up-conversion converters (UC-converters) combined with organic solar cells (OSCs). The optical properties of the external up-conversion layers were investigated, and the optimized layers were laminated with OSCs. Strong photocurrents were observed when OSCs with an UC converter were illuminated by a NIR laser. An improvement of photocurrent and efficiency were also observed under AM 1.5 G sun irradiation. Our investigations show a proof-of-concept that organic solar cells could utilize sub-bandgap photons via integrating up-conversion nanophosphors, which provide us a promising approach to exceed the efficiency limit of single junction organic solar cells.     

Photoresponse of (In,Ga)N-GaN multiple-quantum-well structures in the visible and UVA ranges

Characterization and analysis of photoresponse in p-n diodes with embedded (In,Ga)N-GaN multiple-quantum-well (MQW) structures are reported. Their dependence on the number of wells and In composition are considered. The influence of device structure on electric fields in the active region and on device responsivity has also been studied. Theoretical considerations as well as photocapacitance and photocurrent measurements show that the position of quantum wells (QWs), either in the quasi-neutral region or in the space charge region, is a critical factor in the collection efficiency. Hence, device photoresponse is not proportional to the number of QWs in photovoltaic mode. Present p-MQW-n devices show a promising performance as UVA and visible photodetectors, with detectivities, D/sup */, higher than 1.2/spl times/10/sup 12/ cm/spl middot/Hz/sup 1/2//spl middot/W/sup -1/ and rejection ratios higher than 10/sup 3/.