皮秒脉冲激光照射下碲镉汞光伏红外探测器的负光伏响应新现象

利用皮秒脉冲激光激发碲镉汞线列探测器上的光敏元,发现光伏响应表现为在最初大约15 ns范围内首先形成一个明显的负光生电压的响应谷,之后才演变为正的光伏响应峰.改变入射激光脉冲的光子能量发现,无论是光子能量大于禁带宽度的单光子吸收跃迁还是小于禁带宽度的双光子吸收跃迁,器件的光伏响应随时间的演变均表现出类似的规律.用光阑对探测器的受光面积进行限制将使负的光生电压减弱并接近消失.结合探测器线列的电极分布构形,将负光伏响应指认为p-电极的肖特基接触所致.利用该方法有可能对p-电极是否形成欧姆接触进行判定,其灵敏度应远高于常规的电学测量方法.     

皮秒脉冲激光照射下碲镉汞光伏红外探测器的负光伏响应新现象

利用皮秒脉冲激光激发碲镉汞线列探测器上的光敏元,发现光伏响应表现为在最初大约15 ns范围内首先形成一个明显的负光生电压的响应谷,之后才演变为正的光伏响应峰.改变入射激光脉冲的光子能量发现,无论是光子能量大于禁带宽度的单光子吸收跃迁还是小于禁带宽度的双光子吸收跃迁,器件的光伏响应随时间的演变均表现出类似的规律.用光阑对探测器的受光面积进行限制将使负的光生电压减弱并接近消失.结合探测器线列的电极分布构形,将负光伏响应指认为p电极的肖特基接触所致.利用该方法有可能对p电极是否形成欧姆接触进行判定,其灵敏度应远高于常规的电学测量方法.     

供红外应用的高级碲镉汞光电二极管

本文讨论美国霍尼威尔公司新发展的四种碲镉汞光电二极管:1.2.06微米碲镉汞雪崩光电二极管;2.10.6微米碲镉汞光电二极管;3.R_0A乘积为0.7欧-厘米~2的高D~＊碲镉汞光电二极管(10.6微米);4.半导体致冷10.6微米光混频器。2.06微米雪崩光电二极管是为Q开关的掺钬氟化锂钇(Ho:YLF)激光器发展的。这种器件的雪崩增益为9～36。10.6微米光电二极管的平均量子效率为30％。制备了单元为250微米×250微米的五元线列,其单     

碲镉汞雪崩光电二极管在激光雷达上的应用

首先简要介绍激光雷达的主要军事应用、激光雷达对接收器的性能需求及激光雷达接收器的现状,综述碲镉汞材料特点、碲镉汞雪崩光电二极管探测器特点,与现有激光雷达接收器相比碲镉汞雪崩光电二极管作为激光雷达接收器的优势及制备技术;综述国外碲镉汞雪崩光电二极管用于激光雷达接收器的发展现状;最后分析我国发展用于激光雷达接收器的碲镉汞雪崩光电二极管可行性。     

瞬态光响应法测试中波碲镉汞器件少子寿命的新方法

在测试中波碲镉汞光伏器件的瞬态响应时,当激光光斑照射器件表面位置距离光敏面较远时,器件表现为特殊的双峰脉冲响应现象,分析表明出现这种异常双脉冲现象的原因是光敏区内的少子漂移和光敏区外侧向收集的少子扩散有时间上的差异。通过对器件施加反向偏压,脉冲响应随反向偏压的增大由双峰变成单峰的实验结果,验证了少子侧向收集是导致器件形成双峰的主要原因。对第二个峰拟合得到p区的少数载流子寿命。将瞬态响应获得的少子寿命与该p型中波碲镉汞材料的理论计算和光电导衰退法得到的少子寿命相对比,发现三种方式得到的少子寿命随温度的变化趋势基本一致,这说明了可以通过瞬态光响应得到中波碲镉汞器件的少子寿命。     

可见近红外波段碲镉汞材料光学常数测定与宽谱增透设计

将碲镉汞(Hg_(1-x)Cd_xTe)红外焦平面器件衬底去除后,其响应波段可拓展到可见光波段,在高光谱成像应用中可显著减小系统的尺寸和重量,对光电探测系统的小型化和微型化具有重要实用价值.而明确碲镉汞材料在可见近红外波段的光学常数,对碲镉汞器件在这一响应波段的性能研究具有重要意义.分别测量了不同组分碲镉汞材料的椭圆偏振光谱,拟合得到了其在400~1 600 nm波段范围内的光学常数值,并利用反射光谱对获得的光学常数进行了验证.采用这些碲镉汞外延材料光学常数测量值,并选用Zn S和YF3分别作为高低折射率的增透膜材料,针对不同响应波段的背入射可见近红外碲镉汞焦平面器件,设计了不同的宽谱增透膜系,响应波段范围内的平均透过率高于90%.     

碲镉汞雪崩光电二极管发展现状

碲镉汞雪崩光电二极管探测器具有高增益、高带宽和低噪声因数的显著特点,具有下一代焦平面探测器阵列的多功能、主动/被动探测、双波段和高灵敏度等理想特性,在低光通量探测、超光谱、二维/三维成像方面显示出强大的应用潜力。本文简要介绍了碲镉汞雪崩光电二极管主要器件结构、特点及应用现状。     

用电子束感生电压方法研究碲镉汞光二极管

本文报道用电子束感生电压方法观察碲镉汞光二极管光敏区响应分布,直接显示p-n结耗尽区位置的实验结果。在p型碲镉汞上制成了肖特基势垒二极管。用它测量了碲镉汞的少数载流子扩散长度。     

Al-Si肖特基势垒诱导的光整流与双光子响应机制

通过观测硅光电二极管的双光子响应和Al/Si肖特基势垒处的光生电压的各向异性,从实验和理论两个方面证实了肖特基势垒所产生的内建电场在硅光电探测器中诱发光整流现象,从而推论硅光电二极管的双光子响应机制中必然存在相位失配的倍频吸收.如果内建电场足够强,倍频吸收将成为双光子响应的主要机制.这与传统的认为双光子响应就是双光子吸收的观点不同.     

Al-Si肖特基势垒诱导的光整流与双光子响应机制

通过观测硅光电二极管的双光子响应和Al/Si肖特基势垒处的光生电压的各向异性,从实验和理论两个方面证实了肖特基势垒所产生的内建电场在硅光电探测器中诱发光整流现象,从而推论硅光电二极管的双光子响应机制中必然存在相位失配的倍频吸收.如果内建电场足够强,倍频吸收将成为双光子响应的主要机制.这与传统的认为双光子响应就是双光子吸收的观点不同.     

Two‐Photon Absorption Cross Sections of Dithienothiophene‐Based Molecules

We performed nonlinear transmission measurements and quantum‐chemical calculations on dithienothiophene (DTT)‐based molecules to gain insight into the effect of acceptor and donor groups on two‐photon absorption (TPA) properties. The TPA intensity showed dispersion characteristics of the single‐photon absorption spectrum. When the molecules included an asymmetric donor‐acceptor pair, the single‐ and two‐photon absorption maximum wavelengths were red‐shifted more than when the molecules had a symmetric donor‐donor structure. We interpreted this result as indicating that the S₂ state plays the dominating role in the absorption process of molecules with a symmetric structure. The experimental TPA δ values at the absorption peak wavelength showed a dependence on the structural variations. We found the self‐consistent force‐field theory and Hartree‐Fock Hamiltonian with single configuration interaction formalism to be valid for evaluating TPA δ. Although the quantum‐chemical calculations slightly underestimated the experimental δ values obtained from nonlinear transmission measurements, they reasonably predicted the dependence of the δ value on the structural variations. We confirmed the role of molecular symmetry by observing that donor‐donor substituted structure gave the highest experimental and theoretical TPA δ values and that the donor‐acceptor substituted structure showed a greater red‐shift in the TPA absorption maximum wavelength. Overall, the theoretical δ values of DTT‐based molecules were in the order of 10^??46 cm⁴ · s · photon^?1 and are higher than that of AF‐50 by nearly two orders of magnitude.     

基于硅雪崩光电二极管的双光子吸收实验

研究了硅雪崩光电二极管(APD)对光通信波段近红外光子在不同频率、强度,以及APD 不同偏压下的双光子吸收效应(TPA)。通过实验详细测量了光频率从186.3 THz 到196.1 THz 变化时APD的TPA 效率,结果表明:随着入射光频率的不断增加,TPA 效率呈现出先增大、后减小的规律,并且在190.5 THz 附近达到最优效率。此外,在实验中观察到,随着入射光强的增大,TPA 效率也呈现出先增大、后减小的现象(此实验中的峰值光强度约10 mW)。     

红外焦平面阵列非线性响应的分析和计算

分析了导致红外焦平面阵列响应非线性的各种因素;并以HgCdTe红外焦平面阵列为例,以量子效率与入射光子波长的相关性为基础,计算了在准理想条件下探测器响应的非线性量;结合非均匀性校正,计算了在给定区间定标后的非线性大小;还对实际应用中一例非线性响应所导致的焦平面阵列的非均匀性剩余误差进行了解释。     

Hyperbranched Polyglycerol‐Doped Mesoporous Silica Nanoparticles for One‐ and Two‐Photon Activated Photodynamic Therapy

Two‐photon activated photodynamic therapy (TPA‐PDT) is a recently developed technique that shows a potential for medical application. In contrast to traditional one‐photon activated PDT, TPA‐PDT can increase the treatment depth and decrease the damage to healthy tissue by using a near‐infrared two‐photon laser. However, this technique also suffers from the fact that approved photosensitive drugs have a low two‐photon absorption cross section. In this study, it is demonstrate that doped polyglycerol mesoporous silica nanoparticles can carry a photosensitizer, Rose bengal, and can be applied in one‐ and two‐photon PDT. TPA dye‐doped mesoporous silica nanoparticles have been synthesized using a surfactant‐free route, which can be considered a TPA‐PDT platform after loading normal photosensitive drugs. The doped TPA dyes in the silica nanoparticles can transfer energy to the loading drugs via an intraparticle fluorescence resonance energy transfer (FRET) mechanism. The fluorescence lifetime and confocal laser scanning microscopy (CLSM) images obtained under different conditions demonstrated a FRET effect through both one‐ and two‐photon activated modes. The results of cytotoxicity experiments proved that this TPA‐PDT system could induce cellular apoptosis under one‐ or two‐photon irradiation. This system in principle extends the application range of TPA‐PDT.     

Time-resolved nonlinear absorption modulation in GaAs/AlGaAsmultiple-quantum-well waveguides at 1.06 μm

Time-resolved nonlinear absorption modulation due to two-photon absorption (TPA) and free carrier absorption (FCA) was demonstrated in GaAs/AlGaAs waveguides at 1.06 μm. For a peak input intensity of 4.5×10¹¹ Wm^-2, there was a maximum absorption modulation of 35%. This was caused by TPA, so that the recovery time was limited by the laser pulsewidth alone. At a peak input intensity of 1.5×10¹² Wm^-2, a 65% absorption modulation was observed. This consisted of two components: an instantaneous effect due to TPA and also a slower component, attributed to FCA, whose recovery time was limited by the carrier lifetime. A theoretical model was also derived which provided a good fit to the experimental data     

新型亚波长陷光结构HgCdTe红外探测器研究进展

综述了近几年来亚波长陷光结构Hg Cd Te红外探测器研究进展.系统介绍了一种结合有限元方法与时域有限差分方法对红外探测器的"光""电"特性进行联合模拟和设计方法,以及基于这种新的数值模拟方法对亚波长人工微结构Hg Cd Te红外探测器的模拟和分析结果.理论分析和实验研制数据均显示这种新型亚波长人工微结构结构具有很好的陷光特性,在提高长波红外探测器性能方面具有潜在应用前景.     

MBE HgCdTe for HDVIP Devices: Horizontal Integration in the US HgCdTe FPA Industry

Molecular beam epitaxy (MBE) growth of HgCdTe offers the possibility of fabricating multilayer device structures with an almost unlimited choice of infrared sensor designs for focal-plane array (FPA) fabrication. HgCdTe offers two major advantages that explain its dominance in the infrared photon detector marketplace. The thermal generation rate per unit volume of the material is lower and the quantum efficiency for photon absorption in the infrared is higher in HgCdTe than in any competing material—it yields devices with quantum efficiencies as high as 0.99. Recently, EPIR Technologies and DRS Infrared Technologies agreed to collaborate and examine: (i) the feasibility of employing MBE HgCdTe in the fabrication of high-density vertically interconnected photodiodes (HDVIPs), which are usually fabricated with liquid-phase epitaxy material, and (ii) the potential benefits of horizontal integration, with EPIR supplying the MBE materials to DRS for device and array fabrication. The team designed and developed passivation–absorber–passivation structures that are heavily used by DRS. This paper provides an overview of the characteristics of HDVIP devices and arrays fabricated from MBE HgCdTe and the anticipated advantages of horizontal integration in the industry. Material growth, device fabrication, and test results are presented.     

Detailed study of above bandgap optical absorption in HgCdTe

HgCdTe remains the material of choice for high-performance infrared (IR) detectors due to its tunable direct bandgap energy corresponding to the IR spectral region, and the advancement of HgCdTe materials growth and processing technologies. Accurate knowledge of the HgCdTe optical absorption coefficient is important for IR detector design, layer screening, and device analysis. The spectral response for IR detectors is dependent on optical absorption above the bandgap energy, where much of the study of absorption coefficient in HgCdTe has focused on the bandtail region. In this work, the optical absorption coefficient was studied by theoretical bandstructure calculations and experimental measurements on HgCdTe layers using techniques of IR spectroscopic ellipsometry and IR transmission. The theoretical and experimental results suggest that the absorption coefficient between 600 cm⁻¹ and 5,000 cm⁻¹ is related to energy relative to bandgap with a fractional exponent between 0.6 and 1, rather than the previously used expressions relating to a parabolic or hyperbolic bandstructure. The fitting parameters for Hg_1-xCd_xTe with x=0.22–0.60 are presented to develop a model for the optical absorption coefficient spectra. The calculated detector spectral response using the new and previously reported absorption coefficient models suggests that next generation IR detectors employing multilayer structures with graded compositional profiles will likely benefit from this new model.     

飞秒激光双光子微细结构的制备

基于双光子吸收引发的光聚合局限在紧密聚焦的焦点区域的原理,建立了飞秒激光三维微细加工系统;结合高斯光束的强度分布函数,推导了横向与轴向分辨率的表达式。在ORMOCER材料内实现了双光子光聚合,最高加工精度达到0.7μm。研究表明,加工线宽随功率增加而增加,随加工速度增加而减小;确定了波束腰为0.425μm,双光子吸收截面为2×10-54cm4.s。采用双光子光聚合技术,加工了齿宽5μm的实体微型齿轮,制备三维木堆型光子晶体结构,分辨率为1.1μm,杆间距和层间距均为5μm,实现了飞秒双光子光子晶体结构的制备。     

Application of urbach rule optical absorption to composition measurement of Cd1−yZnyTe

The optical absorption coefficient of Cd_1−yZn_y Te near the fundamental band edge was measured at room temperature using transmission spectroscopy. Like in other II–VI semiconductors, it was found that the absorption coefficient exhibits an exponential dependence on incident photon energy according to Urbach’s rule. It was also found that the exponential parameters depend on composition, y, of Cd_1−y Zn_yTe. A technique is described for determining the composition of Cd_1−y Zn_yTe from optical transmission spectroscopy. This technique has been implemented in the manufacturing of Cd_1−yZn_yTe substrates for lattice matched epitaxial growth of HgCdTe.