高工作温度长波红外量子级联探测器关键技术研究

Quantum cascade detectors (QCDs) operate in photovoltaic mode with no dark current noise. Compared with commercially available HgCdTe photodetectors and quantum well infrared photodetectors (QWIP), QCD has the potential advantage of high operation temperature, but its responsivity is generally lower than MCT and QWIP by 1 to 2 orders of magnitude, which has become the limited factor for QCD to be applied in many fields such as mid-infrared laser spectroscopy based chemical sensors. . This proposed research is in the area of long-wavelength IR QCD with high operation temperature. The main focus of the proposed research is a new design of the band diagram for improved performances, especially for improved responsivity. A novel active region with diagonal transitions between bound to miniband for high escape probability and high absorption transition probability and a local strain compensated superlattice for blocking thermal noise currents in the cascade are suggested in this proposed research. Novel device structures are also suggested including porous cap for light trapping and multi-section parallel structure for multiplication of the photocurrent from individual sections. The overall goal of the proposed research is to improve the responsivity of traditional QCDs by an order of magnitude. In particular, long long-wave infrared QCD devices responding at 8-20um with the responsivities no less than 80mA/W at 77K and the operation temperature no less than 200K will be accomplished by this proposed research. A long-term goal is to develop high-performance QCL-QCD monolithic integrated or board-level combined system for highly sensitive infrared detection and monitoring.

量子级联探测器（QCD）具有无暗电流噪声、背景限温度高等优点，特别在长波、甚长波范围内具有高温工作的潜在优势，但是其响应率指标却较商品化的碲镉汞和QWIP低1～2个量级，这成为QCD进入应用领域的最后一步障碍。本项目针对标准QCD设计响应率低的科学问题，提出了新的束缚态至微带斜跃迁的有源区设计，以提高电子抽取效率并保持高的吸收跃迁几率；在弛豫区引入局部应变补偿的势垒，以提高器件电阻从而获得高的探测率。在优化能带设计的同时，开展新型器件工艺的研究，包括多孔陷光结构及多节并联结构。项目总体目标是将当前的QCD响应率提高一个量级，具体指标是研制8-20um的长波红外QCD器件，77K响应率不低于80mA/W，工作温度不低于200K，更力求实现该波段QCD的近室温工作。长远目标是研发高性能QCL、QCD单片集成或板级组合式高灵敏红外检测、监测系统。

半导体体红外光子探测器具有高灵敏响应快速的有点，非常适合作为基于中红外级联激光器的高灵敏化学传感系统的接收器，与目前常用MCT探测器相比，量子级联探测器（QCD）的响应谱很窄，背景光子噪声更小，但是早期的QCD响应率极低，液氮下只有10mA/W左右，阻碍其应用。响应率率低的原因一方面是子带间跃迁的吸收系数小，另一方面是激发态电子大部分回填到基态，能抽取出来形成光电流的电子数只有30%左右。本项目设计并实现了两种新型有源区结构，分别是束缚-微带斜跃迁和耦合双阱结构，目的是提高抽取效率和子带间吸收系数。束缚-微带斜跃迁有源区将子带间吸收跃迁的末态设计成微带，并且置于抽取区中，吸收跃迁为空间上的斜跃迁，微带上激发态电子有90%甚至更高的抽取效率。斜跃迁初态和末态波函数交叠小于垂直跃迁，但是用态密度更高的微带作为末态，保证了吸收系数不低于垂直跃迁。利用束缚-微带斜跃迁设计，实现了8.6微米、10微米和16微米峰值波长的QCD，其中10微米器件采用窄跃迁垒时峰值波长在液氮下提高到91mA/W，室温下降到4mA/W，采用宽跃迁势垒时峰值波长在液氮为79mA/W，但是室温保持在30mA/W，这是目前QCD所有波段45度入射结构报导的最高室温响应率值。16微米器件的工作温度达到130K，是甚长波半导体光子探测器的最高值。为了进一步提高子带间吸收系数，设计了耦合双阱结构有源区，由于耦合双阱中初、末态的密度高于传统的单吸收阱，计算出吸收系数从单阱的1.14%提高到双阱的3.7%，增加了3倍以上，为了避免传统垂直跃迁抽取效率低的问题，在抽取区中插入了一个耦合阱，计算得到65%的抽取效率，传统抽取结构的理论抽取效率为39%，吸收系数和抽取效率同时提高，理论峰值响应率比传统结构提高了5倍以上，实际的QCD器件在液氮温度下8.2微米的峰值响应率达到166mA/W，高于所有报导的QCD峰值响应率。.通过实施本项目，建立了QCD有源区设计的平台，得到了实验验证，新结构实现了理想了器件性能，后期将开展与QCL集成的高灵敏检测系统的研制。