有机/无机复合结构的近红外-可见光上转换器件研究

The widely available charge coupled device (CCD) and lately CMOS imaging devices have created many applications on a mass scale. However these devices are limited to wavelengths shorter than about 1 μm. Hybrid photon upconversion devices have been developed recently. The end goal is to achieve an alternative technology for imaging in the 1.5-μm region. The hybrid upconversion idea relies on the integration of an infared photodetector and an OLED. Under a forward bias for the OLED, the detected signal in the photodetector is sent to the OLED, resulting in an increase in emission at a shorter wavelength and therefore achieving optical upconversion. As each organic molecule is a topologically perfect structure, the growth of each organic layer does not require "lattice matching", which has been the fundamental limit for inorganic semiconductor monolithic devices.To improve the performance of hybrid upconverter, this proposal will be focused on the issues: Firstly,embedding a metal mirror can substantially enhance the upconversion efficiency by optimizing the top-emission OLED and increasing infrared absorption efficiency.The overall upconversion efficiency can also be increased significantly, by introducing a gain mechanism into the photodetector section of the upconverter. A promising option to implement gain is a heterojunction phototransistor (HPT). An optimized InGaAs HPT will be integrated with an OLED, which can convert 1.5-μm Infrared light to visible light with a built-in electrical gain. Secondly, this upconversion approach can also be used to realize a pixelless imaging device. A pixelless hybrid upconversion device consists of a large-area single-mesa device, where the OLED output is spatially correlated with the input 1.5-μm scene. Only the parts receiving incoming photons will emit output photons. To achieve this functionality, photon-generated carriers must flow mainly along the layer-growth direction when injected from the InGaAs light absorption layer into OLED light emission layer. Finally, One key parameter in determining the carrier transport across an organic/inorganic interface is energy band alignment.X-ray photoelectron spectroscopy (XPS) will be used to measure the band alignment at the organic/inorganic interface. c-AFM (conductive-atomic force microscopy) is a promising technique based on AFM. It maps out experimentally the two-dimensional internal current profile in the transverse cross section of an operating electronic/optoelectronic device with a spatial resolution of 10 nm. The experimental results could lead to the first-ever direct observation of the inner workings of operating devices, as well as revealing the carrier density profile, and the uniformity of the interface.

近红外波段（约1.5 微米）探测在军事和民用领域都具有非常重要的应用，而目前硅CCD成像器件的光探测波长范围短于1微米。有机/无机复合结构（铟镓砷/OLED）近红外上转换器件将近红外光转换成可见光，进而能够与硅CCD组合实现红外探测。该复合结构克服了无机材料集成时晶格匹配的要求，同时具备有机材料的易加工性和无机材料的高量子效率。本项目将通过集成顶发射OLED和在铟镓砷探测器内引入电流增益等方案提高有机/无机上转换器件的性能,研制具有光放大功能的上转换器件。在此基础上，还将研制有机/无机复合结构的新型上转换成像器件，不同于传统的成像方案，即增加像素的方式来提高分辨率，该器件通过无像素的方案，在成像器件中控制光生电流的横向分布来提高分辨率,可极大简化制备工艺并降低红外成像的成本，解决传统红外成像的低分辨率问题。本项目的研究将促进大面积、低成本、高分辨的新型红外成像器件研制。

近红外波段（约1.5 微米）探测在军事和民用领域都具有非常重要的应用，而目前硅CCD成像器件的光探测波长范围短于1微米。有机/无机复合结构（铟镓砷/OLED）近红外上转换器件将近红外光转换成可见光，进而能够与硅CCD组合实现红外探测。本项目围绕有机/无机复合结构的近红外-可见光上转换器件的关键技术问题和难题展开研究，采用异质结微观能带设计和异质结界面宏观电学表征来研究器件结构及界面的优化方案，提升有机/无机近红外成像器件性能。首先建立了准确完善的红外成像器件二维载流子输运模型，研究了光电二极管、光电晶体管、雪崩管以及含超晶格阻挡层等不同成像器件结构中限制电流输运效率的共有因素，明确了通过优化设计异质结界面处能带结构可以调节器件内部电场分布，从而提高光生载流子产生和输运的效率，为增强成像器件性能包括光电流、信噪比等指标提供了器件结构优化方案；同时为优化器件的异质结界面接触特性，建立了界面电学表征方法，研究了成像器件中关键界面包括金属/半导体、金属/绝缘体/半导体等界面的势垒高度、缺陷态密度在不同工作条件下的特性变化，揭示了缺陷态密度、接触势垒等与宏观电学特性的密切联系，提出了降低缺陷态密度、改善器件异质结接触特性的界面优化方案。研究结果综合了微观的能带设计及宏观的实验表征，形成成像器件结构及界面最优化方案，为研制大面积、低成本、高分辨率的新型有机/无机近红外成像器件，提供了准确有效的理论依据和实验验证。发表论文16篇，其中SCI论文8篇，EI论文7篇；培养研究生5名；申请发明专利2项。