Sato Yu, Kanazawa Shohei, Saiki Toshiharu
Department of Electronics and Electrical Engineering, Keio University 3-14-1 Hiyoshi, Kohoku, Yokohama, Kanagawa 223-8522, Japan.
Microscopy (Oxf). 2014 Nov;63 Suppl 1:i10. doi: 10.1093/jmicro/dfu089.
We propose a technique that employs an optical mask layer of a phase-change material, e.g. GeSbTe, which is widely used for rewritable optical recording media, for realizing highly sensitive near-field imaging spectroscopy of single semiconductor quantum constituents at optical telecommunication wavelengths. Semiconductor quantum dots (QDs) have shown great promise as efficient single photon emitters and entangled photon sources, making them attractive for quantum communication and quantum information processing applications. Self-assembled InAs QDs on InP substrate are promising as near-infrared (NIR) single photon and entangled photon emitters. In order to clarify and control the optical properties of QDs for telecommunication devices, photoluminescence (PL) spectroscopy studies of single QDs with high spatial resolution at NIR wavelength is necessary. The most useful technique to attain this is by using near-field scanning optical miscroscopy (NSOM). However, NSOM has a lower PL collection efficiency at NIR wavelength than at visible wavelength [1]. This problem inhibits NIR-PL spectroscopy based on NSOM to be practically realized. Therefore, we deveopled a method to overcome the low NIR-PL spectroscopy by using a nanoaperture on an optical mask layer of phase-change material (PCM) [2]. Due to the large optical contrast between the crystalline and amorphous phases of the phase-change material at visible wavelengths and its high transparency at NIR wavelengths, an amorphous nanoaperture can be used to realize imaging spectroscopy with a high spatial resolution and a high collection efficiency (Fig. 1). We demonstrate the effectiveness of the proposed method by performing numerical simulations and PL measurements of InAs/InP QDs.jmicro;63/suppl_1/i10-a/DFU089F1F1DFU089F1Fig. 1.Schematic illustration of phase change mask method PCM mask effect has also the potential to be applied in emission energy control of QDs. One of the main problems for realization of quantum communication applications is precise control of energy in QDs. We proposed a new approach to control the emission energy of QDs by applying a local strain using volume expansion of phase-change material [3-5]. We calculated the stress and energy shift distribution induced by volume expansion using finite element method. Simulation result reveals that redshift is obtained beneath the flat part of amorphous mark, while blueshift is obtained beneath the edge region of amorphous mark. Simulation result is accompanied by two experimental studies; two-dimensional PL intensity mapping of InAs/InP QD sample deposited by a layer of PCM, and an analysis on the relationship between PL intensity ratio and energy shift were performed.
我们提出了一种技术，该技术采用相变材料（例如广泛用于可重写光记录介质的GeSbTe）的光学掩膜层，以实现光通信波长下单半导体量子成分的高灵敏度近场成像光谱。半导体量子点（QD）作为高效的单光子发射器和纠缠光子源已展现出巨大潜力，使其在量子通信和量子信息处理应用中颇具吸引力。在InP衬底上自组装的InAs量子点有望成为近红外（NIR）单光子和纠缠光子发射器。为了阐明和控制用于光通信设备的量子点的光学特性，有必要在近红外波长下对单个量子点进行具有高空间分辨率的光致发光（PL）光谱研究。实现这一目标最有用的技术是使用近场扫描光学显微镜（NSOM）。然而，NSOM在近红外波长下的PL收集效率低于可见光波长[1]。这个问题阻碍了基于NSOM的近红外PL光谱在实际中得以实现。因此，我们开发了一种方法，通过在相变材料（PCM）的光学掩膜层上使用纳米孔来克服低近红外PL光谱的问题[2]。由于相变材料在可见光波长下的晶态和非晶态之间存在较大的光学对比度，且在近红外波长下具有高透明度，因此非晶态纳米孔可用于实现具有高空间分辨率和高收集效率的成像光谱（图1）。我们通过对InAs/InP量子点进行数值模拟和PL测量，证明了所提出方法的有效性。
图1.相变掩膜方法的示意图
PCM掩膜效应也有可能应用于量子点的发射能量控制。实现量子通信应用的主要问题之一是对量子点中能量的精确控制。我们提出了一种新方法，通过利用相变材料的体积膨胀施加局部应变来控制量子点的发射能量[3 - 5]。我们使用有限元方法计算了由体积膨胀引起的应力和能量位移分布。模拟结果表明，在非晶标记的平坦部分下方会出现红移，而在非晶标记的边缘区域下方会出现蓝移。模拟结果伴随着两项实验研究；对沉积有一层PCM的InAs/InP量子点样品进行二维PL强度映射，并对PL强度比与能量位移之间的关系进行了分析。
