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A Si-based solar cell with Si-equivalent photovoltage and near-infrared absorbing characteristics using a shallow quantum well potential

利用浅量子阱势能具有硅等效光电压和近红外吸收特性的硅基太阳能电池

基本信息

批准号：
09650345
负责人：
FUKATSU Susumu
金额：
$ 2.05万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

项目摘要

An attempt is made to develop a new class of epitaxial Si-based photovoltaic cells and relevant technologies by using multiple quantum well (QW) of a smaller bandgap material as an absorbing layer with the aid of advanced epitaxial techniques and band-gap engineering. The use of Si-lattice-matched, SiGe-alloy-based narrow-gap QWs allows absorption in the wavelength regime longer than 1 mum that is hardly covered by conventional Si-based solar cells (i.e., absorption edge lowering) without sacrificing a high photovoltage equivalent to that of Si.The absorption edge lowering was confirmed by means of standard absorption, photoconductivity and photovoltage measurements, which indicates solar cell operation. The absorption edge of the QW occurred at longer wavelengths than that of a control Si sample, showing a characteristic 3/2 power-law dependence as a function of energy which is consistent with the dimensionality of holes (2-D) and electrons (3-D). Thermal excitation of carriers from t … More he shallow QW to the barrier band edge was confirmed as an exponential increase of shortcircuit current with increasing temperature. QW absorption occurred at energies smaller than the Si bandgap and a photovoltage comparable to that of a Si solar cell (<approximately equal>O.4-O.6V) was obtCarrier transport characteristics were studied in view of achieving a highly efficient photovolliaic effects. It was found that the location of QWs plays an important role in the efficiency of effective carrier blocking due to a QW potential. In fact, anomalies due to carrier redistribution were observed, i.e., dynamical backscattering, in the time-resolved luminescence of a QW blocker under longitudinal electric fields. The results indicates that carrier profiles in a QW photovoltaic cell are controllable by tuning the built-in electric field using intentional doping. The role of a built-in potential was separately studied by photocurrent measurements on a QW with an integrated SiGe-graded buffer. It was found that the photocurrent polarity switches abruptly as the wavelength is scanned in the near-infrared regime above the QW band-gap.To enhance the solar cell capability, the Si/S i02 technique exploited for the realization of a Si-on-insulator QW (SOI-QW). The SOI geometry is expected to allow an enhancement of absorption due to the integrated mirror characteristics and therefore a more efficient solar cell. Spontaneous emission from the QW and normal incidence reflectance showed Fabry-Perot interference fringes, which indicates an optical cavity using QW and 501. Accordingly, absorption characteristics show resonant behavior and wavelength selectivity for prospective use as resonant photodetector. Less

利用先进的外延技术和带隙工程技术，利用较小带隙材料的多量子阱(QW)作为吸收层，开发了一种新型的外延硅基光伏电池及其相关技术。利用与硅晶格匹配的SiGe合金基窄禁带量子阱，可以在常规硅基太阳能电池难以覆盖的波长范围内进行长于1um的吸收(即吸收边降低)，而不会牺牲与硅相当的高光压。通过标准吸收、光电导和光电压测量证实了吸收边降低，这表明太阳能电池的运行。量子阱的吸收边出现在比对照硅样品更长的波长上，表现出与能量的3/2幂函数的特征关系，这与空穴(2-D)和电子(3-D)的维度一致。T-…载流子的热激发随着温度的升高，短路电流呈指数增加，在势垒带边缘有较浅的量子阱。量子波吸收发生在比硅禁带宽度小的能量，并且获得了与硅太阳电池相当的光电压(约等于0.4~0.6V)。为了获得高效的光伏效应，研究了载流子输运特性。研究发现，由于量子波势的存在，量子波的位置对有效阻挡载流子的效率起着重要的作用。事实上，在纵向电场作用下量子波阻滞剂的时间分辨发光中，观察到了载流子再分布引起的反常现象，即动态背向散射。结果表明，量子阱光伏电池中的载流子分布可以通过有意掺杂来调节内置电场来控制。通过对集成了SiGe分级缓冲器的量子阱上的光电流测量，分别研究了内建电势的作用。为了提高太阳电池的性能，利用Si/S i02技术实现了绝缘体上硅量子阱(SOI-QW)。由于集成的镜面特性，SOI几何结构有望允许增强吸收，从而获得更高效的太阳能电池。量子波的自发辐射和垂直入射反射率显示出法布里-珀罗涉条纹，这表明使用量子波和501的光学腔。因此，吸收特性显示出共振行为和波长选择性，有望用作共振光电探测器。较少