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

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，尝试开发一类新型外延硅基光伏电池及其相关技术。使用硅晶格匹配的硅合金窄间隙量子阱允许在波长范围内吸收超过1mum，这很难被传统的硅基太阳能电池覆盖（即吸收边缘降低），而不会牺牲相当于硅的高光电压。通过标准吸收、光电导率和光电压测量证实了吸收边降低，表明太阳能电池工作正常。QW的吸收边缘发生在比对照Si样品更长的波长上，表现出3/2幂律特征，作为能量的函数，这与空穴（二维）和电子（三维）的维数一致。随着温度的升高，载流子从浅量子阱到势垒边缘的热激发表现为短路电流呈指数增长。QW吸收发生在能量小于Si带隙和光电压与Si太阳能电池相当的情况下（<约等于>.4 - 0）。为了实现高效的光伏效应，研究了载流子输运特性。研究发现，量子阱的位置对量子阱势导致的有效载流子阻断效率起着重要作用。事实上，在纵向电场作用下，量子阱阻滞剂的时间分辨发光中发现了载流子再分布的异常现象，即动态后向散射。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调整内置电场来控制。通过对集成sige梯度缓冲器的量子阱进行光电流测量，分别研究了内置电位的作用。研究发现，当波长在近红外波段扫描时，在QW带隙以上，光电流极性突然切换。为了提高太阳能电池的性能，利用硅/二氧化硅技术实现了硅-绝缘体QW （SOI-QW）。由于集成反射镜的特性，SOI的几何形状有望增强吸收，从而提高太阳能电池的效率。QW的自发辐射和法向反射显示出法布里-珀罗干涉条纹，表明存在QW和501组成的光腔。因此，吸收特性表现出谐振行为和波长选择性，有望用作谐振式光电探测器。少

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