【作者】 李果华；

【导师】 严辉；

【作者基本信息】 北京工业大学 ， 材料物理与化学， 2006， 博士

【摘要】 为了能够覆盖整个地球表面,通信卫星通常采用两种方式布置:一种是用三颗地球同步轨道卫星(35,700公里),另一种是需要几十至几百颗的低轨道(700公里)卫星。前者的缺点是由于距离较远因而要求较大的信号功率以及存在较长的信号延迟,而后者则由于卫星数目巨大而费用昂贵。目前认为高度为3000公里的轨道为最佳位置,使得在卫星个数使用、信号发射功率要求以及信号时间延迟之间达到一种平衡。但是,在这个轨道高度上存在所谓van Allen辐射带,在这里即使是“抗辐射”的Si太阳电池也只能正常工作几天时间。因此,为了能使通信卫星在van Allen辐射带正常工作,必须要有一种强抗辐射并且具有较高重量比功率的太阳电池。目前国内外用于航天器上的太阳电池主要为Si和GaAs太阳电池,但这两种材料的抗辐射能力较差,其光电转换效率由于高空辐射衰减很快,因而寿命短,稳定性差,不能满足用于van Allen强辐射带的空间应用需要。InP材料作为一种应用越来越广的半导体材料,除了具有良好的电特性之外,它具有非常突出的抗辐射能力,是下一代航天器用太阳电池的首选材料。通常的太阳电池收集的少数载流子要么是产生于p-n结,要么是少数载流子距离结的距离必须小于其扩散长度。本文比较分析了太阳电池工作的两种可能工作机制:扩散机制和漂移机制。由于漂移机制受辐射损伤影响较小,因而在本研究中实际的工作即是围绕该机制展开。漂移场的形成是通过MBE技术,在结的两侧都采用梯度掺杂(即双梯度掺杂),从而在整个有源层都建立起一个强的(漂移)电场,有效地利用载流子在电场作用下的漂移作用收集少数载流子,使得总内量子效率得以提高。由于双梯度掺杂电池利用的是漂移场收集少数载流子,因而不依赖于其扩散长度以及距结的距离。特别是在强辐射环境中少数载流子的扩散长度会因材料的辐射损伤而下降时,这种设计更显示出其优越性。本工作主要进行了如下几个方面的研究:1.根据太阳电池的太空应用需强抗辐射和高重量比功率的要求,对太阳电池结构进行设计。采用与众不同的通过在p区和n区都采用梯度掺杂这样一个所谓双梯度掺杂,在整个有源层获得高达104 V /cm的漂移电场。使得该太阳电池不同于更多还原

【Abstract】 In order to cover the whole Earth’s surface, telecommunication satellites are arranged in two ways: one is to put three geosynchronous satellites at the geosynchronous orbit (about 35,700km altitude). Another is to put several tens or several hundreds of satellites at low earth orbit (about 700km altitude). The drawbacks of the former one are that higher power is required to reach a satellite at that distance and a substantial round trip signal delay is inevitable. The drawback of the latter one is that it is too expensive to use so many satellites. It is now considered that 3000km orbit is the optimal selection. It makes the number of use of satellites, the requirement of radio power and the delay of round trip signal reach a balance. However, there exist the so-called van Allen radiation belts at this hight. The solar cells would work there for only several days, even for‘radiation hardness’Si solar cells. For this reason, extreme radiation hardness and high power/weight ratio solar cells, which can work properly in van Allen belts, must be developed.At present, the solar cells used on space aircrafts are still mainly Si and GaAs solar cells. However, the radiation resistance ability of these two materials is poor. Since the photoelectric conversion efficiency attenuates rapidly with the radiation, the lifetime of Si and GaAs solar cells is short and their stability is not satisfied for space applications at van Allen belt. As a more and more widely used semiconductor material, InP not only has very good electric properties but also is radiation hardness. InP is the next generation solar cell for space applications.Generally the minority carriers accumulated by the cell are generated either directly from the p-n junction or the distance between the generated minority carriers and the junction is less than the diffusion length of the minority carriers. In this design, two possible working mechanisms, diffusion and drift, are compared and analysed. Since drift-dorminated solar cells are less affected by the radiation, the main work is focused on this design. MBE technology is adoped to realize the drift field. Graded doping is adopted in both sides of the junction (double graded doping). This results in a strong (drift) electric field throughout the whole active layer. This field will accumulate minority carriers effectively and the whole internal quantum efficiency is increased. In this design, the double graded doping solar cell accumulates the minority carriers with the drift field, which is located at the whole graded space. This means that the accumulation of minority carriers doesn’t depend on the above conditions.更多还原