Development of a "near-surface"-photodetector based on anomalous above-band-gap absorption band of SiGe

绝缘体上硅(SOI)衬底最近一直是人们关注的焦点，特别是从开发高速、低功耗电子产品的角度来看。另一方面，隐约可见的硅光子学将把光子学/光电子学引入到这个原本纯粹是电子的SOI芯片上。目前的问题是，传统的光子学/光电子学器件结构不允许高度集成的电路设计，这可以追溯到硅的间接带隙，它只能微弱地吸收光，从而留下相当大的占地面积。在这项研究中，试图创造一种新的强吸收的片上量子光电探测器，它利用在氧化的SiGe中形成的以12 eV为中心的异常近表面吸收带，由于相关的独特电子态，而不是与体相相关的那些。即使在缺乏Ge的硅基系统中，这种带隙以上的吸收带也是可以重现的，这表明它与硅有关，因此它的近表面缺陷也在其中产生。测试了一系列具有肖特基连接的MSM(金属-半导体-金属)光探测器的光谱灵敏度、光响应的动态范围、暗电流、偏振不灵敏以及包括带宽在内的达到亚纳秒域的瞬时响应等特性。有趣的是，没有烧孔表明1.2 eV带并没有均匀展宽。除了在原方案中解决的问题外，在本研究过程中还发现了电吸收和电反射，这在构建电光调制器和可调探测器方面具有相当大的前景。用于多道光谱和透明条纹检测的阵列探测器的制作仍将是未来研究的主题。

Silicon-on-insulator (SOI) substrates have been in the focus of attention these days particularly from the perspective of developing high speed, less power-hungry electronics. The looming silicon-photonics on the other hand is to bring photonics/optoelectronics onto this otherwise purely electronic SOI chip. The problem then is that the conventional architecture of photonics/optoelectronics devices, at it stands, would not allow for a highly integrated circuit design, which can be traced back to the indirect band-gap of silicon that only weakly absorbs light thereby leaving a fairly large footprint.In this study, an attempt is made to create a new class of strongly-absorbing, on-chip quantum photodetector that takes advantage of an anomalous near-surface absorption band centered near 12eV developing in oxidized SiGe due to the relevant unique electronic states as opposed to those pertaining to the bulk. This above-band-gap absorption band was reproducible even in silicon-based systems short of Ge, which shows that it has to do with Si and hence its near-surface defects launched therein. A series of MSM (metal-semiconductor-metal) photodetecotrs prototypes with Schottky links was tested to examine such characteristics as spectral sensitivity in relation to wavelength selective detection, dynamic range of photoresponse, dark current, polarization-insensitiveness, and transient response including bandwidth reaching the subnanosecond domain. Interestingly, the absence of hole burning indicates that the 1.2eV band is not homogeneously broadened. Besides the issues that had been addressed in the original proposal, electroabsorption and electroreflectance were discovered during the course of this study, which holds considerable promise in building electro-optic modulator and tunable detector. The fabrication of an arrayed detector for mulitichannel spectroscopy and transparent fringe detection will remain as a subject of future study.