DEVELOPMENT OF MICROSCOPIC MEASUREMENT OF RESISTIVITY DISTRIBUTION IN MESOSCOPIC REGION

我们发明了一种基于扫描隧道显微镜(STM)的非常高空间分辨率的非接触式深能级瞬变光谱(DLTS)的新方法。用扫描隧道显微镜(STM)针尖探测半导体晶体表面感应表面光电压(SPV)的瞬变。理论研究表明，在适当的条件下，SPV-DLTS信号(SPV-DLTS信号由SPV的衰减分量与SPV的总幅度之比定义)与在照射下捕获少数载流子的亚表面深中心的密度成正比。对于塑性变形的n-GaAs，我们实验上成功地测量了与光学DLTS相匹配的SPV-DLTS谱。通过比较在光谱峰值温度下获得的SPV-DLTS信号的二维图与SPV信号的分布，我们的结论是，SPV-DLTS图像中的图像对比度代表了表面下耗尽层中少数载流子陷阱的存在。即使在这个初步实验中，空间分辨率也达到了10 nm的数量级。如果我们解决了STM针尖在温度扫描过程中的热漂移的技术问题，STM-DLTS将不仅成为局部评估微制造结构的有力工具，而且还将成为研究半导体中晶体缺陷的有力工具。

We have invented a novel methodology of non-contact Deep level transient spectroscopy (DLTS) in very high spatial resolution based on scanning tunneling microscopy (STM). An STM tip is used to detect the transitent of surface photo-voltage (SPV) induced at surfaces of semiconducting crystals. Theoretical considerations showed that under an appropriate condistion, the SPV-DLTS signal, defined by the ratio of the decay component of SPV to the total magnitude of the SPV,is proportional to the density of sub-surface deep centers that trap minority carriers on illumination, We have experimentally succeeded in measureing, for a plastically deformed n-GaAs, SPV-DLTS spectra matching those obtained by optical-DLTS.From comparison of a two-dimensional map of the SPV-DLTS signal, obtained at the spectral peak temperature, with the SPV signal distribution, we concluded that the image contrasts in the SPV-DLTS image represent the presence of minority carrier traps in the depletion layr beneath the surface. The spatial resolution reached the order of 10nm even in this preliminary expriment. If we solve the remaining technical problem of thermal drift of the STM tip during temperature scanning, the STM-DLTS will serve as a powerful tool not only for local assessment of micro-fabricated structures but also for studies of crystalline defects in semiconductors.