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) 的新型非接触式深能级瞬态光谱 (DLTS) 方法，具有非常高的空间分辨率。 STM 尖端用于检测半导体晶体表面感应的表面光电压 (SPV) 瞬态。理论考虑表明，在适当的条件下，SPV-DLTS 信号（由 SPV 的衰变分量与 SPV 总幅度之比定义）与照明时捕获少数载流子的次表面深层中心的密度成正比。我们已经通过实验成功地测量了塑性变形的 n-GaAs，与光学 DLTS 获得的 SPV-DLTS 光谱匹配。通过比较在光谱峰值处获得的 SPV-DLTS 信号的二维图温度，根据 SPV 信号分布，我们得出结论，SPV-DLTS 图像中的图像对比度代表了表面下方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10nm的量级。如果我们解决了温度扫描过程中 STM 尖端热漂移的剩余技术问题，STM-DLTS 将成为一个强大的工具，不仅可以用于微加工结构的局部评估，还可以用于研究半导体中的晶体缺陷。

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.