New STM technique for observation of ballistic electrons in semiconductors

我们提出并证明了一种新的STM技术--扫描热电子显微镜（SHEM），它通过STM探针探测向固体材料表面传播的弹道热电子（HE），测量HE的空间分布和能谱，将针尖和表面之间的电势峰降低到HE能量，导出了针尖和表面功函数、隧道电压和针尖-表面间距的理论关系式。我们设计了一个实验，在大气环境中验证了我们的想法。我们选择Si/CaF_2/Au异质结，自洽地分析了偏压下的能带分布，表明在10 KA/cm ~ 2的电流密度下产生能量为3eV的超热电子的可能性。我们用光刻法制作了面积为10 μ m ~ 2的热电子发射极，获得了设计的发射特性。我们测量了相敏检波器， 关于我们 在发射极上施加3V直流电压、170 mV频率为82 Hz的交流电压和1.5V隧道电压时，探针的PSD输出接近样品表面。当探针接近样品一定距离时，PSD输出突然增加，出现热电子探测，这是探针首次探测到HE。然而，积分需要相当长的时间才能在噪声中获得一个数据点。我们从理论上得到了最佳条件的检测相对于免疫力的尖端振动。我们研制了隧道电流的数字记录和处理系统，分析了噪声特性，提取了HE信号。功率谱分析和上述理论表明，在积分时间为10秒时，PSD可以检测到1 pA的HE信号。通过本研究，建立了系统获取SHEM数据的技术。下一阶段的目标是测量半导体中的超热电子的空间分布和探测超热电子。少

We have proposed and proved a new STM technique, Scanning Hot Electron Microscopy (SHEM), which has detected ballistic hot electrons (HE) propagating towards a surface of a solid material by a probe of STM to measure a spatial distribution and an energy spectrum of the HE.To lower the potential peak between the tip and the surface down to the HE energy, we have derived theoretical relation required for the work functions of the tip and the surface, the tunnel voltage and the tip-surface spacing. We have designed an experiment which has verified our idea in an atmospheric environment. We have selected Si/CaF2/Au heterostructure, analyzed self-consistently a band profile under the bias voltage application to show a possibility of generation of the hot electron with energy of 3eV at current density of 10KA/cm2. We have fabricated hot electron emitters with the area of 10um2 by using photolithography to obtain emission characteristics as designed. We have measured the phase sensitive detec … More tion (PSD) output approaching of the tip to the surface under application of DC voltage of 3V,AC voltage of 170mV at frequency of 82Hz to the emitter and the tunnel voltage of 1.5V.When the tip approached to the sample within certain distance, the output increased suddenly to show the hot electron detection, which was the first detection of the HE by the scanning probe tip. However, it took quite long time for integration to take one data point against the noise. We have theoretically obtained the optimum condition for the detection with respect to the immunity for the tip vibration. We have developed digital recording and processing system of the tunnel current to analyze the noise characteristics and to extract HE signal. It has been made clear from the power spectrum analysis and the above theory that 1pA HE signal can be detected by the PSD at integration time of 10sec. We have established the technique to obtain systematic data of SHEM through this research. The measurement of the spatial distribution of HE and the detection of the hot electron in the semiconductor has been left as the next stage targets. Less