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，即扫描热电子显微镜(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)，以测量HEE的空间分布和能谱。为了将针尖和表面之间的势峰降低到HE能量，我们推导了针尖和表面功函数、隧道电压和针尖-表面间距所需的理论关系式。我们设计了一个实验，在大气环境中验证了我们的想法。我们选择了Si/CaF2/Au异质结，自洽地分析了在偏压作用下产生能量为3 eV的热电子的可能性，电流密度为10kA/cm2。我们用光刻技术制作了面积为10um2的热电子发射体，获得了设计的发射特性。我们测量了相敏的…。在直流电压为3V，发射极交流电压为170 mV，发射极频率为82 Hz，隧道电压为1.5V的条件下，针尖向表面靠近时，PSD输出突然增加，显示出热电子探测，这是扫描探针针尖首次探测到HE。然而，集成需要相当长的时间才能获得一个数据点来对抗噪音。从理论上得到了检测尖端振动免疫的最佳条件。研制了隧道电流数字化记录与处理系统，用于分析隧道电流的噪声特征，提取隧道电流信号。功率谱分析和上述理论表明，PSD可以在10s的积分时间内检测到1pA的HE信号。通过这项研究，我们建立了获得SHM系统数据的技术。He空间分布的测量和半导体中热电子的探测被留作下一阶段的目标。较少

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