Field Emission from two dimensional electrons at a hetero-interface of superlattice and application to picosecond pulse electron source

研究了GaAs/GaAlAs异质界面上二维电子气的场发射特性。研究的目的是阐明二维电子气通过垂直于异质界面的表面势垒的隧穿现象。聚集层中的二维电子气具有高迁移率和高相干的特点。测量发射电子的能量分布和时间响应以及观察场发射图案是本实验研究的目标。在具有超晶格结构的砷化镓晶片的一角制备原子清洁的尖端结构是该研究计划中的一项重要实验技术。我们开发了一种与超高真空环境兼容的切割机制。沿-lt；011&gt；和&lt；011&gt；方向解理，在(100)面上形成尖角为90度的锋利边缘。尖端的曲率半径小于10 nm，足以在表面保持较高的场强。我们已经观察到了从顶点开始的平面发射图案。为了测量皮秒脉冲激光激发后的能量分布和时间响应，我们还研制了能量分辨率为20 meV的半球型静电分析器和时间分辨率为50ps的高灵敏度单电子探测扫描-摄像系统。利用这些新开发的装置，我们将测量发射电子的能量分布和时间响应。

Field emission property of two dimensional electron gas at a GaAs/GaAlAs heterointerface was studied. The aim of the research is to elucidate the tunneling phenomena of two-dimensional electron gas through a surface potential barrier perpendicular to the heterointerface. The two-dimensional electron gas localized in a accumulation layer of GaAs is featured by its high mobility and coherence. The measurement of energy distribution and time response of emitted electrons together with the observation of field emission pattern is a target of this experimental study.Fabrication of atomically-clean apex structure at a corner of the GaAs wafer with superlattice structures was an important experimental technique in the research program. We have developed a cleavage mechanism compatible with ultrahigh vacuum environment. Cleavage along <011> and <011> direction on a (100) plane of a GaAs wafer makes a sharp edge with an apex angle of90o. The curvature radius of the apex was less than 10nm, which is small enough to keep high field strength at the surface. We have observed a planer emission pattern from the apex. For the measurement of energy distribution and time response after photo excitation by a picosecond pulse laser, we have also developed a hemispherical electrostatic analyzer with energy resolution of 20 meV and a streak-camera system which has high sensitivity for single electron detection with time resolution of 50ps. By utilizing these newly developed devices, we are going to measure the energy distribution and the time response of the emitted electrons.