Ultra-Microscopic Analysis of Metal-Compound Semiconductor Interfaces by the Atom-Probe Mass Analyzer

电压脉冲原子探针(A-P)对化合物半导体的分析往往会给出错误的成分，例如，从GaAs中检测到的As离子多于Ga离子。新建立的直型、偏转型和成像型的组合A-P使我们有可能将错误成分的原因解释为附近As原子蒸发后立即发生的Ga择优场蒸发。通过调节偏转器和脉冲电压，成功地证明了A-P可以给出化学计量成分。组合A-P的独特之处在于具有宽有效入射面积的人字形电子倍增器和信号高度分辨时间数字转换器的高离子探测能力，32位计算机的高速数据处理，以及用存储示波器监测成像A-P。另一种分析化合物半导体的预期方法是用0.8 ns宽、峰值功率为200 KW的脉冲激光照射样品来促进场蒸发。本研究指出，即使用脉冲激光器进行A-P分析，也不能给出正确的成分，除非激光功率和尖端电压没有适当地调整。利用本研究的结果，利用脉冲激光A-P对Al-GaAs界面进行了分析，并与电压脉冲A-P的结果进行了比较。出乎意料的是，在AlAs层和衬底GaAs的界面上发现了一层Ga层。目前，Ga层的形成机理正在研究中。

The voltage-pulse atom-probe(A-P) analysis of compound semiconductors tends to give an erroneous composition, e.g. more As ions than Ga ions are detected from GaAs. The newly constructed combined A-P of straight, deflected and imaging types made it possible to clarify the cause of the erroneous compositions as the preferential field evaporation of Ga immediately after the evaporation of nearby As atoms. Then it was successfully demonstrated that the A-P can give stoichiometric compositions by adjusting the deflector and pulse voltages.The unique features of the combined A-P are high ion detectability by a chevron electron multiplier with a wide effective incoming area and by a signal height discriminating time digitizer, high-speed data process by a 32-bit computer, and monitoring of an imaging A-P with a storage oscilloscope.Another anticipated approach to analyzing compound semiconductors is to promote field evaporation by irradiating a specimen with a pulsed-laser beam, 0.8 ns wide and a peak power of 200 KW. The present study pointed out that even the A-P analysis with a pulsedlaser fails to give a right composition unless the laser power and tip voltage are not properly adjusted. Utilizing the result of the present study, Al-GaAs interfaces were analyzed by the pulsed-laser A-P, comparing the result obtained by the voltage-pulse A-P. Unexpectedly, a Ga layer was found at the interface of an AlAs layer and the substrate GaAs. At present, the formation mechanism of the Ga layer is under investigation.