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

化合物半导体的电压脉冲原子探针（A-P）分析容易给出错误的组成，例如从GaAs中检测到的As离子多于Ga离子。新构建的直型、偏转型和成像型的组合A-P可以澄清错误组成的原因是Ga原子在附近as原子蒸发后立即优先场蒸发。然后成功地证明了A-P可以通过调整偏转板和脉冲电压来给出化学计量组成。该组合a - p的独特之处在于：采用宽有效入射面积的v形电子倍增器和信号高度鉴别时间数字化仪，具有高离子探测能力；采用32位计算机进行高速数据处理；采用存储示波器对成像a - p进行监控。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的脉冲激光束照射样品来促进场蒸发。本研究指出，除非激光功率和尖端电压调整不当，否则即使用脉冲激光进行a - p分析也不能给出正确的成分。利用本研究的结果，对Al-GaAs界面进行了脉冲激光A-P分析，并与电压脉冲A-P分析结果进行了比较。出乎意料的是，在砷化镓层和衬底砷化镓的界面上发现了一层镓层。目前，镓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.