Transferred-Electron Induced Current Instabilities in Heterojunction Bipolar Transistors

9422538半导体电流中的贾拉利不稳定性一直是人们感兴趣的问题。一个众所周知的例子是技术上重要的Gunn效应，它已经在直接带隙半导体中观察到，其中偏置的n+-n-n+二极管的电场分布塌陷到高场域中。这个区域在一个特征时间t内被扫出n区，产生频率为f=1/t的电流脉冲。自从1963年Gunn第一次观测到转移电子效应以来，这种器件已经成功地实现了微波和毫米波辐射的低噪声源。III-V异质结双极晶体管(HBT)的集电区与耿氏二极管的漂移区之间的相似性促使我们探索双极晶体管中的Gunn-Hilsum现象。通过数值模拟，我们发现在改进的HBT结构中可以观察到由转移电子效应引起的电流不稳定性，在这种结构中，集电极中的电场分布得到了适当的设计。这些结果为设计一种新的三端双极振荡器奠定了基础，该振荡器有可能融入现有的HBT集成电路技术中，我们将在本项目中研究这一点。所提出的器件将被用作一种新的光谱工具，其中可以独立地改变半导体区域中出现稳定的电压和电流。利用这一性质，我们可以应用广泛的偏置条件来评估Landau-Ginzburg相变理论对描述振荡阈值附近的涨落的适用性。***

9422538 Jalali Instabilities in current flow in semiconductors has been of interest of some time. A well known example is the technologically important Gunn effect which has been observed in direct bandgap semiconductors such as InP and GaAs in which the electric field profile of a biased n+-n-n+ diode collapses into a high field domain. This domain is swept out of the n-region in a characteristic time, t and results in current pulses of frequency f=1/t. Since the first observation of the transferred electron effect by Gunn in 1963 the devices have been successfully implemented as low noise source of microwave and millimeter-wave radiation. The similarity between the collector region of a III-V heterojunction bipolar transistor (HBT) and the drift region of a Gunn diode has motivated us to explore the Gunn-Hilsum phenomenon in bipolar transistors. Using numerical simulations, we have shown that current instabilities resulting from the transferred electron effect can be observed in modified HBT structures in which the electric field profile in the collector has been properly engineered. These results have established design criteria for a new three terminal bipolar oscillator with the potential for incorporation into existing HBT integrated circuit technology, which we shall study in the this project. The proposed device will be used as a novel spectroscopic tool in which it is possible to independently vary voltage and current flow in the region of semiconductor where stability occurs. Using this property we can apply a wide range of bias conditions to assess the applicability of the Landau-Ginzburg theory of phase transitions to describe fluctuations near oscillation threshold. ***