Development of a Heterojunction Structure Detector in the Submillimeter Wave Region

本文研究了一种新型毫米波和亚毫米波检波/混频器--异质结双极晶体管（HBT）结构检波器。在100 GHz到THz的频率范围内，该探测器的灵敏度比肖特基二极管高得多。首先，我们对HBT探测器进行了理论模拟和模型实验研究。结果表明，MM和SMM检波器/混频器的发射极、基极和集电极结构的特殊设计是可行的，我们首先设计并制作了AlAs/GaAs异质结的发射极-基极结构，并成功地获得了良好的I-V特性。接下来，我们开始设计和制作基极-集电极结构。然而，选择性湿法刻蚀工艺的集电极是不容易获得精确的蚀刻轮廓，我们不能观察到良好的集电极电流与集电极-发射极电压的影响，大的漏电流。作为一种新的制作工艺，我们采用ECR等离子体刻蚀技术对其进行了改进，虽然漏电流有所降低，但仍不足以作为晶体管使用。当集电极电流达到几十mA时，器件的寿命也会出现问题。考虑到基极电流密度，减小基极面积的结构可能是改善这一问题的必要措施。现在我们正在重新设计HBT探测器器件的基础结构和制作。

A Heterojunction Bipolar Transistor (HBT) structure detector has been studied as a new type detector/mixer in the millimeter (MM) and submillimeter (SMM) wave region. The detector may have much higher sensitivity compared to the Schottky Barrier Diode in the frequency range from 100GHz to THz.Primarily, we have studied the HBT detector as a theoretical simulation and a model experiment using a Si bipolar transistor in the microwave region. The result has suggested a feasibility of special design of the emitter, base, and collector structure for MM and SMM wave detector/mixers.We designed and fabricated the emitter-base structure using AlAs/GaAs heterojunction first, and have obtained good I-V characteristics successfully. Next, we started to design and fabricate base-collector structure. However, selective wet etching process of collector was not easy to obtain precise etching profile, and we could not observe good collector current versus collector-emitter voltage influenced by large leakage current. As a new fabrication process, an ECR plasma etching has been introduced to improve it. The leakage current was reduced a little, but it was not enough to operate as a transistor. Another problem of device lifetime appeared when the collector current applied up to several tens mA.A reduced area base structure could be necessary taking into account of the base current density to improve such problems. Now we are going on redesigning the base structure and fabrication of the HBT detector device.