Development of a Heterojunction Structure Detector in the Submillimeter Wave Region

异质结双极晶体管(HBT)结构探测器是一种新型的毫米波和亚毫米波探测器/混频器。与肖特基势垒二极管相比，该探测器在100 GHz到THz的频率范围内具有更高的灵敏度。首先，我们对HBT探测器进行了理论模拟和在微波区使用硅双极晶体管的模型实验。研究结果表明，对MM和SMM波探测器/混频器的发射极、基区和集电极结构进行特殊设计是可行的。我们首次设计并制作了AlAs/GaAs异质结发射极基区结构，并成功地获得了良好的I-V特性。接下来，我们开始了基极集电极结构的设计和制作。然而，集电极的选择性湿法刻蚀工艺不易获得精确的刻蚀轮廓，而且由于漏电流较大，无法观察到良好的集电极电流与集电极-发射极电压的关系。作为一种新的制造工艺，ECR等离子体刻蚀被引入以改进其性能。漏电流略有降低，但还不足以作为晶体管工作。当集电极电流施加到几十mA时，出现了器件寿命的另一个问题。考虑到基极电流密度，可能需要减小面积的基极结构来改善这种问题。现在我们正在重新设计HBT探测器器件的基座结构和制造工艺。

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.