Development of a Heterojunction Structure Detector in the Submillimeter Wave Region

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A heretojunction bipolar transistor (HBT) structure detector has been studied as a new type detector in the millimeter (MM) and submillimeter (SMM) wave region. The detector which may have much higher sensitivity compared to the Schottky Barrier Diode (SBD) in the frequency range from 100GHz to 1THz.Primarily, we have studied the heterojunction structure detector theoretically as a simulation taking into account of transit time and parasitic elements, and experimentally as a model experiment using a Si bipolar transistor in the microwave region.The video sensitivity of 5x10^5 V/W has been obtained in the low frequency range, which is much higher than that of the diode detector. And also, the sensitivity of 2x10^3 V/W is obtained even at the frequency of about 8 times higher than the cutoff frequency (ft) of the transistor. The influence of the parasitic capacitance between base and corrector is not high for detector operation, not for amplifier operation, as predicted by the theoretical simulation. The result has suggested a possibility of special design of the emitter, base, corrector structure for the SMM wave detector.We have designed the emitter base structure specially for the SMM detector and AlGaAs/GaAs semiconductor layer and impurities structure for it. And we have completed semiconductor deposition precisely using the MBE method.Now the fabrication process of the detector are improved and going on using photolithography, ECR plasma etching, and selective wet etching.