Schottky barriers are used extensively in high frequency switching, mixing and rectifying circuit for their good DC and RF characteristics. In this paper we report that devices measured in a double-balance mixer circuit show that the typical value of the DBS noise figure of the mixer diode is 6.1 dB at 89.5 GHz. Very good results were also observed in the 12.5, 8, 5 and 4mm bands. However, the barrier height is virtually constant and the operation stability depends strongly on the metallurgy of the Schottky contact. In addition, properties of planar doped barrier (PDB) diodes with an n(+) /i/p ' /i/n(+) configuration grown by molecular beam epitaxy (MBE) with precise control of the barrier height, were also studied. The results of artificial tailored I-V characteristics, junction capacitance and the detector application are also presented.