A Planar IC-Compatible Transferred Electron Device for Millimeter-Wave Operation.

Computer simulations are presently being performed in order to optimize device parameters. Both optimum donor density and drift length will be calculated. 70% of the fabricated devices exhibit the precalculated low field characteristics such as DC-resistance and Schottky diode characteristics. Radiofrequency performance in the transit-time independent mode is not yet satisfactory. However, very good efficiencies have been measured in the transit-time mode: At 19 GHz efficiencies between 3.5% and 4% have been measured. In this mode domain formation occurred somewhere underneath the negatively biased gate. This device is an excellent planar Gunn oscillator. The goal is to operate this device at non-transit time related frequencies above the transit time frequency with comparable or higher efficiency. Up to now the tested devices did not exhibit sufficiently large negative conductance in Ka band (26.5 - 40 GHz). Certainly, one reason for measuring low small signal gain is the low characteristic impedance of the stripline test circuit (50 Ohms). Other reasons might be some losses of the FET like cathode contact and the steeply falling electric field distribution in the drift region due to the large donor density. Future devices therefore will be made from lower doped epitaxial layers and will be mounted in specially designed stripline circuits containing impedance transformers and resonators.