Effects of doping profile upon electrical characteristics of Gunn diodes

A one-dimensional computer simulation of Gunn diodes with zero-impedance external load has been made for various nonuniform doping profiles including asymmetrical step-like ones, linearly graded ones, and a periodic square-wave one. The distances between the electrodes and the doping level are taken as 10 µ and an order of 10
¹⁵
cm
^-3
, respectively. Current-voltage characteristics, oscillation current waveforms, oscillation frequency versus applied voltage characteristics, and electric field distributions as well as their dynamic changes were computed for the profiles with various parameters. The results show that with asymmetrical doping profiles, Gunn oscillation takes place when the cathode is on the higher resistance side, while for the opposite polarity it is difficult for the oscillation to occur. In the latter case, a static high-field domain is built up in the vicinity of the anode. The results also show that the voltage dependence of oscillation frequency is enhanced by an asymmetrical nonuniformity in the doping profiles. A considerable rise of the threshold voltage of the oscillations is found for the periodic square-wave profile. An experimental result is analyzed on the basis of the computed results.