The Gunn effect in n-CdTe

We have observed Gunn-effect oscillations from samples of n-CdTe 25 to 450 microns long with doping levels between 5 × 10¹⁴and 5.3 × 10¹⁵cm^-3. The room temperature threshold electric field for these oscillations varies from about 9500 V/cm for samples 450 microns long to about 15 000 V/cm for samples 25 microns long. For samples longer than 80 microns, the oscillation is seen as a train of spikes in current. The period of these spike waveforms increases linearly with sample length, giving a calculated value of 0.7×10⁷cm/s for the high-field domain drift velocity. At 77°K, the threshold electric field drops to about 8000 V/cm for 150 micron samples and the domain drift velocity increases by about 25 percent. In all samples tested, a current runaway effect is observed after several cycles of oscillation, with the runaway occurring sooner for increasing voltage drive to the sample. This runaway dominates the sample behavior for driving voltages well above Gunn-effect threshold.