Comprehensive characterization of Gunn oscillations in In0.53Ga0.47As planar diodes

In this work, In0.53Ga0.47As planar Gunn diodes specifically designed for providing oscillations at frequencies below 30 GHz have been fabricated and characterized. Different types of measurements were used to define a set of consistent methods for the characterization of the oscillations that can be extended to the sub-THz frequency range. First, negative differential resistance and a current drop are found in theI-Vcurve, indicating the potential presence of Gunn oscillations (GOs), which is then confirmed by means of a vector network analyzer, used to measure both theS(11)parameter and the noise power density. The onset of unstable GOs at applied voltages where the negative differential resistance is hardly visible in theI-Vcurve is evidenced by the observation of a noise bump at very low frequency for the same applied voltage range. Subsequently, the formation of stable oscillations with an almost constant frequency of 8.8 GHz is observed for voltages beyond the current drop. These results have been corroborated by measurements performed with a spectrum analyzer, which are fully consistent with the findings achieved by the other techniques, all of them applicable to Gunn diodes oscillating at much higher frequencies, even above 300 GHz.