Responsivity and Noise Measurements of Zero-Bias Schottky Diode Detectors

Schottky barrier diodes can be used as direct detectors throughout the millimeterand submillimeterwave bands. When the diodes are optimized to have a low forward turn-on voltage, the detectors can achieve excellent frequency response and bandwidth, even with zero-bias. This paper reports on the characterization of VDI’s zerobias Schottky detectors. Responsivity typically ranges from 4,000 V/W at 100 GHz to 400 V/W at 900 GHz and each detector achieves good responsivity across the entire singlemoded bandwidth of the input rectangular waveguide. Under low power operation the detectors achieve a measured noise-equivalent-power (NEP) of about 1.5x10 W/√Hz, even without signal modulation. Such high sensitivity is expected for any zero-bias diode detector with high responsivity when there is no incident RF power; since only thermal noise can be generated under this condition. However, as the input power is increased, excess noise is generated. This noise typically has a 1/f power spectrum and is commonly known as flicker noise. Flicker noise becomes increasingly important as the input power is increased and signal modulation is generally required to achieve maximum sensitivity. The signal-to-noise of the VDI zero-bias detectors has been carefully measured as a function of input power and modulation rate. This data allows the user to understand the sensitivity of the detector under real operating conditions, and is therefore far more useful than the simple measurement of detector NEP with zero RF power, which is commonly quoted in the literature for new diode detector designs. Index Terms — Terahertz detectors, zero-bias detectors, noise-equivalent power, flicker noise.