Noise in Microwave and Millimeter-Wave Pt-GaAs Schottky Diodes

We report measurements of frequency and bias dependent noise of dc-biased mm-wave Schottky-barrier GaAs diodes. The measurements are performed at room temperature and at cryogenic (20 K) temperatures. It is shown, that the noise can be described as consisting of two parts. One contribution is frequency dependent, characterized with time constants between 20 and 100 ps (varies from diode to diode). The other contribution is closely predicted by Monte-Carlo simulations for calculating hot electron noise. The frequency dependent contribution is believed to be affected by the GaAs material and/or the diode processing. The frequency independent hot electron noise can only be avoided by making sure that the fields in the epilayer are low enough. Is is recommended to use moderate bias and local oscillator drive levels for low noise mixer operation.