Photocurrent effects on noise in silicon IMPATT oscillators

Experimental results are reported on the effect of electron-dominated and hole-dominated photocurrent on silicon flat-profile X-band IMPATT oscillators. Electron-dominated photocurrent noise is shown to degrade oscillator characteristics more than hole-dominated photocurrent noise, and this is attributed to the higher electron ionisation coefficient in silicon. The nominal photocurrent level is shown to reduce FM noise at large signal levels, as previously predicted. This noise reduction is only observed with hole-dominated photocurrent, owing to the longer intrinsic response time. The experimental results indicate that fluctuations in effective leakage current levels of 0.1% can significantly increase the oscillator noise level.