A low-noise Ku-band silicon Pt-n-p+diode oscilator

The possibility of using a variety of transit-time delay effects in semiconductors to generate microwave power has been much discussed in the literature. A transit-time negative resistance silicon diode without avalanching has been successfully operated at Ku-band frequencies. The diode is a Pt-n-p⁺structure, comprising a heavily doped p⁺substrate with a 1 Ω-cm n-type epitaxial layer 4.5µm thick and a platinum barrier contact. When biased with the barrier junction in reverse, breakdown is observed at ∼ 30 V and when biased with the p⁺n junction in reverse, breakdown is ∼ 50 volts. In the 50 volt direction with a diode current of 30 mA (∼ 200 A/sq.-cm), CW powers of about 5 mW have been obtained over a frequency range of 11.5 - 14.5 GHz. The experimental units have low efficiencies but there are obvious improvements to be made in this respect. More significant is the very low AM and FM noise observed for this oscillator, being comparable or even less than that of a high quality Gunn diode.