Frequency-locked GaAs/AlAs superlattice oscillator for tunable narrowband microwave generation

We observed frequency locking of a wide-miniband GaAs/AlAs superlattice oscillator. The oscillator showed a free self-sustained current oscillation giving rise to microwave generation (power 100 μW) at a natural frequency (near 5 GHz) and ultraharmonics. A narrowband driving field locked the oscillator and caused a drastic narrowing (from 10
⁶
Hz to less than 10 Hz) of the halfwidths of the microwave lines, now centered at the driving frequency and its harmonics; at a driving power of 10 μW we obtained a locking range of 1% around the natural frequency. Our experiment, performed with a superlattice integrated in a planar microwave circuit, shows that a locked superlattice oscillator is suitable for tunable narrowband generation of high-frequency radiation.