Shot noise enhancement and suppression in multiple quantum well resonant tunneling diodes

A physical model based on the coherent theory of electron tunneling is developed to analyze the shot noise characteristics of multiple-quantum-well resonant tunneling diodes (RTD). The shot noise factors at different regions of the current-voltage (I-V) characteristics of a double barrier RTD are computed. Results show shot noise suppression in the positive differential resistance (PDR) regions and shot noise enhancement in the negative differential resistance (NDR) regions. Unlike previous analyses, the current model is applicable for all regions of the I-V characteristic.; A microwave noise measurement system at 1.75 GHz is built to measure the shot noise characteristics of a triple-quantum-well RTD at the PDR regions. The measured shot noise factors show significant shot noise suppression. To investigate the shot noise characteristics in the NDR regions where the RTD is unstable, an X-band RTD waveguide oscillator was built. The oscillator's injection locking range, the output signal's phase noise characteristics and other parameters are measured. The device's shot noise factor versus oscillator d.c. bias is deduced from the measurement data. Significant shot noise enhancement is measured in the NDR region.