Acoustical phonon induced and polaron induced modulational amplification in polar semiconductors: a comparative study

The paper aims to comparatively study the amplification and excitation characteristics of polaron induced and acoustical phonon induced modulators. Based on the hydrodynamic model, an analytical investigation of frequency modulational interaction is made. An explicit expression for the growth rate and threshold electric field for the onset of the acoustic phonon driven and polaron driven instability is presented and analyzed analytically. We have numerically investigated the dependence of the threshold electric field for different values of the external parameters of a typical polar semiconductor (InSb) and have given a numerical estimation of the growth rate. We also found that the amplification coefficient in polaron induced modulation enhances by a factor of 10 as compared to acoustical phonon induced modulation; though polaron induced modulational instability occurs at a lower threshold than acoustical phonon induced modulational instability. The cyclotron frequency can be used as a control parameter to reduce thresholds and improve growth rates. These results could be important for understanding and improving the performance of modulators. It is hoped that a low cost modulator using the n-InSb–CO2 system can be fabricated as the outcome of this work. (paper)