Ultra-high-frequency coherent sound generation in resonant tunneling

In this paper we propose a device capable of generating ultra-high-frequency coherent sound. It is called SASER by analogy to laser. The device consists of a double barrier heterostructure (DBHS) tailored to permit phonons to resonate with the electronic system. The condition for resonance is fulfilled when the energy difference between the first and second resonant peaks of the electronic DOS in the well matches the LO-phonon frequency. Due to the low energy and short wavelength of the phonon beam this device could be useful for imaging and for the non-destructive characterization of nanostructures. It could also be used to build phonoelectronic systems (analogous to optoelectronics). We establish kinetic equations for the number of electrons in each level, the number of LO-phonons in the well and for the number of coherently generated secondary TA phonons that results from the LO-phonon decay due to anharmonicity. Coefficients of the equations that describe the tunneling process have to be obtained in a self-consistent way, considering the effects of space charge inside the well and the accumulation and depletion layers in the emitter and collector, respectively. The steady solution of the system is analyzed and the conditions for "SASER action" are discussed. The I(V) characteristics show the well known bistability at the negative differential resistence region. Also, at the beginning of the SASER emission this curve shows chaotic behaviour.