tailieunhanh - Báo cáo " The dependence of the parametric transformation coefficient of acoustic and optical phonons in doped superlattices on concentration of impurities"

The parametric transformation of acoustic and optical phonons in doped superlattices is theoretically studied by using a set of quantum kinetic equations for the phonons. The analytic expression of parametric transformation coefficient of acoustic and optical phonons in doped superlattices is obtained, that depends non-linear on the concentration of impurities. Numerical computations of theoretical results and graph are performed for GaAs:Si/GaAs:Be doped superlattices | VNU Journal of Science Mathematics - Physics 25 2009 123-128 The dependence of the parametric transformation coefficient of acoustic and optical phonons in doped superlattices on concentration of impurities Hoang Dinh Trien Nguyen Vu Nhan Do Manh Hung Nguyen Quang Bau Faculty of Physics College of Science VNU 334 Nguyen Trai Thanh Xuan Hanoi Vietnam Received 30 July 2008 received in revised form 15 August 2009 Abstract. The parametric transformation of acoustic and optical phonons in doped superlattices is theoretically studied by using a set of quantum kinetic equations for the phonons. The analytic expression of parametric transformation coefficient of acoustic and optical phonons in doped superlattices is obtained that depends non-linear on the concentration of impurities. Numerical computations of theoretical results and graph are performed for GaAs Si GaAs Be doped superlattices. Keywords parametric transformation doped superlattices. 1. Introduction It is well known that in presence of an external electromagnetic field an electron gas becomes non-stationary. When the conditions of parametric resonance are satisfied parametric resonance and transformation PRT of same kinds of excitations such as phonon-phonon plasmon-plasmon or of different kinds of excitations such as plasmon-phonon will arise . the energy exchange process between these excitations will occur 1-9 . The physical picture can be described as follows due to the electron-phonon interaction propagation of an acoustic phonon with a frequency a r accompanied by a density wave with the same frequency W. When an external electromagnetic field with frequency is presented a charge density waves CDW with a combination frequency Vj lW l 1 2 3 4. will appear. If among the CDW there exits a certain wave having a frequency which coincides or approximately coincides with the frequency of optical optical phonons will appear. These optical phonons cause a CDW with a combination frequency of Vj lW .