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In this article, the comparison of excitation in high frequencies of acoustic-electromagnetic wave in piezoelecric crystal and crystal with potential of deformation GaAs is investigating. Possible mechanisms of coupling different hybrid waves are the piezoeffect and the deformation potential. As a model it is analyzing a film of crystal places between two symmetrical substrates with the other materials without an acoustic contact. This film includes 2D electron gas with a high negative differential conductivity and uniform initial distribution of electrons. The hybrid acoustic-electromagnetic wave and hybrid space charge wave interact. Amplification of space charge wave takes place due to negative differential conductivity in GaAs. This amplification of space charge waves is causing the amplification of acoustic-electromagnetic wave. It is to show that the symmetric modes, emerging as transverse ones, interact more effectively with the space charge waves. Another important result is the following: at the frequencies f ≈ 10 GHz, the excitation efficiency of acoustic-electromagnetic wave with transverse displacement due to piezoeffect is more effective, but at higher frequencies, the deformation potential is dominating.

The amplification of the acoustic-electromagnetic waves is very important problem [_{c} = 3.5 kV/cm that it is good for analysis of amplification in different mechanisms like piezoeffect or deformation potential so as other materials have very big critical field like crystal InP and GaN.

The present paper is focused on theoretical research of excitation of acoustic-electromagnetic waves (AEW) in GaAs films of a sub-micron thickness placed between non-piezoelectric substrates. The spatial increments of SCW due to NDC have been calculated for two mechanisms like piezoeffect and deformation potential. An amplification of SCW is possible for frequencies from 10 GHz for case of piezoeffect. For deformation potential the frequencies range increase from 10 GHz to 30 GHz, so the mechanism of deformation potential is more useful in high frequencies.

The thin GaAs film plays the role in a transducer of acoustic electromagnetic waves. The amplification has a resonant character, and the intensities of energy may reach the values of 10 W/cm^{2}. The realization of the good amplification has showed that usefulness of hybrid waves in high frequencies range more f ≈ 10 GHz is very important for application in communication, medicine and control systems. The analysis of basic mechanisms of amplification is given in this article. The resonance excitation and amplification of acoustic-electromagnetic wave with space mode in structure of GaAs is analyzing for two cases of piezoeffect and deformation potential, but the amplification of high frequencies are realizing only in case of deformation potential.

Let us to consider a thin film of n-GaAs located between two mediums, the substrates are from material without piezoeffect, and the transversal wave passed along z axis. The component of displacement U is in direction of the y axis. The film consists of a 2D gas with a high negative differential mobility. The value L is the length of the element (along axis OZ), h is the thickness of film (see

Let us to analyze the simplest transversal in displacements u mode using elastic theory equation with the pie-

zoeffect [

potential

where s » 3 × 10^{5} cm/s is the sound velocity,

The boundary conditions are in (Equation 1(c)). In the case of free very thin film it is

case it is necessary to consider the viscosity coefficient

where

Resonance condition

where

Parameters

and

These conditions for the amplification are better for the symmetric modes if the displacement

Boundary conditions are taken in case of the absent of the acoustic contact of the film with the environment (Equation 1(c)).

In the simulation it is to use Equation (1) and the resonance condition (2). It is necessary to take into account the 2D electron gas of n-GaAs thin film and the equations for slow changing amplitudes of acoustic-electro- magnetic hybrid wave with potential_{0} » 10^{15} cm^{−3}, the electron concentration in the film, v_{0} » 2 × 10^{7} cm/s, the electron velocity, L = 0.1 cm, the length of the film H = 1 mm. The intensity of wave can reach value of 10 W/cm^{2} at microwave frequencies w = 5 × 10^{10} - 2 × 10^{11} s^{−}^{1}. In the Figures 2-4, the amplification of the acoustic-electromagnetic wave in microwave range is to present.

Traditional construction for realization of acoustic-electromagnetic amplification is in ^{11} Hz ranges too.

Additionally, in simulations it is considering the electric variable field distribution in input antenna like Gauss impulse.

Electric variable field distribution in input antenna has parameters: z_{1} = 0.001 cm, z_{0} = 0.0001 cm; y_{1} = 0.05 cm, y_{0} = 0.02 cm; t_{1} = 2.5 ns, t_{0} = 1.25 ns; E_{10} = 200 V/cm and E_{B} = 4.56 kV/cm, the drift field, n_{0} = 10^{11} cm^{−2}, the 2D concentration of electron gas, and q, the transverse wave number (index m equal 5) of the acoustic-electro- magnetic mode.

Excitation of the acoustic-electromagnetic wave due to deformation potential is in the Lamb’s acoustic mode [_{1}, 0, u_{3}) takes a form.

Here _{ij} are the elastic constants [^{L}, n^{G} for the valleys G, L are present in the Equations (3).

As in the case of piezoactive transverse modes, the effective excitation of acoustic-electromagnetic waves with displacement like in Equations (3) takes place near cut-off frequency. It is shown that the symmetric modes emerging as transverse ones interact more effectively with the space charge waves. A distribution of the displacements near cut-off is

here s_{l} » 5.5 × 10^{5} cm/s is the longitudinal sound velocity in GaAs [

The computer modeling in the base of Equations (3) and (4) is the same like for case the piezoeffect. This modeling has demonstrated that the distributions in the plane of the film of excited acoustic-electromagnetic waves are very similar to those obtained for piezoeffect. But it is shown ¡ that the efficiency of excitation due to deformation potential becomes dominating at higher frequencies f > 30 GHz.

The resonant interaction of space charge waves with acoustic-electromagnetic waves in thin GaAs films can be used for effective in microwave wave range. At the frequencies f < 30 GHz efficiency of excitation of acoustic- electromagnetic due to piezoeffect is more effective, but at higher frequencies, deformation potential is dominating. An intensity of acoustic-electromagnetic waves can reach 10 W/cm^{2} at microwave frequencies range f = 10 GHz ÷ 30 GHz. To increase a frequency of excited wave to millimeter range, it is possible to choose the resonant excitation of acoustic-electromagnetic waves at the second harmonic of the input signal.

Authors thank SEP-CONACyT for the support of our work.

S.Koshevaya,V.Grimalsky,Y.Kotsarenko,J.Escobedo-Alatorre, (2015) Comparison of Excitation of Acoustic-Electromagnetic Wave in Piezoelecric Crystal and Crystal with Potential of Deformation. Journal of Electromagnetic Analysis and Applications,07,259-264. doi: 10.4236/jemaa.2015.710027