Plasmon Spectra at Wurtzite Aluminum Gallium Nitride / Silicon Carbide Heterojunctions
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Plasmon Spectra at Wurtzite Aluminum Gallium Nitride / Silicon Carbide Heterojunctions Choudhury Jayant Praharaj previously with University of Utah, Salt Lake City, 84112 USA
Abstract We present theoretical calculations for electron plasmon spectra at wurtzite Aluminum Gallium Nitride/ Silicon Carbide heterojunctions. Spontaneous and piezoelectric polarizations in wurtzite semiconductors give rise to polarization discontinuities at interfaces and to bound interface sheet charges. These charges are of the order of 1013 electrons per cm2 and give rise to two dimensional electron or hole gases near heterojunctions. Electron-electron interactions in the two-dimensional electron gases give rise to collective plasmon excitations. We calculate the dielectric function in these electron gases under the well-known and widely studied random phase approximation. Our calculations are relevant to the determination of the plasmon spectra at wurtzite Aluminum Gallium Nitride / Silicon Carbide heterojunctions and are of potential interest for determining the limits of mobility in two-dimensional electron gases. They are also of interest for terahertz electronics applications.
Introduction Two dimensional electron gases at wurtzite heterojunctions form the basis of electronic devices like the high electron mobility transistor. They are also of intrinsic interest due to novel material properties like spontaneous and piezoelectric polarization and due to the ability to sustain high electric fields and voltages in device applications. Plasmon excitations are of potential interest in semiconductors because they provide a pathway for inelastic scattering of carriers. Therefore, they can contribute to limiting the mobility in doped semiconductors and also in electron and hole gases. Also, they are of potential interest in terahertz detection and absorption [ 1 ] . The wurtzite Aluminum Gallium Nitride/ Silicon Carbide heterojunction wide band-gap heterojunction has large polarization discontinuities of the order of 1013 electrons per cm2. For some values of aluminum composition and some directions of growth, it is possible to get twodimensional electron gases at these heterojunctions. We present theoretical calculations for the electron plasmon spectra at these heterojunctions. The band-gaps of 4H SiC and 6H SiC are very similar, and the conduction band discontinuities to AlGaN are not known very precisely. Therefore, the qualitative features of our results can be taken to be valid for both.
Polarization-induced charges at wurtzite AlGaN / SiC interfaces Wurtzite Aluminum Gallium Nitride has spontaneous polarization given by Psp(AlxGa1-xN) = -0.090x - 0.034(1-x) + 0.021x(1-x) Cm-2
(1)
where the direction of polarization is along (0001). The piezoelectric polarization along (0001) is given by Ppiezo = 2((a-a0)/a0)(e31 – e33C13/C33 ) Cm-2
(2)
where a0 is the equilibrium lattice constant, and e31 , e33 , C13 , C33 are piezoelectric and elastic constants. For pseudomorphic layers, the piezoelectric polarization is directly proportional
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