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17 Fall

-Hexagonal symmetry crystals are strongly influenced by the piezoelectricity where the strain and electric fields are also coupled.

-A representative sample is LED made of InGaN quantum wells and GaN barriers which have opposite strain signs, thus, have opposite direction of piezoelectric field (PEF).  This PEF should be added into external fields due to voltages and depletion fields due to p-i-n doping.

-As we introduced previously, the strain components in hexagonal symmetry in wurtzite GaN are coupled with the electric field distributions as εm =dnmEn (m=1, 2,…, 6), where nonzero electric field values of E3 = Ez and E1= Ex lead to the normal (εzz = ε3) and shear strain components (εzx = ε5) in the x-z plane.

-The presence of piezoelectricity modifies the propagation characteristics (phase velocities and polarizations) of the acoustic modes. We develop the Christoffel equation for piezoelectric classes, show the dependence of piezoelectricity on the crystal orientation.

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