zvOptical properties of low symmetry materials and their determination by spectroscopic ellipsometry
Sprache des Vortragstitels:
E- MRS Spring Meeting 2021
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Resume : Wide-bandgap materials, which are interesting for opto-electronic devices, like Ga2O3, exhibit often a low crystal symmetry. Here, we present the determination of the optical properties of such materials by spectroscopic ellipsometry. For the investigation of the nature of the underlying excitations, we present a general approach for the decomposition of the dielectric function by taking into account the dipole orientation distribution of each excitation into account. The application of this approach is demonstrated exemplary on an orthorhombic KTiOPO4, monoclininc Ga2O3 and triclinic K2Cr2O7. Without making any assumptions, we show that the tensor elements of the dielectric function in general are not independent of each other. The dielectric function can be described by a superposition of electronic transitions. For each transition an eigensystem exists in which the contribution to the dielectric function is given by a diagonal susceptibility tensor. The relative magnitude of these tensor elements is given by the dipole orientation distribution of the corresponding transition. In the limiting case, the oriented dipole approach is obtained as well as the tensor for uniaxial and isotropic materials. It is also shown that the imaginary part of the non-diagonal tensor elements can become negative, which is forbidden in scalar systems.
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