PT Unknown
AU Schley, P
TI Optische Eigenschaften von InN und InN-basierten Halbleitern
PD February
PY 2011
WP https://www.db-thueringen.de/receive/dbt_mods_00017547
LA de
DE Spektroskopische Ellipsometrie; Gruppe-III-Nitride; InN; optische Eigenschaften; dielektrische Funktion; Bandlücke; kritische Punkte der Bandstruktur; Bandlückenrenormierung; Burstein-Moss-Shift
AB In this work, new methods were presented to determine experimentally the optical properties of InN and its alloys with GaN and AlN and to analyse the obtained data. Spectroscopic ellipsometry from the mid-infrared via the near-infrared towards the vacuum-ultravio\-let spectral region has been proven as a very powerful tool for studying the absorption related properties of those materials.Taking for the data analysis surface roughness and interface layers into account, a reliable dielectric function is obtained in the primary step which reflects the essential features of the materials. The interpretation of the spectral dependence represents the second step of the studies from which sample-dependent  parameters such as the frequencies of the coupled phonon-plasmon modes, the spacing between the conduction and valence bands at the Fermi wave vector, or the transition energies at the Van Hove singularities are determined. The intrinsic properties of the compounds were attained in the final step by correcting these data for carrier-induced band-gap renormalization and the Burstein-Moss shift as well as for strain for the first time.Due to an electron accumulation layer at the surface of the films, the electron density in the bulk-like part is determined by Infrared ellipsometry. From the MIR data the plasma frequency is extracted. It can be used for an accurate determination of the electron concentration in the bulk-like part of the layers.The fundamental interband absorption edge in the NIR range is affected by the presence of high electron concentrations and band non-parabolicity. The NIR data have to be self-consistently analysed (coupled to MIR results) by calculating the imaginary part of the DF via Fermi's Golden rule. The method yields 0.675 eV for the zero-density strain-free gap of hexagonal InN at room temperature. The value for the cubic counterpart is by 80 meV lower and was determined to be 0.595 eV. Analyzing the DF of hexagonal InGaN and InAlN alloys in a similar way, the bowing parameters of the E_A gaps were obtained. They amount to b_A = 1,71 eV (InGaN) und b_A = 4,0 eV (InAlN). A main result of this work is the determination of the DFs in the UV-VUV spectral region and their comparison to results of the theoretical calculations. Theory results on the imaginary part of the DF of InN are only in excellent agreement with the experimental data if electron-hole interaction (exciton effects) is consequently taken into account. The Coulomb correlation leads to redshift of the absorption peaks and a redistribution of oscillator strength in comparison to the independent quasi-particle DF.
ER