M. Schubert

Raman scattering in ZnO thin films doped with Fe, Sb, al, Ga, and Li

Polarized micro-Raman measurements were performed to study the phonon modes of Fe, Sb, Al, Ga, and Li doped ZnO thin films, grown by pulsed-laser deposition on c-plane sapphire substrates. Additional modes at about 277, 511, 583, and 644 cm−1, recently assigned to N incorporation [A. Kaschner et al., Appl. Phys. Lett. 80, 1909 (2002)], were observed for Fe, Sb, and Al doped films, intentionally grown without N. The mode at 277 cm−1 occurs also for Ga doped films. These modes thus cannot be related directly to N incorporation. Instead, we suggest host lattice defects as their origin. Further additional modes at 531, 631, and 720 cm−1 seem specific for the Sb, Ga, and Fe dopants, respectively. Li doped ZnO did not reveal additional modes.

Dielectric functions (1 to 5 eV) of wurtzite MgxZn1−xO (x⩽0.29) thin films

The optical dielectric functions for polarization perpendicular and parallel to the c-axis (optical axis) of pulsed-laser-deposition grown wurtzite MgxZn1−xO (0⩽x⩽0.29) thin films have been determined at room temperature using ellipsometry for photon energies from 1 to 5 eV. The dielectric functions reveal strong excitonic contributions for all Mg concentrations x. The band gap energies (E0A=3.369 eV for ZnO to 4.101 eV for x=0.29) show a remarkable blueshift. The exciton binding energy (61 meV for ZnO) decreases to approximately 50 meV for x≈0.17 and increases to approximately 58 meV for x=0.29. In contrast to ZnO, the MgxZn1−xO alloys are found uniaxial negative below the band gap energy, opposite to previously reported results.

Infrared dielectric functions and phonon modes of wurtzite MgxZn1-xO (x≤0.2)

Infrared dielectric function spectra and phonon modes with polarization parallel and perpendicular to the c axis of high quality, highly relaxed, and single crystalline wurtzite MgxZn1−xO films with 0⩽x⩽0.2 prepared by pulsed-laser deposition on c-plane sapphire substrates were obtained from infrared spectroscopic ellipsometry (380–1200 cm−1) and Raman scattering studies. A two-mode behavior is found for the modes with E1 symmetry, a lattice mode and an impurity-type mode are obtained for the A1 symmetry phonons. Model dielectric function spectra will become useful for future infrared ellipsometry analysis of complex MgxZn1−xO-based heterostructures.

Infrared dielectric function and phonon modes of Mg-rich cubic MgxZn1-xO (x≥0.67) thin films on sapphire (0001)

Infrared dielectric function spectra and phonon modes of single-phase rocksalt-type MgxZn1−xO thin films with 0.67⩽x⩽1 prepared by pulsed-laser deposition on c-plane sapphire substrates were obtained from infrared spectroscopic ellipsometry (360cm−1 to 1500cm−1). A one-mode behavior is found. Phonon mode frequencies, the high-frequency limit of the dielectric function, and phonon mode broadening parameters reflect a considerable and systematic dependence on the Mg content x. X-ray diffraction measurements revealed the single-phase growth and a decreasing lattice constant with increasing x.

Far-infrared-magneto-optic ellipsometry characterization of free-charge-carrier properties in highly disordered n-type Al0.19Ga0.33In0.48P

For highly disordered n-type Al0.19Ga0.33In0.48P grown lattice matched to an undoped GaAs substrate, using far-infrared-magneto-optic generalized ellipsometry, the room-temperature free-charge-carrier parameters effective mass m*=0.12(0.01) m0, concentration N=6.7(0.2)×1017 cm−3, and mobility μ=339(15) cm2/(V s) are determined by modeling the observed magneto-optic birefringence originating from the far-infrared free-charge-carrier excitations in the Al0.19Ga0.33In0.48P layer without additional electrical measurements.

Infrared dielectric function and vibrational modes of pentacene thin films

Generalized infrared spectroscopic ellipsometry over the wave-number range from 300 to 2000 cm−1 is used for precise determination of the dielectric function, frequency, amplitude, and broadening parameters of 27 infrared active modes for polarization parallel to the growth surface of pentacene thin films obtained by molecular-beam deposition on glass. No in-plane anisotropy was detected, which is indicative for a random orientation of crystallites around the growth direction supporting previous x-ray diffraction results.

Carrier redistribution in organic/inorganic (poly(3,4-ethylenedioxy thiophene/poly(styrenesulfonate)polymer)-Si) heterojunction determined from infrared ellipsometry

Carrier redistribution in organic/inorganic (poly(3,4-ethylenedioxy thiophene/poly(styrenesulfonate)polymer)-Si) heterojunction determined from infrared ellipsometry