-
Determination of the Fermi Level Position in Dilute Magnetic Ga$_{1-x}$Mn$_{x}$N Films
Authors:
Stefan Barthel,
Gerd Kunert,
Mariuca Gartner,
Mihai Stoica,
Daniel Mourad,
Carsten Kruse,
Stephan Figge,
Detlef Hommel,
Gerd Czycholl
Abstract:
We report on a combined theoretical and experimental determination of the Fermi level position in wurtzite Ga$_{1-x}$Mn$_{x}$N films with $x=4\%$ and $x=10\%$ as grown by molecular beam epitaxy. By means of ellipsometric measurements the real part of the frequency-dependent conductivity is determined. An electronic model in the framework of the effective bond-orbital model is parameterized in orde…
▽ More
We report on a combined theoretical and experimental determination of the Fermi level position in wurtzite Ga$_{1-x}$Mn$_{x}$N films with $x=4\%$ and $x=10\%$ as grown by molecular beam epitaxy. By means of ellipsometric measurements the real part of the frequency-dependent conductivity is determined. An electronic model in the framework of the effective bond-orbital model is parameterized in order to theoretically reproduce the measured transport properties. Predictions for the long-wavelength behaviour as a function of the Fermi level are made. The corresponding density of states obtained in this model is in qualitative agreement with first-principle calculations. The absence of a significant experimental peak in the AC conductivity for small frequencies indicates that the Fermi level lies in a gap between two Mn-related impurity bands in the host band gap.
△ Less
Submitted 12 March, 2014; v1 submitted 27 January, 2014;
originally announced January 2014.
-
Phase diagram and critical behavior of the random ferromagnet $Ga_{1-x}Mn_xN$
Authors:
S. Stefanowicz,
G. Kunert,
C. Simserides,
J. A. Majewski,
W. Stefanowicz,
C. Kruse,
S. Figge,
Tian Li,
R. Jakiela,
K. N. Trohidou,
A. Bonanni,
D. Hommel,
M. Sawicki,
T. Dietl
Abstract:
Molecular beam epitaxy has been employed to obtain Ga1-xMnxN films with x up to 10% and Curie temperatures T_C up to 13 K. The magnitudes of T_C and their dependence on x, T_C(x) ~ x^m, where m = 2.2 +/- 0.2 are quantitatively described by a tight binding model of superexchange interactions and Monte Carlo simulations of T_C. The critical behavior of this dilute magnetic insulator shows strong dev…
▽ More
Molecular beam epitaxy has been employed to obtain Ga1-xMnxN films with x up to 10% and Curie temperatures T_C up to 13 K. The magnitudes of T_C and their dependence on x, T_C(x) ~ x^m, where m = 2.2 +/- 0.2 are quantitatively described by a tight binding model of superexchange interactions and Monte Carlo simulations of T_C. The critical behavior of this dilute magnetic insulator shows strong deviations from the magnetically clean case (x = 1), in particular, (i) an apparent breakdown of the Harris criterion; (ii) a non-monotonic crossover in the values of the susceptibility critical exponent gamma_eff between the high temperature and critical regimes, and (iii) a smearing of the critical region, which can be explained either by the Griffiths effects or by macroscopic inhomogeneities in the spin distribution with a variance Delta x = (0.2 +/- 0.1)%.
△ Less
Submitted 21 June, 2013;
originally announced June 2013.
-
GaMnN epitaxial films with high magnetization
Authors:
Gerd Kunert,
Sylwia Dobkowska,
Tian Li,
Helfried Reuther,
Carsten Kruse,
Stephan Figge,
Rafal Jakiela,
Alberta Bonanni,
Jörg Grenzer,
Wiktor Stefanowicz,
Maciej Sawicki,
Tomasz Dietl,
Detlef Hommel
Abstract:
We report on the fabrication of pseudomorphic wurtzite GaMnN grown on GaN with Mn concentrations up to 10% using molecular beam epitaxy. According to Rutherford backscattering the Mn ions are mainly at the Ga-substitutional positions, and they are homogeneously distributed according to depth-resolved Auger-electron spectroscopy and secondary-ion mass-spectroscopy measurements. A random Mn distribu…
▽ More
We report on the fabrication of pseudomorphic wurtzite GaMnN grown on GaN with Mn concentrations up to 10% using molecular beam epitaxy. According to Rutherford backscattering the Mn ions are mainly at the Ga-substitutional positions, and they are homogeneously distributed according to depth-resolved Auger-electron spectroscopy and secondary-ion mass-spectroscopy measurements. A random Mn distribution is indicated by transmission electron microscopy, no Mn-rich clusters are present for optimized growth conditions. A linear increase of the c-lattice parameter with increasing Mn concentration is found using x-ray diffraction. The ferromagnetic behavior is confirmed by superconducting quantum-interference measurements showing saturation magnetizations of up to 150 emu/cm^3.
△ Less
Submitted 17 May, 2012; v1 submitted 15 May, 2012;
originally announced May 2012.
-
High-reflectivity broadband distributed Bragg reflector lattice matched to ZnTe
Authors:
W. Pacuski,
C. Kruse,
S. Figge,
D. Hommel
Abstract:
We report on the realization of a high quality distributed Bragg reflector with both high and low refractive index layers lattice matched to ZnTe. Our structure is grown by molecular beam epitaxy and is based on binary compounds only. The high refractive index layer is made of ZnTe, while the low index material is made of a short period triple superlattice containing MgSe, MgTe, and ZnTe. The hi…
▽ More
We report on the realization of a high quality distributed Bragg reflector with both high and low refractive index layers lattice matched to ZnTe. Our structure is grown by molecular beam epitaxy and is based on binary compounds only. The high refractive index layer is made of ZnTe, while the low index material is made of a short period triple superlattice containing MgSe, MgTe, and ZnTe. The high refractive index step of Delta_n=0.5 in the structure results in a broad stopband and the reflectivity coefficient exceeding 99% for only 15 Bragg pairs.
△ Less
Submitted 31 March, 2009;
originally announced March 2009.
-
Optical Properties and Modal Gain of InGaN Quantum Dot Stacks
Authors:
Joachim Kalden,
Kathrin Sebald,
Juergen Gutowski,
Christian Tessarek,
Timo Aschenbrenner,
Stephan Figge,
Detlef Hommel
Abstract:
We present investigations of the optical properties of stacked InGaN quantum dot layers and demonstrate their advantage over single quantum dot layer structures. Measurements were performed on structures containing a single layer with quantum dots or threefold stacked quantum dot layers, respectively. A superlinear increase of the quantum dot related photoluminescence is detected with increasing…
▽ More
We present investigations of the optical properties of stacked InGaN quantum dot layers and demonstrate their advantage over single quantum dot layer structures. Measurements were performed on structures containing a single layer with quantum dots or threefold stacked quantum dot layers, respectively. A superlinear increase of the quantum dot related photoluminescence is detected with increasing number of quantum dot layers while other relevant GaN related spectral features are much less intensive when compared to the photoluminescence of a single quantum dot layer. The quantum dot character of the active material is verified by microphotoluminescence experiments at different temperatures. For the possible integration within optical devices in the future the threshold power density was investigated as well as the modal gain by using the variable stripe length method.
△ Less
Submitted 1 December, 2008;
originally announced December 2008.