Virtual interface approximation model applied to spectroscopic ellipsometry for on-line composition determination of metalorganic chemical vapor deposition grown ternary nitrides

Bonanni, A.; Schmidegg, K.; Montaigne-Ramil, Alberto; Sitter, H.; Hingerl, Kurt; Stifter, David

doi:10.1116/1.1585078

Cited by 9 publications

(6 citation statements)

References 19 publications

(10 reference statements)

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“…The samples have been continuously rotated during growth in order to promote the deposition homogeneity. High-resolution X-ray diffraction measurements gave for all the samples a full-width-at-the-half-maximum (FWHM) of 240-280 arcsec, comparable with state-of-theart device-quality nitride material [13]. The total Fe and Mg concentration in the layers has been determined via secondary-ion mass spectroscopy (SIMS).…”

Section: Methodsmentioning

confidence: 99%

Doping of GaN with Fe and Mg for spintronics applications

Bonanni

Simbrunner

Wegscheider

et al. 2006

Physica Status Solidi (b)

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Metal-organic chemical vapour deposition of GaN : Fe and (Ga, Fe)N : Mg has been carried out in order to optimize the growth process and to investigate the effectiveness of Fe ions and Mg acceptors incorporation. All samples have been investigated via high-resolution X-ray diffraction, secondary-ion mass spectroscopy, electron paramagnetic resonance (EPR) and magnetization measurements. Co-doping of Fe and δ -Mg has been found to promote the acceptors incorporation and EPR data, supported by superconducting quantum interference device magnetometry experiments, reveal the presence of Fe ions in two charge states, namely the Fe 3+ responsible for Curie paramagnetism and the Fe 2+ tentatively correlated to van Vleck paramagnetism.

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Section: Methodsmentioning

confidence: 99%

Doping of GaN with Fe and Mg for spintronics applications

Bonanni

Simbrunner

Wegscheider

et al. 2006

Physica Status Solidi (b)

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“…37 The broadening of the GaN(0002) reflex is found to depend both on the iron doping level and on the growth temperature. The minimum FWHM is obtained for the lowest Cp 2 Fe flow rate, 50 sccm, and the highest growth temperature, 950 • C. Despite the importance of HRXRD for the routine structural characterization of the layers, the inadequacy of standard X-ray diffraction methods for nanoscale investigations (detection of the presence of non-uniform magnetic ion distribution) is already widely accepted.…”

Section: High-resolution X-ray Diffractionmentioning

confidence: 99%

ParamagneticGaN:Feand ferromagnetic(Ga,Fe)N: The relationship between structural, electronic, and magnetic properties

et al. 2007

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We report on the metalorganic chemical vapor deposition (MOCVD) of GaN:Fe and (Ga,Fe)N layers on c-sapphire substrates and their thorough characterization via high-resolution x-ray diffraction (HRXRD), transmission electron microscopy (TEM), spatially-resolved energy dispersive X-ray spectroscopy (EDS), secondary-ion mass spectroscopy (SIMS), photoluminescence (PL), Hall-effect, electron-paramagnetic resonance (EPR), and magnetometry employing a superconducting quantum interference device (SQUID). A combination of TEM and EDS reveals the presence of coherent nanocrystals presumably FexN with the composition and lattice parameter imposed by the host. From both TEM and SIMS studies, it is stated that the density of nanocrystals and, thus the Fe concentration increases towards the surface. According to Hall effect measurements, electrons from residual donors are trapped by mid-gap Fe acceptor states in the limit of low iron content x 0.4%, indicating that the concentration of Fe 2+ ions increases at the expense of Fe ions in the 3+ charge state. This effect is witnessed by photoluminescence (PL) measurements as changes in the intensity of the Fe 3+ -related intra-ionic transition, which can be controlled by co-doping with Si donors and Mg acceptors. In this regime, EPR of Fe 3+ ions and Curie-like magnetic susceptibility are observed. As a result of the spin-orbit interaction, Fe 2+ does not produce any EPR response. However, the presence of Fe ions in the 2+ charge state may account for a temperature-independent Van Vleck-type paramagnetic signal that we observe by SQUID magnetometry. Surprisingly, at higher Fe concentrations, the electron density is found to increase substantially with the Fe content. The co-existence of electrons in the conduction band and Fe in the 3+ charge state is linked to the gradient in the Fe concentration. In layers with iron content x 0.4% the presence of ferromagnetic signatures, such as magnetization hysteresis and spontaneous magnetization, have been detected. A set of precautions has been undertaken in order to rule out possible sources of spurious ferromagnetic contributions. Under these conditions, a ferromagnetic-like response is shown to arise from the (Ga,Fe)N epilayers, it increases with the iron concentration, it persists up to room temperature, and it is anisotropic -i.e., the saturation value of the magnetization is higher for in-plane magnetic field. We link the presence of ferromagnetic signatures to the formation of Fe-rich nanocrystals, as evidenced by TEM and EDS studies. This interpretation is supported by magnetization measurements after cooling in-and without an external magnetic field, pointing to superparamagnetic properties of the system. It is argued that the high temperature ferromagnetic response due to spinodal decomposition into regions with small and large concentration of the magnetic component is a generic property of diluted magnetic semiconductors and diluted magnetic oxides showing high apparent Curie temperature.

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“…The CPA is only valid for absorbing layers and thus only channels lying above both band gaps can be used for our calculations. Constant values for GaN are followed by damped oscillations during AlGaN growth, which describe converging spirals when hiis plotted in the complex plane [5,11]. The spiral convergence points represent the dielectric function of the AlGaN compound for the respective wavelength.…”

Section: Resultsmentioning

confidence: 99%

“…We recently reported on the implementation of an algorithm based on the virtual interface approximation model for the determination of layer compositions of AlGaN in real-time [4,5]. In the present paper, we extend the in situ monitoring capability 11.192 by performing on-line SE measurements with a multiple wavelength ellipsometer.…”

Section: Introductionmentioning

confidence: 91%