Overgrowth experiments of ferromagnetic (MnGa)As-cluster layers by MOVPE

Lampalzer, M.; Volz, Kerstin; Treutmann, W.; Nau, Siegfried; Torunski, T.; Megges, Klaus; Lorberth, Jörg; Stolz, W.

doi:10.1016/s0022-0248(02)01920-6

Cited by 24 publications

(28 citation statements)

References 8 publications

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“…The segregation of TM-rich nanocrystals towards the surface of the samples, seems to represent a general phenomenon in highly TM-doped MOCVD III-V compounds: a similar effect has been observed for MnAs nanocrystals in MOCVD grown (Ga,Mn)As. 38 We estimate that the nanocrystals occupy less than 1% of the film volume and their diameter varies from 5 to 50 nm. Some precipitates are elongated in the growth direction, as shown in Fig.…”

Section: A Transmission Electron Microscopymentioning

confidence: 96%

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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Section: A Transmission Electron Microscopymentioning

confidence: 96%

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

et al. 2007

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“…Using such LT-MBE growth technologies, device structures for waveguide-type optical isolators utilizing MnAs nano-clusters have been proposed recently [4]. Although metal-organic vapor phase epitaxy (MOVPE) is one of the most important technologies for the fabrication of highly integrated PICs, only a few studies on MOVPE growth of III-V DMS materials were reported [5][6][7]. In the MOVPE growth of magnetic semiconductors related to Mn-incorporated GaAs layers, ferromagnetic MnGaAs cluster structures were formed in GaAs host matrices [5].…”

Section: Introductionmentioning

confidence: 99%

“…Although metal-organic vapor phase epitaxy (MOVPE) is one of the most important technologies for the fabrication of highly integrated PICs, only a few studies on MOVPE growth of III-V DMS materials were reported [5][6][7]. In the MOVPE growth of magnetic semiconductors related to Mn-incorporated GaAs layers, ferromagnetic MnGaAs cluster structures were formed in GaAs host matrices [5]. In (InMn)As layers grown by MOVPE on GaAs substrates, single-phase (InMn)As DMS alloy films were formed [6].…”

Section: Introductionmentioning

confidence: 99%

Cluster formation and magnetic properties of Mn-incorporated (GaIn)As/InP layers grown by metal-organic vapor phase epitaxy

Hara

Lampalzer

Torunski

et al. 2004

Journal of Crystal Growth

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“…It is known that the increase of substrate temperature leads to an enhancement of phase segregation in GaMnAs [3,4], namely the MnAs clusters' size increases with increasing of T s , but on the other hand, the density of the clusters could rather decrease [12,13]. Hence, the variation of the hole concentration with T s may be explained by the varying content of the MnAs clusters with T s , and which in turn changes the concentration of the acceptor Mn in the GaMnAs matrix.…”

Section: Resultsmentioning

confidence: 99%