Manganese bis(cyclopentadienyl) MnCp2 (manganocene)
Bis-cyclopentadienyl manganese (Cp2Mn) has been applied as Mn precursor for the growth of GaMnN thin films by MOCVD (with GaMe3 and NH3 as
Ga and N sources). GaMnN samples with high Mn concentrations demonstrated ferromagnetism at room temperature (RT); an absorption band at ~1.5 eV was observed, whose intensity and linewidth scaled with the Mn concentration and with the RT saturation magnetization
(the broadening of the absorption band was introduced by the high Mn concentration). This band was assigned to the internal Mn3+ transition between the 5E and the partially filled 5T2 levels of the 5D state. Recharging of the Mn3+ to Mn2+ effectively suppressed
these transitions resulting in a significant reduction of the RT magnetization. Magnetization behavior of the grown Ga1−xMnxN epilayers can be predicted from the pronounced sensitivity of the relative position of the Fermi level and 1.5 eV absorption
band. Raman spectroscopy revealed the absence of doping-induced strain. EPR spectroscopy confirmed the structural quality and the presence of Mn2+ ions; no Mn-Mn interactions were observed.[[i] ]
[i] Strassburg Martin, Senawiratne Jayantha, Hums Christoph, Dietz Nikolaus, Kane Matthew H., Asghar Ali, Summers Christopher J., Haboeck Ute, Hoffmann Axel, Azamat Dmitry, Gehlhoff Wolfgang and Ferguson Ian T , MRS Proceedings / Volume 831 / 2004, DOI:/10.1557/PROC-831-E9.5
Optical and Structural Investigations on Mn-Ion States in MOCVD-grown Ga1−xMnxN, http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8002348
Di‐π‐cyclopentadienyl manganese MnCp2 has been successfully applied as Mn precursor for the doping of ZnS:Mn films, grown by low-pressure MOCVD on ITO- coated glass substrates at 225°C. The concentration of manganese in the films was varied by changing of MnCp2 bubbler temperature. The crystallinity and morphology of the deposited ZnS:Mn layers was studied by XRD and AFM; the average grain size was estimated ~43 nm by Debye‐Scherrer relation. ZnS:Mn ac thin film electroluminescent devices with a double insulating layer structure had luminance >1500 cd/m2, higher than the previously reported 680 cd/m2, obtained using same Mn source (MnCp2). [[i]]
[i] S. H. Su, P. R. Tsai, M. Yokoyama and Y. K. Su, J. Electrochem. Soc. 1996 volume 143, issue 12, 4116-4118; doi: 10.1149/1.1837347, http://jes.ecsdl.org/content/143/12/4116.short
Use of Di‐π‐cyclopentadienyl Manganese as a Dopant Source for ZnS in Metallorganic Chemical Vapor Deposition
Di-π-cyclopentadienyl manganese [(C5H5)2Mn] (MnCp2) has been successfully applied as Mn dopant precursor for the growth of ZnSe:Mn layers by plasma-assisted MOCVD. These layers were used for the preparation of Al/ZnSe:Mn/ITO (indium tin oxide) dc-electroluminescent cells. [[i]]
As a manganese source, Di‐π‐cyclopentadienyl manganese [(C5H5)2Mn] (MnCp2) was used as Mn source for the growth of epitaxial ZnSe:Mn thin films (with ZnEt2 and SeEt2 as Zn and Se precursors) at the low substrate temperature of 250 °C by plasma‐assisted MOCVD, the technique combining rf glow discharge (at 13.56 MHz) precursor decomposition with conventional MOCVD, which brings advantages such as low-temperature growth, high chemical reactivity, cleaning effect of substrate surface, and good surface morphology. The deposited ZnSe:Mn films had excellent surface morphology and uniformity. These layers were used in the fabrication of the Al/ZnSe:Mn/ITO (indium tin oxide) dc‐operated electroluminescent cells.[ii]
[i] Naoki Mino, Masakazu Kobayashi, Makoto Konagai and Kiyoshi Takahashi
Jpn. J. Appl. Phys. 24 (1985) pp. L383-L385 , http://jjap.jsap.jp/link?JJAP/24/L383/ ZnSe:Mn DC-Electroluminescent Cells Using Di-π-Cyclopentadienyl Manganese as a New Manganese Source Fabricated by Plasma-Assisted MOCVD
[ii] Naoki Mino, Masakazu Kobayashi, Makoto Konagai and Kiyoshi Takahashi, J. Appl. Phys. 59, 2216 (1986); http://dx.doi.org/10.1063/1.336362
http://scitation.aip.org/content/aip/journal/jap/59/6/10.1063/1.336362
Plasma‐assisted metalorganic chemical vapor deposition of ZnSe films
Manganese bis(methylcyclopentadienyl) Mn(MeCp)2
Bis-(methylcyclopentadienyl) manganese (MCp2Mn) was applied as Mn precursor for the growth of nitrogen/manganese codoped ZnO (ZnM- nO:N) thin films by MOCVD at 400 °C (with DEZn as Zn precursor and N2O as nitrogen doping source ). Impurity carbon unintentionally introduced in N-doped ZnO:Mn during MOCVD growth was studied by TEM and Raman spectroscopy (it is important because unintentional doped carbon may form graphite clusters along grain boundaries resulting in n-type domains and possibly be a big obstacle for the realization of p-type conductivity). It was found that the enhanced desorption rate of hydrocarbon radicals by high temperature and oxygen atoms can significantly suppress carbon incorporation rate and therefore minimize carbon impurity for realization of p-type N-doped ZnO:Mn.[[i]]
The influences of Mn doping (using bis(methylcyclopentadienyl) manganese Mn(MeCp)2 as manganese source) on the electrical
and optical properties of the Zn1−xMnxO:N films grown by MOCVD was studied. (ZnEt2 was used as Zn source). It was found that Mn incorporation occupying on the Zn site led to the increase of lattice constant and the bandgap of the films accompanied by
the deterioration of the structural quality). Zn1−xMnxO:N electrical properties changed significantly with Mn content in the films, due to the changes in the amount of the NO acceptors and CN compensation centers formed in the films by Mn incorporation,
as revealed by XPS. The chemical states of Mn was Mn2+ and Mn4+, corresponding to Mn occupying on the Zn site and MnO2 second phase, respectively. The conductivity behaviour and the Mn2+ content of the films showed a strong effect on the magnetic properties,
explained by the Mn 3d and N 2p ferromagnetic (hole) coupling influence on the ferromagnetism. Uncompensated spins from nonuniform distribution of Mn atoms in ZnO may also be responsible for the observation of ferromagnetism signature at least in the high
resistant samples.[[ii]]
[i] Tang, Kun, Gu, Shulin ; Zhu, Shunming ; Liu, Wei ; Ye, Jiandong ; Zhu, Jianmin ; Zhang, Rong ; Youdou Zheng ; Xiaowei Sun, Applied Physics Letters (Vol.93 , Iss. 13 ), Sep 2008, p.132107 - 132107-3
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=4834819&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D4834819
Carbon clusters in N-doped ZnO by metal-organic chemical vapor deposition
[ii] Kongping Wu, Shulin Gu, Kun Tang, Shunming Zhu, Mingxiang Xu, R. Zhang, Y. Zheng, J. Appl. Phys. 106, 113710 (2009); http://dx.doi.org/10.1063/1.3266165
http://scitation.aip.org/content/aip/journal/jap/106/11/10.1063/1.3266165
Mn incorporation induced changes on structure and properties of N-doped ZnO
Bis (methylcyclopentadienyl) manganese BCPM Mn(MeCp)2 has been applied as Mn dopant precursor for the preparation of ZnS:Mn polycrystalline films by MOCVD (and compared to CPM [(C5H5)2Mn: di-π-cyclopentadienyl manganese] MnCp2 and TCM [(CH3C5H4)Mn(CO)3: tricarbonyl methylcyclopentadienyl manganese] Mn(MeCp)(CO)3.
Mn(MeCp)2 and MnCp2 were completely decomposed around the optimum
ZnS growth temperature (280–350°C), in contrast to Mn(MeCp)(CO)3, which only partially decomposes even at 400-500°C. Mn(MeCp)2 and MnCp2 upon thermal decomposition do not form luminescence-harmful by-products (in contrast to Mn(MeCp)(CO)3 which
produces a by-product containing Mn and carbonyl, which do not contribute to the luminescence). The double-insulator type electroluminescent (EL) devices prepared using Mn(MeCp)2
and MnCp2 showed higher luminance than those grown using Mn(MeCp)(CO)3. A 500 nm thick ZnS:Mn layer by MnCp2 had maximum efficiency (ηmax) 4.8 lm/W and a saturated luminance (Lsat) 4300 cd/m2 at 1 kHz sine wave excitation. With Mn(MeCp)2 , Lsat of 3150
cd/m2 was obtained. For comparison, devices prepared with Mn(MeCp)(CO)3 had Lsat <1000 cd/m2 and a low efficiency < 1 lm/W., ZnS:Mn layers grown using Mn(MeCp)2 and MnCp2 also
demonstrated efficient red EL (by using combination with red filters). Using glass filter with cut-off wavelength is 590 nm, the EL device prepared with MnCp2 gave Lsat=1420 cd/m2 and ηmax=1.6 lm/W (color coordinates, x=0.626 and y=0.373) at 1 kHz sine
wave excitation.[[i]]
[i]M.Migita, O. Kanehisa, M.Shiiki, H.Yamamoto, J.Cryst.Growth, Vol93, Iss1–4, 1988, p.686
The preparation of ZnS:Mn electroluminescent layers by MOCVD using new manganese sources
Bis(methylcyclopentadienyl)manganese has been applied as Mn precursor for the
atomic layer epitaxy (ALE) preparation of GaMnAs layers on GaAs(001) substrates. (with GaMe3 and As(NMe2)3 as Ga and As sources). Although the growth of GaMnAs was carried out at a high growth temperature (500 °C), a distinct self-limiting mechanism was
observed for the manganese alloy composition up to 6%, with no indications of including MnAs phase into the epitaxial layer. The GaMnAs layer showed an atomically flat surface morphology reflecting the self-limiting growth. The self-limiting mechanism was
strongly affected by the lattice mismatch between GaMnAs epitaxial layer and GaAs substrate: when Mn alloy composition exceeded 7%, the self-limiting mechanism was broken and MnAs precipitates were observed in the epitaxial layer.[[i]]
[i] M. Ozeki, T. Haraguchi, A. Fujita, physica status solidi (a), 2007, Vol 204, Iss 4, pages 992–997, http://onlinelibrary.wiley.com/doi/10.1002/pssa.200674101/abstract
Atomic layer epitaxy of GaMnAs on GaAs(001)
Bis(methylcyclopentadienyl)manganese Mn(MeCp)2 was applied as Mn source for
the growth of AlN:Mn films with Mn concentrations 2 × 1018 to 1 × 1021 cm−3 by MOCVD. AlN:Mn films grown at 1050 °C were polycrystalline, while at substrate temperatures (Ts) <800 °C a mixture of polycrystalline and amorphous AlN:Mn
were obtained, with the ratio of the amorphous phase increasing with decreasing Ts. AlN:Mn films demonstrated red–orange photoluminescence based on the transitions of d-electrons in Mn4+ ions at room temperature; the intensity of the Mn-related emission
increased with decreasing Ts. The electroluminescence properties were also srudied by fabricating thin film EL devices on glass substrates. [[i]]
[i] K. Hara, A. Sato, K. Azumada, T. Atsumori and M. Shiratori, physica status solidi (c), 2003, Special Issue: 5th International Conference on Nitride Semiconductors (ICNS-5), Vol0, Iss7, p.2274, http://onlinelibrary.wiley.com/doi/10.1002/pssc.200303318/abstract , Preparation of AlN:Mn films by metalorganic chemical vapor deposition for thin film electroluminescent devices
Bis (monomethycyclopentadienyl) manganese Mn(MeCp)2 has been
applied as Mn source for the growth of Ga1−xMnxN films by MOCVD (with GaMe3 and NH3 as Ga and N sources). The structural, optical and magnetic properties of deposited Ga1−xMnxN films were studied; the
valence band structure was analysed by the XPS measurements. Fermi level shift was observed with increasing Mn composition in the GaN; this shift was attributed to the donor-like defects induced by the Mn doping in the heavily doped samples, the presence of
these defects was confirmed by the cathodoluminescence spectroscopy. The additional peak around 2.0 eV in the heavily doped Ga1−xMnxN layers corresponded to the intra-d-shell transitions of Mn2+. This Mn2+ state was formed by trapping the electrons
released from the donor-like defects, consistent with the XPS results. [[i] ]
[i] X L Yang, Z T Chen, L B Zhao, W X Zhu, C D Wang, X D Pei and G Y Zhang, J. Phys. D: Appl. Phys. 2008 , 41 245004 doi:10.1088/0022-3727/41/24/245004, http://iopscience.iop.org/0022-3727/41/24/245004
Structural, optical and magnetic properties of Ga1−xMnxN films grown by MOCVD
Mn(EtCp)2 for Mn and MnOx metal films by MOCVD
Bis(ethylcyclopentadienyl)manganese Mn(EtCp)2 was applied as a metal-organic precursor for the growth of thin films of metallic manganese Mn and manganese oxides MnOx by thermal CVD on a TEOS-SiO2 substrates (p-type Si wafers with 100nm plasma TEOS-SiO2 layer). Mn(EtCp)2 precursor was vaporized and transported into a hot-wall reaction chamber with H2 carrier gas.
The microstructure and chemical composition of the CVD-grown Mn layer were studied by cross-sectional TEM combined with an EDS and XPS. By comparing the samples grown at 200, 400, and 500 °C (growth time 30 min), it was found that below 400 °C, a thin layer of MnOx (with C impurity) is formed on SiO2, but at 500 °C not only layer of MnOx (with C), but also large particles of metallic Mn were obtained on the surface.
The thickness of the deposited MnOx layer gradually increased from 2.6 to ~10 nm with substrate temperature increase from 100°C to 400 °C (activation energy was 17.7 kJ/mol, determined from plot in Arrhenius coordinates)
The thickness of the MnOx film as a function of growth time (at 200 °C) was investigated and it was found, that a thin and uniform MnOx film was formed on SiO2 already after reaction time of 1 min, and there was no notable growth of the MnOx film with firther increase of the reaction time.
Diffusion barrier properties of the Mn oxide film were investigated by annealing of Cu-covered layers at high temperature: the amorphous MnOx film deposited at 100 °C/30 min was annealed at 400°C for 100 h in vacuum (<1.0*10−5 Pa): after annealing, the MnOx layer remained amorphous, and no Cu diffusion into the SiO2 layer was observed by EDS, confirming that grown MnOx is good diffusion barrier.
The Mn film deposited at 500 °C consisted of metallic Mn particles as well as of thin continuous MnOx layer, indicating that thermal decomposition of Mn(EtCp)2 occurred >500 °C. (Similar results were reported for the CVD using (MeCp)MnCO3 precursor: in that case thermal decomposition (with breaking of Mn–Cp bond) occurred >410 °C depositing metallic Mn films. [S. Wen-bin, K. Durose, A. W. Brinkman, and J. Woods, J. Cryst. Growth, 1991, 113, 1]. The thermal decomposition of the Mn(EtCp)2 precursor was suggested to occur as well by the breaking Mn–Cp bond.
In contrast, below 400 °C the deposition behavior was completely different: only a thin layer of MnOx was formed below 400 °C with an activation energy of 17.7 kJ/mol, much smaller than the reported dissociation energies of 212 and 308 kJ/mol for Mn–Cp bonds,[9,10][9. J. R. Clipperfield, J. C. R. Sney, and D. E. Webster, J. Organomet. Chem.178, 177, 1979, 10. J. Opitz, Eur. J. Mass Spectrom. 7, 55 , 2001.] , indicating the presence of an enhancing mechanism to dissociate Mn to form the MnOx at low temperatures, f.e. by the capture of electrons from Mn atoms by oxygen ions .
Growth of MnOx by MOCVD using Mn(EtCp)2 is a promising
technique to form a conformal and reliable barrier layer for an advanced large-scale integrated interconnect structure.[[i]]
[i] K. Neishi, Sh. Aki, K. Matsumoto, H. Sato, H. Itoh, Sh. Hosaka, J. Koike, APPLIED PHYSICS LETTERS (2008), 93, 032106, http://ir.library.tohoku.ac.jp/re/bitstream/10097/46375/1/ApplPhysLett_93_032106.pdf Formation of a manganese oxide barrier layer with thermal chemical vapor deposition for advanced large-scale integrated interconnect structure
Bisethylcyclopentadienyl manganese (EtCp)2Mn has been applied as precursor for the CVD growth of Mn films on TEOS-based SiO2 substrates (as an alternative to PVD-CuMn option); the incorporation of Mn on the dielectric was found to be promoted by water present within the insulator. In contrast to TEOS-based SiO2, SiCOH dielectric materials are made hydrophobic in order to keep the dielectric constant low. As a result, formation of a Mn-based copper diffusion barrier by CVD of (EtCp)2Mn on SiCOH low-k dielectrics (which is needed for advanced technologies) is not expected.
However, PECVD process using (EtCp)2Mn precursor was
demonstrated to lead to similar Mn dose incorporated regardless of the amount of moisture available within the dielectric, meaning that PECVD Mn growth does not require moisture within the substrate to enable Mn incorporation, in contrast to CVD-Mn process.
Only a 2 nm PECVD-Mn based layer on a SiCOH dielectric material with a k of 3.2 exhibited an intrinsic barrier performance equivalent to a 6 nm industry established PVD-TaN/Ta barrier; the conformal growth (in a trench with an aspect ratio of 3) was demonstrated.
[[i]]
[i] Nicolas Jourdan, Yohan Barbarin, Kristof Croes, Yong Kong Siew, Sven Van Elshocht, Zsolt Tőkei and Eric Vancoille, ECS Solid State Lett. 2013 volume 2, issue 3, P25-P27 , “Plasma Enhanced Chemical Vapor Deposition of Manganese on Low-k Dielectrics for Copper Diffusion Barrier Application”, doi: 10.1149/2.002303ssl
Bisethylcylopentadienyl manganese Mn(EtCp)2 was applied as MOCVD precursor for the growth of thin-amorphous MnOx layers at 400-500°C temperature on TEOS-grown SiO2 substrates by thermal MOCVD, which demonstrated a good diffusion barrier properties, as well as adhesion properties in PVD-Cu/CVD-MnOx/SiO2/Si structures. The temperature dependence of the adhesion properties was correlating with the chemical composition and valence state of Mn (which were investigated by SIMS and Raman spectroscopy.) [i],[ii]
In another study, bisethylcyclopentadienyl manganese, Mn(EtCp)2 was applied as a metal-organic Mn precursor for the growth of manganese oxide (MnOx) thin films (20 nm thick) by the thermal-CVD process, which were investigated as Cu diffusion barrier by XPS, TEM), and C-V measurements. 2 different substrates were compared: on plasma-TEOS SiO2 substrates (showed good barrier properties up to 400°C, but at higher temperatutres the barrier properties was found deteriorated), whereas on the ozone-TEOS SiO2 substrates the barrier properties were negligibly small: even at room-temperature, the Cu2p signal emanating from MnOx/SiO2 region was observed. Therefore, care must be taken while using either MnOx as a barrier layer upon ozone-TEOS
SiO2 or ozone-TEOS SiO2 itself as a dielectric liner in along the side wall of TSVs, before integrating them into 3D-LSIs.. The Mn precursor was vaporized and introduced into a hot-wall reaction chamber containing hydrogen carrier gas. [[iii]]
[i] Koji Neishi, Shiro Aki, Jun Iijima, Junichi Koike, MRS Proc. /Volume 1079 / 2008, DOI: http://dx.doi.org/10.1557/PROC-1079-N03-11 Formation of Mn Oxide with Thermal CVD and its Diffusion Barrier Property Between Cu and SiO2
[ii]Koji Neishi, Vijay K. Dixit, S. Aki, J. Koike, K. Matsumoto, H. Sato, H. Itoh, S. Hosaka, MRS Proceedings / Volume 1156 / 2009, DOI: http://dx.doi.org/10.1557/PROC-1156-D04-10, “Adhesion and Cu Diffusion Barrier Properties of a MnOx Barrier Layer Formed with Thermal MOCVD”
http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=7968404
[iii] Murugesan, M., Bea, J.C.; Lee, K.W. ; Fukushima, T. ; Tanaka, T. ; Koyanagi, M.; Sutou, Y.; Wang, H.; Koike, J., 3D Systems Integration Conf. (3DIC), 2013 IEEE International, 2-4 Oct. 2013, p.1-4, “Effect of CVD Mn oxide layer as Cu diffusion barrier for TSV”
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=6702364&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D6702364
Bisethylcyclopentadienyl manganese Mn(EtCp)2 was applied as Mn precursor for the growth of MOCVD-self-formed-MnSixOy layers which were studied as Cu diffusion barriers. It was suggested that CVD-based MnSixOy films are serious candidates for sub-30 nm wide trench technologies because of their conformal
nature and ability to act as an efficient Cu diffusion barrier in the range of 2 nm thickness. [[i]]
[i] Nicolas Jourdan, Laureen Carbonell, Nancy Heylen, Johan Swerts, S. Armini, A. Maestre Caro, S. Demuynck, K. Croes, G. Beyer, Zsolt Tökei, S. Van Elshocht, E. Vancoille, ECS Trans. 2011, vol.34, iss.1, 515-521 , doi: 10.1149/1.3567629, “ Evaluation of Metallization Options for Advanced Cu Interconnects Application”, http://ecst.ecsdl.org/content/34/1/515.short
Mn(EtCp)2 was tested as a Mn precursor for the MOCVD growth of Mn-doped InGaN and GaN (Mn:InGaN and Mn:GaN) layers for their application as dilute magnetic semiconductors showing ferromagnetic behavior at room temperature and above. Curie temperatures of Mn-doped InxGa1- xN with x < 0.15 from 300 to 700 K (and for Mn:GaN films ranged from 228 to 520 K), as determined by temperature dependent SQUID and extraordinary Hall effect (EHE) measurements. Ferromagnetic properties were observed for Mn:InGaN for Mn concentration range of 0.12-8% and for Mn:GaN for 0.09-3.5% Mn, depending on the growth technique. The Mn:InGaN films coercivity ranged 100-800 Oe (the saturation magnetization varied from 1 to 28 emu/cm3)., whereas for Mn:GaN from 100 to 1500 Oe (saturation magnetization varied from 2 to 45 emu/cm3).
The easy axis of magnetization depends on the stress state of the InxGa 1-xN film and rotated from in-plane to out of plane by changing the film thickness, thus going from strained to fully relaxed films. For intermediate film thickness a transition region of partially relaxed film was identified with isotropic magnetic behavior.
The electrical properties of the Mn:InGaN and Mn:GaN films indicated that the films were highly resistive or n-type.
Temperature dependent SQUID and EHE measurements verified the absence of superparamagnetism in the films, confirming the absence of small phase separated particles within the films. XRD and TEM determined that no secondary phases were present in any of the
films studied, confirming that the ferromagnetic properties result from a solid solution of Mn in the InGaN or GaN lattice. [[i] ]
[i]Reed, Meredith Lynn, ProQuest Dissertations And Theses; Thesis (Ph.D.)--North Carolina State Univ., 2003.; Publ.Number: AAI3099013; ISBN: 9780496466177; Source: Dissertation Abstracts Intern., Vol. 64-07, Section: B, page: 3475.;263p., http://adsabs.harvard.edu/abs/2003PhDT........72R
“Growth and characterization of room temperature ferromagnetic manganese:gallium nitride and manganese:gallium indium nitride for spintronic applications”
Mn(EtCp2) was applied as the precursor for in-situ Mn doping for the GaMnN films grown by MOCVD. The dilute magnetic semiconductor GaMnN films showed ferromagnetism behavior above room temperature. GaMnN films were structurally characterized by XRD, SIMS and TEM ; they confirmed that the films were single crystal solid solutions without the presence of secondary phases. Manganese was incorporated homogeneously throughout the 0.7μm thick GaMnN layer, according to SIMS analysis. Ferromagnetic behavior for these films was observed in a Mn concentration range of 0.025–2% along the c-direction (out of plane orientation). The saturation magnetization of the GaMnN films ranged from 0.18–1.05 emu/cc depending on growth conditions; Curie temperatures was 270 to >400K, depending on Mn concentration. This dependence of Curie temperature on concentration of Mn in GaMnN indicated that the grown films were random solid solutions. The possibility of spin-glass and superparamagnetism in these MOCVD grown GaMnN films was ruled out by SQUID measurements. The grown films were electrically semi-insulating; however PL measurements showed that the films were still optically active after Mn doping. It was shown that the growth of III-Nitride films doped with Mn required a narrow growth conditions window (especially growth temperature and (EtCp)2Mn flux) to achieve ferromagnetism above room temperature, and the magnetic response of the film depended on the Fermi level position. It was suggested that ferromagnetism occurred when the Fermi level lied within the Mn energy level which is 1.4 eV above the GaN valence band. [[i][, [ii]]
In another study (Ga,Mn)N films were grown by MOCVD on c−plane sapphire substrates in a RF heated vertical chamber using bisethylcylo−pentadienyl manganese Mn(EtCp)2, Trimethylgallium GaMe3, and NH3 precursors, with he purpose to demonstrate room temperature ferromagnetic MOCVD grown (Ga,Mn)N, and investigate influence of growth parameters on the solubility limits of Mn in GaN as well as magnetic response.
The (Ga,Mn)N growth temperatures varied from 850 °C to 1040 °C, and pressures 100−760 Torr, the deposited (Ga,Mn)N film thickness ranged 0.6−1.4 μm (layers were grown on buffer consisted of thin 40 nm low temperature (500 oC) GaN nucleation layer and ~0.1 µm 1040 ºC-grown undoped GaN epitaxial layer (a template for (Ga,Mn)N). Thecrystal quality and the nature of any secondary phases was studied by XRD and TEM; the chemical composition of Mn in the resulting (Ga,Mn)N films was studied by SIMS. The magnetic properties of the films were investigated by Vibrating Sample Magnetometer (VSM) and SQUID measurements; electrical properties were studied by Hall measurements.
The influence of Mn(EtCp)2 flux, TMGa flux, growth temperature, and growth pressure on the range of solid solubility of Mn in GaN wasi nvestigated. The formation of secondary phases was independent of growth pressure,
but was critically dependent on the Mn(EtCp)2 flux for a given TMGa flux and growth temperature: single crystal (Ga,Mn)N could be obtained
only for (EtCp)2Mn <0.1 µmole. The Ga flux (i.e. growth rate) and the EtCp)2Mn/TMGa partial pressure ratio also affected the occurrence of secondary phases at a given growth temperature: even for a fairly low Mn flux (as low as 0.01 µmole) secondary
phases formed readily at lower growth rates indicating that secondary phase formation depends on growth kinetics as well as thermodynamic considerations. The growth temperature influenced formation of secondary phases, as well: at high growth temperatures
it was possible for kinetics to dominate where the Mn diffusivity was increased due to an increase in the total number of Ga vacancies which can enhance the formation of secondary phases. Thus single crystal (Ga,Mn)N can only be achieved in a narrow window
of optimal growth rate, growth temperature and Mn(EtCp)2 flux in the gas phase. The boundary between single crystal and multi−phase region is an approximation of the Mn solubility limit in GaN. Most of the (Ga,Mn)N films in the single crystal region
were determined to be ferromagnetic at room temperature: single crystal (Ga,Mn)N sample N153−02 showing ferromagnetic behavior was measured by SQUID at room temperature:
Mn concentration [Mn] = 4.313 X 1019 atoms/cm3 within the (Ga,Mn)N film was estimated, the saturation moment was ~ 1 μB/Mn atom, with a coercivity of ~ 100 Oe. Assuming that Mn2+ atom substitutes for Ga site in the GaN lattice so that J = 5/2, the Mn concentration
[Mn] calculated from the magnetization curves using MS = [Mn]gμBS was 3.88 X 1019 atoms/cm3, where MS is the saturation magnetization and the g−factor is 2. This indicated a 17% difference in Mn concentration when compared with values obtained from
SIMS, suggesting that not all of the Mn ions were contributing to ferromagnetic coupling. Growth conditions for sample N153−02 and N174−02 were nearly identical with the exception of the growth pressure, where samples were grown at 500 Torr and
760 Torr, respectively; their magnetic properties were very similar indicating that the growth pressure did not play a critical role for controlling the magnetic properties of the Mn:GaN films. The Curie temperature of ~ 400 K was measured by SQUID (based
on the measurement of saturation magnetization MS as a function of temperature for N153−02).[[iii]]
[i]Erkan Acar Berkman, Mason J. Reed, F. Erdem Arkun, Nadia A. El-Masry, John M. Zavada, M. Oliver Luen, Meredith L. Reed and Salah M. Bedair, Mater. Res. Soc. Symp. Proc. Vol. 834, 2005 Materials Research Society J7.3.1, “The Effect of Mn Concentration on Curie Temperature and Magnetic Behavior of MOCVD Grown GaMnN Films”
http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8002133
[ii] Arkun, Fevzi Erdem , “Study of manganese doped gallium nitride for spintronic applications”, Thesis (Ph.D.)--North Carolina State University, 2006.; Publication Number: AAI3247001; Source: Dissertation Abstracts International, Volume: 67-12, Section: B, page: 7306.; 215 p., http://adsabs.harvard.edu/abs/2006PhDT.......141A
[iii] N.A. Elmasry , M.L. Reed , S.M. Bedair , “Magnetic Properties of Mn−Doped III−Nitrides Grown by MOCVD”, 10th European Workshop on MOVPE, Lecce (Italy) 8−11 June 2003, http://siba-ese.unile.it/index.php/ewmovpex/article/download/7031/6394
Mn(EtCp)2 (DECPM) was introduced by the H2 carrier gas to the reaction chamber evacuated to ~ 1×10-7 Torr, followed by the introduction of vapor of ZnEt2:SEt2 adduct (or ZnEt2:SMe2, or ZnMe2:SMe2, or ZnMe2:SMe2), and H2S as the VI group source, which are contacting the insulating layer on the GaAs substrate at temperatures 100° to 450° C, forming a ~500nm thick ZnS:Mn crystal layer 24 having a thickness of about 500 nm. A ~250nm insulating layer of Ta2 O5 /SiO2 is formed then on the ZnS:Mn layer followed by the deposition of Al metal electrodes to obtain an electroluminescent device. The device prepared at a substrate temperature of 300° C exhibits a maximum intensity 1800 ft-L for an AC sinusoidal wave voltage of 220 volts, 1 kHz. For comparison, an electroluminescent device prepared using TCM as a source of manganese had max intensity of only 340 ft-L (prepared at the 430° C substrate temperature).
Thus, the prepared electriluminescent
devices exhibits favorable characteristics even when fabricated using DECPM as a manganese material at a substrate temperature of 300° C only. [[i]]
[i] Masahito Migita, Osamu Kanehisa, Masatoshi Shiiki, Hajime Yamamoto, “Method of manufacturing zinc chalcogenide semiconductor devices using LP-MOCVD”, US 5026661 A, Publ.Jun 25, 1991, http://www.google.com/patents/US5026661
Mn(iPrCp)2 for CdMnTe films by MOCVD
Bis(isopropylcyclopentadienyl) manganese Mn(iPrCp)2 (in combination with.CdMe2 and TeEt2 or Te(allyl)2 as Cd and Te sources), was applied as manganese precursor for the growth of polycrystalline CdMnTe thin films by MOCVD on CdS/SnO2/glass substrates; the layers had bandgaps of 1.65 – 1.75 eV for the top of a two-cell tandem design. P-i-n cells were fabricated and tested using Ni/p+-ZnTe as a back contact to the ternary films. [[i]]
Bis (isopropylcyclopentadienyl) manganese Mn(iPrCp)2 (BCPMn) (and for comparison MnCp(CO)3) ) was applied as Mn source for the growth of polycrystalline Cd1-xMn xTe (x = 0–0.25) films by MOCVD on CdS/SnO2/glass substrates for solar cell applications (Cd and Te sources were CdMe2 and TeiPr2). The Mn(iPrCp)2 source temperature was 100°C, the film growth temperature 420-450°C, the growth pressure 50-250 Torr. The compositional uniformity and interface quality of the films were studied by XRD, surface photovoltage, and Auger depth profile measurements to establish a correlation between growth conditions and lattice constant, atomic concentration, and bandgap of the ternary films. Cd1-x Mn x Te films grown by MOCVD in the temperature range of 420–450° C were compositionally non-uniform. In the MOCVD-grown Cd1-x Mn x Te/CdS, preferential exchange between Cd from the CdS layer and Mn from the Cd1-x Mn x Te film was observed. The compositional uniformity of MOCVD-grown polycrystalline Cd1-x Mn x Te films grown on CdS/SnO2/glass substrates was found to be a strong function of the growth conditions as well as the Mn source.[[ii] ]
Bis -isopropylcyclopentadienyl manganese Mn(iPr)2 (and for comparison MnCp(CO)3) were applied as Mn source materials (with CdMe2 and TeEt2 as Cd and Te sources) for the growth of CdMnTe films by MOCVD on glass/SnO 2 /CdS substrates.
The grown layers were applied for the preparation of high efficiency thin film solar cell devices. [[iii]]
[i] A. Rohatgi, S.A. Ringel, R. Sudharsanan, Solar Cells, 1989,Vol.27, Iss1–4, p.219–230, “Investigation of polycrystalline CdZnTe, CdMnTe, and CdTe films for photovoltaic applications”, http://www.sciencedirect.com/science/article/pii/0379678789900306
[ii]S. A. Ringel, R. Sudharsanan, A. Rohatgi, W. B. Carter, J. Electronic Materials, March 1990, Volume 19, Issue 3, pp 259-263, “A study of polycrystalline Cd(Zn, Mn)Te/Cds films and interfaces”, http://link.springer.com/article/10.1007/BF02733816
[iii] Summers, K A [ed.], Photovoltaic Program Branch annual report, FY 1989,
High Efficiency Cadmium and Zinc Telluride Based Thin Film Solar Cells
Mn(tBuCp)2, Mn(Me4Cp)2, Mn(Me5Cp)2 – potential precursors for Mn metal films by MOCVD
Bis(t-butylcyclopentadienyl)manganese Mn(tBuCp)2 (Mn(C4H9C5H4)2), bis(tetramethylcyclopentadienyl)manganese(II) Mn(Me4Cp)2 (Mn(C5(CH3)4H)2) and bis(pentamethylcyclopentadienyl)manganese(II) Mn(Me5Cp)2 (Mn(C5(CH3)5)2) were proposed as potential precursors for the growth of Mn metal films by MOCVD[.[i]]
[i] Hidenori Miyoshi , US 20090324827 A1, “Cvd film forming method and cvd film forming apparatus”, http://www.google.com/patents/US20090324827