. Pp, 81.15.Hi    Ternary MnGeP 2 thin films have been grown on GaAs substrate using MBE technique. The films prepared at 435 °C showed ferromagnetism at room temperature. TEM observation revealed a segregation of MnP tile-shaped grains. Films grown at 585 °C showed no trace of ferromagnetic secondary phases in XRD profiles and were found to show no ferromagnetic behaviors down to 77 K. This is consistent with theoretical prediction that stoichiometric MnGeP 2 is antiferromagnetic, and our previous experimental results that the MnGeP 2 layer existing at the top of ZnGeP 2 : Mn has no contribution to ferromagnetic properties of the latter

A D Bouravleuv

K Minami

K Sato

N Kuwano

T Ishibashi

Y Sato

CiteSeerX

phys. stat. sol. (a) 203, No. 11, 2788–2792 (2006) / DOI 10.1002/pssa.200669595 
 © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 
MBE growth and TEM analyses in Mn–Ge–P compounds 
K. Minami*, 1, A. D. Bouravleuv1,2, Y. Sato1, T. Ishibashi1, N. Kuwano3, and K. Sato1 
1 Department of Applied Physics, Tokyo Univ. of Agriculture and Technology, Koganei,  
184-8588 Tokyo, Japan 
2 A. F. Ioffe Physico-Technical Institute, 194021 St. Petersburg, Russia 
3 Art, Science and Technology Center for Cooperative Research, Kyusyu Univ., Kasuga,  
816-8580 Fukuoka, Japan 
Received 9 March 2006, revised 9 April 2006, accepted 26 June 2006 
Published online 31 August 2006 
PACS 61.10.Nz, 75.50.Pp, 81.15.Hi 
Ternary MnGeP2 thin films have been grown on GaAs substrate using MBE technique. The films pre-
pared at 435 °C showed ferromagnetism at room temperature. TEM observation revealed a segregation of 
MnP tile-shaped grains. Films grown at 585 °C showed no trace of ferromagnetic secondary phases in 
XRD profiles and were found to show no ferromagnetic behaviors down to 77 K. This is consistent with 
theoretical prediction that stoichiometric MnGeP
2
 is antiferromagnetic, and our previous experimental re-
sults that the MnGeP
2
 layer existing at the top of ZnGeP
2
:Mn has no contribution to ferromagnetic prop-
erties of the latter. 
© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 
1 Introduction 
We have been working with chalcopyrite-based magnetic semiconductors (MS) prepared by thermal 
diffusion of Mn into the bulk II–IV–V2 single crystals, and discovered that these materials exhibit fer-
romagnetic properties at room temperature (RT) [1–6]. In addition, reflection high energy electron dif-
fraction (RHEED) observation during the deposition of Mn at 400 °C and in-situ photoemission studies 
indicate that novel chalcopyrite-type material MnGeP2 was formed on the top surface layer of Mn-doped 
II–IV–V2 semiconductors [7]. Additionally, photoemission and magnetic studies suggested that the 
MnGeP2 top layer was non-magnetic and the origin of ferromagnetism of ZnGeP2 :Mn was due to the 
Mn-substituted MS layer. On the basis of these previous results, we started to prepare the novel ternary 
compound MnGeP2 by a molecular beam epitaxy (MBE) technique. We have succeeded in preparation 
of well-defined MnGeP2 on InP(001) substrates at the substrate temperature of 435 °C [8]. In order to 
improve the surface morphology of the epitaxial films we used Ge buffer layer and succeeded in obtain-
ing a very flat surface [9]. The films were found to show ferromagnetism with the Curie temperature (Tc) 
as high as 320 K [10]. However, the origin of ferromagnetic properties was not clarified.  
 In this article, we analyzed crystalline properties of the ternary film grown on the Ge buffer layer 
using a transmission electron microscopy (TEM), from which an existence of a secondary ferromagnetic 
phase was confirmed. In order to avoid the secondary phase formation we prepared the ternary com-
pounds at an elevated substrate temperature, in which magnetic properties were investigated. 
 
 
 
 * Corresponding author: e-mail: minami_5@cc.tuat.ac.jp, Phone: +81 42 388 7432, Fax: +81 42 387 8151 
phys. stat. sol. (a) 203, No. 11 (2006)  2789 
www.pss-a.com © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 
Original
Paper
2 Experiments 
The crystal growth of ternary compound thin films was performed using an MBE technique [9]. Mn and 
Ge were evaporated using conventional Knudsen cells (K-cell) at temperatures of 620–680 °C and 1000 
–1050 °C, respectively. The both beam flux intensity of Mn and Ge were adjusted at 0.6–0.64 × 10–8 
Torr. Phosphorus was supplied as P2 by cracking the tertiary butyl phosphine (TBP) gas source using a 
cracking cell at 835 °C. The flow rate of TBP was fixed at 2.0 sccm using mass flow controller. 
GaAs(001) and (111)B single crystals were used as substrates. In this study, we prepared two kinds of 
samples. Films were grown at 435 °C on a Ge buffer layer prepared on GaAs(001) and (111)B substrates. 
The Ge buffer layer was prepared at 380 °C with the thickness of 25 nm. After growth of the ternary thin 
film Ge was deposited at RT as cap layer in order to prevent main epitaxial films from oxidation. We 
also performed MBE growth of the ternary films on GaAs(001) substrate at 485–585 °C without Ge 
buffer layer. The crystal structure of the thin film was analyzed using RHEED, X-ray diffraction (XRD) 
and transmission electron microscopy (TEM). The TEM observation was carried out at the Research Labo-
ratory for High Voltage Electron Microscopy, Kyushu University using the FEI type Tecnai-F20 apparatus. 
Additionally, chemical compositions were analyzed using an energy dispersive X-ray spectroscopy (EDS) 
attached with the TEM and a scanning electron microscope (SEM). Magnetic field dependences of mag-
netization of films prepared were investigated using a vibrating sample magnetometer (VSM) at 77 K. 
3 Results and discussion 
3.1 TEM analyses of ternary thin films 
Ternary thin films of 90 nm and 55 nm in thickness were grown at 435 °C on a Ge buffer layer prepared 
on GaAs(001) and (111)B substrates. During the growth of both Ge buffer layer and the ternary thin film, 
RHEED showed streaky patterns due to the zincblendelike phase. In addition, diffraction spots due to a 
secondary phase assignable to the MnP were observed, an existence of a trace of MnP phase having been 
confirmed by the 2θ–θ XRD measurement. SEM observations of the MnGeP2 film prepared on the Ge-
buffer revealed a drastic improvement of the surface flatness compared with the film prepared without  
a buffer layer [9]. As described in our previous paper [10], MnGeP2 film exhibited a ferromagnetic be-
haviour up to 320 K in the M–T curve measured using super conducting quantum interference  
device (SQUID) magnetometer. Subsequently, the crystal structure and areal distribution of all elements 
were analyzed using TEM and attached EDS apparatus. Figure 1 shows a diffraction image of the sample 
grown on the GaAs(111)B. The electron beam was parallel to GaAs[112]. Diffraction spots close to  
those of GaAs substrate (e.g. A–C) indicate an orientational overgrowth of the ternary phase on the 
substrate. In cross sectional TEM images, it was affirmed that tile-shaped crystals were partially embed- 
 
Diffraction spots of Ge or GaAs 
A 
111 3 11 
2 2 0 
B 
C 
  
Fig. 1 (online colour at: www.pss-a.com) Diffraction image of the 
film grown on a Ge/GaAs(111)B. E-beam  GaAs [112 ]. 
2790 K. Minami et al.: MBE growth and TEM analyses in Mn–Ge–P compounds 
© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.pss-a.com 
(d) (e) (f)
(b) (c)
20nm
(a)
A
 
Fig. 2 (online colour at: www.pss-a.com) Dark field image of TEM (a), and distribution maps of  all 
elements; (b) Ga, (c) As, (d) Mn, (e) P and (f) Ge, respectively. 
 
ded into ternary film grown on the Ge buffer layer. Figure 2(a) shows a dark field TEM image of the thin 
film grown on the GaAs(111)B substrate. It is clearly observed that tile-shaped crystal grains with thick-
ness of ~50 nm are grown on the Ge buffer layer. Figure 2(b)–(f) show atomic distribution of all elements 
in the thin film taken at the same area of the dark field TEM image (Fig. 2(a)). The EDS profiles clearly 
shows the Ge buffer layer is formed on the GaAs substrate with a sharp boundary and on the buffer layer 
crystalline grains are grown. In the area marked A in the dark-field image all the constituent elements, 
Mn, Ge and P are found, while in the area B only Mn and P are observed. The ternary Mn–Ge–P and 
binary Mn–P areas were clearly separated from each other. In the case of GaAs(001) substrate, separa-
tion of Mn–P and Mn–Ge–P areas were also observed. Therefore, in order to obtain intrinsic magnetic 
properties of MnGeP2, single phase film without ferromagnetic secondary phases should be prepared. 
3.2 High temperature growth of MnGeP2 
As a preliminary investigation to obtain single phase thin films of MnGeP2, we carried out a thermody-
namic calculation in MnP–GeP system [11]. This result indicates that MnP should disappear and only 
MnGeP2 can be grown at an elevated temperature higher than 435 °C. On the basis of theoretical predic-
tion, ternary thin films were grown at 485–585 °C directly on GaAs(001) substrate without buffer layers. 
Figure 3 shows 2θ–θ XRD profiles of the thin film grown at 585 °C near 002 and 004 diffraction lines of 
GaAs. Close in the higher angle side of the diffraction peaks of the substrate, strong lines from the thin 
film were observed and were assigned to 004 and 008 diffractions from MnGeP2. These lines were 
shifted to slightly higher angle from that observed in our previous works. The estimated lattice constant 
of c-axis of the present film is 11.264 Å, slightly smaller that 11.303 Å obtained in the previous study. 
Assuming that a-axis is not different between two films, the tetragonality is found to be more enhanced 
in the present film. This difference may be caused by a change of the ordering of cation sites to form 
stoichiometric MnGeP2 due to high temperature growth. Chemical ratio of the thin film measured using 
EDS attached SEM apparatus was Mn:Ge:P = 0.7:1.0:2.7, where atomic ratios were normalized to Ge. 
It is considered that Mn was poor compared with Ge due to the re-evaporation and GeP was formed by 
the combination of excess Ge and P. In a wide range 2θ–θ XRD charts, no traces of ferromagnetic sec-
ondary phases such as MnP were detected except for MnGeP2 and GeP, the latter being known to be non-
magnetic. Appearance of GeP may be attributed to incomplete adjustment of source elements ratios. In 
the cases of substrate temperature lower that 585 °C, i.e., at 485 and 535 °C, MnGeP2 diffraction lines 
could not be discriminated from GaAs 002, 004 lines probably weakness of diffraction due to poor crys-
tallinity of MnGeP2. 
phys. stat. sol. (a) 203, No. 11 (2006)  2791 
www.pss-a.com © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 
Original
Paper
L
o
g
ar
it
h
m
ic
 s
ca
le
 o
f 
in
te
n
si
ty
 [
cp
s]
2Theta [degree]
10
102
103
10
4
30 31 32 33 34
G
aA
s 
(0
0
2
)
M
n
G
eP
2
 (
0
0
4
)
G
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 (
0
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)
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10
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M
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)
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 (
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)
  
 
 Figure 4 shows magnetization-magnetic field (M–H) curve of MnGeP2 thin film grown at 585 °C 
measured using VSM at 77 K. Magnetic field was applied parallel to the surface of the thin film and 
ranged from –20 kOe to 20 kOe. No ferromagnetic behaviours were observed in contrast to the ternary 
thin film grown at lower temperature in previous works [10]. No magnetic signals were detected at RT as 
well. This result indicates that MnGeP2 thin film grown at 585 °C does not show ferromagnetic behav-
iour down to 77 K and no ferromagnetic secondary phases with Tc over 77 K exist in the film. Further-
more, it is consistent with the previous photoemission study in which MnGeP2 does not give any mag-
netic contribution. It should also be noted that in the theoretical work by Zhao et al. [12], they reported 
that antiferromagnetism is the most stable magnetic phase of chalcopyrite-type MnGeP2. 
 Here we give a brief discussion on the origin ferromagnetism observed in our previous study MnGeP2 
prepared at low substrate temperatures. According to theoretical studies ternary Mn-containing com-
pounds become ferromagnetic when point defects are introduced [13]. There is a possibility of ferromag-
netism due to the point defect formation in our MnGeP2, since the XRD results show that MnGeP2 pre-
pared at low temperatures has a less tetragonality suggesting that the material structure is close to zinc-
blende probably due to a randomness of cation distribution. We believe that the ferromagnetism of our 
film with Tc of the film 320 K is not due to MnP since it is considerably higher than that of MnP single 
crystal and ferromagnetic-antiferromagnetic phase transition at 47 K is missing. 
 
-5
0
5
-20 -15 -10 -5 0 5 10 15 20
M
ag
n
et
iz
at
io
n
 [
x
1
0
-3
 e
m
u
]
Magnetic field [kOe]   
Fig. 3 2θ–θ XRD profiles of MnGeP2 thin film gown on 
a GaAs(001) at 585 °C. 
 
Fig. 4 M–H curve of MnGeP
2
 thin film at 77 K.  
2792 K. Minami et al.: MBE growth and TEM analyses in Mn–Ge–P compounds 
© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.pss-a.com 
4 Summary 
MnGeP2 thin films were prepared using MBE on GaAs substrates with Ge buffer layers. Tile-shaped 
crystal grains were observed to grow on the Ge buffer layer at 435 °C in TEM analyses. Atomic distribu-
tion map indicates that the film consists of Mn–P and Mn–Ge–P areas clearly separated from each 
other. 
 We have found that the films grown at higher substrate temperature of 585 °C show no traces of MnP 
secondary phases and strong diffraction intensity of chalcopyrite-like MnGeP2 in the XRD profiles. Fur-
thermore, magnetic properties of MnGeP2 prepared at 585 °C are found to be quite different from MnP 
and do not show ferromagnetism down to 77 K, which is consistent with our previous works and theo-
retical study by Zhao et al. in which antiferromagnetism should be the most stable phase for stoichio-
metric chalcopyrite-type MnGeP2. 
Acknowledgements This work has been carried out under the 21st Century COE program on “Future Nano-
Material” of TUAT and supported in part by the Grant-in-Aid for Scientific Research (B) (No. 17360009). The TEM 
observations have been carried out at the Research Laboratory for High Voltage Electron Microscopy, Kyushu 
University. The authors are also thankful to Sumitomo Electric Industries, Ltd. for supplying GaAs substrates. 
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MBE growth and TEM analyses in Mn-Ge-P compounds

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MBE growth and TEM analyses in Mn-Ge-P compounds

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