Photon Factory Activity Report 2005 #23 Part B (2006)
Electronic Structure of Condensed Matter

18A/2004G002

In-situ depth profile resonant photoemission study ofGaN:Mn prepared by thermal diffusion of Mn
Jong-Il HWANG*, Masaki KOBAYASHI, Yoshitaka OSAFUNE, Kazuaki EBATA,
Yasuhiro OOKI, Yukiaki ISHIDA, Atsushi FUJIMORI,
1
Department of Complexity Science and Engineering, Department of Physics, Univ. of Tokyo,
Kashiwanoha, Kashiwa 277-8561, Japan
Introduction
Recent theoretical studies have predicted that
Mn-doped GaN shows ferromagnetism with high Curie
temperatures. After the theoretical predictions,GaN-based diluted magnetic semiconductors (DMSs)
such as Ga1-xMnxN have been widely studied
experimentally. Although most of Ga1-xMnxN samples
have been grown by molecular-beam epitaxy, Reed et. al.
[1] have reported that Mn-doping into GaN was achievedby thermal diffusion method and such a sample showed
ferromagnetism. However, the diffusion profile of thesample and its electronic structure have not been studied
so far. The investigations of the diffusion profile and theelectronic structure are needed to understand the origin of
the ferromagnetism in the GaN:Mn samples prepared bythermal diffusion.
We have performed an in-situ depth profile
photoemission study of GaN:Mn prepared by the thermal
diffusion method. 3 nm-thick Mn was deposited on aclean p-GaN surface at room temperature. The sample
was then annealed at 500 °C for 6 hours. This procedure
was done in the photoemission spectrometer chamber andthe photoemission measurement was performed in situ
without exposing the sample to atmosphere. Resonant
photoemission spectroscopy (RPES) using synchrotron
radiation is a powerful tool to investigate the electronic
structure of solids because one can extract the Mn partial
density of states (PDOS) from the valence band using theelement selectivity of the RPES. The depth profile study
has been performed by repeating the RPES and Ar-ion
sputter-etching. The sputter-etching rate is 0.2 Å/min
Result and Discussions
Figure 1 (a) shows the depth profile of total electron
yield recorded in the Mn 3p-3d core-excitation region. An
absorption edge due to metallic Mn at 46.2 eV wasreduced while an edge at 49 eV appeared with sputtering.
Comparing the absorption spectrum after 350 min
sputtering with that of reference GaN as shown in theinset, it has been revealed that a Mn-derived peak islocated at 50 eV
Figure 1 (b) and (c) show valence-band photoemission
spectra in the Mn 3p-3p core-excitation region in thesputtering series. In the spectra for 40 min sputtering (Fig.
1 (b)), a clear Fermi edge was observed with an Augeremission due to Mn M2,3M4,5M4,5 as indicated by triangles
in the figure. In the spectra for 350 min sputtering, the78

Users' ReportFermi edge disappeared and Mn 3d resonant
photoemission effect without the Auger signal wasobserved, which rises from interference between thenormal photoemission and 3p-to-3d transition followed
by a 3p-3d-3d super-Coster-KrÖnig decay. This indicatesthat the character of Mn 3d states changed from itinerant
character to localized one with sputtering. In RPES,
because Mn 3p-3d absorption occurs at photon energies
above 49 eV, one can obtain Mn 3d PDOS by subtracting
the off-resonant spectrum (48.5 eV) from theon-resonance (50 eV) one. The Mn 3d PDOS thus
obtained is shown at the bottom panel of Fig. 1 (c). The
Mn 3d PDOS indicates a peak at 5 eV, a shoulder at 2 eV
and a satellite structure at 10 eV. The line shape is close tothat in MBE-grown Ga1-xMnxN [2].
These results
suggest that the Ga1-xMnxN
is formed in the deep
region of this sample
preparedbythermal
diffusion method.
Fig.1 (a) Mn 3p-3d total
electron yield in depth
profile. (b) , (c) Resonant
photoemission
spectrarecorded around Mn 3p-3d
core-excitation threshold.

References[1] M. L. Reed et al., Appl. Phys. Lett. 79, 3473 (2001).
[2] J. I. Hwang et al., Phys. Rev. B. 71, 085216 (2005).
*hwang@wyvern.phys.s.u-tokyo.ac.jp