Photon Factory Activity Report 2004 #22 Part B (2005)
Materials Science

1C/2002S2-002

Electronic structure of Ga1-xCrxAs studied by in-situ photoemission spectroscopy
Ken KANAI, Jun OKABAYASHI, Kanta ONO1, Masaharu OSHIMAThe University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan1
KEK-PF, Tsukuba, Ibaraki 305-0801, Japan

Experimental
Ga1-xCrxAs samples were grown by low-temperature(LT) -MBE methods on GaAs (001) substrates. The 100nm Ga1-xCrxAs layer was grown on the GaAs buffer layer
at 200°C and the evaporation temperature of Cr ions waschanged from 1140°C to 1240°C to fabricate the different
Cr-concentration samples. The MBE system used in thisstudy was connected to the synchrotron-radiation
photoemission spectroscopy chamber at BL-1C of Photon
Factory, High-Energy Accelerator Research Organization(KEK). The samples grown by MBE were transferred into
the photoemission chamber without breaking theultrahigh vacuum. In-situ photoemission spectroscopy
was performed at room temperature.
Results and discussion
Figure 1 shows the valence-band spectra of Ga1-xCrxAs
depending on the Cr concentration. As references,spectrum for GaAs is also shown. Valence-band spectra
taken at photon energy hν = 60 eV show new states near
EF derived from the Cr 3d states as shown by arrow in Fig.
1. One can see that the intensity in new states depends on
the Cr concentration. These states appear by the132

Users' Reporthybridization between Cr 3d and As 4p states. Peakpositions are shifted toward lower binding energy withincreasing the Cr concentration, suggesting the Fermilevel shifts due to the hole doping. The Cr substitution
3+2+
into Ga site will derive the hole doping by Cr → Cr +hole through the hybridization between Cr 3d and As 4pstates. Spectra for higher Cr concentrations than 11%
doping show a clear Fermi edge. For Ga1-xMnxAs, the Mn
3d states are located around ~4 eV and p-d exchangeinteraction through the hybridization Mn 3d and As 4p
states is important for the ferromagnetic ordering[4]. On
the other hand, the new states appearing by the Cr doping
may be responsible for the double-exchange mechanism
for the ferromagnetism.
References[1] H. Ohno et al., Appl. Phys. Lett. 69, 15 (1996).
[2] K. W. Edmonds et al., Appl. Phys. Lett. 81, 4991
(2002).
[3] L. M. Sandratskii et al., Phys. Rev. B 67, 214402(2003).
[4] J. Okabayashi et al., Phys. Rev. B 65, 161203(R)(2002).

Intensity (arb. units)

Introduction
Since the first reports of ferromagnetism in Mn-doped
III-Vsemiconductors synthesized the “spinelectronics”
research field using molecular-beam epitaxy (MBE),
diluted magnetic semiconductors (DMS) have become
key materials for the functional device application
combining magnetic and semiconducting properties[1].
The Mn doping into GaAs leads to carrier-induced
ferromagnetism because hole carriers introduced into thesystem mediate the ferromagnetic coupling between theMn ions although its microscopic mechanism has been
controversial until now. The Curie temperature (TC) inGa1-xMnxAs has not exceeded 150 K so far due to thesolubility limit of Mn and the carrier selfcompensation[2]. To overcome these problems in Ga1xMnxAs, the investigations for the chemical trends in III-V
based DMS can bring us a new information about afunctional material design. First-principle band-structurecalculation predicts that the Cr doping into GaAs
stabilizes the ferromagnetic states because the Cr 3d
states are located near the Fermi level (EF)[3]. The Cr
doping into GaAs has a high potential to design the highTC ferromagnetic semiconductors. We have fabricated theGa1-xCrxAs by MBE and discussed the electronic structureby the Cr doping into GaAs using in-situ photoemission
spectroscopy. We focused on the transition-metal 3d
states in Ga1-xCrxAs comparing with those in Ga1xMnxAs[4].

Valence band
Ga1-xCrxAs Cr 3dhν=60 eVx=
0.20
0.11
0.05
0.03
GaAs

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20Binding Energy (eV)FIG. 1: Valence-band photoemission spectra ofGa1-xCrxAs depending on the Cr concentration.
kanai@sr.t.u-tokyo.ac.jp