実験報告書様式（一般利用課題・成果公開利用）

MLF Experimental Report

提出日 Date of Report
2012/03/05

課題番号 Project No.

装置責任者 Name of responsible person

2010A0059

Yasuhiro Miyake

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

MuSR study on isolated hydrogen charge state in oxgenD1deficient SrTiO3

実施日 Date of Experiment

実験責任者名 Name of principal investigator

2010/5/25,26,28

Koichiro Shimomura
所属 Affiliation
KEK-IMSS
試料、実験方法、利用の結果得られた主なデータ、考察、結論等を、記述して下さい。（適宜、図表添付のこと）
Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
1. 試料 Name of sample(s) and chemical formula, or compositions including physical form.
SrTiO3

2. 実験方法及び結果 （実験がうまくいかなかった場合、その理由を記述してください。）
Experimental method and results. If you failed to conduct experiment as planned, please describe reasons.
Hydrogen is a ubiquitous impurity in most semiconductors, including elemental (e.g., Si), compound (e.g., GaAs)
one. In these systems, hydrogen is known to be amphoteric, forming an acceptor level in n-type and a donor levelin p-type materials. In contrast, hydrogen can lead to electron conduction in some wide gap semiconductors such
as ZnO. Motivated by this theoretical prediction, SR Studies on ZnO and electron-nuclear resonancemeasurements on n-type ZnO supported the hypothesis that hydrogen is a shallow donor. Several other studies
show evidence that hydrogen is related to n-type conductivity in ZnO.
These observations raise the question of what is the basic systematic at work here: if H can be incorporated intosome materials, which one will be doped by H (i.e., become conductive) and which will not? Experimentally,SR studies have played pioneering roles on this subject. While the dynamical aspects (e.g., diffusion) may beconsiderably different between Mu and H due to the light mass of Mu (mass~ 1/9mp), the local electronic
structure of Mu is virtually equivalent to that of H after a small correction due to the difference in the reduced
mass (~0.4%). Recently, a novel Mu state having an extremely small hyperfine parameter (10-4 times smaller
than the muonium in vacuum) and a low ionization energy (~10meV) was reported in several compound
semiconductors including CdS , ZnSe, InN and GaN, implying that Mu (and hence H) can act as a donor in thesematerials. On the other hand, considerable theoretical studies were also performed. Very recently Iwazaki andTsuneyuki performed interesting theoretical work on SrTiO3 related these subjects.

12. 実験方法及び結果（つづき） Experimental method and results (continued)
The physical properties of SrTiO3 have been extensively investigated over the years mainly due to its potentiality
for device applications, especially, in ceramic condensers, photo catalysis, and sensors. Electrically conducting
SrTiO3 crystals are often obtained by annealing in highly reducing, hydrogen containing atmospheres. The roleof hydrogen is complicated. Subsequent anneals at 800 °C in forming gas, which contained 10% hydrogen,returned the crystals into the insulating, Understanding the roles of hydrogen related these phenomena in SrTiO3
is also of technical importance. Forming gas, which contains hydrogen, is used in semiconductor device
processing and causes a drastical change in the leakage current of SrTiO3 films
However, some theoretical work suggests interstitial hydrogen has been suggested to act as a shallow donor in
SrTiO3 and related materials. Thus both oxygen vacancies and hydrogen may potentially contribute to theelectrical conductivity of SrTiO3. Iwezaki and Tsuneyuki theoretically point out the hydrogen in oxygen deficient
SrTiO3 can form the negative charge state, therefore, it might suppress the electrical conductivity (passivation).
This theoretical picture well explains the phenomena mentioned above.
To check these theoretical predictions by experimentally, we performed the MuSR measurements. For the firststage the comparison of the muon spin relaxation rate in TF and ZF field between normal and annealed SrTiO3samples. As shown in Fig.1, there is a drastic change for typical time differential spectrum between them at theroom temperature. However, in that time, beam time and intensity were very limited, therefore, we could not
performed detailed temperature dependence.

t.

Fig.1 TF spectrum of Oxygen defficient (above)and normal SrTiO3 at 300K.

2