Enhanced damage buildup in C-implanted GaN film studied by a monoenergetic positron beam

Li, X. F.*; Chen, Z. Q.*; Liu, C.*; Zhang, H.; Kawasuso, Atsuo

Journal of Applied Physics, 117(8), p.085706_1 - 085706_6, 2015/02

https://doi.org/10.1063/1.4913523

Vacancy-type defects in C-implanted GaN were probed using a slow positron beam. The increase of Doppler broadening S parameter indicates introduction of arge vacancy clusters. Post-implantation annealing at temperatures up to 800C makes these vacancy clusters to agglomerate into microvoids. The vacancy clusters or microvoids show high thermal stability, and they are only partially removed after annealing up to 1000C. Amorphous regions are observed by high resolution transmission electron microscopy measurement, which directly confirms that amorphization is induced by C-implantation. The disordered GaN lattice is possibly due to special feature of carbon impurities, which enhance the damage buildup during implantation.

Effect of ion species on the production and thermal evolution of implantation induced defects in ZnO

Chen, Z. Q.; Maekawa, Masaki; Kawasuso, Atsuo; Sakai, Seiji; Naramoto, Hiroshi*

JAEA-Review 2005-001, TIARA Annual Report 2004, p.232 - 234, 2006/01

https://jopss.jaea.go.jp/pdfdata/JAEA-Review-2005-001-p0001-p0126.pdf

no abstracts in English

Interaction of nitrogen with vacancy defects in N-implanted ZnO studied using a slow positron beam

Chen, Z. Q.; Maekawa, Masaki; Kawasuso, Atsuo; Suzuki, Ryoichi*; Odaira, Toshiyuki*

Applied Physics Letters, 87(9), p.091910_1 - 091910_3, 2005/08

https://doi.org/10.1063/1.2037847

Zinc oxide crystals were implanted with N, O, and co-implanted with O/N ions. Positron annihilation measurements show the introduction of vacancy clusters upon implantation. In the N-implanted sample, these vacancy clusters are only partially annealed at 800C as compared to their full recovery in the O-implanted sample, suggesting a strong interaction between nitrogen and vacancy clusters. At 1000-1100C, nitrogen also forms stable complexes with thermally generated vacancies. To remove all the detectable vacancy defects, a high temperature annealing at 1250C is needed. Furthermore, Hall measurements of this sample show n-type conductivity though nitrogen is expected as acceptors. On the contrary, in the O/N co-implanted sample, most vacancy clusters disappear at 800C. Probably oxygen scavenges nitrogen to form N-O complexes and hence enhance the annealing of vacancy clusters. A highly compensated semi-insulating layer is formed in the co-implanted sample.

Microvoid formation in hydrogen-implanted ZnO probed by a slow positron beam

Chen, Z. Q.; Kawasuso, Atsuo; Xu, Y.; Naramoto, Hiroshi*; Yuan, X. L.*; Sekiguchi, Takashi*; Suzuki, Ryoichi*; Odaira, Toshiyuki*

Physical Review B, 71(11), p.115213_1 - 115213_8, 2005/03

https://doi.org/10.1103/PhysRevB.71.115213

ZnO crystals were implanted with 20-80 keV hydrogen ions up to a total dose of 4.410 cm. Positron annihilation measurements show introduction of zinc vacancies, which are filled with hydrogen atoms. After isochronal annealing at 200-500 C, the vacancies agglomerate into hydrogen bubbles. Further annealing at 600-700 C causes release of hydrogen out of the bubbles, leaving large amount of microvoids. These microvoids are annealed out at high temperature of 1000 C. Cathodoluminescence measurements reveal that hydrogen ions also passivate deep level emission centers before their release from the sample, and lead to the improvement of the UV emission.

Construction of intense positron source based on AVF cyclotron for high brightness positron beam, 2

Maekawa, Masaki; Kawasuso, Atsuo; Kashima, Fumihiko*; Chen, Z. Q.

JAERI-Review 2004-025, TIARA Annual Report 2003, p.299 - 301, 2004/11

https://jopss.jaea.go.jp/pdfdata/JAERI-Review-2004-025-p0248-p0374.pdf

no abstracts in English

A Coherent positron beam for reflection high-energy positron diffraction

Kawasuso, Atsuo; Ishimoto, Takayuki*; Maekawa, Masaki; Fukaya, Yuki; Hayashi, Kazuhiko; Ichimiya, Ayahiko

Review of Scientific Instruments, 75(11), p.4585 - 4588, 2004/11

https://doi.org/10.1063/1.1806651

A 10 keV positron beam has been developed using coaxially symmetric electromagnetic lenses for reflection high-energy positron diffraction (RHEPD) experiments. The beam brightness is 10 e/sec/cm/rad/V which is comparable to that obtained using brightness enhancement technique. The beam parallel and normal coherence lengths are over 100 and 40 , respectively, which are long enough to observe diffraction patterns associated with large surface super-structures. RHEPD patterns from a Si(111)-(77) reconstructed surface have been successfully observed with a much better quality than previously reported.

N ion-implantation-induced defects in ZnO studied with a slow positron beam

Chen, Z. Q.; Sekiguchi, Takashi*; Yuan, X. L.*; Maekawa, Masaki; Kawasuso, Atsuo

Journal of Physics; Condensed Matter, 16(2), p.S293 - S299, 2004/01

https://doi.org/10.1088/0953-8984/16/2/035

Undoped ZnO single crystals were implanted with multiple energy N ions ranging from 50 to 380 keV with dose from 10/cm to 10/cm. Positron annihilation measurements show that vacancy defects are introduced in the implanted layers. The concentration of the vacancy defects increases with increasing ion dose. Annealing behavior of the defects can be divided into four stages, which correspond to the formation and recovery of large vacancy clusters, formation and disappearance of vacancy-impurity complexes, respectively. All the implantation induced defects are removed by annealing at 1200C. Cathodoluminescence measurements show that the ion implantation induced defects act as nonradiative recombination centers to suppress the ultraviolet emission. After annealing, these defects disappear gradually and the ultraviolet emission reappears, which coincides with positron annihilation measurement. The Hall measurements reveal that after N-implantation, the ZnO layer still shows n-type conductivity.

Ion-implantation induced defects in ZnO studied by s slow positron beam

Chen, Z. Q.; Maekawa, Masaki; Sekiguchi, Takashi*; Suzuki, Ryoichi*; Kawasuso, Atsuo

Materials Science Forum, 445-446, p.57 - 59, 2004/00

no abstracts in English

Development of reflection high-energy positron diffraction (RHEPD) based on an electrostatic positron beam

Ishimoto, Takayuki*; Kawasuso, Atsuo; Ito, Hisayoshi; Okada, Sohei

JAERI-Tech 2003-091, 32 Pages, 2003/12

JAERI-Tech-2003-091.pdf:3.96MB

no abstracts in English

Study of ion beam induced defects in ZnO by using slow positron beam

Chen, Z. Q.; Maekawa, Masaki; Yamamoto, Shunya; Sekiguchi, Takashi*; Kawasuso, Atsuo

JAERI-Review 2003-033, TIARA Annual Report 2002, p.209 - 211, 2003/11

https://jopss.jaea.go.jp/pdfdata/JAERI-Review-2003-033-p0001-p0187.pdf

Undoped ZnO crystals were implanted with Al, N and Al/N respectively. The implantation induced defects and their recovery were studied using a variable energy slow positron beam. Vacancy clusters are introduced in all the implanted samples. The annealing of the defects in Al-implanted sample shows two stages, which might be due to the agglomeration of vacancy clusters and their recovery, respectively. Large voids are also observed when the Al dose is higher than 10 cm, which suggest amorphization of ZnO. However, for both the N-implanted and the Al/N co-implanted sample, the annealing behavior of the defects shows four stages. The last two stages might be related with the formation and recovery of nitrogen related defect complexes. Hall measurements show a strong n-type conductive layer after Al implantation and annealing, suggesting that all the Al ions are activated. However, for the N-implanted and Al/N co-implanted ZnO, the implanted layer still shows n-type conductivity. The possible reason is discussed.