論文 - 鈴木 秀俊
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Suzuki H., Nishimura K., Saito K., Ohshita Y., Kojima N., Yamaguchi M.
Journal of Crystal Growth 311 ( 10 ) 2821 - 2824 2009年5月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Journal of Crystal Growth
The change in the surface concentration of N ([N] s ) on a GaAs surface under N and As source injections is investigated using the N atomic layer doping (N-ALD) technique, and the key factor determining [N] s is discussed. The As and N precursors source gases are trisdimethylaminoarsenic (TDMAAs, [N (CH 3 ) 2 ] 3 As) and monomethylhydrazine (MMHy, N 2 H 3 CH 3 ), respectively. N-ALD layers are prepared by using two gas injection sequences (A: MMHy injection and B: MMHy and TDMAAs injections). [N] s increases with decreasing growth temperature in both sequences. [N] s in sequence A is higher than that of sequence B. In sequence B, Δ [N] s / Δ t is proportional to exp (- t / τ N ), where t and τ N are the gas injection time and the residence time of N, respectively. It is observed that the number of vacant sites, [V] s, N , remaining constant during gas injections. In sequence A, Δ [N] s / Δ t cannot be fitted by a single exponential function, indicating that [V] s, N is not constant. From these results, we suggest that the vacant sites at the surface are created not only by N desorption but also by As desorption. It has been found that As desorption is enhanced by MMHy injection. As desorption reaction has been confirmed by in situ auger electron spectroscopy measurements. These results indicate that [N] s is determined by the competitive absorption between N and As, [V] s, N , and τ N . © 2009 Elsevier B.V. All rights reserved.
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Fabrication of GaAsN homo-junction solar cells by chemical beam epitaxy
Suzuki H., Nishimura K., Hashiguchi T., Saito K., Balasubramanian B., Yamamoto S., Inagaki M., Ohshita Y., Kojima N., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2008年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Conference Record of the IEEE Photovoltaic Specialists Conference
The reduction of residual acceptors in GaAsN films and the improvement of GaAsN crystal quality evidenced by hole mobility and PL intensity were reported. Si doping using a SiH 4 gas was also studied. Based on these results GaAsN homo-junction solar cells were fabricated by CBE at the first time. The short circuit current, open circuit voltage, fill factor and conversion efficiency of the GaAsN solar cell are 8.99 mA/cm 2 , 0.48 V, 0.43, and 1.93 %, respectively. © 2008 IEEE.
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Electrical properties of Mg doped C60 thin films
Kojima N., Natori M., Suzuki H., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2008年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Conference Record of the IEEE Photovoltaic Specialists Conference
C 60 solids have been known as high resistive semiconductor materials. Such high resistivity is one of the reasons of low charge transport efficiency in organic solar cells. Mg doping in C 60 films was done by the co-evaporation method of C 60 and Mg sources. The conductivity could be controlled by the composition ratio of Mg/C 60 , and its dependence is divided into 3 ranges (Mg/C 60 = 0∼2, 2∼6, ≫6). Temperature dependence of the conductivity shows hopping conduction mechanism, and suggesting the same hopping center origin in the first and second ranges. From Raman scattering spectroscopy and XRD measurements, the crystal structure disordering by Mg-doping was observed. It is thought that Mg composition dependence of the conductivity is related to both of the conduction mechanism change and the structural change. © 2008 IEEE.
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Crystal structures of copper-phthalocyanine on C60(111) surface grown by molecular beam epitaxy
Suzuki H., Yamashita Y., Kojima N., Yamaguchi M.
Japanese Journal of Applied Physics 47 ( 8 PART 3 ) 6879 - 6882 2008年8月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Japanese Journal of Applied Physics
Crystal orientation and morphologies of copper-phthalocyanine (CuPc) on the C 60 (111) surface were investigated. CuPc thin films were grown on C 60 (111) by the molecular beam epitaxy technique. The CuPc molecular column was parallel to the C 60 (111) surface. CuPc formed two types of structure on C 60 (111). Structure 1 was shaped similarly to straight fibers and covered the entire surface. Structure 1 lay along three directions equivalent to 〈112〉 on C 60 (111). This indicated the epitaxial growth of CuPc on the C 60 (111) surfaces. Structure 2 was also fiberlike in shape and dispersed randomly on Structure 1. Both structures were observed on the CaPc/C 60 (111) surface at growth temperatures of 60-160 °C. The orientation of Ce 60 (111) surfaces affected the formation of CuPc crystals even at 60 °C. ©2008 The Japan Society of Applied Physics.
DOI： 10.1143/JJAP.47.6879
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Suzuki H., Nishimura K., Saito K., Hashiguchi T., Ohshita Y., Kojima N., Yamaguchi M.
Japanese Journal of Applied Physics 47 ( 8 PART 3 ) 6910 - 6913 2008年8月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Japanese Journal of Applied Physics
The electrical behavior of nitrogen-hydrogen (N-H) complexes and carbon (C) atoms in GaAsN films grown by the chemical beam epitaxy (CBE) method have been studied by comparing H concentrations and hole concentrations. The contributions of H and C concentrations ([H] and [C] ) to ionized impurity scattering have been also investigated. In the GaAsN films, there were three acceptor levels (A0, A1, and A2). The energy levels of A1 and A2 were 130 and 55meV, respectively. The concentration of the deepest acceptor (A0) was more than 10 19 cm -3 , which was higher than [H] and [C] . A2 was observed only in films with a high [C]. The amount of A1 was proportional to [H] . Most of the residual H formed N-H complexes; thus, it is concluded that the N-H complex behaved as an acceptor in GaAsN films. At low temperatures, ionized impurity scattering limited the total hole mobility. The inverse numbers of the coefficients for the ionized scattering were consistent with [C] instead of [H] . This suggests that all the residual C atoms were ionized owing to compensation by the donors. A disagreement between N composition and alloy scattering has been also detected. This might indicate a fluctuation in the N composition in the GaAsN films. © 2008 The Japan Society of Applied Physics.
DOI： 10.1143/JJAP.47.6910
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Carbon reduction in GaAsN thin films by flow-rate-modulated chemical beam epitaxy
Nishimura K., Suzuki H., Saito K., Ohshita Y., Kojima N., Yamaguchi M.
Japanese Journal of Applied Physics 47 ( 4 PART 1 ) 2072 - 2075 2008年4月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Japanese Journal of Applied Physics
The flow-rate-modulated chemical beam epitaxy (FM-CBE) method was developed and implemented on the basis of the discussion of the desorption velocities of absorbed species originating from N source gas [MMHy, (CH 3 )N 2 H 3 ] for decreasing the residual carbon (C) concentration in GaAsN films. In this method, the Ga source [TEGa, Ga(C 2 H 5 ) 3 ] was supplied intermittently, while the As [TDMAAs, As(N(CH 3 ) 2 ) 3 ] and N sources (MMHy) were supplied continuously. Below growth temperatures of 440°C, the residual C concentrations in GaAsN films was reduced to 1/10 that in conventional CBE films, with no change in N concentration. However, above 440°C, N concentration decreased drastically with FM-CBE. It was concluded that the reduction in C concentration by FM-CBE was attributed to the decrease in -NHCH 3 coverage on the growing surface by -NH 2 substitution during the intermittence of the TEGa flow. FM-CBE was an effective method for decreasing residual C concentration while maintaining the N concentration in GaAsN films below 440°C. © 2008 The Japan Society of Applied Physics.
DOI： 10.1143/JJAP.47.2072
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Hydrogen reduction in GaAsN thin films by flow rate modulated chemical beam epitaxy
Saito K., Nishimura K., Suzuki H., Ohshita Y., Yamaguchi M.
Thin Solid Films 516 ( 11 ) 3517 - 3520 2008年4月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Thin Solid Films
The amount of residual H in the GaAsN film grown by chemical beam epitaxy (CBE) can be decreased by flow rate modulation growth. Many H atoms in the films grown by CBE exist as N-H or N-H 2 structures. Although a higher growth temperature was required for decreasing the H concentration ([H]), it caused a decrease in the N concentration ([N] ). A reduction in [H] while keeping [N] constant was necessary. By providing an intermittent supply of Ga source while continuously supplying As and N sources, [H] effectively decreased in comparison with the [H] value in the film grown at the same temperature by conventional CBE without reducing [N]. © 2007 Elsevier B.V. All rights reserved.
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Al-induced one dimensional nano-facet formation on Si(113) surface
Mino M., Nakahara H., Saito Y., Suzuki H.
e-Journal of Surface Science and Nanotechnology 6 45 - 48 2008年2月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：e-Journal of Surface Science and Nanotechnology
We have studied surface morphology and surface reconstruction of an Al adsorbed Si(113) surface using a scanning tunneling microscope. A clean Si(113) surface is atomically flat, but well-ordered one-dimensional (1D) nano-facet structures with their width of about 2.5 nm are formed on this surface after 1 ML of Al deposition. In the faceting process, the initial stage is Al atoms replacement with Si atoms at 0.4 ML of Al deposition. Replaced Si atoms stick to steps, causing the change of steps shape. These Si atoms also form two-dimensional (2D) islands. The next stage is growth of 2D islands toward [3̄3̄2] direction at 0.6 ML of Al deposition. At this coverage, 2D islands consist of (9̄61), (69̄1), and (332̄) steps. For further Al deposition, (9̄61) and (69̄1) steps become unstable and (332̄) and (3̄3̄2) steps become stable. Finally, (332̄) and (3̄3̄2) steps change into two kinds of nano-facet structures, i.e. (112) and (115) facets. Pn the (112) facet, a mixture of N X 1 structures (N = 3-8) is observed. The most abundant value of N is 6, which well agrees with the first principle calculation. While on the (115) facet, 4 × 1 structures areobserved. © 2008 The Surface Science Society of Japan.
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Novel materials for high-efficiency III-V multi-junction solar cells
Yamaguchi M., Nishimura K., Sasaki T., Suzuki H., Arafune K., Kojima N., Ohsita Y., Okada Y., Yamamoto A., Takamoto T., Araki K.
Solar Energy 82 ( 2 ) 173 - 180 2008年2月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Solar Energy
As a result of developing wide bandgap InGaP double hetero structure tunnel junction for sub-cell interconnection, InGaAs middle cell lattice-matched to Ge substrate, and InGaP-Ge heteroface structure bottom cell, we have demonstrated 38.9% efficiency at 489-suns AM1.5 with InGaP/InGaP/Ge 3-junction solar cells by in-house measurements. In addition, as a result of developing a non-imaging Fresnel lens as primary optics, a glass-rod kaleidoscope homogenizer as secondary optics and heat conductive concentrator solar cell modules, we have demonstrated 28.9% efficiency with 550-suns concentrator cell modules with an area of 5445 cm 2 . In order to realize 40% and 50% efficiency, new approaches for novel materials and structures are being studied. We have obtained the following results: (1) improvements of lattice-mismatched InGaP/InGaAs/Ge 3-junction solar cell property as a result of dislocation density reduction by using thermal cycle annealing, (2) high quality (In)GaAsN material for 4- and 5-junction applications by chemical beam epitaxy, (3) 11.27% efficiency InGaAsN single-junction cells, (4) 18.27% efficiency InGaAs/GaAs potentially modulated quantum well cells, and (5) 7.65% efficiency InAs quantum dot cells. © 2007 Elsevier Ltd. All rights reserved.
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Electrical properties of GaAsN film grown by chemical beam epitaxy
Nishimura K., Suzuki H., Saito K., Ohshita Y., Kojima N., Yamaguchi M.
Physica B: Condensed Matter 401-402 343 - 346 2007年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Physica B: Condensed Matter
The local vibrational modes (LVMs) observed by Fourier transform infrared (FTIR) spectroscopy in GaAsN films grown by chemical beam epitaxy (CBE) was studied, and the influence of the nitrogen-hydrogen bond (N-H) concentration on the hole concentration was investigated. The absorption peak around 936 cm -1 is suggested to be the second harmonic mode of the substitutional N, N As , LVM around 469 cm -1 . The absorption peak around 960 cm -1 is suggested to be the wagging mode of the N-H, where the stretch mode is observed around 3098 cm -1 . The hole concentration linearly increases with increasing N-H concentration, and the slope increases with increasing growth temperature. It indicates that the hole concentration in GaAsN film is determined by both the number of the N-H and unknown defect, such as impurities, vacancies, and interstitials. This defect concentration increases with increasing growth temperature, suggesting that it is determined by Arrhenius type reaction. © 2007 Elsevier B.V. All rights reserved.
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Role of nitrogen and impurity on free carrier concentration in GaAsN grown by chemical beam epitaxy
Imai T., Lee H., Nishimura K., Suzuki H., Kawahigashi T., Sasaki T., Ohshita Y., Yamaguchi M.
Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4 1 842 - 844 2007年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4
GaAsN thin films were grown by chemical beam epitaxy using monomethylhydrazine ((CH 3 )N 2 H 3 ) as the N sources, and the role of the nitrogen (N) and impurities (hydrogen (H), carbon (C)) on free carrier concentration was investigated. The N, H, and C concentrations increased with decreasing growth temperature. GaAsN thin film grown at 470°C was n-type conduction, and the donor is thought to be the same in GaAs thin film. On the other hand, the films grown at 390-460°C were p-type conduction. In the range of 420-460°C, the hole concentration increased with decreasing growth temperature, and it decreased below 420°C, respectively. In order to clarify the origin of acceptor in p-GaAsN thin films, the dependence of growth temperature on the hole concentration and N, H, and C concentration were investigated, and the relationship between them was discussed. © 2006 IEEE.
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Reduction of residual carbon in GaAsN films grown by chemical beam epitaxy
Suzuki H., Nishimura K., Lee H., Saito K., Kawahigashi T., Imai T., Ohshita Y., Yamaguchi M.
Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4 1 819 - 822 2007年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4
Crystal quality of GaAsN films can be improved by using chemical beam epitaxy method for low-temperature growth. However, low-temperature growth increases carbon (C) incorporation in the films, which degrades their electrical properties. To reduce the C concentration in the films, C incorporation process was investigated in view of the surface reaction of nitrogen (N) sources on a substrate surface, and monomethylhydrazine (MMHy) and 1,1-dimethylhydrazine (DMHy) were compared. When MMHy was used as an N source, the C concentration in GaAsN drastically increases below 380°C than that in GaAs due to insufficient CH x desorption. In the case of DMHy, N(CH 3 ) 2 is desorbed more readily than CH x , Therefore, the C concentration can then be reduced by using DMHy. © 2006 IEEE.
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Novel materials and structures for super high efficiency multi-junction solar cells
Yamaguchi M., Suzuki H., Nishimura K., Kojima N., Ohsita Y., Okada Y.
ISES Solar World Congress 2007, ISES 2007 2 1028 - 1032 2007年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：ISES Solar World Congress 2007, ISES 2007
III-V compound multi-junction solar cells have great potential for space and terrestrial applications because they have high efficiency potential of more than 50% and superior radiation-resistance. As a result of developing wide bandgap InGaP double hetero structure tunnel junction for sub-cell interconnection, InGaAs middle cell lattice-matched to Ge substrate, and InGaP-Ge heteroface structure bottom cell, we have demonstrated 38.9% efficiency at 489-suns AM1.5 with InGaP/InGaP/Ge 3-junction solar cells In order to realize 40% and 50% efficiency, new approaches for novel materials and structures are being studied. We have obtained promising results: 1) high quality (In)GaAsN material with higher mobility by chemical beam epitaxy compared to those grown by the other growth methods, 2) 11.27% efficiency InGaAsN single-junction cells for 4-and 5-junction applications.
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Mg doping in C<inf>60</inf> layer for C<inf>60</inf>/a-C superlattice solar cells
Kojima N., Terayama T., Honda K., Suzuki H., Ohshita Y., Yamaguchi M.
Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4 1 53 - 55 2007年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4
Carbon materials can be expected as one of the promising materials for next generation low-cost solar cells. We have proposed C 60 /a-C superlattice structures as absorption layers. Superlattice structure has advantages to control the optical and electrical properties easily. In this paper, we will report Mg-doping in C 60 films to control the conductivity of C 60 layers for C 60 /a-C superlattice solar cells. Mg doping in C 60 films was done by the co-evaporation method of C 60 and Mg sources. The resistivity of Mg-doped C 60 films reduces in 6 orders of magnitude at the ratio of Mg/C 60 of 0.57. It is thought that Mg atoms act as dopant effectively. © 2006 IEEE.
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Interface structure analysis between C60 and CuPc for organic solar cells
Yamashita Y., Suzuki H., Kojima N., Ohshita Y., Yamaguchi M.
Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4 1 263 - 266 2007年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4
The CuPc crystal structure and molecular orientation on the C 60 was investigated by AFM and XRD as preliminary step to clarify the relationship the interface structure and electric property for organic solar cells. It is figure out that the CuPc grows grainy on the C 60 by the AFM measurement. The area density of the CuPc grain on the C 60 /mica became larger, and the grain diameter became smaller with increasing the substrate temperature. By the XRD, it became clear that the CuPc forms a-type mainly. The molecular column of deposited CuPc on C60 would be parallel to the substrate surface. © 2006 IEEE.
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Nishimura K., Lee H., Suzuki H., Kawahigashi T., Imai T., Saito K., Ohshita Y., Yamaguchi M.
Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4 1 815 - 818 2007年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4
GaAsN epitaxial thin films were grown on GaAs (001) substrate by chemical beam epitaxy with dimethylhydrazine ((CH 3 ) 2 N 2 H 2 ). In the dependence of growth temperature on the N concentration, there were three distinct regions in which the dependence was different. At the growth temperature of 420°C, the N concentration increased with increasing surface step density that corresponds to misorientation angle of GaAs (001) substrate. When the samples grown on 2 and 10° off substrates were compared, the root-mean-squares of surface roughness decreased from 1.1 nm to 0.3nm, despite of the increase of N concentration. In addition, the reduction of the impurity concentrations (hydrogen and carbon) in the sample grown on the 10° off substrate was also observed. These results showed the surface morphology of the GaAsN thin films is affected by the step density, and the possibility to obtain (In)GaAsN thin film that has high N and low impurity concentration with keeping crystal quality. © 2006 IEEE.
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Hydrogen treatment effects of a-C films for C<inf>60</inf>/a-C superlattice solar cells
Honda K., Kojima N., Imaizumi T., Terayama T., Suzuki H., Ohshita Y., Yamaguchi M.
Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4 1 142 - 145 2007年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4
The film quality improvement of amorphous carbon (a-C) layers for C 60 /a-C superlattice solar cells has been intended. a-C:N films were deposited by C 60 -cage breaking, and the layer-by-layer hydrogen treatment method was applied to the a-C:N films for the improvement of the film quality, and the structural change by the hydrogen treatment was investigated. Hydrogen radicals reconstruct carbon bonding structure of a-C:N film surface by etching the weak carbon bonds. Such structural change causes reducing the optical gap and changing the peak intensity ratio of Raman scattering spectra, which is concerned with sp 2 cluster size. The spin defect density much depends on the hydrogen treatment time. It is clear that the spin defect density has minimum at the particular time of the hydrogen treatment, so that hydrogen radicals also affect to cut the carbon bonds and induce defects. It is necessary to optimize hydrogen treatment time to improve film quality. ©2006 IEEE.
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Chemical beam epitaxy of GaAsN thin films with monomethylhydrazine as N source
Nishimura K., Lee H., Suzuki H., Ohshita Y., Yamaguchi M.
Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers 46 ( 5 A ) 2844 - 2847 2007年5月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers
GaAsN thin films were grown by chemical beam epitaxy (CBE) with monomethylhydrazine (MMHy) as a N source. Processes that determine the N composition in the GaAsN thin films were investigated in the growth temperature range from 340 to 480°C. When growth temperature is low (340-390°C), N composition is mainly determined by the supply of N species generated from MMHy and growth rate, since the desorption rate of N species from the growing surface is low. The effect of the desorption of N species on N composition is enhanced by increasing growth temperature (390-445°C). When growth temperature is high (445-480°C), the degree of N atom segregation from the grown layer increases, resulting in a marked decrease in N composition. Thus, N composition is determined by the balance of supply and desorption of N species, and growth rate. © 2007 The Japan Society of Applied Physics.
DOI： 10.1143/JJAP.46.2844
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Suzuki H., Nishimura K., Lee H., Ohshita Y., Kojima N., Yamaguchi M.
Thin Solid Films 515 ( 12 ) 5008 - 5011 2007年4月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Thin Solid Films
Crystal quality of GaAsN films can be improved by using CBE for low-temperature growth. However, low-temperature growth increases C incorporation in the films, which degrades their electrical properties. Consequently, C incorporation was investigated in view of the surface reaction of N sources on a substrate surface, and MMHy and DMHy were compared. When MMHy was used as an N source, C concentration in GaAsN drastically increases below 380 °C than that in GaAs due to insufficient CH x desorption. In the case of DMHy, N(CH 3 ) 2 is desorbed more readily than CH x , therefore, the C concentration can then be reduced using DMHy. © 2006 Elsevier B.V. All rights reserved.
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Influence of surface steps on N incorporation in GaAsN grown by chemical beam epitaxy
Nishimura K., Lee H., Suzuki H., Kawahigashi T., Imai T., Saito K., Ohshita Y., Yamaguchi M.
Physica Status Solidi (C) Current Topics in Solid State Physics 3 ( 8 ) 2689 - 2692 2006年10月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Physica Status Solidi (C) Current Topics in Solid State Physics
GaAsN epitaxial thin films were grown on GaAs (001) substrate by chemical beam epitaxy (CBE) with dimethylhydrazine ((CH 3 ) 2 N 2 H 2 , DMHy) as the N source that decomposes at a low temperature. We investigated the influences of the gas flow ratio of DMHy to the group V sources ([DMHy]/V), and surface steps on the N composition in GaAsN thin films. At the growth temperature of 420 °C, the N composition increased with increasing [DMHy] /V, indicating the N composition is determined by the amount of N supplied to the growing surface. In addition, the N composition also increased with increasing surface step density on GaAs (001) substrate orientated towards [010] from 0 to 10°. However, when the density of surface step is low (0-3 × 10 2 μm -1 ), the dependence of N composition on surface step density cannot be explained by only the N incorporation at the surface steps on the GaAs substrate. In this case, the surface morphology thought to be rough, since it suggest that N atoms are incorporated at the steps around the nuclei on the growing surface. On the contrary, when the density of surface step is high (3-7 × 10 2 μm -1 ), the N incorporation occurs at the steps as they move forward, resulting in the flat surface morphology. It was confirmed by the surface morphology observation of the samples grown on 2 and 10° off substrates, and the root-mean-squares of surface roughness were 1.1 and 0.3nm, respectively. These results indicate the surface morphology of the GaAsN thin films is affected strongly by the step density. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.