Semiconducting polymers with alkylated naphtho [1,2b:5,6-b′]dithiophene (NDT3) and naphtho[2,1-b:6,5-b′]dithiophene (NDT4) are synthesized and characterized. The solubility of the present polymers is significantly improved as compared to the nonalkylated counterparts with preserving the good charge transport properties. Interestingly, the effect of alkylation is found to be quite distinct between the NDT3 and NDT4 cores. In the NDT3-based polymers, alkylation leads to the more ordered backbone structure and thus the increased crystalline order in the thin film. On the other hand, in the NDT4-based polymers, alkylation is detriment to the backbone ordering, which gives rise to the face-on orientation or amorphous like film structure. This difference can be qualitatively explained by the different alkyl placement; all the neighboring alkyl groups are in the anti arrangement in the NDT3-based polymers, whereas the arrangement is a mixture of anti and syn in the NDT4-based polymers, which likely causes steric impact on the backbone. These observations make us better understood how the alkylation affect the ordering structures, which would be an important guideline for the design of superior semiconducting polymers.

Although angular-shaped naphthodifurans, naphtho[1,2-b;5,6-b']- and naphtho[2,1-b;6,5-b']-difuran, are formally isoelectronic with chrysene as their thiophene counterparts, naphtho[1,2-b;5,6-b']- and naphtho[2,1-b;6,5-b']-dithiophene, the HOMO energy level of naphthodifurans is much higher than those of naphthodithiophenes and chrysene. The difference in electronic structure in the ground state can be explained by distinct electronic perturbation from the outermost aromatic rings.

This paper reports the atmospheric-pressure MOVPE growth of In-rich InAlN. All InAlN films prepared here (Al content:0 0.43) do not show phase separation. The incorporation of Al in InAlN is decreased with increasing growth temperature. A decrease in Al content is also observed for films grown at a position farther from the up-stream end of the susceptor. The marked decrease in the Al content along the gas flow direction seems to be caused by the shortage of TMA supply at the downstream by the parasitic reaction of TMA. A single-crystalline InAlN film with an Al content of 0-0.43 is successfully grown by adjusting growth temperature and TMA/(TMI+TMA) molar ratio. FWHM of X-ray rocking curve for InAlN is increased with increasing Al content. The carrier concentrations in InAlN films are comparable to that in InN (1-5 × 10^19 cm^<-3>). All the single-crystalline InAlN films with an Al content of 0-0.3 show a photoluminescence at room temperature

This paper reports the crystallographic degradation of MOVPE InN during the growth. Using FWHMs of X-ray rocking curve, tilt ( (0002)) and twist ((10-10)) angle distributions are evaluated and effects of the major growth parameters, such as growth temperature, growth time and with/without GaN buffer in the degradation, are revealed. With increasing either thickness of grown InN or growth temperature up to 600 ˚C, the tilt angle distribution is markedly increased, indicating the crystallographic degradation of grown films. The use of a GaN buffer reduces such degradation. Since the twist angle distribution is scarcely changed by such growth parameters, the destruction of InN crystals during growth and annealing is concluded to be anisotropic. The trends of the crystallographic degradation revealed here are in good agreement with those for the electrical and optical degradation previously reported. , in III-nitrides, although it is still a less studied material compared with other III-nitride semiconductors. Therefore, the material is very promising as a channel material in high-speed and high-frequency electron devices. Compared with MBE InN, MOVPE InN has been less studied. For MBE InN, it has been reported that the electrical properties are improved and a carrier concentration in the order of 10 17 cm -3 is attained by increasing thickness of the films [3]. For MOVPE InN, on the other hand, the carrier concentration has been still in the middle of 10 18 cm -3 [4]. Therefore, it is highly desirable to clarify the causes for the lower quality of MOVPE InN.It is noted that the growth temperature of InN is different between MBE and MOVPE. The optimum growth temperature for MBE InN is about 550 °C [5], while that for MOVPE InN is around 600 °C, giving the lowest carrier concentration [6]. From the view point of PL peak energy, a temperature as high as 620 °C was reported to be optimum [6]. Thus, the optimum growth temperature of MOVPE is higher by 50 °C or more than that of MBE. Such a high temperature needed for the MOVPE InN is to enhance the thermal decomposition of NH 3 . It is well-known that InN is a thermally unstable material because of the low bonding strength for In-N compared with those for . Recently, we have reported the electrical and optical degradation of MOVPE InN during the growth and post-growth annealing [8]. The PL measurement from both the surface and interface with different wavelength excitation sources revealed the degradation of InN near the interface. No degradation was found at the surface. Such degradation was found to be enhanced when samples were grown/annealed at a high temperature (-620 °C) and/or for a long time (-4 h).

Polarity control of MOVPE InN on sapphire (0001) was investigated. Two kinds of polarity InN films on sapphire substrate by MOVPE have been prepared by controlling the substrate nitridation process and/or the LT-GaN buffer annealing process. Surface of the nitrided sapphire is a crucial factor in determining the polarity of InN film. N-polarity InN film was grown on the 1000 °C-nitrided substrate without LTGaN buffer; while In-polarity InN film was grown on the 900 °C-nitrided substrate. In the case of InN growth with a LT-GaN buffer, buffer annealing is a crucial issue in determining the polarity of InN film. N-and In-polarity InN films were obtained on the long-time-annealed buffer and the short-time-annealed buffer, respectively.1 Introduction Among the group-III nitrides, InN recently has attracted more attention due to the newly-suggested small band gap of 0.7 eV [1-3], which potentially extends the spectral range covered by group-III nitrides to the infrared. In addition, InN has a very small electron effective mass [4] and a high electron drift velocity [5], which makes the material also promising in high-speed and high-frequency electronic devices. However, the fabrication of InN based devices has been hindered now, due to lack of high quality InN single crystal film. Therefore, growth of high quality InN film is highly required.Polarity is an important property of group-III nitrides with wurtzite structure. The effects of polarity on the growth of InN film by MBE have been reported recently [6,7]. N-(-c) polarity layers could be grown at higher substrate temperature compared with the In-(+c) polarity films; The surface of Npolarity InN film is more smooth than that of In-polarity InN film, and the quality of -c polarity film is better than that of +c polarity film. The situation is very much different from that of other typical IIInitrides of GaN and AlN, where +c polarity is better than -c polarity. This brings us a light to improve the InN film's quality by controlling the polarity. However, it is still not very clear how to control the polarity of InN grown by MOVPE up to now. In this work, we report the growth of -c and +c polarity InN on sapphire substrate by MOVPE.