Wurtzite AlN film is a promising material for deep ultraviolet light-emitting diodes. However, some properties that attribute to its crystal orientation, i.e., c-axis orientation, are obstacles in realizing high efficiency devices. Constructing devices with non-c-axis oriented films is a solution to this problem; however, achieving it with conventional growth techniques is difficult. Recently, we succeeded in growing a-axis oriented wurtzite heavily Fe-doped AlN (AlFeN) films via sputtering. In this article, we report the electronic structures of AlFeN films investigated using soft X-ray spectroscopies. As-grown films were found to have conduction and valence band structures for a film with c-axis in film planes. Simultaneously, it was found that large gap states were formed via n-p and Fed hybridization. To remove the gap states, the films were annealed, thereby resulting in a drastic decrease of the gap states while maintaining a-axis orientation. We offer heavy Fe-doping and post annealing as a new technique to obtain non-polar AlN films. Wurtzite III-nitride semiconductors centred on GaN are proven materials for light emitting diodes (LEDs) because they have direct band gaps covering the spectral region of ultraviolet (UV), visible, and infrared lights via band gap engineering for the past quarter-century 1-4. AlN is one of the III-nitrides and it is a promising material for deep UV LEDs 5,6 by virtue of its wide band gap of 6.1 eV 7 along with its high thermal conductivity and chemical stability 8. However, AlN and AlGaN with a high AlN mole ratio confront difficult issues to realize high efficiency devices owing to some electronic properties in the form of thin films, which are traced back to its crystal axis orientations, i.e. c-axis orientation. In the c-axis direction of a wurtzite structure, electronic polarization can exist owing to a large deference of electronegativities between Al and N, which align along the c-axis, as shown in Fig. 1a. Electronic polarization can build internal electric fields in vertical LED structures, which cause low recombination efficiencies due to the quantum confined Stark effect 9,10. Additionally, the split regimes in the top of valence band (VB) can be another obstacle. Optical dipole transitions between the top of the VB and the bottom of the conduction band (CB) are forbidden for the light with electric fields in the c-plane 11 , which result in low extraction efficiency. Considering the above mechanisms of obstacles for the realization of high efficiency deep UV LEDs, laying c-axes in film planes would be a simple solution. Significant efforts have been made to grow films with m-and a-axes orientations, which are known as non-polar films 12,13. However, with conventional techniques based on epitaxial growth regimes, there are difficulties in choosing an appropriate substrate 14-17 ; moreover, wurtzite films are subjected to the formation c-axis orientation. Very recently, we succeeded in obtaining a-axis oriented films via heavily Fe-doping AlN by radio-frequency sput...

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The cooling process of a biological phantom using ice slurries with different geometries in a limited space was experimentally investigated. Ice slurry has recently been considered to as a solution to cool organs in the abdominal cavity efficiently and rapidly to suppress biological reactions during minimally invasive laparoscopic surgeries. However, previous studies have not focused on the interactions between ice slurry and biological tissues in the abdominal area. In this study, we aimed to investigate the effects of ice slurry geometry, enclosure width Lw, and mimic-blood flow rate Qb on the cooling of a biological phantom using ice slurry in a limited space. We prepared the same volume of ice slurry using different geometries with an ice packing factor of 25 wt% using a scraper-type method to place on the phantom surface. We observed the melting behaviors of the ice slurries and measured the surface and core temperatures of the biological phantom. It was found that the supply methods of the ice slurry affected the cooling of biological tissues significantly. When the ice slurry width was the same as that of the enclosure, the ice slurry floated on the melted slurry and inhibited the cooling of the biological phantom. When the slurry width was small compared to that of the enclosure, the slurry remained in contact with the phantom, thus resulting in its efficient and rapid cooling. The mimic-blood flow promoted the melting of the ice slurry increased the heat flux on the phantom surface. However, the core temperature was not affected. Thus, the core temperature cannot be reduced unless the blood flow is occluded.

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