The influence of GaN column diameter DGaN on structural properties was systematically investigated for InGaN nanocolumns (NCs) grown on top of GaN NCs. We demonstrated a large critical layer thickness of above 400 nm for In0.3Ga0.7N/GaN NCs. The structural properties were changed at the boundary of DGaN=D0 (∼120 nm). Homogeneous InGaN NCs grew axially on the GaN NCs with DGaN≤D0, while InGaN-InGaN core-shell structures were spontaneously formed on the GaN NCs with DGaN>D0. These results can be explained by a growth system that minimizes the total strain energy of the NCs.

A new method of two-step selective area growth (SAG) by RF-plasmaassisted molecular beam epitaxy is developed, enabling the growth of uniform arrays of thin GaN nanocolumns (NCs) with diameters <50 nm. In the SAG, the migration-enhanced epitaxy mode with an alternating supply of Ga and active nitrogen was employed during the initial growth of NCs on small-nanohole-patterned substrates to complete the crystal nucleation in the nanoholes. Once the nucleation occurred, the growth mode to the simultaneous supply of Ga and nitrogen is immediately switched. In the second step, the growth temperature is increased and the nitrogen flow rate to suppress the lateral growth rate is decreased. A high-density uniform array of very thin NCs in a triangular lattice with a diameter of 26 nm and a lattice constant of 60 nm is demonstrated; the NC density is 3.2 × 10 10 cm −2 .Introduction: GaN nanocolumns (NCs), which are independent onedimensional nanocrystals, were first fabricated on (0001) sapphire substrates [1, 2] and then on (111) Si substrates [3] through self-assembly by RF-plasma-assisted molecular beam epitaxy (RF-MBE). The selfassembled GaN NCs have been utilised in the fabrication of InGaN-based light-emitting diodes (LEDs) on Si [4][5][6][7]. However, randomness of the size and position of the NCs was inevitably introduced by the self-assembly of NCs, which is initiated by random and spontaneous nucleation, frequently resulting in the multicolour emission of LEDs in microscale areas [5]. At the same time, precise control of the NC size and position was achieved by the development of selective area growth (SAG) [8][9][10][11]. However, the uniform arrays of GaN NCs fabricated by SAG had NC diameters (D) larger than ∼100 nm [8][9][10][11][12]. It was therefore considered a challenge to grow well-ordered thin GaN NCs with D < 100 nm, even though the diameter of self-assembled NCs typically varies from 50 to 100 nm [1,5]. In axial InGaN/GaN heterojunction NCs, the in-plane spatial separation of electrons and holes occurs, reducing the internal quantum efficiency (IQE) [13]. According to a theoretical prediction, however, reducing the NC diameter to 40 nm significantly increases the electron-hole ground state overlap, thus providing a promising approach for achieving a higher IQE [14]. In this Letter, we report having developed a two-step SAG method for improving the growth control of thin NCs and having demonstrated a high-density array of very thin NCs in a triangular lattice with D = 26 nm and a NC density of 3.2 × 10 10 cm −2 . The lattice constant (L) was 60 nm.

Emission mechanisms in regularly arrayed InGaN/GaN quantum structures on GaN nanocolumns were investigated, focusing on the spatial emission distribution at the nanocolumn tops and the carrier recombination dynamics. The double-peak emission originated from the dot- and well-like InGaN areas with different In compositions was observed. From the results regarding the spatial emission distribution, we proposed a simple analytical approach to evaluating the carrier recombination dynamics using the rate equations based on the two energy states. The considerable six lifetimes can be uniquely determined from the experimental results. Carrier transfer from the high- to the low-energy state is dominant at high temperatures, producing the increased total emission efficiency of the inner low-energy area. In addition, the internal quantum efficiency should not be simply discussed using only the integrated intensity ratio between low and room temperatures because of the carrier transfer from high- to low-energy states.

The fundamental skills for information system development such as system designing, programming and project management are very similar to the fundamentals of general problem solving. In this paper, we proposed an education framework for practical problem solving based on system designing technologies and an application of proposed framework on video training materials to train the skills of modeling and understanding from ambiguous matter in practical problem via nonverbalized video training material. Our framework uses Resource Flow Diagram (RFD) to support the understanding of procedure and resources on problem solving. RFD is our proposed visualization method for procedure and resource management based on Sequence Diagram in Unified Modeling Language (UML). RFD is designed for the intuitive representation of the procedure flow and required resources since UML could not define them with single diagram. In this experiment, proposed education framework was applied for the understanding of cooking procedure from the cooking exhibition videos on the demonstrative lecture.

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