The internal quantum efficiency (IQE) of InGaN/GaN multiple quantum wells (MQWs) with blue light emission was improved by inserting an InGaN/GaN superlattice (SL) beneath the MQWs. While the SL technique is useful for improving the light-emitting diode (LED) performance, its effectiveness from a multilateral point of view requires investigation. V-shaped pits (V-pits), which generate a potential barrier and screen the effect of the threading dislocation, are one of the candidates for increasing the light emission efficiency of LEDs exceptionally. In this research, we investigated the relationship between the V-pit and SL and revealed that the V-pit diameter is strongly correlated with the IQE by changing the number of SL periods. Using scanning near-field optical microscopy and photoluminescence measurements, we demonstrated the distinct presence of the potential barrier formed by the V-pits around the dislocations. The relationship between the V-pit and the number of SL periods resulted in changing the potential barrier height, which is related to the V-pit diameter determined by the number of SL periods. In addition, we made an attempt to insert pit expansion layers (PELs) composed of combination of SL and middle temperature grown GaN layer instead of only SL structure. As a result of the evaluation of LEDs using SL or PEL, the EL intensity was strongly related to pit diameter regardless of the structures to form the V-pits. In addition, it was clear that larger V-pits reduce the efficiency droop, which is considered to be suppression of the carrier loss at high injection current.

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Since lean premixed combustion in gas turbine combustors undergoes in elevated pressure condition, it is important to know NO X formation characteristics under elevated pressure. Generally, effects of pressure on NO X formation characteristics are evaluated by using pressure coefficient on conventional systems. However, the value of pressure coefficient distributes widely from-0.2 to 0.5. This difference in the pressure coefficient stems from differences in experimental conditions and formation processes of NO X. As a result, effects of pressure on different NO X formation mechanisms have not been elucidated yet because of difficulties of temperature control of combustion region. In this study, to clarify the effects of pressure on the prompt NO X formation process is set as the objective. Experimental measurements and numerical simulation with detailed elementary reactions are conducted. The temperature controllable premixed flat flame burner is fabricated in the elevated pressure combustion chamber, and measurement of NO X concentration is conducted in the chamber. Both the experimental and numerical results clearly show that the pressure does not affect to the prompt NO X formation.

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