We investigated the effects of the well protection layer (WPL) and electron reservoir layer (ERL) on the emission properties of InGaN/GaN green multiple quantum wells (MQWs). In order to increase their emission wavelength by preventing the volatile InGaN well, a thin GaN WPL was coated subsequently on each well layer at the same temperature before ramping-up the temperature to grow the GaN barrier. It was found that the WPL directly influenced the indium content and optical properties of the MQW. The indium content was in fact increased, as was evident from the x-ray diffraction and photoluminescence experiments. Then, to explore the possibility of enhancing the quantum efficiency by increasing the electron capture rate, a superlattice ERL composed of ten pairs of InGaN/GaN was embedded between the MQW and n-GaN. The electroluminescence intensity of the green light emitting diode with the ERL was up to three times higher than that of the diode without the ERL. These results imply that the carrier capture by the MQW is significantly improved by the additional superlattice ERL, which consequently leads to the enhancement of the quantum efficiency.

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Recently, the demand for small, low-cost electronics has increased the use of cost-effective tiny inductors in power-management ICs (PMICs). However, the conduction loss caused by the parasitic DC resistance (RDCR) of a small inductor leads to low efficiency, which reduces the battery usage time and may also cause thermal problems in mobile devices. In particular, these issues become critical when a conventional boost converter (CBC) is used to achieve high-output voltage due to the large inductor current. In addition, as the output voltage increases, a number of issues become more serious, such as large output voltage ripple, conversion-ratio limit, and overlap loss. To solve these issues, this paper proposed a high-voltage boost converter with dual-current flows (HVDF). The proposed HVDF can achieve a higher efficiency than a CBC by reducing the total conduction loss in heavy load current conditions with a small inductor. Moreover, because in the HVDF, the current delivered to the output becomes continuous, unlike in the CBC with its discontinuous output delivery current, the output voltage ripple can be significantly reduced. Also, the conversion gain of the HVDF is less sensitive to RDCR than that of the CBC. To further increase the conversion gain, a time-interleaved charge pump can be connected in series with the HVDF (HVDFCP) to achieve higher output voltage beyond the limit of the conversion gain in the HVDF while maintaining the advantages of a low inductor current and small output voltage ripple. Simulations using PSIM were performed along with a detailed numerical analysis of the conduction losses in the proposed structures. The simulation results were discussed and compared with those of the conventional structures.