## 3 Results  
The current-voltage (I-V) characteristic under CW regime at 300 K was studied for the LEDs from the same wafer. The I-V curve was fitted with a parallel and series resistance for leakage analysis. The obtained parameters are: 170 MOhm parallel resistance, ideality factor of 4.3, series resistance of 25 Ohm, and saturation current of 1.5 \(\times\) 10\({}^{-14}\) A. The electroluminescence (EL) performance of monolithic white LEDs was studied at room temperature in continuous wave (CW) regime. Figure 2 shows EL spectra for these devices with increasing currents up to 500 mA. The further increase of current was limited by the damage of p-n junction due to due overheating under CW regime, especially for longer durations. Two distinct peaks in Figure 2 indicate that both shallow and deep QWs are operating in their respective blue and green spectral regions. Figure 2a shows that at lower currents less than 80 mA the green peak dominates the emission spectrum with blue emission getting stronger with increasing carrier concentration. We attribute this to the non-uniform distribution of injected holes. Primarily, due to their lower mobility, higher effective mass, and poor transport among the MQW structure [23] holes will radiatively recombine in the QW closer to the p-side. However, with further increase in current, more holes travel through the barrier layer and are available for recombination in blue QWs. In MQW structures, non-uniform hole redistribution leading to dominant EL intensity from the QW at lower currents has been observed. Methods such as quaternary electron blocking layer [23], InGaN barrier layers [24] and varying thickness of the barrier layers [25] have been proposed to achieve better hole injection and transport among the QWs. Figure 1: Conduction band schematic for the monolithic white LEDs depicting blue and green quantum wells (QWs) with bottom SPSL grown on top of n-GaN in order to facilitate carrier injection and improve growth. Figure 2: Electroluminescence (EL) spectra of monolithic white LED pumped with the continuous wave (CW) current of: (**a**) 50–250 mA; and (**b**) 300–500 mA. On further increasing the current up to 100 mA, the emission from green QW is clamped and the radiative recombination in the blue QW is enhanced. For very high CW current injection, i.e., >300 mA, increased radiative recombination in green QW and saturated blue emission peak is observed (Figure 2b). This is believed to be caused by the carrier redistributing due to band-filling of blue QW leading to electron overflow thus making more carriers, i.e., electron available for recombination in green QW. The EQE for these devices exhibit a dome-like dependence on current characteristic similar to mono-color InGaN LEDs. The EQE for devices tested from different parts of the wafer varied from below 1% to 4%. This can be further improved by catering for procedures, during growth and fabrication, to improve light extraction efficiency. To correctly estimate and improve the internal quantum efficiency more studies concerning the crystalline structure, Indium composition, distance between QWs and p-doped region are required. The tuning of CCT with varying current is shown in Figure 3. The dashed red line associates the highest CCT obtained from this device to the minima of green/blue (G/B) integrated intensity ratio. This indicates the dominance of blue peak in this region of operation. For injection current between 100 mA and 350 mA, G/B ratio is <1 and blue peak dominates resulting in cool white emission. For other regions, increase in green intensity results in tuning of emission towards warmer color temperature. Commission International de I'Eliarage (CIE 1931) chromaticity coordinates with associated CCT at different currents is shown in Figure 4. The coordinates (0.4172, 0.4375) at 40 mA moves to (0.2686, 0.2716) at 240 mA and CCT increase from 3600 K to 13,240 K (Figure 4a). With further increase in current, a movement towards warmer CCT values can be seen with 4775 K at (0.3607, 0.4278) for 500 mA.