Color‐Tunable 3D InGaN/GaN Multi‐Quantum‐Well Light‐Emitting‐Diode Based on Microfacet Emission and Programmable Driving Power Supply

Abstract

Color‐tunable InGaN/GaN multi‐quantum‐well (MQW) light‐emitting diodes (LEDs) are reported based on GaN microfacet structure directly grown on c‐plane patterned sapphire substrate by metal organic vapor phase epitaxy (MOVPE) through promoting 3D growth. By adjusting GaN growth temperature and pattern arrangement, a GaN microfacet with almost pure {10true1¯1} semipolar facets is obtained. The multifacetted InGaN/GaN MQW LED chip evolves three distinct emission peaks around 630, 530, and 450 nm in electroluminescence (EL) as injection current increases from 1 to 100 mA. The EL behavior originates from locally different facets of the complex 3D structure: MQWs grown on c‐planes and semipolar facets, respectively, which is confirmed by cathodoluminescence characterization in a scanning transmission electron microscope (STEM‐CL). Considering the dependence of emission wavelength and intensity on injection currents, a programmable power supply is designed to drive the LED. The specific color of the LED is tuned by time‐shared driving of the currents based on three channels with controllable magnitudes and duty cycle from the power supply, covering red, yellow, green, cyan, blue, and purple. Furthermore, white LEDs with high color rendering index (CRI) up to 96.1 and correlated color temperature (CCT) between 4000 and 10 000 K are achieved.

Realizing Single Chip White Light InGaN LED via Dual-Wavelength Multiple Quantum Wells

“…The LED structure is further confirmed by the TEM. The selected area diffraction patterns (SADPs) are represented in Figure 2 a, where the zone axis (ZA) is along the [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ] direction. The MQWs’ structure is shown in Figure 2 b, where the 4× blue MQWs and 1× green QW are clear to be seen.…”

“…As shown in Figure 2 c,d, the MQWs on the sidewall of V-pits are more than half thinner than the normal MQWs; therefore, the emission peak should demonstrate a large blue-shift. Moreover, as the sidewalls of V-pits are semi-polar planes, where the indium incorporation efficiency is lower than the c-plane, the blue-shift of the emission peak will be exacerbated further, thus leading to the additional emission peak between GaN and blue MQWs [ 9 , 27 ]. The peaks are fitted by a Gaussian function, and the peak energies as well as the PL integral intensity for each peak are represented in Figure 3 b.…”

“…The most popular method to realize white light emission at present is the combination of blue InGaN LEDs with scattered yttrium aluminum garnet (YAG) phosphor, which will emit yellow light when excited by the blue light, thus mixing with the excitation light to render a white light from sight view. However, such a method has some limitations such as the low color rendering index (CRI), high correlated color temperature (CCT) and nonuniform colors with different sight view angles [ 9 , 10 ]. Combining three red, blue and green (RGB) LEDs together would significantly improve the CRI, and the light quality could be modulated as the three chips are pumped by different circuits.…”

“…In addition, the optically pumped monolithically multi-color lasing is demonstrated from an InGaN microdisk structure [ 15 ]. Wang et al fabricate a 3D InGaN/GaN MQWs LED structure, the colors of which could be tuned from red to blue [ 9 ]. With the aid of V-pits and a programmable driving power supply module, they demonstrate a single chip white light emission with a CRI value larger than 90.…”

Wavelength-Tunable Green Light Sources Based on ZnO:Ga Nanowire/p-InGaN Heterojunctions

“…The above analysis indicates that the light color of the fabricated LEDs based on the n-ZnO:Ga MW/p-InGaN heterojunction covering the whole green−yellow light region is achieved by tuning the Gadoping concentration in the as-prepared MWs. 9,24,25…”