Origin of huge photoluminescence efficiency improvement in InGaN/GaN multiple quantum wells with low-temperature GaN cap layer grown in N₂/H₂mixture gas

Abstract

The nominal internal quantum efficiency of InGaN/GaN multiple quantum wells significantly increases from 5.6 to 26.8%, as a low-temperature GaN cap layer is grown in N2/H2 mixture gas. Meanwhile, the room-temperature photoluminescence (PL) peak energy shows a merely 73 meV blue shift. On the basis of temperature-dependent PL characteristics analysis, the huge improvement in PL efficiency arises mainly from the “etching effect” of hydrogen, which reduces the defect density and indium segregation at the upper well/barrier interface, and consequently contributes to the decrease in the number of nonradiative recombination centers and the enhancement of carrier localization.

Surface morphology and optical properties of InGaN quantum dots with varying growth interruption time

“…high-indium regions. Such high-indium-content-cluster regions are considered to act as the non-radiative recombination centers [26]. By further increasing the growth interruption time, we found the surface became even rougher.…”

“…During the InGaN growth period, the indium clusters are prone to accumulate around the dislocations which are depicted in figure 2(a). Such a behavior will deteriorate the optical property of the materials [26]. The optical property will become even worse when high-indium-composition materials are grown.…”

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.…”

“…However, the peak energies of blue MQWs and green QW exhibit an S-shaped curve when the temperature ranges from 15 K to 300 K due to the carrier transition from deep localized states to shallow localized states drifted by the thermal-activated energy. The S-shaped curves are fitted by the band-tail Varshni equation [ 3 ]: where E(T) is the peak energy at a certain temperature T , E g (0) is the peak energy at 0 K, α and β are the fitting parameters, k is the Boltzmann constant and Λ is the degree of localized states. A higher value of Λ signifies a higher degree of localized states.…”

“…Indium gallium nitride (InGaN) light-emitting diodes (LEDs) are essential for high quality illumination [ 1 , 2 , 3 ] and high resolution, high brightness and fast response displays [ 4 , 5 , 6 ], thus playing an important role in lighting, high definition TV (HDTV), visual reality (VR)/augmented reality (AR) displays, etc. [ 7 , 8 ].…”