Influence of the quantum-well shape on the light emission characteristics of InGaN/GaN quantum-well structures and light-emitting diodes

Abstract

Structural and optical properties of various shapes of quantum wells (QWs), including rectangular, triangular, trapezoidal, and polygonal ones are investigated. Photoluminescence (PL) measurements show that the highest light emission efficiency and the best reproducibility in the intensity and wavelength are obtained from trapezoidal QWs. The temperature dependence of PL spectra indicates the more localized nature of excitons in the trapezoidal QWs. A plan-view transmission electron microscopy shows that quantum dots (QDs) are formed inside the dislocation loop in trapezoidal QWs. The distribution of QDs in size and composition becomes more uniform with trapezoidal QWs than with rectangular QWs, leading to superior light-emission characteristics. It is suggested that QD engineering and dislocation control are possible, to some extent, by the modulation of the QW shape in InGaN/GaN-based light-emitting devices.

Characteristics of GaN‐based light emitting diode grown on circular convex patterned sapphire substrate

“…These dark spots, which have been resulted from non-radiative recombination center, appeared on the CC region [17]. Also, the NSOM image shows inhomogeneous emission intensity from the trench region, similar to previously observed phenomenon which had been attributed to excitons localized at the potential minima acting as self assembled quantum dots [18,19]. Using the NSOM-PL spectra, the band-edge emission intensity from trench (A) and CC (B) region marked in the inset of Fig.…”

High brightness blue and green light emitting quantum wells with graded‐In‐content profile grown by MOCVD

“…The formation of quantum-dot-like features and spatial phase separation was previously observed in the graded-In-content, trapezoidal-shape InGaN MQWs by transmission electron microscope images [4]. Cathodoluminescence (CL) measurement was also carried out to distinguish the origin of the different InGaN-related emissions for the blue light emitting sample.…”

“…Recently, it has been reported that the degree of carrier localization caused by the spatial compositional fluctuation can be varied by adjusting the profile of the nominal In composition (x) profile during the In x Ga 1-x N well growth procedure, and this shape of In content profile of the In x Ga 1-x N well region strongly influences the emission characteristics of In x Ga 1-x N/GaN QW LED structures [4]. Since this method can be used for the effective formation of quantum dot-like structures and the dislocation density control, superior optical properties even in the longer wavelength region (e.g., green) can be achieved by adopting the trapezoidal-shape, graded-In-content InGaN QWs.…”

Multiple defects in GaInN multiple quantum wells grown on ELO GaN layers and on GaN substrates

“…However, one technological problem that effects the growth of GaInN alloys with high indium concentrations is low miscibility of InN and GaN. This leads to the composition fluctuations and/or the phase separation in the alloys, which in turn leads to the formation of In-rich precipitates and clusters [2,3]. Another type of structural defects that is frequently reported in GaInN alloys is the so-called "V defect" [4][5][6][7][8], which takes the form of an open hexagonal, inverted pyramid with {1011} side walls [5].…”