Origins of efficient green light emission in phase-separated InGaN quantum wells

Abstract

Green-light-emitting InGaN/GaN multiple quantum wells (MQWs) with high luminescent efficiency were grown by metalorganic chemical vapour deposition (MOCVD). The microstructure of the sample was studied by high-resolution transmission electron microscopy (HRTEM) and high-resolution x-ray diffraction, while its optical behaviour was analysed in great detail by a variety of photoluminescence methods. Two InGaN-related peaks that were clearly found in the photoluminescence (PL) spectrum are assigned to quasi-quantum dots (516 nm) and the InGaN matrix (450 nm), respectively, due to a strong phase separation observed by HRTEM. Except for the strong indium aggregation regions (511 meV of Stokes shift), slight composition fluctuations were also observed in the InGaN matrix, which were speculated from an ‘S-shaped’ transition and a Stokes shift of 341 meV. Stronger carrier localization and an internal quantum efficiency of the dot-related emission (21.5%), higher than the InGaN-matrix related emission (7.5%), was demonstrated. Additionally, a shorter lifetime and ‘two-component’ PL decay were found for the low-indium-content regions (matrix). Thus, the carrier transport process within quantum wells is suggested to drift from the low-In-content matrix to the high-In-content dots, resulting in the enhanced luminescence efficiency of the green light emission.

Titanium oxide nanoparticles spin-coated onto r-plane sapphire substrate: Effects on structural and optical properties of nonpolar a-plane GaN and InGaN/GaN multiple quantum wells

“…The PL peak energy for the InGaN/GaN MQWs in the temperature range from 10 to 300 K shows an S-shaped (redshift-blueshift-redshift) behavior, which could be caused by a change in the carrier dynamics, by carrier localization and potential inhomogeneity [37,38]. Similar features to those reports are also observed in Fig.…”

“…Therefore, the most likely mechanism of thermal quenching is attributed to thermionic emission of the carriers from localized energy states, caused by QW width fluctuations at the interface and indium alloy fluctuations [37]. Although an alloy fluctuation may be expected in the active layer, the observed ratio, 0.34, of I (300 K) to I 0 (13 K), indicates good quantum efficiency, compared to other reports for QWs with polar orientation [38,40].…”

“…E A1 means the exciton binding energy in the QWIR at temperatures below 70 K, and E A2 means the activation energy of the thermally-activated carrier required to escape from the confining potential at temperatures above 70 K [38,39]. In our case, the best fit is also obtained only if two nonradiative channels are included.…”

Quantized level transitions and modification in InGaN∕GaN multiple quantum wells

“…The blueshift is attributable to the charge screening effect of quantum-confined Stark effect ͑QCSE͒ and the band-filling effect. 13,14 However, by further increasing the injection current, P Q1 monotonically redshifts which is suggested to be induced by the band gap renormalization and self-heating effect. 7,15,16 In the case of P Q2 , as a result of a competition between those blueshifting and redshifting mechanisms discussed above, initial blueshift and then redshift can be observed more simply by increasing the injection current.…”

Improved Yellow Light Emission in the Achievement of Dichromatic White Light Emitting Diodes

“…Recently, tremendous progress has been made in InGaN/GaN based blue, green and shorter-wavelength light-emitting diodes (LEDs) [1][2][3][4][5][6]. It is of great interest to design an monolithic white LED without the need of a phosphor converter for long-wavelength light [7][8][9][10][11][12].…”