Quantum‐well thickness dependence of stimulated emission in InGaN/GaN structures

Abstract

PACS 78.45.+h, 78.47.+p, 78.55.Cr, 78.67.De Room-temperature lateral emission in In 0.15 Ga 0.85 N/GaN multiple quantum wells (MQWs) of various well thicknesses has been studied by means of excitation-density and time-resolved photoluminescence spectroscopy. The lowest threshold of stimulated emission and the highest emission efficiency has been observed in the structures with the well thickness d = 3 nm. The existence of an optimal well thickness is attributed to enhanced nonradiative recombination for thinner wells and to larger-well-width−invoked indium segregation that results in broadening of the local-state distribution.1 Introduction Ternary InGaN-based multiple quantum wells (MQWs) are the key structures for high efficiency, long lifetime violet, blue, and green light emitting diodes and laser diodes [1,2]. Although optical properties of InGaN/GaN quantum well structures are being widely investigated, the emission mechanism is not completely identified so far [1−8]. Well-width and composition fluctuations, complete phase separation, and built-in electric field can lead to formation of localised states of various origin [1][2][3][4][5][6][7][8] with the impact of each effect depending in a complex manner on MQW parameters and growth conditions. To maximise spontaneous and stimulated emission, the underlying physics should be cleared out and the growth conditions and structure of the MQWs are to be optimised.The crucial parameter of a MQW structure is the thickness of the quantum-well layer. Variation in well width results not only in alteration of electronic states by quantum size effect, but also in the quantum-confined Stark effect, as well as in intricate changes of thermodynamics of In segregation that is due to lattice mismatch between InN and GaN. Our previous study on optical and structural properties of InGaN/GaN MQWs has evidenced that an increased well thickness invokes formation of spatially separated In-rich and In-poor regions in the quantum well layers [9][10][11]. Here we report on a study of excitation-density dependent and time-resolved lateral emission in InGaN/GaN MQW structures with various well thickness, d. The high-excitation regime applied enabled us to minimise the built-in electric field effect on emission from localised states.

Improved Structural Quality and Carrier Decay Times in GaN Epitaxy on SiN and TiN Porous Network Templates

“…The 15 min nitridation sample exhibits decay times [(τ 1 , τ 2 ) = (0.47 ns, 1.86 ns)] that are comparable to that of a freestanding GaN sample. The slow decay constants measured here are longer than those reported for Si-doped MOCVD-grown GaN/sapphire (740 ps) [3], HVPE-grown GaN templates (205-530 ps) [4,5,6], homoepitaxial GaN layers (445-506 ps) [6,7], epitaxial lateral overgrown (ELO) GaN (400-459 ps) [8,9], and bulk GaN (722-860 ps) [8,9].…”

Recent Research on Indium-Gallium-Nitride-Based Light-Emitting Diodes: Growth Conditions and External Quantum Efficiency

“…In addition to the width of the QW, it was noted the SRH lifetime also can be pointedly increased by increasing the number of QWs. A thick QW structure (width > 2.5 nm) [92][93][94][95] grown on a c-plane shows better efficiency than a thin wall. However, the oscillator strength in thick polar QW is reduced via polarization, which implies a substantially extended radiative lifetime of thick c-plane QWs.…”