Enhanced efficiency and reduced spectral shift of green light-emitting-diode epitaxial structure with prestrained growth

Abstract

The enhanced emission efficiency and reduced spectral shifts of a green InGaN/GaN quantum-well (QW) light-emitting-diode epitaxial structure by using the prestrained growth technique when compared with a control sample of the same emission spectrum with conventional growth are demonstrated. By adding an ∼7%-indium InGaN/GaN QW to the structure before the growth of designated emitting high-indium QWs, the growth temperature of the emitting QWs can be raised by 30 °C while keeping about the same emission wavelength around 544 nm in photoluminescence (PL) and 525 nm in electroluminescence (EL). The internal quantum efficiency, room-temperature PL intensity, and EL intensity at the injection current of 20 mA are increased by ∼167%, ∼140%, and ∼182%, respectively. Also, the spectral blueshift range in increasing injection current in the range of 50 mA is decreased by 46%. Based on the pump-power dependent PL measurement, it is found that the quantum-confined Stark effect (QCSE) becomes weaker in the prestrained growth sample. Also, from the calibration of the Arrhenius plots, the carrier localization effect is observed to become weaker under prestrained growth. Therefore, the enhanced emission efficiency is mainly attributed to the decreased defect density and the reduced QCSE in the prestrained sample.

Microstructures produced during the epitaxial growth of InGaN alloys

“…Both will affect the formation of S-K islands. For example, Huang et al [66] found enhanced emission efficiency for green InGaN/GaN QW LEDs when a pre-strained buried layer was added. Park et al [67] used surface roughening to enhance PS in thin InGaN layers grown on GaN.…”

Effect of superlattice on light output power of InGaN‐based light‐emitting diodes fabricated on underlying GaN substrates with different dislocation densities

“…We believe that the existence of V-pits in the active layer improves the emission characteristics. To fabricate highefficiency InGaN-based LEDs on a sapphire substrate, an InGaN/GaN superlattice (SL) beneath MQWs is often used [11][12][13]. Some mechanisms are reported in which a higher hole injection efficiency and formation of a potential barrier at dislocations are achieved, as well as a reduction in the strain in MQWs, preventing the propagation of dislocations or point defects and decreasing electron mobility [14,15].…”

Tunable emission wavelength of InGaN/GaN multiquantum wells employing strain-accommodative structures

“…Although blue LEDs are already commercially available, it is still difficult to fabricate long wavelength LEDs [4][5][6] because of the large (11%) lattice mismatch between InN and GaN and the strong piezoelectric field-induced quantum-confined Stark effect bGuoq J( $IGPEG LG!O[ nuqobGq (QCSE) [7,8] induced by the high strain due to lattice mismatch. Extensive researches have recently focused on adjusting the strain in the quantum well layer [9][10][11][12][13] to improve the device efficiency and change the emission wavelength. Nanhui et al [9,10] introduced a strain-relief underlying layer to reduce the strain in the InGaN well layers and enhance the output power.…”

“…Nanhui et al [9,10] introduced a strain-relief underlying layer to reduce the strain in the InGaN well layers and enhance the output power. Professor Yang's team [11][12][13] used the prestrained growth technique to elongate the emission wavelength and enhance emission efficiency.…”