Quantum-well-width dependencies of postgrowth thermal annealing effects of InGaN/GaN quantum wells

Abstract

Optical measurements of temperature-dependent photoluminescence ͑PL͒ spectral peak, integrated PL intensity and PL decay time, and microstructure analyses with high-resolution transmission electron microscopy showed the strong dependencies of thermal annealing effects on quantum well ͑QW͒ width in InGaN/GaN QW structures. With different QW widths, different levels of strain energy were built. Upon thermal annealing, energy relaxation resulted in the reshaping of quantum dots and hence the changes of optical properties. Thermal annealing at 800 °C of a narrow QW width ͑2 nm͒ structure led to regularly distributed quantum dots ͑QDs͒ and improved optical quality. However, thermal annealing at the same temperature of a sample of larger QW width ͑4 nm͒ did not show QD formation. In this situation, even higher local strains around QWs were speculated. Also, degraded optical quality was observed.

Luminescence mechanism and carrier dynamic studies of InGaN-based dichromatic light emitting diodes with ultraviolet and blue emissions

“…Also, the blue peak positions of the blue-UV sample are red-shifted to those of the UV-blue sample while the UV peak positions of the blue-UV sample are blue-shifted to those of the UV-blue sample. In previous studies, we have shown that thermal annealing results in Inrich cluster size reduction and the blue-shift of PL peak positions [19]. The peak shifting of the UV and blue emissions can be due to the fact that in growing the upper active region, the high growth temperature conducts a thermal annealing effect on the lower active region.…”

A comparative analysis of the photoluminescence spectra of annealed ultrasmall In-rich InGaN/GaN quantum dots and wells

“…Intermediate stages of annealing have not been considered in our computations. It may be pointed out at this juncture that extraordinary PL results on annealing of InXGa1-XN/GaN QWs of 3 nm and 4 nm widths have been reported by Chung Yi -Yin et al [5]. It is interesting to note that the annealed QWs show a primary redshift of the PL peak followed by a blueshift.…”

“…InXGa1−XN/GaN QWs and QDs are especially important since they are promising materials for the violet-blue-green range [1][2][3]. Due to a large lattice mismatch ~ 10% between InN and GaN, InXGa1−XN/GaN QWs suffer from high defect density, misfit dislocations and wide composition fluctuations [4,5]. It is also expected that in order to push the emission to longer wavelengths by increasing the indium concentration, the crystal film quality worsens due to increased piezoelectric polarization.…”

Improvement of green LED by growing p-GaN on In0.25GaN/GaN MQWs at low temperature

“…5(a). Several studies have reported that the indium composition in InGaN/GaN MQWs changed as a result of thermal annealing [23], and the thickness of the quantum wells and barriers is also influenced by a hightemperature heat treatment [24]. Moreover, the line-width narrowing was observed due to the enhanced interdiffusion between the dot-like structures and the surrounding indium-deficient matrices by thermal annealing [25].…”