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Photoluminescence studies of a perceived white light emission from a monolithic InGaN/GaN quantum well structure.

Ben-Sedrine N, Esteves TC, Rodrigues J, Rino L, Correia MR, Sequeira MC, Neves AJ, Alves E, Bockowski M, Edwards PR, O'Donnell KP, Lorenz K, Monteiro T - Sci Rep (2015)

Bottom Line: As-grown and thermally annealed samples at high temperature (1000 °C, 1100 °C and 1200 °C) and high pressure (1.1 GPa) were analysed by spectroscopic techniques, and the annealing effect on the photoluminescence is deeply explored.Under laser excitation of 3.8 eV at room temperature, the as-grown structure exhibits two main emission bands: a yellow band peaked at 2.14 eV and a blue band peaked at 2.8 eV resulting in white light perception.The room temperature white emission is studied as a function of incident power density, and the correlated colour temperature values are found to be in the warm white range: 3260-4000 K.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Física e I3N, Universidade de Aveiro, Campus Universitário de Santiago,3810-193 Aveiro, Portugal.

ABSTRACT
In this work we demonstrate by photoluminescence studies white light emission from a monolithic InGaN/GaN single quantum well structure grown by metal organic chemical vapour deposition. As-grown and thermally annealed samples at high temperature (1000 °C, 1100 °C and 1200 °C) and high pressure (1.1 GPa) were analysed by spectroscopic techniques, and the annealing effect on the photoluminescence is deeply explored. Under laser excitation of 3.8 eV at room temperature, the as-grown structure exhibits two main emission bands: a yellow band peaked at 2.14 eV and a blue band peaked at 2.8 eV resulting in white light perception. Interestingly, the stability of the white light is preserved after annealing at the lowest temperature (1000 °C), but suppressed for higher temperatures due to a deterioration of the blue quantum well emission. Moreover, the control of the yellow/blue bands intensity ratio, responsible for the white colour coordinate temperatures, could be achieved after annealing at 1000 °C. The room temperature white emission is studied as a function of incident power density, and the correlated colour temperature values are found to be in the warm white range: 3260-4000 K.

No MeSH data available.


Related in: MedlinePlus

Laser power density dependence PL spectra at RT of the as-grown (a) and HTHP-1000 (b) samples obtained with 325 nm laser excitation. (c) Integrated PL intensity for YB and BB emissions (scatters) fitted to the power law  (lines).
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f4: Laser power density dependence PL spectra at RT of the as-grown (a) and HTHP-1000 (b) samples obtained with 325 nm laser excitation. (c) Integrated PL intensity for YB and BB emissions (scatters) fitted to the power law (lines).

Mentions: In order to study in more detail the white emission observed in the as-grown and the HTHP-1000 samples, the RT PL response was measured as a function of the laser power density. The RT PL spectra are represented in Fig. 4 for the as-grown [Fig. 4 (a)] and the HTHP-1000 [Fig. 4 (b)] samples. It can be seen that no power-dependent shift in the BB and YB maxima is observed for either samples. The integrated PL intensity (IPL) for YB and BB emissions can be well fitted to a power law33: , where I is the laser power density, and k the slope in a log-log plot [Fig. 4 (c)]. We have found a slope k ≅ 1 for the BB emission of the as-grown and HTHP-1000 samples, consequently, the BB can be attributed to a free-exciton transition in the InGaN/GaN QW structure. For both samples, a slope of ~0.7 was determined for the YB emission, indicating free-to-bound or donor acceptor pair transitions involving a deep defect level in GaN accordingly with the aforementioned recombination model. Figure 4 (a,b) shows that increasing the power density over two decades results in a gradual increase of the BB PL intensity, while the increase of the power density up to I0 causes a decrease in the YB/BB intensity ratio from ~1.6 to ~0.6 for the as-grown sample, and from ~2.0 to ~0.7 for the HTHP-1000 sample. The distinct recombination models for the BB (excitonic in nature) and YB (e-A or DAP) PL bands are expected to respond differently to the excitation density. Particularly, for short lived excitonic well recombination such as green3435 and blue36 emissions in similar structures, the PL intensity is expected to increase with excitation density almost linearly. However, for the long lived YB28, saturation effects are more pronounced even for low laser power densities. This explains the perceived change in the PL colour when observed with the naked eye, whereby the yellowish white emission turns to white when increasing the laser power density.


Photoluminescence studies of a perceived white light emission from a monolithic InGaN/GaN quantum well structure.

Ben-Sedrine N, Esteves TC, Rodrigues J, Rino L, Correia MR, Sequeira MC, Neves AJ, Alves E, Bockowski M, Edwards PR, O'Donnell KP, Lorenz K, Monteiro T - Sci Rep (2015)

Laser power density dependence PL spectra at RT of the as-grown (a) and HTHP-1000 (b) samples obtained with 325 nm laser excitation. (c) Integrated PL intensity for YB and BB emissions (scatters) fitted to the power law  (lines).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4559898&req=5

f4: Laser power density dependence PL spectra at RT of the as-grown (a) and HTHP-1000 (b) samples obtained with 325 nm laser excitation. (c) Integrated PL intensity for YB and BB emissions (scatters) fitted to the power law (lines).
Mentions: In order to study in more detail the white emission observed in the as-grown and the HTHP-1000 samples, the RT PL response was measured as a function of the laser power density. The RT PL spectra are represented in Fig. 4 for the as-grown [Fig. 4 (a)] and the HTHP-1000 [Fig. 4 (b)] samples. It can be seen that no power-dependent shift in the BB and YB maxima is observed for either samples. The integrated PL intensity (IPL) for YB and BB emissions can be well fitted to a power law33: , where I is the laser power density, and k the slope in a log-log plot [Fig. 4 (c)]. We have found a slope k ≅ 1 for the BB emission of the as-grown and HTHP-1000 samples, consequently, the BB can be attributed to a free-exciton transition in the InGaN/GaN QW structure. For both samples, a slope of ~0.7 was determined for the YB emission, indicating free-to-bound or donor acceptor pair transitions involving a deep defect level in GaN accordingly with the aforementioned recombination model. Figure 4 (a,b) shows that increasing the power density over two decades results in a gradual increase of the BB PL intensity, while the increase of the power density up to I0 causes a decrease in the YB/BB intensity ratio from ~1.6 to ~0.6 for the as-grown sample, and from ~2.0 to ~0.7 for the HTHP-1000 sample. The distinct recombination models for the BB (excitonic in nature) and YB (e-A or DAP) PL bands are expected to respond differently to the excitation density. Particularly, for short lived excitonic well recombination such as green3435 and blue36 emissions in similar structures, the PL intensity is expected to increase with excitation density almost linearly. However, for the long lived YB28, saturation effects are more pronounced even for low laser power densities. This explains the perceived change in the PL colour when observed with the naked eye, whereby the yellowish white emission turns to white when increasing the laser power density.

Bottom Line: As-grown and thermally annealed samples at high temperature (1000 °C, 1100 °C and 1200 °C) and high pressure (1.1 GPa) were analysed by spectroscopic techniques, and the annealing effect on the photoluminescence is deeply explored.Under laser excitation of 3.8 eV at room temperature, the as-grown structure exhibits two main emission bands: a yellow band peaked at 2.14 eV and a blue band peaked at 2.8 eV resulting in white light perception.The room temperature white emission is studied as a function of incident power density, and the correlated colour temperature values are found to be in the warm white range: 3260-4000 K.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Física e I3N, Universidade de Aveiro, Campus Universitário de Santiago,3810-193 Aveiro, Portugal.

ABSTRACT
In this work we demonstrate by photoluminescence studies white light emission from a monolithic InGaN/GaN single quantum well structure grown by metal organic chemical vapour deposition. As-grown and thermally annealed samples at high temperature (1000 °C, 1100 °C and 1200 °C) and high pressure (1.1 GPa) were analysed by spectroscopic techniques, and the annealing effect on the photoluminescence is deeply explored. Under laser excitation of 3.8 eV at room temperature, the as-grown structure exhibits two main emission bands: a yellow band peaked at 2.14 eV and a blue band peaked at 2.8 eV resulting in white light perception. Interestingly, the stability of the white light is preserved after annealing at the lowest temperature (1000 °C), but suppressed for higher temperatures due to a deterioration of the blue quantum well emission. Moreover, the control of the yellow/blue bands intensity ratio, responsible for the white colour coordinate temperatures, could be achieved after annealing at 1000 °C. The room temperature white emission is studied as a function of incident power density, and the correlated colour temperature values are found to be in the warm white range: 3260-4000 K.

No MeSH data available.


Related in: MedlinePlus