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1

Stimulated Emission in InGaN/GaN Multiple Quantum Wells with Different Indium Content

100%

Miasojedovas S., Juršėnas S., Kurilčik G., Žukauskas A., Springis M., Tale I., Yang C.

Acta Physica Polonica A

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2005

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vol. 107

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issue 2

256-260

EN

We report on high-excitation luminescence spectroscopy of In_xGa_{1-x}N/GaN multiple quantum wells with a high indium content (x=0.22÷0.30). High excitation conditions enabled us to achieve screening of built-in field by free carriers. This allowed for the evaluation of the influence of the band potential fluctuations due to variation in In-content on optical properties. Enhanced spontaneous emission was found for x≫0.22 due to carrier localization within the chaotic band potential. Meanwhile the stimulated emission was found to be the highest for structures with x≈ 0.25-0.27. We attribute the In-content dependence of the stimulated emission intensity to a trade-off between an increased carrier density and a decrease in the density of states.

2

Photoluminescence and Photoconductivity Dynamics in Semi-Insulating Epitaxial GaN Layers

100%

Gaubas E., Juršėnas S., Kazlauskas K., Miasojedovas S., Vaitkus J., Žukauskas A.

Acta Physica Polonica A

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2005

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vol. 107

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issue 1

215-219

EN

The transients of fast free-carrier recombination and of multi-trapping processes due to different species of defects have been investigated by photoluminescence and by contact and microwave photoconductivity. Three distinct stages of relaxation, namely, of stimulated emission, of recombination due to point defects and capture into trapping centers associated with dislocations, and a non-exponential stage with a stretched-exponent asymptotic decay ascribed to dislocations mediated multi-trapping were distinguished by correlated examination of time-resolved photoluminescence and photoconductivity transients.

3

Luminescence of Highly Excited Nonpolar a-Plane GaN and AlGaN/GaN Multiple Quantum Wells

84%

Juršėnas S., Kuokštis E., Miasojedovas S., Kurilčik G., Žukauskas A., Chen C., Yang J., Adivarahan V., Asif Khan M.

Acta Physica Polonica A

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2004

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vol. 105

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issue 6

567-573

EN

Carrier recombination dynamics in polar and nonpolar GaN epilayers and GaN/AlGaN multiple quantum wells grown over sapphire substrates with various crystallographic orientation were studied under high photoexcitation by 20 ps laser pulses. The transient of luminescence featured a significant enhancement in nonradiative recombination of free carriers for nonpolar a-plane GaN epilayers compared to conventional c-plane samples. The epitaxial lateral overgrowth technique was demonstrated to significantly improve the quality of nonpolar a-plane films. This was proved by more than 40-fold increase in luminescence decay time (430 ps compared to ≤10 ps in the ordinary a-plane epilayer). Under high-excitation regime, a complete screening of built-in electric field by free carriers in multiple quantum wells grown on c-plane and r-plane sapphire substrates was achieved. Under such high excitation, luminescence efficiency and carrier lifetime of multiple quantum wells was shown to be determined by the substrate quality.

4

Luminescence in Highly Excited InGaN/GaN Multiple Quantum Wells Grown on GaN and Sapphire Substrates

84%

Miasojedovas S., Juršėnas S., Kurilčik G., Žukauskas A., Ivanov V., Godlewski M., Leszczyński M., Perlin P., Suski T.

Acta Physica Polonica A

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2004

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vol. 106

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issue 2

273-279

EN

We report on high-excitation luminescence spectroscopy in In_xGa_{1-x}N/GaN multiple quantum wells grown by MOCVD over sapphire and bulk GaN substrates. High excitation conditions enabled us to achieve a screening of the built-in field by free carriers. This allowed for the evaluation of the influence of band potential fluctuations due to the variation in In-content on efficiency of spontaneous and stimulated emission. InGaN/GaN multiple quantum wells grown on bulk GaN substrate exhibit a significantly lower stimulated emission threshold and thus enhanced lateral emission. Transient and dynamic properties of luminescence indicate a significant reduction in compositional disorder in homoepitaxially grown structures

5

Luminescence of Highly Photoexcited GaN Epilayers and Heterostructures Grown on Different Sapphire Crystal Planes

84%

Juršėnas S., Miasojedovas S., Kurilčik G., Liuolia V., Žukauskas A., Chen C., Yang J., Kuokštis E., Adivarahan V., Asif Khan M.

Acta Physica Polonica A

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2005

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vol. 107

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issue 2

235-239

EN

GaN epilayers and AlGaN/GaN multiple quantum wells grown by metalorganic chemical vapor deposition on different crystal planes (c, a, and r) of the sapphire substrate were studied by excitation intensity dependent and time-resolved photoluminescence. In polar multiple quantum wells grown on a- and c-planes, a blueshift of the luminescence band with increasing the excitation energy was observed, indicating that screening of built-in field by free carriers takes place, whereas in nonpolar r-plane grown multiple quantum wells, the luminescence band maintained an almost constant peak position. Full screening of built-in field was achieved at the excitation densities higher than 0.3 mJ/cm^2. Under conditions of screened built-in electric field the structures were characterized by carrier lifetime. It was shown that nonpolar multiple quantum wells suffer from high density of nonradiative traps that can be due to substrate related threading dislocations.

6

Transients of Carrier Recombination and Diffusion in Highly Excited GaN Studied by Photoluminescence and Four-Wave Mixing Techniques

84%

Juršėnas S., Miasojedovas S., Kurilčik G., Žukauskas A., Aleksiejūnas R., Malinauskas T., Sūdžius M., Jarašiūnas K.

Acta Physica Polonica A

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2005

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vol. 107

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issue 2

240-244

EN

Time-resolved photoluminescence and four-wave mixing techniques have been combined for studies of carrier relaxation dynamics in a highly photoexcited GaN epilayer. For a moderate excitation density below 1 mJ/cm^2, carrier recombination was due to free carrier capture by deep traps. The characteristic time of carrier capture,τ_e=550 ps, was measured under deep trap saturation regime. The ambipolar diffusion coefficient for free carriers, D=1.7 cm^2/s, was estimated from the analysis of the transients of the light-induced gratings of various periods. A complete saturation of the four-wave mixing efficiency was observed for the excitation energy density exceeding 1.5 mJ/cm^2. The latter saturation effect was shown to be related to electron-hole plasma degeneration, which results in a significant enhancement of carrier recombination rate due to onset of stimulated emission.

7

Stimulated Emission from the MBE Grown Homoepitaxial InGaN Based Multiple Quantum Wells Structures

68%

Ivanov V., Godlewski M., Miasojedovas S., Juršėnas S., Kazlauskas K., Žukauskas A., Skierbiszewski C., Siekacz M., Leszczyński M., Perlin P., Suski T., Grzegory I.

Acta Physica Polonica A

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2005

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vol. 107

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issue 2

225-229

EN

We report on photoluminescence characterization of InGaN based laser structures grown by homoepitaxial radio frequency plasma-assisted molecular beam epitaxy. Owing to Si doped barriers, the structures show a negligible impact of the built-in electric field, which was proved by excitation intensity dependent and quantum well width dependent luminescence experiments. Relatively low variation in band potential due to inhomogeneous distribution of In was quantitatively estimated from the photoluminescence temperature behavior using Monte Carlo simulation of in-plane carrier hopping and optically detected cyclotron resonance experiments. Efficient stimulated emission with a low threshold for optically pumped laser structures was observed.

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7 Acta Physica Polonica A

5 2005

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7 Juršėnas S.

7 Miasojedovas S.

7 Žukauskas A.

5 Kurilčik G.

2 Adivarahan V.

2 Asif Khan M.

2 Chen C.

2 Godlewski M.

2 Ivanov V.

2 Kazlauskas K.

2 Kuokštis E.

2 Leszczyński M.

2 Perlin P.

2 Suski T.

2 Yang J.

1 Aleksiejūnas R.

1 Gaubas E.

1 Grzegory I.

1 Jarašiūnas K.

1 Liuolia V.

1 Malinauskas T.

1 Siekacz M.

1 Skierbiszewski C.

1 Springis M.

1 Sūdžius M.

1 Tale I.

1 Vaitkus J.

1 Yang C.

Stimulated Emission in InGaN/GaN Multiple Quantum Wells with Different Indium Content

Photoluminescence and Photoconductivity Dynamics in Semi-Insulating Epitaxial GaN Layers

Luminescence of Highly Excited Nonpolar a-Plane GaN and AlGaN/GaN Multiple Quantum Wells

Luminescence in Highly Excited InGaN/GaN Multiple Quantum Wells Grown on GaN and Sapphire Substrates

Luminescence of Highly Photoexcited GaN Epilayers and Heterostructures Grown on Different Sapphire Crystal Planes

Transients of Carrier Recombination and Diffusion in Highly Excited GaN Studied by Photoluminescence and Four-Wave Mixing Techniques

Stimulated Emission from the MBE Grown Homoepitaxial InGaN Based Multiple Quantum Wells Structures