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1

Interplay between Internal and External Electric Field Studied by Photoluminescence in InGaN/GaN Light Emitting Diodes

100%

Staszczak G., Khachapuridze A., Grzanka S., Czernecki R., Piotrzkowski R., Perlin P., Suski T.

Acta Physica Polonica A

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2011

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vol. 120

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issue 5

891-893

EN

We have studied a series of polar InGaN/GaN light emitting diodes, consisting of either a blue (440-450 nm) quantum well, or combination of blue and violet (410 nm) quantum wells (with indium content 18% and 10%, respectively). The blue quantum well was always placed close to p-type region of the particular LED. We found that the electroluminescence induced by low current is characterized by light emission from the blue quantum well only. In comparison, optical excitation of our LEDs leads to light emission with energies characteristic either for blue and/or violet quantum wells. The corresponding microphotoluminescence spectra evolve depending on external polarization and variable light intensity of excitation supplied by He-Cd laser. Interplay between built-in electric field and externally applied polarization/screening decides about the band structure profiles and thus radiative recombination mechanisms.

2

Impact of Thin LT-GaN Cap Layers on the Structural and Compositional Quality of MOVPE Grown InGaN Quantum Wells Investigated by TEM

100%

Ivaldi F., Kret S., Szczepańska A., Czernecki R., Kryśko M., Grzanka S., Leszczyński M.

Acta Physica Polonica A

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2011

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vol. 119

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issue 5

660-662

EN

Two samples containing InGaN quantum wells have been grown by metal-organic vapor phase epitaxy on high pressure grown monocrystalline GaN (0001). Different growth temperatures have been used to grow the wells and the barriers. In one of the samples, a low temperature GaN layer (730°C) has been grown on every quantum well before rising the temperature to standard values (900°C). The samples have been investigated by transmission electron microscopy and X-ray diffraction. Photoluminescence spectra have been measured as well. The influence of the LT-GaN has been investigated in regard to its influence on the structural and compositional quality of the sample.

3

Deep Levels in GaN p-n Junctions Studied by Deep Level Transient Spectroscopy and Laplace Transform Deep-Level Spectroscopy

100%

Dyba P., Placzek-Popko E., Zielony E., Gumienny Z., Grzanka S., Czernecki R., Suski T.

Acta Physica Polonica A

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2011

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vol. 119

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issue 5

669-671

EN

p^+-n GaN diodes were studied by means of conventional deep level transient spectroscopy and Laplace transform deep-level spectroscopy methods within the temperature range of 77-350 K. Deep level transient signal spectra revealed the presence of a majority and minority trap of indistinguishable signatures. The Laplace transform deep-level spectroscopy technique due to its superior resolution allows us to unambiguously identify and characterize the traps. The apparent activation energy and capture cross-section for the majority trap were found to be equal to 0.63 eV and 2 × 10^{-16} cm^2 and for the minority trap 0.66 eV and 1.6 × 10^{-15} cm^2. It has been confirmed that the Laplace transform deep-level spectroscopy technique is a powerful tool in characterization of the traps of close signatures.

4

High Power Continuous Wave Blue InAlGaN Laser Diodes Made by Plasma Assisted MBE

68%

Skierbiszewski C., Siekacz M., Wiśniewski P., Perlin P., Feduniewicz-Żmuda A., Cywiński G., Smalc J., Grzanka S., Grzegory I., Leszczyński M., Porowski S.

Acta Physica Polonica A

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2006

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vol. 110

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issue 3

345-351

EN

Room temperature, continuous wave operation of InGaN multi-quantum wells laser diodes made by rf plasma assisted molecular beam epitaxy at 411 nm wavelength is demonstrated. The threshold current density and voltage were 4.2 kA/cm^2 and 5.3 V, respectively. High optical power output of 60 mW was achieved. The lifetime of these laser diodes exceeds 5 h with 2 mW of optical output power. The laser diodes are fabricated on low dislocation density bulk GaN substrates, at growth conditions which resembles liquid phase epitaxy. We demonstrate that relatively low growth temperatures (600-700°C) pose no intrinsic limitations for fabrication of nitride optoelectronic components by plasma assisted molecular beam epitaxy.

5

Crack Free GaInN/AlInN Multiple Quantum Wells Grown on GaN with Strong Intersubband Absorption at 1.55μm

68%

Cywiński G., Skierbiszewski C., Feduniewicz-Żmuda A., Siekacz M., Nevou L., Doyennette L., Julien F., Prystawko P., Kryśko M., Grzanka S., Grzegory I., Porowski S.

Acta Physica Polonica A

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2006

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vol. 110

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issue 2

175-181

EN

Crack free GaInN/AlInN multiple quantum wells were grown by rf plasma-assisted molecular beam epitaxy on (0001) GaN/sapphire substrates. The strain-engineering concept was applied to eliminate cracking effect for growth of intersubband structures on GaN. Indium contained ternary compounds of barrier and well layers are contrary strained to the substrate material. A series of crack free GaInN/AlInN intersubband structures on (0001) GaN was fabricated and investigated. The assumed composition and layered structure were confirmed by room temperature photoluminescence and X-ray diffraction measurements. The intersubband measurements were done in multipass waveguide geometry by applying direct intersubband absorption and photoinduced intersubband absorption measurements. The optimized structure design contains forty periods of Si-doped GaInN/AlInN quantum wells and exhibits strong intersubband absorption.

6

Thin Film ZnO as Sublayer for Electric Contact for Bulk GaN with Low Electron Concentration

68%

Grzanka S., Łuka G., Krajewski T., Guziewicz E., Jachymek R., Purgal W., Wiśniewska R., Sarzyńska A., Bering-Staniszewska A., Godlewski M., Perlin P.

Acta Physica Polonica A

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2011

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vol. 119

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issue 5

672-674

EN

Fabrication of low resistivity ohmic contacts to N polarity gallium nitride crystal is an important issue for the construction of the vertical current flow devices like laser diodes and high brightness light emitting diodes. Gallium nitride is a challenging material because of the high metal work function required to form a barrier-free metal-semiconductor interface. In practice, all useful ohmic contacts to GaN are based on the tunneling effect. Efficient tunneling requires high doping of the material. The most challenging task is to fabricate high quality metal ohmic contacts on the substrate because the doping control is here much more difficult that in the case of epitaxial layers. In the present work we propose a method for fabricating low resistivity ohmic contacts on N-side of GaN wafers grown by hydride vapor phase epitaxy. These crystals were characterized by a n-type conductivity and the electron concentration of the order of 10^{17} cm^{-3}. The standard Ti/Au contact turned out to be unsatisfactory with respect to its linearity and resistance. Instead we decided to deposit high-n type ZnO layers (thickness 50 nm and 100 nm) prepared by atomic layer deposition at temperature of 200°C. The layers were highly n-type conductive with the electron concentration in the order of 10^{20} cm^{-3}. Afterwards, the metal contact to ZnO was formed by depositing Ti and Au. The electrical characterization of such a contact showed very good linearity and as low resistance as 1.6 × 10^{-3} Ω cm^2. The results indicate advantageous properties of contacts formed by the combination of the atomic layer deposition and hydride vapor phase epitaxy technology.

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Interplay between Internal and External Electric Field Studied by Photoluminescence in InGaN/GaN Light Emitting Diodes

Impact of Thin LT-GaN Cap Layers on the Structural and Compositional Quality of MOVPE Grown InGaN Quantum Wells Investigated by TEM

Deep Levels in GaN p-n Junctions Studied by Deep Level Transient Spectroscopy and Laplace Transform Deep-Level Spectroscopy

High Power Continuous Wave Blue InAlGaN Laser Diodes Made by Plasma Assisted MBE

Crack Free GaInN/AlInN Multiple Quantum Wells Grown on GaN with Strong Intersubband Absorption at 1.55μm

Thin Film ZnO as Sublayer for Electric Contact for Bulk GaN with Low Electron Concentration