Search results for: U. Zehnder

Items from 1 to 20 out of 29 results

chapter

Beryllium-containing II–VI compounds: Properties and applications

A. Waag, Th. Litz, F. Fischer, H.-J. Lugauer, more

Advances in Solid State Physics > Advances in Solid State Physics 37 > 43-66

chapter

A study of the failure of GaN-based LEDs submitted to reverse-bias stress and ESD events

M Meneghini, A Tazzoli, E Ranzato, N Trivellin, more

2010 IEEE International Reliability Physics Symposium > 522 - 527

2010 IEEE International Reliability Physics Symposium (IRPS 2010)

This paper describes an extensive analysis of the degradation of InGaN-based LEDs submitted to reverse-bias stress and Electrostatic Discharge events. Results described within the paper indicate that: (i) reverse-bias current flows through localized leakage paths, related to the presence of structural defects; (ii) the position of these paths can be identified by means of emission microscopy; (iii)...

article

Degradation of High-Brightness Green LEDs Submitted to Reverse Electrical Stress

M. Meneghini, U. Zehnder, B. Hahn, G. Meneghesso, more

IEEE Electron Device Letters > 2009 > 30 > 10 > 1051 - 1053

This letter describes an extensive analysis of the reverse-bias degradation of green light-emitting diodes. The analysis consists in a wide set of stress tests carried out under different negative-bias levels. The results presented in this letter indicate the following: 1) Leakage current is strongly correlated to the presence of reverse-bias luminescence; 2) reverse current flows through preferential...

chapter

Reversible Degradation of GaN LEDs Related to Passivation

M. Meneghini, L.-R. Trevisanello, R. Penzo, M. Benedetti, more

2007 IEEE International Reliability Physics Symposium Proceedings. 45th Annual > 457 - 461

2007 IEEE International Reliability Physics Symposium Proceedings

This paper analyzes the stability of gallium nitride blue light emitting diodes (LEDs) at high temperature levels. It is shown that high temperature storage can induce significant degradation of the electrical and optical characteristics of the samples. The most important failure modes detected after thermal stress are output power decrease, emission crowding and forward voltage increase. The degradation...

article

Reversible Degradation of Ohmic Contacts on p-GaN for Application in High-Brightness LEDs

M. Meneghini, L.-R. Trevisanello, U. Zehnder, G. Meneghesso, more

IEEE Transactions on Electron Devices > 2007 > 54 > 12 > 3245 - 3251

This paper analyzes the high-temperature long-term stability of ohmic contacts on p-type gallium nitride (p-GaN). The contributions of the ohmic contacts and semiconductor material degradation are separated by adopting the transmission line method (TLM). Before stress, the current-voltage (I-V) curves measured at the pads of the TLMs showed a linear shape, indicating a good ohmic behavior of the contacts...

chapter

Failure mechanisms of gallium nitride LEDs related with passivation

M. Meneghini, L.R. Trevisanello, S. Levada, G. Meneghesso, more

IEEE InternationalElectron Devices Meeting, 2005. IEDM Technical Digest. > 4 pp. - 1012

International Electron Devices Meeting 2005

This paper analyzes the thermally-activated failure mechanisms of GaN LEDs under thermal overstress related with the presence of a PECVD SiN passivation layer. It is shown that the properties of the passivation layer can remarkably affect devices reliability during high-temperature stress: degradation mechanisms identified consist in emission crowding and series resistance increase, attributed to...

article

Industrial production of GaN and InGaN-light emitting diodes on SiC-substrates

U. Zehnder, A. Weimar, U. Strauss, M. Fehrer, more

Journal of Crystal Growth > 2001 > 230 > 3-4 > 497-502

Blue light emitting diodes (LEDs) based on GaN or InGaN have a large market, e.g. for communication, industry and automotive applications. Since 1998, OSRAM Opto Semiconductors has been producing blue LEDs on a large scale, concentrating on the automotive market. LEDs in the wavelength range 450–480nm are grown by metalorganic vapour phase epitaxy (MOVPE) on SiC. This substrate material offers many...

article

Influence of strain on growth mode and electro-optical properties of high-brightness InGaN-LEDs on SiC

J. Baur, U. Strauss, G. Bruederl, D. Eisert, more

Journal of Crystal Growth > 2001 > 230 > 3-4 > 507-511

We present a detailed study, on the influence of buffer strain on the MOVPE crystal growth mode in the QW active layer of high-brightness InGaN LEDs on SiC substrate. While highly strained buffers are related to InGaN QWs with homogeneous In-distribution, low In-concentration and reduced quantum efficiency, buffers with reduced strain are shown to induce InGaN-QW growth with a dot-like In-distribution,...

article

Magneto-optical study of ZnSe-based quantum wells

W Ossau, D.R Yakovlev, U Zehnder, G.V Astakhov, more

Physica B: Physics of Condensed Matter > 1998 > 256-258 > Complete > 323-326

Heterostructures with ZnSe quantum wells and different barrier materials (Zn _1−x Mg _x S _1−y Se _y and Zn _1−x Be _x Se) are investigated by means of photoluminescence and reflectivity in external magnetic fields up to 20 T. Up to four exciton excited states are well-resolved in the photoluminescence excitation spectra of undoped structures. Model calculations...

article

Novel beryllium containing II-VI compounds: basic properties and potential applications

A. Waag, Th. Litz, F. Fischer, H.-J. Lugauer, more

Journal of Crystal Growth > 1998 > 184-185 > 1-10

An additional, yet untried approach to further improve the reliability of ZnSe-based devices is to use beryllium containing II-VI compounds. BeS, BeSe and BeTe are characterized by a considerable amount of covalent bonding and a high bond energy. This distinguishes these materials from the conventional ionic wide gap II-VI semiconductors like ZnSe, ZnTe or CdTe. Recently, thin film structures using...

article

Homogeneous linewidth of the direct exciton in a type-II ZnSe/BeTe quantum well

A.V. Platonov, D.R. Yakovlev, U. Zehnder, V.P. Kochereshko, more

Journal of Crystal Growth > 1998 > 184-185 > 801-805

We present an optical study of novel ZnSe/BeTe heterostructures with a type-II band alignment based on beryllium chalcogenides. A strong exciton transition involving a confined electron and a quasibound hole state (both in the ZnSe layer) is observed in photoluminescence, photoluminescence excitation and reflectivity spectra. This exciton state is drastically broadened by increasing temperature due...

article

Homogeneous linewidth of the direct exciton in a type-II ZnSe/BeTe quantum well

D.R. Yakovlev, U. Zehnder, W. Ossau, F. Fisher, more

Journal of Crystal Growth > 1998 > 184-185 > 801-805

article

Optical properties of laser diodes and heterostructures based on beryllium chalcogenides

U. Zehnder, D.R. Yakovlev, W. Ossau, T. Gerhard, more

Journal of Crystal Growth > 1998 > 184-185 > 541-544

Laser diodes and heterostructures based on beryllium chalcogenides have been characterized optically by means of photoluminescence and photoluminescence excitation spectroscopy in the temperature range from 1.6 to 300 K. The study was performed on real lasing structures. An efficient photoluminescence at room temperature was observed in heterostructures with (ZnCd)Se and (BeZnCd)Se quantum wells (L...

article

Novel beryllium containing II-VI compounds: Basic properties and potential applications

Th. Litz, F. Fischer, H.-J. Lugauer, T. Baron, more

Journal of Crystal Growth > 1998 > 184-185 > 1-10

article

Optical properties of laser diodes and heterostructures based on beryllium chalcogenides

U. Zehnder, D.R. Yakovlev, W. Ossau, T. Gerhard, more

Journal of Crystal Growth > 1998 > 184-185 > 541-544

article

Be-chalcogenides: heteroepitaxy and interface properties

M.Th. Litz, F. Fischer, H.-J. Lugauer, M. Keim, more

Applied Surface Science > 1998 > 123-124 > Complete > 429-434

We report on the molecular beam epitaxy and the properties of Be-chalcogenides. Especially the interface between ZnSe and BeTe and BeTe/ZnSe superlattices have been studied by means of HRXRD (high resolution X-ray diffraction), HRTEM (high resolution transmission-electron-microscopy), RHEED (reflection-high-energy-electron-diffraction), photo-electron-spectroscopy (PES) and photo-luminescence (PL)...

article

Investigation of Spin-Glass Transition in Semimagnetic Quantum Wells Based on Cd_{1-x}Mn_{x}Te by Means of Optical Spectroscopy

U. Zehnder, D. Yakovlev, W. Ossau, A. Waag, more

Acta Physica Polonica A > 1997 > 92 > 5 > 1075-1078

The spin-glass transition in Cd_{1-x}Mn_{x}Te epitaxial layers and bulk samples with 0.24 ≤ x ≤ 0.43 and in quantum well structures on the basis of Cd_{1-x}Mn_{x}Te were investigated by means of optical spectroscopy. Reduction of dimensionality of Cd_{1-x}Mn_{x}Te layers down to the quasi-two-dimensional case realized in Cd_{1-x}Mn_{x}Te/Cd_{1- y}Mn_{y}Te heterostructures frustrates the spin-glass...

article

Exciton States in Type-II ZnSe/BeTe Quantum Wells

A. Platonov, D. Yakovlev, U. Zehnder, V. Kochereshko, more

Acta Physica Polonica A > 1997 > 92 > 5 > 953-957

We present an optical investigation of novel heterostructures based on beryllium chalcogenides with a type-I and type-II band alignment. In the type-II quantum well structures (ZnSe/BeTe) we observed a strong exciton transition involving an electron confined in the conduction band well and a hole localized in the valence band barrier (both in ZnSe layer). This transition is drastically broadened by...

article

Growth by molecular beam epitaxy and magnetooptical studies of (100)- and (120)-oriented digital magnetic quantum well structures

M. Kutrowski, G. Karczewski, G. Cywiński, M. Surma, more

Thin Solid Films > 1997 > 306 > 2 > 283-290

We report on growth by molecular beam epitaxy and magnetooptical investigations of digital alloys of diluted magnetic semiconductors, The digital alloys, i.e., very short-period superlattices, of interest here, were grown from nonmagnetic CdTe and magnetic Cd ₁ _- _x Mn _x Te. In particular, quantum well structures containing the digital alloys in the regions of the quantum wells...

article

II-VI light-emitting devices based on beryllium chalcogenides

F. Fischer, G. Landwehr, Th. Litz, H.J. Lugauer, more

Journal of Crystal Growth > 1997 > 175-176 > Part 1; PART 1 > 532-540

Beryllium chalcogenides are semiconductors with a large band gap. They have a higher-degree of covalent bonding than all of the other II-VI compounds. The bond energies of BeTe, BeSe and BeS are comparable to those of GaN. Due to their band gaps and their lattice constants they can be incorporated in quaternary mixed crystals which are lattice matched to GaAs. The hardness of II-VI materials containing...

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INFONA - science communication portal

Search results for: U. Zehnder

Beryllium-containing II–VI compounds: Properties and applications

A study of the failure of GaN-based LEDs submitted to reverse-bias stress and ESD events

Degradation of High-Brightness Green LEDs Submitted to Reverse Electrical Stress

Reversible Degradation of GaN LEDs Related to Passivation

Reversible Degradation of Ohmic Contacts on p-GaN for Application in High-Brightness LEDs

Failure mechanisms of gallium nitride LEDs related with passivation

Industrial production of GaN and InGaN-light emitting diodes on SiC-substrates

Influence of strain on growth mode and electro-optical properties of high-brightness InGaN-LEDs on SiC

Magneto-optical study of ZnSe-based quantum wells

Novel beryllium containing II-VI compounds: basic properties and potential applications

Homogeneous linewidth of the direct exciton in a type-II ZnSe/BeTe quantum well

Homogeneous linewidth of the direct exciton in a type-II ZnSe/BeTe quantum well

Optical properties of laser diodes and heterostructures based on beryllium chalcogenides

Novel beryllium containing II-VI compounds: Basic properties and potential applications

Optical properties of laser diodes and heterostructures based on beryllium chalcogenides

Be-chalcogenides: heteroepitaxy and interface properties

Investigation of Spin-Glass Transition in Semimagnetic Quantum Wells Based on Cd_{1-x}Mn_{x}Te by Means of Optical Spectroscopy

Exciton States in Type-II ZnSe/BeTe Quantum Wells

Growth by molecular beam epitaxy and magnetooptical studies of (100)- and (120)-oriented digital magnetic quantum well structures

II-VI light-emitting devices based on beryllium chalcogenides

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