Norbert Linder

Osram AG · Corporate Technology

Lighting represents a major part of building energy use. Therefore, energy savings in a lighting system can be very important for reducing building energy consumption. This article presents a study of the energy performance of various lighting systems and control strategies applied in open-plan offices. All of the experiments were carried out on a...

How much electricity lighting system consumes is up to number of factors, for instance architecture design, glazing specifications, light source, and so on. In order to improve lighting efficiency even more, proper control strategies are necessary to be applied. In which occupant behavior and visual comfort perception have to be considered at the s...

A method for manufacturing an optically pumped surface-emitting semiconductor laser device, wherein a surface-emitting semiconductor laser layer sequence having a quantum confinement structure is applied onto a common substrate. The surface-emitting semiconductor laser layer sequence outside an intended laser region is removed and a region is expos...

Building energy consumption mainly consists of three components: lighting, HVAC and electrical equipment. Artificial lighting needs electricity and itself is also a heat source during operation, which causes cooling loads. Therefore energy saving in lighting system could be very important for reduction of building energy consumption, especially in...

Leuchtdioden (LEDs) glänzen durch lange Lebensdauer, gute Farbwiedergabe, schnelle Einschaltzeit und Dimmbarkeit. Das macht sie zunehmend attraktiv für die Allgemeinbeleuchtung. Vor allem benötigen sie weniger Energie als konventionelle Leuchtmittel. Als Materialsysteme haben sich AlInGaN und AlInGaP etabliert, die Lichtfarben in einem breiten Spek...

We demonstrate the morphological properties of height, diameter and shape controlled N-face GaN nanorods (NRs) by adjusting conventional growth parameters of a standard metalorganic vapour phase epitaxy (MOVPE) growth process. Particularly the hydrogen fraction within the carrier gas was shown to be an important shaping tool for the grown nanostruc...

We demonstrate the fabrication of N-face GaN nanorods by metal organic vapour phase epitaxy (MOVPE), using continuous-flux conditions. This is in contrast to other approaches reported so far, which have been based on growth modes far off the conventional growth regimes. For position control of nanorods an SiO(2) masking layer with a dense hole patt...

A two-dimensional self-consistent laser model has been used for the simulation of the facet heating of red emitting AlGaInP lasers. It solves in the steady-state the complete semiconductor optoelectronic and thermal equations in the epitaxial and longitudinal directions and takes into account the population of different conduction band valleys. The...

Photonic crystals (PhCs) have now been firmly established as an efficient means for light extraction from light emitting diodes (LEDs). We analyze the diffraction properties from thin GaN micro-cavity LEDs with hexagonal lattices that feature three guided TE modes only. In contrast to common design rules, we find that high order diffraction contrib...

A theoretical approach based on coupled-mode theory is presented in order to determine the radiation pattern of LEDs incorporating a shallow photonic crystal. From this, a fundamental limit for the directionality of the diffraction of a single guided mode is given. Additionally, the Fabry-Perot resonances are shown to have significant impact on the...

Fully microscopic many-body models are used to study the importance of radiative and Auger carrier losses in InGaN/GaN quantum wells. Since the usual direct bandto-band Auger losses are too small to explain the experimentally observed droop of the external quantumefficiency in such structures, phonon assisted Auger processes are discussed. First nu...

In this paper, we discuss the physics of recombination in thick InGaN quantum-well (QW) based structures. Thick InGaN QWs have been suggested as one concept to reduce the typical decrease of internal efficiency of InGaN based light emitters towards high current densities. We show that at typical operation current densities, recombination in such th...

We identify a quantum well internal high density Augerlike loss process as the origin of the so called ‘droop’ of internal quantum efficiency (IQE) in InGaN based light emitters. The IQE of such a device peaks at small current densities and then monotonously decreases towards higher currents. The origin of this ‘droop’ has been widely discussed rec...

Photonic crystals (PhCs) have attracted much attention during the last decade as a solution to overcome the low extraction efficiency of as-grown light-emitting diodes (LEDs). In this review we describe the underlying physics and summarize recent results obtained with PhC LEDs. Here, the main focus is on diffracting PhC. In order to quantify the be...

A large variety of nanostructures including surface roughening, photonic crystals and plasmonics has been applied to light-emitting diodes in order to improve their performance. This paper gives an overview of the different approaches and the obtained results and compares their relevance for commercial LED applications, focussing on solid-state lig...

Photonic crystals (PhCs) are known to diffract guided modes in a light-emitting diode into the light extraction cone according to Bragg´s law. The extraction angle of a single mode is determined by the phase match between the guided mode and the reciprocal lattice vector of the PhC. Hence, light extraction by PhCs enables strong beam-shaping if th...

We report directional light extraction from AlGaInP thin-film resonant cavity light emitting diodes (RCLEDs) with shallow photonic crystals (PhCs). Diffraction of guided modes into the light extraction cone enhances the light extraction by a factor of 2.6 compared to unstructured RCLEDs, where the farfields still show higher directionality than Lam...

A self-consistent laser simulator has been set up for the simulation of edge-emitting GaInP/AlGaInP red lasers. The modeling results have been compared with experiments in broad area 635 nm GaInP/AlGaInP laser diodes. The leakage of electrons and its dependence on the temperature and the p-doping level are analyzed.

We investigate the use of photonic crystals for light extraction from high-brightness thin-film AlGaInP light-emitting diodes with different etch depths, lattice constants, and two types of lattices (hexagonal and Archimedean). Both simulations and experimental results show that the extraction of high order modes with a low effective index neff is...

Fully microscopic many-body models are used to study the importance of radiative and Auger carrier losses in InGaN/GaN quantum wells. Auger losses are found to be negligible in contrast to recent speculations on their importance for the experimentally observed efficiency droop. Good agreement with experimentally measured threshold losses is demonst...

We estimated the influence of surface plasmon polaritons on the internal efficiency of LEDs by 3D FDTD calculations. It turns out, that SPP LEDs outperform standard LEDs if non-radiative losses are high.

Photonic crystals are known to enhance the extraction efficiency of LEDs and simultaneously shaping the emission pattern. In order to determine the radiation pattern we developed a model based on coupled mode theory that takes into account the lattice pattern, etch depth and the mode distribution. From a basic geometrical consideration a fundamenta...

The measurement of bias and temperature dependent photoluminescence, photocurrent and their decay times allows to deduce important physical properties such as barrier height, electron-hole overlap and the magnitude of the piezoelectric field in InGaN quantum wells. However the analysis of these experiments demands for a detailed physical model base...

IntroductionRequirements for a Conversion LED ModelColor Metrics for Conversion LEDsPhosphor Model Phosphor MaterialsLuminescence and Absorption of Phosphor ParticlesScattering of Phosphor ParticlesDetermination of Material ParametersLED Ray Tracing ModelSimulation ExamplesConclusions References Phosphor MaterialsLuminescence and Absorption of Phos...

The measurement of the bias and temperature dependent photoluminescence, photocurrent and their decay times allows to deduce important physical properties such as barrier height, electron-hole overlap and the magnitude of the piezoelectric field in InGaN quantum wells. However the analysis of these experiments demands for a detailed physical model...

The internal quantum efficiency as a function of the internal electric field was studied in InGaN/GaN based quantumwell heterostructures. Most striking, we find the IQE to be independent of the electron hole overlap for a standard green-emitting single quantum-well LED structure. In standard c-plane grown InGaN quantum wells, internal piezo-fields...

Along with advances in LED manufacturing technology software tools for device modelling have become available to support LED design work. Yet there is still a variety of fundamental problems in LED technology which are beyond the capabilities of standardized design methods. In this paper we discuss the suitability of modelling approaches for variou...

We present a method to calculate the diffraction efficiency of a two dimensional photonic crystal (2D PC) surface structure for light emitting diodes. To give appropriate results not only the diffraction properties of the 2D PC is taken into account, but also the mode structure of the light emitting diode. The method is sufficiently general that an...

We have realized a 76 MHz white-light differential transmission spectroscopy system. The technique employs a Ti:sapphire laser oscillator and a tapered fiber to generate a white-light continuum spanning almost the full visible to near-infrared spectral range. Using acousto-optical modulation and subsequent lock-in detection, transient relative tran...

The waveguides of 650 nm emitting high-power laser diodes are analyzed regarding the presence of deep level defects by photoelectrical techniques, namely, photocurrent spectroscopy, laser beam induced current, and near-field optical beam induced current (NOBIC). Deep level configurations in pristine devices and the kinetics of defect creation durin...

The internal quantum efficiency of (AlxGa1−x)0.5 In0.5P light-emitting devices (LEDs), with an emission wavelength ranging from 650 to 560 nm, is determined by means of a model that takes into account the radiative and nonradiative recombination in the active layer, the diffusive leakage of carriers into the confining layers, and the influence of p...

We present high-power emission from semiconductor disk lasers. By intra-cavity frequency-doubling of multi-Watt infra-red emission, more than 0.5W of blue and green have been generated. 200 mW have been achieved directly for red emitters.

The internal quantum efficiency of light emitting diodes (LEDs) based on the AlGaInP material system was analysed. This study formulated a comparatively simple rate equation model to gain a quantitative understanding of the contributions of the different loss mechanisms. On the experimental side a series of LED structures was grown with multiple (A...

Operation-induced degradation of internal quantum efficiency of high-brightness (AlxGa1-x)0.5In0.5P light-emitting devices (LEDs) is analysed experimentally and theoretically. A test series of LEDs was grown by MOCVD with identical layer sequence but different Aluminum content x in the active AlGaInP layer resulting in devices emitting light betwee...

900 mW of continuous-wave power has been achieved in AlInGaP tapered lasers at 640 nm. Good beam quality and high device efficiency are obtained. Superluminescent diodes show strongly increased spectral width while retaining the good beam properties.

We present visible high power AlInGaP lasers and laser bars from 635nm to 670nm. At room temperature we achieved 5.3W of cw power at 642nm from a 10mm bar with an overall efficiency of 17%.

The optically pumped semiconductor thin-disk laser with external-cavity (OPS-TDL) is a new type of semiconductor laser structure with the capability of achieving high output power while retaining good beam quality. We demonstrate the first AlGaInP-based red light emitting OPS-TDL structure. The device has been pumped optically with an argon-laser a...

The electronic transport in biased semiconductor superlattice structures is investigated on the basis of hopping transitions between the partially localized states of the Wannier-Stark ladder. The drift velocity is calculated numerically by summing all transitions between any two states of the ladder according to their respective weight due to the...

Summary form only given. We have for the first time implemented an optically pumped semiconductor thin-disk laser (OPS-TDL) emitting at visible wavelengths around 660 nm. The gain element is based on the AlGaInP material system, grown lattice-matched on GaAs. The epitaxial structures consist of a resonant periodic gain structure with varying number...

We report new methods of identifying the effects of aging on the light–current (L–I) and current–voltage (I–V) characteristics of AlInGaP light-emitting diodes (LEDs). We believe that these methods are also applicable to other III–V compound semiconductors. We observe a broadening of the nonlinear range of the L–I characteristic accompanied by a sh...

There is a large number of new applications in lighting and display technology where high-brightness AlGaInP-LEDs can provide cost-efficient solutions for the red to yellow color range. Osram Opto Semiconductors has developed a new generation of MOVPE-grown AlInGaP-LEDs to meet these demands. Our structures use optimized epitaxial layer design, imp...

The hopping transport model (Phys. Rev. B 12 (1975) 680) for vertical transport in superlattices has been extended towards a self-consistent calculation of the Wannier–Stark state distribution functions for plane–parallel electron motion. This way, the influence of field-induced electron heating could be investigated in the negative differential co...

The dc current in strongly coupled superlattices can either be described in a semiclassical picture in terms of miniband transport or in a quantum mechanical theory based on hopping transitions between the localized wave functions of the Wannier-Stark ladder. We demonstrate the equivalence of both models in the field regime of Bloch-oscillating ele...

We present a theory of time-resolved Faraday rotation forsemimagnetic quantum well structures in the Voigt configuration.The nonlinear part of the Faraday rotation signal is expressedas probing the carrier spin population requiring an off-resonant probe frequency. Our computed results confirm experimental findings of electron spin precession andind...

We compare the description of electronic transport in a semiclassical miniband model and within the hopping transport model. While the miniband theory is correct at low fields, quantum mechanical corrections to the Bloch oscillation picture due to the formation of the Wannier–Stark ladder at high fields have to be treated within the hopping theory....

The formation of an electron miniband has been investigated in two differently realized graded-gap superlattices (SL's). The first SL is compositionally graded, while the second system consists of layers with different well and barrier thicknesses. The formation of the miniband in the conduction band is studied experimentally by photocurrent (PC),...

We calculate the d.c.-current of a semiconductor superlattice in the hopping conduction picture. Electronic transport in this regime is described by hopping transitions between the partially localized Wannier–Stark states. In our numerical model we start from the exact wavefunctions of the superlattice and include both impurity and acoustic phonon...

We calculate the field-dependent excitonic absorption spectra of semiconductor superlattices by diagonalizing the full Hamiltonian of the problem. Our model therefore includes both bound and continuum states of the excitons. The theoretical results are compared with experiments. We first show that the Coulomb interaction does not destroy the field-...

A detailed analysis of the optical and transport properties of semiconductor superlattices in the high-field regime is presented. Electronic Bloch oscillations and the resulting terahertz emission signals are computed including phonon damping in the presence of the electric field. The modifications of the phonon-induced terahertz signal decay are a...

We use the k⋅p formalism to calculate Franz-Keldysh (FK) absorption spectra in direct-band-gap III-V semiconductors. This method allows us to include band anisotropy and nonparabolicity as well as band mixing. With k⋅p models of various complexity, we investigate how these phenomena influence the main features of the electroabsorption using GaAs as...

We have measured the electroabsorption in low‐temperature grown GaAs by performing room‐temperature transmission experiments in the spectral range from 1.3 to 1.9 eV for different electric fields induced by a voltage applied to a metal‐semiconductor‐metal structure. The devices were separated from the substrate by using an epitaxial liftoff techniq...

We report on a novel electro-optic modulator structure based on the two-dimensional Franz- Keldysh effect (2D-FKE) in multiple quantum well (MQW) structures. Due to the increased electron-hole interaction in these quasi-two-dimensional systems, strong excitonic resonances are observed even at room temperature. If an electric field is applied parall...

The optical absorption of short-period semiconductor superlattices with an electric field perpendicular to the layer plane is studied. The applied fields cover the range from the ‘‘miniband regime’’ (low fields), where Franz-Keldysh (FK) oscillations can be observed, up to the regime of Wannier-Stark (WS) transitions (high fields). Special emphasis...

The linearity of electrooptical waveguide modulators based on the Franz-Keldysh effect with respect to the voltage-transmission characteristic has been investigated experimentally and theoretically. For a GaAs-AlGaAs double heterostructure modulator the values of the signal-to-noise ratio due to anharmonic and intermodulation distortion have been f...

A graded-gap superlattice was investigated by electroreflectance (ER) at 80 K. With increasing electric-field strength the ER transitions of the individual wells exhibit first a redshift of 15 meV. At larger electric fields the typical blueshift of the Wannier-Stark localization is observed. This redshift of the transitions is explained by the form...

We report on photoluminescence and absorption measurements in type-I hetero n-i-p-i structures. The electron density in the pseudomorphic InGaAs/GaAs quantum wells is tunable between zero and more then 5 · 1012 cm-2. This electrical tuning of the subband filling is achieved by a variable voltage applied between selective n-and p-contacts fabricated...

In multiple quantum well (MQW) structures strong excitonic absorption peaks can be observed at room temperature due to enhanced electron hole confinement. If an electric field is applied parallel to the layers very weak fields are sufficient to cause field-ionization of the exciton. As a consequence, the excitonic absorption peak is expected to dis...

We present calculations and optical experiments performed at 77 K on a GaAs/AlAs superlattice with only one monolayer AlAs barriers and a combined miniband width of 380 meV. In particular the field dependent transition from the 3D miniband system to the 2D Wannier Stark (WS) regime is investigated. Using Differential Photocurrent Spectroscopy we ar...

Using differential photocurrent spectroscopy we have studied the field dependent absorption in GaAs/AlAs superlattices, which have only one monolayer AlAs barriers, with unpreceded dynamical resolution. We are able to resolve a symmetric Wannier-Stark (WS) fan up to an index of +/-9 and for the first time Franz-Keldysh (FK) oscillations across the...

A GaAs/AlGaAs p-i-n double heterostructure waveguide modulator based on the Franz-Keldysh effect is reported. On/off ratios up to 40 dB are obtained over a broad range of wavelengths (>or=32 dB between 905 nm and 960 nm), while absorption loss in the on-state is very low (<1 cm/sup -1/). The polarization dependence of the Franz-Keldysh effect is re...

For many applications in opto-electronic integrated circuits (OEIC) and for optical analogue modulation, there is a strong interest in waveguide modulators with linear relation between transmission and applied voltage. In recent years much effort has been devoted to studying the different effects that can be used for intensity modulation in wavegui...

We have performed calculations of the field dependent excitonic absorption spectra of semiconductor superlattices in a model which is capable of fully taking into account the Coulomb interaction and both bound and continuum excitonic states. Results are obtained for the complete range of fields from the Franz-Keldysh to the Wannier-Stark regime. Th...

Transmission changes in a n‐i‐p‐i doping superlattice have been measured. The structures were grown by a newly developed epitaxial shadow mask technique allowing to apply selective contacts to the n and p layers. For a voltage swing between only U pn =-4 and 0.8 V relative transmission changes of 65% below the band gap have been measured in a 2.66‐...

We report on electro-optical modulators with high contrast ratio. The on/off ratio of a homogenous GaAs n-i-p-i structure only 3.9mum thick is larger than 6:1, without additional cavity effects for a voltage swing of only 7V. This change of the reflection corresponds to an absorption change of more than 2000 cm-1, averaged over the whole sample thi...

We used a new modulation technique, the wavelength modulated photocurrent spectroscopy, to study the field dependent transition from the miniband to the Wannier-Stark regime in GaAs-AlAs-superlattices. In the zero field limit the edges of the joint miniband density of states between electrons and heavy as well as light holes create characteristic f...

We have studied the field dependence of the absorption coefficient of three GaAs-AlAs superlattices using a new modulation technique, the wavelength modulated photocurrent spectroscopy. At small applied electric fields we observe transitions corresponding to the edges of the joint miniband density of states between electrons and heavy holes as well...

Optical nonlinearities in n–i–p–i and hetero-n–i–p–i structures with selective ohmic contacts, are reported. In this kind of structures strong changes of the absorption and refractive index are achieved either by field effects and/or with phase space filling. The latter one is always present in normal n–i–p–i structures but relatively weak because...

The optical properties of a GaAs/Al0.3Ga0.7As hetero-n-i-p-i crystal with GaAs quantum wells in the intrinsic region (‘‘type II’’) have been investigated by photoreflectance measurements. To understand the complex spectra we have varied several measurement parameters such as ac pump intensity, dc pump intensity, pump frequency, and temperature. The...

We performed room temperature photo- and electro-modulation measurements on MBE-grown GaAs pnp and pin structures with large layer thicknesses. In these crystals the optical properties are expected to be dominated by the local field-induced changes of the dielectric function rather than by subband-transitions. The dominating effect in the pnp-struc...

We report results of photoreflectance (PR) investigations of GaAs/Alo.3Gao.7As hetero-n-i-p-i crystals with either GaAs-QWs ("type II") in the intrinsic region or GaAs-QWs interspersed in the n-region ("type I"). To understand the complex PR-spectra of these samples we changed several measurement parameters such as ac-pump-intensity, dc-pump-intens...

The modulation of the energy bands of a doping superlattice corresponds to periodic changes of the optical refractive index in the direction of growth. Moreover the tunability of the electronic structure allows for variation of both strength and spatial dependence. These features imply the possibility of designing a highly wavelength-selective and...

We demonstrate that suitable sample and circuit design of n-i-p-i photo-detectors allows one to achieve linearity of the photoresponse over many orders of magnitude in optical power (more than 8 orders of magnitude in the present investigation) and, at the same time to maintain the extremely high photoconductive gain which is characteristic for n-i...

Diss. - Bibliogr. s. 243-256