Showing papers by "Jürgen H. Werner published in 2012"

Laser induced lifetime degradation in p-type crystalline silicon

Abstract: Pulsed, green laser irradiation of uncoated p-type silicon leads to a significant reduction of the effective minority carrier lifetime. The reason for the lifetime drop lies in the introduction of recombination centres into the laser melted and recrystallized surface layer, leading to a low local minority carrier lifetime τ ≈ 10 ns inside this surface layer. The laser treatment introduces the impurities oxygen, carbon and nitrogen into the silicon and further leads to an n-type doping of the surface layer. There are strong indications that these impurities are responsible for the observed n-type doping, as well as the lifetime reduction after irradiation. Both effects are removed by thermal annealing. An estimate shows that the low local lifetime does nevertheless not affect the performance of industrial or contacted selective solar cell emitter structures.

Laser synthesis of germanium tin alloys on virtual germanium

Abstract: Synthesis of heteroepitaxial germanium tin (GeSn) alloys using excimer laser processing of a thin 4 nm Sn layer on Ge has been demonstrated and studied. Laser induced rapid heating, subsequent melting, and re-solidification processes at extremely high cooling rates have been experimentally achieved and also simulated numerically to optimize the processing parameters. “In situ” measured sample reflectivity with nanosecond time resolution was used as feedback for the simulations and directly correlated to alloy composition. Detailed characterization of the GeSn alloys after the optimization of the processing conditions indicated substitutional Sn concentration of up to 1% in the Ge matrix.

Room Temperature Direct Band Gap Emission from Ge p-i-n Heterojunction Photodiodes

Abstract: Room temperature direct band gap emission is observed for Si-substrate-based Ge p-i-n heterojunction photodiode structures operated under forward bias. Comparisons of electroluminescence with photoluminescence spectra allow separating emission from intrinsic Ge (0.8 eV) and highly doped Ge (0.73 eV). Electroluminescence stems from carrier injection into the intrinsic layer, whereas photoluminescence originates from the highly n-doped top layer because the exciting visible laser wavelength is strongly absorbed in Ge. High doping levels led to an apparent band gap narrowing from carrier-impurity interaction. The emission shifts to higher wavelengths with increasing current level which is explained by device heating. The heterostructure layer sequence and the light emitting device are similar to earlier presented photodetectors. This is an important aspect for monolithic integration of silicon microelectronics and silicon photonics.

Direct band gap luminescence from Ge on Si pin diodes

Abstract: Germanium (Ge) pin photodiodes show clear direct band gap emission at room temperature, as grown on bulk silicon in both photoluminescence (PL) and electroluminescence (EL). PL stems from the top contact layer with highly doped Ge because of strong absorption of visible laser light excitation (532 nm). EL stems from the recombination of injected carriers in the undoped intrinsic layer. The difference in peak positions for PL (0.73 eV) and EL (0.80 eV) is explained by band gap narrowing from high doping in n+-top layer. A superlinear increase of EL with current density is explained by a rising ratio of direct/indirect electron densities when quasi Fermi energy level rises into the conduction band. An analytical model for the direct/indirect electron density ratio is given using simplifying assumptions.

Search for New Physics with Same-Sign Isolated Dilepton Events with Jets and Missing Transverse Energy

Abstract: A search for new physics is performed in events with two same-sign isolated leptons, hadronic jets, and missing transverse energy in the final state. The analysis is based on a data sample corresponding to an integrated luminosity of 4.98 fb(-1) produced in pp collisions at a center-of-mass energy of 7 TeV collected by the CMS experiment at the LHC. This constitutes a factor of 140 increase in integrated luminosity over previously published results. The observed yields agree with the standard model predictions and thus no evidence for new physics is found. The observations are used to set upper limits on possible new physics contributions and to constrain supersymmetric models. To facilitate the interpretation of the data in a broader range of new physics scenarios, information on the event selection, detector response, and efficiencies is provided.

Strain relaxation of metastable SiGe/Si: Investigation with two complementary X-ray techniques

Abstract: Metastable and strain relaxed SiGe layers with about 20% Ge content have been grown by molecular beam epitaxy on Si substrates at 550 °C. The thickness regime of metastability and the onset of strain relaxation were investigated on dust particle free surfaces obtained by careful chemical cleaning and epitaxy loading under clean room conditions. Compared to earlier results true metastable regime without misfit dislocations was obtained up to 140 nm thickness. The onset of strain relaxation started with heterogeneous nucleation sites of misfit dislocations. X-ray topography proved to be a unique monitoring tool to observe a low density of single dislocations. From these results we suggested to define a critical thickness band with lower bound tcl from dislocation nucleation to an upper bound tco (600 nm in our case) defined by the onset of considerable strain relaxation. The strain relief was measured by X-ray diffraction (reciprocal space mapping) and found to be very abrupt (76% strain relaxation at 800 n...

Silicon germanium tin alloys formed by pulsed laser induced epitaxy

Abstract: Pulsed lased induced epitaxy is used to obtain heteroepitaxial Ge1−xSnx and Si1−x−yGexSny alloys with graded composition on Si(001) substrates. The transition from Ge1−xSnx to Si1−x−yGexSny was achieved by varying the number of laser pulses accordingly with the level of intermixing between Si, Ge, and Sn. Melt duration, predicted by numerical methods, is experimentally confirmed by "in-situ" reflectivity measurements and relates, like the end reflectivity value, to the level of intermixing. The possibility to adjust concentration profiles through laser processing of Sn films on virtual germanium buffer layers for lattice engineering of Ge1−xSnx and Si1−x−yGexSny alloys on silicon substrates is demonstrated.

Full area laser doped boron emitter silicon solar cells

Abstract: We present full area laser doped boron emitter n-type silicon solar cells using sputtered boron as dopant source. Quasi-steady-state photo conductance decay measurements show a low emitter saturation current density J 0e] and an open circuit voltage limit of V{inoc,lim = 702 mV for a 128 Ω/sq emitter proving the high quality of the laser doped boron emitters. The first 4 cm2 cell yield efficiencies up to η= 16.7% without optimization of the cell structure.

Colored Ribbons Achieve +0.28% $_{\bf abs.}$ Efficiency Gain

Abstract: Flat metallic ribbons connect the solar cells in conventional crystalline silicon modules. Acting like a mirror, they reflect incoming radiation out of the module. The area covered by the ribbons (around 3.5%) is mainly lost for photovoltaic conversion. We present colored cell connectors which scatter incident irradiation. Due to subsequent total internal reflection at the glass/air interface, the photons get a second chance to reach the active module area. White ribbons increase the module efficiency from η = 14.7% by Δη = 0.28%abs. to nearly 15%. Applying ultraviolet (UV) fluorescent dye on top of the white paint increases the quantum efficiency of lower wavelengths even further. Reduced optical losses allow a novel optimization of optical versus electrical losses. A simulation determines the optimum amount of white painted ribbons, balancing of the lower optical shadowing, and the higher series resistance of the module. The simulation predicts an efficiency gain Δη = 0.33%abs..

Verfahren zum Kontaktieren eines Halbleitersubstrates, insbesondere zum Kontaktieren von Solarzellen, sowie Solarzellen

Abstract: Es wird ein Verfahren zum Kontaktieren eines Halbleitersubstrates, insbesondere zur Kontaktierung von Solarzellen (10), angegeben, insbesondere zur Herstellung von Frontkontakten (19) an Solarzellen (10), bei dem zunachst eine metallische Saatstruktur (20) auf der zu kontaktierenden Oberflache mittels eines LIFT-Prozesses erzeugt wird und anschliesend eine Siebdruckschicht (22) auf die Saatstruktur (20) mittels eines Siebdruckverfahrens aufgedruckt wird.

Search for supersymmetry in events with b-quark jets and missing transverse energy in pp collisions at 7 TeV

Abstract: Results are presented from a search for physics beyond the standard model based on events with large missing transverse energy, at least three jets, and at least one, two, or three b-quark jets. The study is performed using a sample of proton-proton collision data collected at sqrt(s)=7 TeV with the CMS detector at the LHC in 2011, with the missing transverse energy distribution as the principal search variable. The integrated luminosity of the sample is 4.98 inverse femtobarns. The observed number of events is found to be consistent with the standard model expectation, which is evaluated using control samples in the data. The results are used to constrain cross sections for the production of supersymmetric particles decaying to b-quark-enriched final states in the context of simplified model spectra.

Manufacture of semiconductor layer e.g. passivation film for solar cell, involves separating silicon layer, silicon oxide layer, silicon carbide layer or silicon germanium layer from substrate, and performing microwave treatment

Abstract: Layer chosen from silicon layer, silicon oxide layer, silicon nitride layer, silicon carbide layer and silicon germanium layer is separated from a substrate, and subsequently microwave treatment is performed to obtain semiconductor layer.

Verfahren und Vorrichtung zum Prüfen von Photovoltaikmodulen Method and device for testing of photovoltaic modules

Abstract: Es werden ein Verfahren und eine Vorrichtung zum Prufen von Photovoltaikmodulen angegeben, wobei die Leistung, die ein Photovoltaikmodul (12) abgibt oder aufnimmt, moduliert wird, das Photovoltaikmodul (12) mit einer Kamera (26) gescannt wird und das von der Kamera (26) erzeugte Kamerasignal ausgewertet wird, um ein Lumineszenzbild (32) des Photovoltaikmoduls (12) zu erhalten, wobei das Photovoltaikmodul (12) nur in der Vorwartsrichtung betrieben wird und der Kamera (26) ein Filtersystem vorgeschaltet ist, das insbesondere im Frequenzbereich der Lumineszenzsignale durchlassig ist ( Disclosed are a method and a device specified for testing of photovoltaic modules, wherein the power delivered or receives a photovoltaic module (12) is modulated, the photovoltaic module (12) is scanned by a camera (26) and the from the camera (26 ) camera signal produced is analyzed in order to obtain a luminescence image (32) of the photovoltaic module (12), wherein said photovoltaic module (12) is operated only in the forward direction and the camera (26), a filter system is connected upstream of the permeable in particular in the frequency range of the luminescence is ( 1 1 ). ).

A method for contacting a semiconductor substrate, in particular for contacting of solar cells, and solar cells

Abstract: There is provided a method for contacting a semiconductor substrate, in particular for contacting of solar cells (10), provided, in particular for the production of front contacts (19) of solar cells (10), in which firstly a metallic seed structure (20) on the surface to be contacted by means of a LIFT-process is generated and then a screen printing layer (22) on the seed structure (20) by means of a screen printing method is printed.

Method and device for testing of photovoltaic modules

Abstract: There are a method and an apparatus for testing of photovoltaic modules specified, wherein the power delivered by a photovoltaic module (12) or recording, is modulated, the photovoltaic module (12) is scanned by a camera (26) and by the camera (26 ) camera signal produced, is analyzed to obtain a luminescence image (32) of the photovoltaic module (12), said photovoltaic module (12) is operated only in the forward direction and the camera (26), a filter system is connected upstream of the permeable in particular in the frequency range of the luminescence is ( 1 ).