44 research outputs found
Bandgap narrowing in Mn doped GaAs probed by room-temperature photoluminescence
The electronic band structure of the (Ga,Mn)As system has been one of the
most intriguing problems in solid state physics over the past two decades.
Determination of the band structure evolution with increasing Mn concentration
is a key issue to understand the origin of ferromagnetism. Here we present room
temperature photoluminescence and ellipsometry measurements of
Ga_{100%-x}Mn_{x}As alloy. The up-shift of the valence-band is proven by the
red shift of the room temperature near band gap emission from the
Ga_{100%-x}Mn_{x}As alloy with increasing Mn content. It is shown that even a
doping by 0.02 at.% of Mn affects the valence-band edge and it merges with the
impurity band for a Mn concentration as low as 0.6 at.%. Both X-ray diffraction
pattern and high resolution cross-sectional TEM images confirmed full
recrystallization of the implanted layer and GaMnAs alloy formation.Comment: 24 pages, 7 figures, accepted at Phys. Rev. B 201
Intense green-yellow electroluminescence from Tb+-implanted silicon-rich silicon nitride/oxide light emitting devices
High optical power density of 0.5 mW/cm2, external quantum efficiency of 0.1%, and population inversion of 7% are reported from Tb+-implanted silicon-rich silicon nitride/oxide light emitting devices. Electrical and electroluminescence mechanisms in these devices were investigated. The excitation cross section for the 543ânm Tb3+ emission was estimated under electrical pumping, resulting in a value of 8.2âĂâ10â14 cm2, which is one order of magnitude larger than one reported for Tb3+:SiO2 light emitting devices. These results demonstrate the potentiality of Tb+-implanted silicon nitride material for the development of integrated light sources compatible with Si technology
Silizium-basierte Lichtemitter : Neue Möglichkeiten fĂŒr Lab-on-Chip Systeme?
Die Realisierung von Lichtemittern in herkömmlicher Siliziumtechnologie ist ein groĂer Traum der Mikroelektronik. Aufgrund seines indirekten Bandgaps ist Silizium prinzipiell schlecht als Lichtemitter geeignet. Teure und aufwendige andere Verfahren und Werkstoffe (z.B. Verbindungshalbleiter wie GaAs, GaN, SiC usw.) fanden Verwendung fĂŒr Leuchtdioden und werden heute kommerziell eingesetzt. Diese sind jedoch nicht in herkömmliche Silizium-Chipstrukturen integrierbar. Die Integration in die Silizium â Technologie ist jedoch von eminenter Bedeutung fĂŒr die kostengĂŒnstige Herstellung von Emitterarrays, die neben der Nutzung fĂŒr integrierte Systeme der Mikrosystemtechnik und der optischen InformationsĂŒbertragung auf und zwischen Chips auch zur Lumineszenzanregung von FarbstoffmolekĂŒlen in Lab-on-Chip Systemen dienen können. Seit Anfang der 90er Jahre kann durch modifizierte Schichten und Strukturen im Nanometerbereich die bisherige BeschrĂ€nkung des Siliziums ĂŒberwunden werden. So können in Siliziumdioxid eingebettete Nanostrukturen aufgrund ihrer speziellen Eigenschaften zur Lumineszenz angeregt werden. In den hier beschriebenen Untersuchungen werden Nanostrukturen durch Ionenimplantation in thermisch auf einen Siliziumwafer (100, n-Typ) aufgewachsene SiO2 â Schichten erzeugt. Im AnschluĂ an die Ionenimplantation werden durch eine Temperung StrahlenschĂ€den ausgeheilt und die Clusterbildung angeregt. Die so erhaltenen Nanocluster weisen GröĂen von 4 ... 6 nm auf. Als Frontkontakt der Lumineszenzstrukturen wird eine aufgesputterte transparente Indium-Zinnoxid (ITO) - Schicht lithographisch in kreisrunde FlĂ€chen von 0.2mm2 strukturiert. Der RĂŒckseitenkontakt wird durch Al - Beschichtung der WafersrĂŒckseite hergestellt
Detecting Bacterial Cell Viability in Few ”L Solutions from Impedance Measurements on Silicon-Based Biochips
Using two different types of impedance biochips (PS5 and BS5) with ring top electrodes, a distinct change of measured impedance has been detected after adding 1â5 ”L (with dead or live Gram-positive Lysinibacillus sphaericus JG-A12 cells to 20 ”L DI water inside the ring top electrode. We relate observed change of measured impedance to change of membrane potential of L. sphaericus JG-A12 cells. In contrast to impedance measurements, optical density (OD) measurements cannot be used to distinguish between dead and live cells. Dead L. sphaericus JG-A12 cells have been obtained by adding 0.02 mg/mL of the antibiotics tetracycline and 0.1 mg/mL chloramphenicol to a batch with OD0.5 and by incubation for 24 h, 30 âŠC, 120 rpm in the dark. For impedance measurements, we have used batches with a cell density of 25.5 Ă 108 cells/mL (OD8.5) and 270.0 Ă 108 cells/mL (OD90.0). The impedance biochip PS5 can be used to detect the more resistive and less capacitive live L. sphaericus JG-A12 cells. Also, the impedance biochip BS5 can be used to detect the less resistive and more capacitive dead L. sphaericus JG-A12 cells. An outlook on the application of the impedance biochips for high-throughput drug screening, e.g., against multi-drug-resistant Grampositive bacteria, is given
Unbound states in quantum heterostructures
We report in this review on the electronic continuum states of semiconductor Quantum Wells and Quantum Dots and highlight the decisive part played by the virtual bound states in the optical properties of these structures. The two particles continuum states of Quantum Dots control the decoherence of the excited electron â hole states. The part played by Auger scattering in Quantum Dots is also discussed
Electroluminescence induced by Ge nanocrystals obtained by hot ion implantation into SiO2
Commonly, electroluminescence (EL) from Ge nanocrystals (Ge NCs) has been obtained by room temperature (RT) Ge implantation into a SiO2 matrix followed by a high temperature anneal. In the present work, we have used a novel experimental approach: we have performed the Ge implantation at high temperature (Ti) and subsequently a high temperature anneal at 900 °C in order to grow the Ge NCs. By performing the implantation at Ti=350 °C, the electrical stability of the MOSLEDs were enhanced, as compared to the ones obtained from RT implantation. Moreover, by changing the implantation fluence from Ί=0.5x1016 and 1.0x1016 Ge/cmÂČ we have observed a blueshift in the EL emission peak. The results show that the electrical stability of the hot implanted devices is higher than the ones obtained by RT implantation