Standortkarte der Vegetation in Hessen 1:200 000 (potentielle natuerliche Vegetation der Waldflaeche und natuerliche Standorteignung fuer Acker- und Gruenland)

SIGLETIB Hannover: RO 1602(33)+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Wasserumsatz im Boden. Ergebnisse der Lysimeter-, Bodenfeuchte- und Verdunstungsmessungen 1971-1990. T. 1 Suedhessen

Available from TIB Hannover: RO 1602(139)+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Electron Beam Pumping in Nitride Vertical Cavities with GaN/ Al_0.25 Ga_0.75 N Bragg Reflectors

AbstractElectron beam pumped surface emitting lasers are of great interest for a variety of applications, such as Laser Cathode Ray Tubes (LCRT) in projection display technology or high power UV light sources for photolithography.Two distributed Bragg reflector (DBR) samples were grown by plasma assisted molecular beam epitaxy (PAMBE). The active regions of the samples are a GaN:Si bulk layer and a multihetero (MH) structure, respectively.Also, a separately grown single DBR stack was studied to find optical transmission and reflection properties which were compared to transfer matrix simulations.Scanning electron beam pumping at 80 K with an excitation energy of 40 keV at varying beam currents revealed luminescence emission maxima located at about 3.45 eV for the sample with the MH structure active region. Optical modes appeared for excitation powers greater than 0.85 MW/ cm2. Further increasing the excitation power density the number of modes increased and a broadening and redshift of the luminescence spectrum could be observed.Based on our experimental results, we discuss the dependence of optical parameters of the nitride vertical cavity and sample surface reactions on primary electron beam power.</jats:p

Characterization of Al_xGa_1-xN/ AlyGa1-yN Distributed Bragg Reflectors Grown by Plasma Assisted Molecular Beam Epitaxy

AbstractAlxGa1-xN/ AlyGa1-yN Distributed Bragg Reflectors (DBRs) with up to 45 periods have been grown on (0001) sapphire substrates by r.f. plasma-assisted molecular beam epitaxy (PAMBE) with the aid of two Al effusion cells. Several samples were grown with an Al mole fraction varying between 0.38 ≤ x ≤ 1 (0 ≤ y ≤ 0.4) at temperatures of up to 890°C. In all samples, an AlxGa1-xN buffer layer was used to prevent cracking of the quarter wave stack and improving surface morphology by choosing the Al content so that strain energy in the DBR structure would be compensated.X-ray diffraction (XRD) and scanning electron microscopy (SEM) investigations were performed to determine the thickness of the quarter wave layer periods and the Al mole fraction of corresponding AlxGa1-xN single layers.Room-temperature calibrated reflection and transmission (R&amp;T) measurements were performed. Thus stray and self-absorption of the DBRs were extracted from reflectance and transmittance. The thickness of the quarter wave layers was designed such that the measured peak reflectances appeared between 346 nm to 421 nm. The dispersion data, including refractive indices and absorption coefficients, used in the calculation were extracted from R&amp;T measurements done on the above mentioned AlxGa1-xN single layers.</jats:p

Electron Beam Pumping in Nitride Vertical Cavities with GaN/ Al_0.25 Ga_0.75 N Bragg Reflectors

Electron beam pumped surface emitting lasers are of great interest for a variety of applications, such as Laser Cathode Ray Tubes (LCRT) in projection display technology or high power UV light sources for photolithography.Two distributed Bragg reflector (DBR) samples were grown by plasma assisted molecular beam epitaxy (PAMBE). The active regions of the samples are a GaN:Si bulk layer and a multihetero (MH) structure, respectively.Also, a separately grown single DBR stack was studied to find optical transmission and reflection properties which were compared to transfer matrix simulations.</jats:p