Transmission electron microscopy investigation of segregation and critical floating-layer content of indium for island formation in InGaAs

We have investigated InGaAs layers grown by molecular-beam epitaxy on GaAs(001) by transmission electron microscopy (TEM) and photoluminescence spectroscopy. InGaAs layers with In-concentrations of 16, 25 and 28 % and respective thicknesses of 20, 22 and 23 monolayers were deposited at 535 C. The parameters were chosen to grow layers slightly above and below the transition between the two- and three-dimensional growth mode. In-concentration profiles were obtained from high-resolution TEM images by composition evaluation by lattice fringe analysis. The measured profiles can be well described applying the segregation model of Muraki et al. [Appl. Phys. Lett. 61 (1992) 557]. Calculated photoluminescence peak positions on the basis of the measured concentration profiles are in good agreement with the experimental ones. Evaluating experimental In-concentration profiles it is found that the transition from the two-dimensional to the three-dimensional growth mode occurs if the indium content in the In-floating layer exceeds 1.1+/-0.2 monolayers. The measured exponential decrease of the In-concentration within the cap layer on top of the islands reveals that the In-floating layer is not consumed during island formation. The segregation efficiency above the islands is increased compared to the quantum wells which is explained tentatively by strain-dependent lattice-site selection of In. In addition, In0.25Ga0.75As quantum wells were grown at different temperatures between 500 oC and 550 oC. The evaluation of concentration profiles shows that the segregation efficiency increases from R=0.65 to R=0.83.Comment: 16 pages, 6 figures, 1 table, sbmitted in Phys. Rev.

Laser-induced forward transfer on compliant receivers

Laser-induced forward transfer (LIFT) is a technique for the transfer of materials in solid or liquid phase. During LIFT a thin film (donor) previously coated onto a transparent carrier substrate is transferred by the explosive expansion of a small part of the donor volume after the absorption of a laser pulse at the interface of donor and carrier, accelerating a part of the thin film (flyer) towards a receiving substrate (receiver) [1]. When transferring a solid flyer via LIFT, it is possible to preserve its phase and physical properties, however such an intact transfer also depends strongly on the mechanical properties of the flyer and the receiver, and the flyer’s velocity during transfer. For inelastic materials and high flyer velocities the resulting stresses on impact can exceed the flyer’s mechanical strength and thus cause its undesirable shattering. To mitigate this effect, we have introduced a compliant polymer film capping the receiver and have studied experimentally the effect of such a film on the morphology and adhesion of a LIFTed deposit. Furthermore we modelled via finite element software (Comsol Multiphysics®) the impact of a flyer onto such a receiver for different material parameters and transfer conditions, and compared it to the case of LIFT onto a bare glass receiver

Waveguide mode filters fabricated using laser-induced forward transfer

Titanium (Ti)-in-diffused lithium niobate waveguide mode filters fabricated using laser-induced forward transfer followed by thermal diffusion are presented. The mode control was achieved by adjusting the separation between adjacent Ti segments thus varying the average value of the refractive index along the length of the in-diffused channel waveguides. The fabrication details, loss measurements and near-field optical characterization of the mode filters are presented. Modeling results regarding the device performance are also discussed

Cold cathode electron beam sources for high-rate PVD

Electron beams (EB) are known to be powerful and versatile tools for materials evaporation and physical vapor deposition (PVD) of thin films. Regardless the beneficial technological features of the EB?PVD, established designs of high-power electron beam sources based upon thermionic emitters as well as their supply and control systems are complex and expensive. Hence, business economics prevent their application in many thin film processes. Alternative EB sources with cold cathodes have nowadays attracted enhanced interest because of their prospects as economic beam sources for a broader spectrum of applications, including PVD. A simple but efficient high-power, cold cathode electron source has been developed and tested recently. Inside this EB gun, a high-voltage glowdischarge (HVGD) is sustained. Ions from the plasma are accelerated in the cathode fall and hit the cathode thus releasing secondary electrons. These electrons gain energy on the reverse path. Beside to the greatly simplified mechanical design and electric supply circuitry, cost reductions result also from the facts that the HVGD beam source does not require differential high-vacuum pumping and that it can be operated in a wide range of acceleration voltages without the need for movable electrodes. Particle-in-cell (PIC) simulations of the HVGD and of the beam formation in a simple geometry have been carried out to study the effects of the electrodes' geometry and of several discharge parameters on the electron-optical characteristics. Understanding the interaction of cathode material and plasma work gas as well as the handling of arc phenomena are crucial for stable operation of the EB source and have been addressed by experimental investigations therefore. Finally, a compact, cost efficient compound evaporator with an integrated beam bending system and a specially shaped vapor aperture will be introduced. It was successfully tested together with a 30 kV / 60 kW HVGD EB gun in evaporation of copper for high-rate metallization of plastics