No abstract

Fluidic self-assembly is a new technique which makes possible the integration of devices fabricated using dissimilar materials and processes. The integration is accomplished by fluidically transporting trapezoidally shaped blocks made of one material into similarly shaped holes in a receptor substrate. In this paper, a systematic study of the FSA integration efficiency is presented. Blocks and holes were formed from silicon using anisotropic etching. Two different sizes were considered: large blocks of dimension 1.0 mm x 1.2 mm, and small blocks of dimension 150 p m x 150 pm.FSA wm performed in either water or methanol using a bubble pump apparatus to recirculate blocks. FSA of large blocks resulted in 100% fXng of a substrate containing 191 holes within 2.5 minutes. Similar experiments with small blocks and a substrate with a 64 x 64 array of holes yielded a fill ratio of 70%, due to undesirable adhesion of blocks to the substrate surface. Roughening the substrate resulted in a fill ratio of 90%. Also presented is a simple rate equation model of the FSA process, along with a discussion of which process parameters are important and how they can be optimized. BACKGROUND

Room-temperature cw electrically pumped external-cavity surface-emitting laser diodes are reported. The external cavity provides a way to control the transverse modes of the surface-emitting laser diodes. Powers greater than 100 mW pulsed and 2.4 mW cw in the lowest order (TEM00) transverse mode are reported. The surface-emitting laser diode was grown on a p-doped substrate, resulting in uniform current injection in devices as large as 100 μm in diameter. To our knowledge, this is also the first report of a working surface-emitting laser diode grown on a p-type substrate.

The thermal characteristics of p-type substrate external-cavity surface-emitting laser diodes (SELDs) under pulsed and continuous-wave operation are studied both theoretically and experimentally. The theoretical work establishes models for the current flow, spontaneous emission transfer, heat generation, and temperature rise in the laser. The models incorporate the reduced and anisotropic electrical and thermophysical properties of the Bragg reflectors. The temperature rise at the active region of an external-cavity SELD is determined by measuring the output wavelength as a function of the injection current, modulation frequency, and substrate temperature. Simulation results agree reasonably well with experimental data on the external-cavity SELD. It is shown that the thermal resistance of the studied laser is smaller than previously reported values for the n-type substrate SELDs because of the current spreading in the p-type mirror and its close proximity to the substrate.

Transverse mode control is demonstrated in an electrically pumped surface-emitting laser diode coupled to an external microcavity with room-temperature single-mode powers reaching 2.0 mW continuous wave and 36.7 mW pulsed. The wavelength chirp is less than 0.044 nm for the pulsed results. The external microcavity is formed with a flat dielectric mirror placed less than 700 μm from the wafer surface. Diffraction and spatial filtering in the external cavity provide high-order mode suppression and produce a large fundamental mode of width 36 μm. This external cavity geometry readily lends itself to integration.