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Material properties and performance of metamorphic optoelectronic integrated circuits grown by molecular beam epitaxy on GaAs substratesA technique for the heteroepitaxy of GaAs/Si films having reduced threading dislocation density is presented. The important attribute of this technique is the suppression of three-dimensional Volmer-Weber island formation during initial deposition. This suppression is achieved by deposition of a stoichiometric GaAs buffer layer by a migration-enhanced epitaxy technique on silicon at 348 K to a thickness greater than the ''monolithic thickness,'' h m . Subsequent GaAs films deposited by conventional molecular beam epitaxy on buffer layers of thickness greater than h m possess structural and optical characteristics that exceed those for state-of-the-art GaAs/Si layers: an x-ray full width at half maximum ͑FWHM͒ of 110 arcsec with a dislocation density at the film surface of 3ϫ10 6 cm Ϫ2 and a concomitant 4 K photoluminescence FWHM of 2.1 meV. The p-i-n structures suitable for use as light-emitting diodes ͑LEDs͒ that were grown on the reduced threading dislocation density GaAs/Si and by means of forward-and reverse-bias measurements, demonstrated an ideality factor of nϭ1.5, an increased reverse-bias breakdown electric field of 2.1ϫ10 7 V/m, and an intrinsic region resistivity of 4ϫ10 7 ⍀ cm for LEDs of increasingly smaller mesa size.

Values of the aspect ratio for trenches etched into HgCdTe by an electron cyclotron resonance (ECR) plasma containing hydrogen and argon are limited by the phenomenon of etch lag. Modeling this plasma as an ion assisted, reactiveetching process leads to a set of conditions that greatly reduces etch lag. Use of these new process conditions produces trenches with aspect ratios greater than 3, widths less than 3 m, and depths in excess of 15 m.