General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. We demonstrate a method for synthesizing free standing silicon nanocrystals in an argon/silane gas mixture by using a remote expanding thermal plasma. Transmission electron microscopy and Raman spectroscopy measurements reveal that the distribution has a bimodal shape consisting of two distinct groups of small and large silicon nanocrystals with sizes in the range 2-10 nm and 50-120 nm, respectively. We also observe that both size distributions are lognormal which is linked with the growth time and transport of nanocrystals in the plasma. Average size control is achieved by tuning the silane flow injected into the vessel. Analyses on morphological features show that nanocrystals are monocrystalline and spherically shaped. These results imply that formation of silicon nanocrystals is based on nucleation, i.e., these large nanocrystals are not the result of coalescence of small nanocrystals. Photoluminescence measurements show that silicon nanocrystals exhibit a broad emission in the visible region peaked at 725 nm. Nanocrystals are produced with ultrahigh throughput of about 100 mg/min and have state of the art properties, such as controlled size distribution, easy handling, and room temperature visible photoluminescence.

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We report on the etching characteristics of GaAs and AlGaAs in capacitive BCl 3 /SF 6 plasmas modulated at a pulse timing of a few milliseconds. Under such conditions, we obtained GaAs etch rates in the 0.25 m min −1 range, with selectivities over AlGaAs of ϳ100. The effects of plasma-induced damage to GaAs were also measured by diode ideality factor and barrier height measurements. The electrical characteristics of the diodes show less prominent dry etch damage than in the continuous reactive ion-etching conditions, a promising result for optimized gate recess in the fabrication of AlGaAs/GaAs high-electron-mobility transistors.AlGaAs/GaAs high electron mobility transistors ͑HEMTs͒ are an integral part of many monolithic microwave integrated circuits used in wireless communications such as hand-held phones. Plasma processing of AlGaN/GaN heterostructures is a key to the ability to manufacture HEMTs with high yield. A key etching step is the selective removal of the GaAs cap layer to expose the AlGaAs donor layer for deposition of the gate metal. This can be achieved with very high selectivities using plasmas involving a mixture of chlorine-and fluorine-containing gases. While fluorine is added to the plasma for the formation of the nonvolatile AlF 3 , chlorinated chemistries are used for the formation of GaCl 3 and AsCl 3 , two products suitable for spontaneous desorption. 1,2 Several authors have examined the etching characteristics of GaAs and related materials using either laser irradiation, chemical solutions, or plasma discharges ͑see, e.g., Ref. 3-16͒. Among the etching tools investigated, high-density plasmas such as electron cyclotron resonance ͑ECR͒, helicon wave plasmas ͑HWP͒, and inductively coupled plasmas ͑ICP͒ were found to have many advantages. These advantages include the generation of higher density plasmas at lower pressures, higher ionization efficiencies, and more controllable ion energies than can be obtained in more conventional capacitive discharges ͓commonly referred to as reactive ion etchers ͑RIE͔͒. A tradeoff still exists, however, between anisotropy and selectivity, and also between a high etching rate and damage-free etching. For example, despite the higher etch rate, the amount of charge accumulation during high-density plasma etching can cause serious problems such as lateral etching ͑notching͒, trenching, bowing, and dielectric breakdown. 17 Due to the lower ion densities, RIE may therefore still represent a reasonable choice to achieving simultaneous high selectivity, high anisotropy, reasonable etch rate, and low plasma-induced damage.In this article, we examine the potential of pulse-time modulated capacitive discharges in SF 6 /BCl 3 chemistry for etching of GaAs and AlGaAs. For Si, modulation of the plasma at a pulse timing of a few milliseconds was found to considerably reduce charge-induced damage such as notching. 18 In the case of GaAs, it is shown that such plasmas can offer simultaneously reduced plasma-induced damage, reasonable GaAs etch rates with relatively high sel...