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Published April 1, 1986 | Published
Journal Article Open

Supersonic cluster beams of III–V semiconductors: GaxAsy


Supersonic beams of semiconductor clusters with the formula GaxAsy were generated by laser vaporization of a disc of pure GaAs mounted on the side of a pulsed supersonic nozzle. These cluster beams were characterized by laser photoionization with various fixed-frequency lasers followed by time-of-flight mass spectrometry. Mass analysis of the clusters with x+y>10 showed all clusters in the composition range from Gax+y through GaxAsy to Asx+y to be present in roughly the amount expected from a binomial distribution. In the smaller clusters strong variations were observed from this expected binomial distirbution as a result of kinetic effects in the cluster formation process. Photoionization with an ArF excimer laser at very low pulse energy revealed a pronounced even/odd alternation in the photoionization cross section of the GaxAsy clusters, depending only on the total number of atoms in the cluster. Clusters in the 5–21 atom range with an odd number of atoms were one-photon ionized by the 6.4 eV ArF excimer laser photons. This even/odd alternation in ionization properties of the clusters supports the view that the even clusters have fully paired singlet ground states with no dangling bonds. At higher ArF excimer laser fluences, the observed mass spectrum became increasingly affected by fragmentation. As is true with bulk GaAs surfaces, these GaxAsy clusters evaporate largely by the loss of arsenic (probably As2) when heated by the laser, leaving behind clusters which are richer in gallium.

Additional Information

© 1986 American Institute of Physics. Received 2 August 1985; accepted 27 December 1985. The authors are greatly appreciative of the help and suggestions of Dr. M.C. Smayling of Texas Instruments Inc., and in particular for supplying the GaAs wafer used in this study. Principal support for our studies of semiconductor cluster beams is provided through Grant DAAG 29-85-K-0029 of the U.S. Army Research Office. Portions of this work were also supported through grants from the Robert A. Welch Foundation and the Exxon Education Foundation.

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