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In situ preparation of the semiconductor–superconductor interface: Nb contacts on InAs quantum wells

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3 Author(s)
Bellomi, G. ; Center for Quantized Electronic Structures (QUEST), University of California, Santa Barbara, California 93106 ; Mitchell, W.J. ; Hu, E.L.

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In this article we describe an in situ, low damage, process sequence designed to provide a more reliable, higher quality metal (superconductor)–semiconductor interface. We produce discrete Nb contacts on an InAs quantum well (125 Å) that is embedded within thick (∼3000 Å) Al0.5Ga0.5Sb barrier layers by utilizing a multichamber ultrahigh vacuum system, in which two Varian GenII, Molecular Beam Epitaxy chambers are directly connected to a high vacuum etch station. The principal process steps include (1) a short, “selective” thermal Cl2 etch of the top barrier layer to expose and define the InAs contact region, (2) a post-etch anneal (under As2 flux) to desorb residual etch products (i.e., InCl3) and restore a clean and well-ordered InAs (2×4) surface, (3) a Sb capping/passivation layer on the treated surface, (4) atmospheric transfer of the capped sample to a remote Nb deposition chamber, and (5) a post-anneal (in vacuum) to desorb the Sb cap immediately followed by Nb deposition. The priority throughout is minimizing damage and impurity exposure to the InAs surface. Morphology and roughness of the etched surface are explicitly considered in terms of the (1) initial native oxide removal: short Ar+ sputter at room temperature versus thermal desorption at 530 °C under Sb2 flux, (2) thermal Cl2 etch temperature (180–260 °C), and (3) annealing temperature for Sb desorption (430–530 &#x- - b0;C). © 1999 American Vacuum Society.

Published in:

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures  (Volume:17 ,  Issue: 5 )