AVS 45th International Symposium
    Electronic Materials and Processing Division Thursday Sessions
       Session EM-ThM

Paper EM-ThM1
Air-Stable Sulfur-Based Passivation of III-V Compound Semiconductor Surfaces

Thursday, November 5, 1998, 8:20 am, Room 316

Session: Compound Semiconductor Surface Chemistry
Presenter: C.I.H. Ashby, Sandia National Laboratories
Authors: C.I.H. Ashby, Sandia National Laboratories
K.R. Zavadil, Sandia National Laboratories
A.G. Baca, Sandia National Laboratories
P.-C. Chang, Sandia National Laboratories
B.E. Hammons, Sandia National Laboratories
Correspondent: Click to Email
Although the surface state density can be greatly reduced by sulfur bonding to III-V surfaces, this improvement is transient due to rapid oxidative loss of S from the surface. We have developed a method for stabilizing the improved properties of the semiconductor surface in the presence of S by stabilizing the S against air-oxidation. We employ a two-step process that forms an air-stable metal-S-semiconductor structure. A monolayer of S is applied by UV photodissociation of sulfur vapor. The sulfided surface is then reacted with a metal salt to form an insoluble metal-S overlayer on the semiconductor. XPS characterization of this overlayer shows the presence of the metal, S, and O in the overlayer. Photoluminescence (PL), and Raman spectroscopies have been employed to characterize the effect of the overlayer on surface-recombination-sensitive properties of the interface. For 7x10@super 16@/cm@super 3@ n-GaAs, a 15-fold increase in PL intensity results with the metal-S overlay, which is double the improvement obtained with S-treatment alone. Unlike photosulfidation or the more conventional sufidation with NH@sub 4@S@sub x@, PL intensity following metal-S overlayer deposition does not degrade rapidly in air at room temperature. Passivation of 1.8x10@super 18@/cm@super 3@ n-GaAs produces a 20-30% increase in PL intensity that is retained after more than 10 months in air. In addition, the PL improvements due to the metal-S overlayer are retained following low-temperature deposition of SiNx dielectric coatings. Application of the metal-S passivation layer to GaAs HBTs followed by SiNx encapsulation has produced an increase in dc current gain from 40 to nearly 100 for 2.5x5 µm devices and from 90 to over 100 for large-area (100x100 µm) devices, consistent with a large reduction in surface recombination in these devices. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.