Solid-phase regrowth of compound semiconductors by reaction-driven decomposition of intermediate phases
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E. D. Marshall and L. C. Wang Department ofElectrical Engineering and Computer Sciences, University of California at San Diego, LaJolla, California 92093 (Received21 December 1987; accepted9 June 1988) The solid-phase epitaxial regrowth of a III-V compound semiconductor by a two-stage reaction between a two-layer metallization and a compound semiconductor substrate is described. The regrowth process begins with a low-temperature reaction between a metal M (e.g. Ni, Pd, or Pt) and a compound semiconductor substrate, AB, to produce an intermediate M x AB or MBX phase. A subsequent reaction at a higher temperature between an overlayer of Si, Ge, Al, or In and the intermediate phase results in the decomposition of the intermediate phase and the epitaxial regrowth of a layer of the compound semiconductor. This regrowth mechanism is verified experimentally for the specific case of the Si/Ni/GaAs system. Rutherford backscattering spectrometry and transmission electron microscopy data show that the ternary phase Nix GaAs, formed during the initial stage of the reaction, decomposes to NiSi and GaAs by reaction with the Si overlayer. The incorporation of the overlayer element into the regrown semiconductor layer is proposed as a mechanism to explain the formation of Ohmic contacts in Si/Pd/«-GaAs, In/Pd/«-GaAs, In/Pt/n-GaAs, and similar two-layer metallization systems on «-GaAs.
I. INTRODUCTION Annealing metal films on compound semiconductor substrates at temperatures above or slightly below the eutectic temperature of the metallization-compound semiconductor system can result in the dissolution of the compound semiconductor and the subsequent precipitation or regrowth of a heavily doped or alloyed epitaxial layer. 12 The Ohmic properties of the eutectic Au-Ge-based metallizations to n-GaAs, for example, have been attributed, in part, to the formation of a Ge-doped GaAs layer by dissolution and regrowth.3 Similarly, formation of In, _ x Ga x As has been observed as a result of annealing In films on GaAs at temperatures above the melting point of In (156°C).2>4 The presence of a liquid phase at the interface, however, results in laterally nonuniform morphologies that may prevent the application of these contacts in devices that require control of contact dimensions on the 0.1-0.01 /im scale. In this article we describe a regrowth mechanism based on the reaction-driven decomposition of intermediate phases that occurs in the solid state at temperatures well below the melting point of the interfacial phases, thereby producing laterally uniform regrown layers. The regrowth of doped or lightly alloyed compound semiconductor layers by reaction-driven decomposition of intermediate ternary phases can be described as follows: Films of the two elements M and M' are deposited 914
J. Mater. Res. 3 (5), Sep/Oct 1988
http://journals.cambridge.org
on a compound semiconductor substrate AB. The film adjacent to the substrate consists of a metal M that reacts at low temperatures to form a ternary phase 1VLAB: + AB->M X AB.
The second film
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