Epitaxial Growth of GaAs-AIGaAs Quantum Wire Superlattices on Vicinal Surfaces.
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EPITAXIAL GROWTH OF GaAs-AIGaAs QUANTUM WIRE SUPERLATTICES ON VICINAL SURFACES.
P.M.Petroff, M.Krishnamurthy, M.Wassermeier, M.Miller, H.Weman, H.Kroemer, J.Merz. Materials Department and Electrical and Computer Engineering Department. University of California, Santa Barbara. CA.93106 ABSTRACT: This paper reviews the problems that are generic to the direct epitaxy of quantum wire superlattices on (100) and (110) vicinal surfaces using molecular beam epitaxy. INTRODUCTION:
The direct epitaxial growth of quantum wire superlattices presents a scientific and engineering challenge that will be met only through a better understanding of the kinetics and thermodynamics that control the epitaxy of semiconductors. This form of epitaxy calls for a 3 dimensional template rather than for the usual 2 dimensional template that is required for the epitaxy of thin films. In addition to the template provided by the surface Bravais lattice, a second template is introduced by using a vicinal surface. A well ordered vicinal surface will be formed of a periodic array of atomic steps separated by flat terraces and provides the third template for epitaxy. The step period on the vicinal surface is function of the vicinal angle, and typical values for GaAs (100) surfaces with monoatomic steps, are below 200A. The basic principle in the obtention of a quantum wire superlattice calls for the alternate deposition of 2 semiconductors with different band gaps on an ordered vicinal surface. If the deposition sequences involve only submonolayers, a Tilted superlattice (TSL) will be be formed [1-3]. For example, a (GaAs)m-(AIAs)n TSL will be formed with a period of 80A if a (1001 20 misoriented vicinal surface is used for the deposition if m,n the fractional coverages are smaller than 1. We have previously shown that for a per cycle coverage p=m+n=l, the TSL is vertical while its angle with respect to the substrate may be continuously adjusted by varying the per cycle coverage during growth [1,2]. These TSL have been used in the direct growth of quantum wire superlattices simply by sandwiching a TSL layer between two wider ban gap semiconductor layer. A second approach to the direct epitaxy of quantum wire superlattices is a modification of the TSL epitaxial growth scheme. The so called Serpentine superlattices (SSL) have a "build in" quantum wire array. The SSL is composed of a periodic lattice of quantum wells with parabolic interfaces between the well and the barrier. The change in the quantum well shape insures a 2 dimensional carrier confinement and a wire state at the apex of the parabola [4-6]. The perfection and uniformity of these quantum wire superlattices relies heavily on the interface quality and therefore on the kinetics and thermodynamics during epitaxy. The purpose of this paper is to describe some of the crystal growth problems with this form of epitaxy. Mat. Res. Soc. Symp. Proc. Vol. 237. @1992 Materials Research Society
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2) THE QUANTUM WIRE SERPENTINE SUPERLATTICE:
This section gives a brief overview of the main charac
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