Formation of Highly-Uniform and Densely-Packed Arrays of GaAs Dots by Selective Epitaxy
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CHARLES S. TSAI, ROBERT B. LEE, AND KERRY J. VAHALA California Institute of Technology, Department of Applied Physics, Mail Stop 128-95, Pasadena, CA 91125
ABSTRACT Formation of highly-uniform and densely-packed arrays of GaAs dots by selective epitaxy using diethylgallium-chloride and arsine is reported. The arrays of GaAs dots are imaged using atomic force microscopy (AFM). Accounting for the AFM tip radius of curvature, the smallest GaAs dots formed are 15-20 nm in base diameter and 8-10 nm in height with slowgrowth crystal planes limiting individual dot growth. Completely selective GaAs growth within dielectric-mask openings at these small size-scales is also demonstrated. The uniformity of the dots within each array ranged from 6% for the larger dots to 16% for the smallest dots (normalized standard deviations of the areas of individual dots within each array).
INTRODUCTION Semiconductor structures that exhibit quantum confinement effects in three dimensions (quantum dots) have attracted considerable attention for their potential in improving optoelectronic devices. For these optical effects to be observable at room temperature, the necessary dimensions are on the order of 10-20 nm. Many approaches to form these 1 nanostructures (quantum dots) have been studied, including selective disordering or physical
patterning 2 ,3 of epitaxially-grown quantum-well materials, in situ strain-induced formation of epitaxial islands, 4 and many others. Selective epitaxy, which refers to the laterally-controlled growth of epitaxial material within openings of a masking material, has also produced very promising results to date. In particular, highly-organized dot structures exhibiting excellent 5 uniformity and good luminescence efficiency have been formed by selective epitaxy. -7 In this report, we demonstrate the successful formation of highly-uniform and densely8 packed arrays of GaAs dots by selective epitaxy using diethylgallium-chloride and arsine. ,9 Imaged by atomic force microscopy (AFM), the GaAs dots are as small as 15-20 nm in base diameter and 8-10 nm in height. Completely selective GaAs growth within dielectric-mask openings is also confirmed at these small size-scales using AFM. To our knowledge, this is the first demonstration of selective epitaxial growth in dielectric-mask openings at these small sizescales.
DOT FORMATION The substrates prepared for this study contained a 2-jim Si-doped Al0. 3Ga 0 .7 As layer and a 10-nm undoped GaAs cap layer, both deposited by low-pressure organometallic vapor-phase epitaxy (OMVPE), on Si-doped (100) GaAs substrates. A dielectric masking layer of silicon 969 Mat. Res. Soc. Symp. Proc. Vol. 358 01995 Materials Research Society
nitride was deposited by plasma-enhanced chemical vapor deposition on the substrates and then annealed under an arsine ambient at typical OMVPE growth conditions. The thickness of the annealed silicon.-nitride layer was approximately 15 nm before lithographic patterning. 40 gm x 40 gm arrays of dot openings with center-to-center spacings of 100
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