Formation of Self-Assembled Nanometer-Scale InP Islands on Silicon Substrates
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ISLANDS ON SILICON SUBSTRATES A.S. Bakin*, D. Piester%, H.-H. Wehmann*, A.A. Ivanov*, A. Schlachetzki*, K.D. Becker" *Institut fuir Halbleitertechnik, Technische Universitat Braunschweig, Hans-Sommer-StraBe 66, D-38106 Braunschweig, Germany *Institut fur Festkdrperchemie, Abteilung Physikalische Chemie, Technische Universitat Braunschweig, HansSommer-StraBe 10, D-38106 Braunschweig, Germany
ABSTRACT Three-dimensional islands of InP have been reproducibly grown in the Stranski-Krastanow growth mode on Si (001) and (111) by using metal-organic vapor phase epitaxy in order to obtain nanometer-scale quantum dots. Atomic-force microscopy was used to determine the morphology of the samples and to evaluate the dimensions of the islands. Formation of threedimensional islands with densities as high as 2.5x101° cm2 and small sizes have been observed. The evolution of island morphology is explained in terms of strain-relaxing mechanisms at the first stages of InP/Si heteroepitaxy. INTRODUCTION Self-organized nanometer-scale structures are at present topics of considerable interest due to their potential in optoelectronic and electronic device application and due to their processunaffected and damage-free features. "- Supporting this statement is the experimental finding with InSb dots on InP substrates that Lomer-type of dislocations form a 900 grid at the substrate-island interface relaxing the mechanical tensions within the islands.' Thus we can expect that the bulk of the islands is defect-free as demonstrated by InAs dots on InP.4' 9 The heterostructures of direct-band gap materials like InP on indirect-band gap silicon have the potential for a new generation of optoelectronic devices monolithically integrated with siliconbased microelectronics. This will ultimately lead to the fabrication of light sources on silicon. It is the intention of this paper to study the experimental conditions required for the formation of InP dots on Si substrates. Very little has been published on such islands. The knowledge of optimized growth conditions is essential for an effective control of the dot size. The growth was performed in a horizontal infrared-heated metal-organic vapor phase epitaxy (MOVPE) machine designed by AIXTRON and operated at low pressure (20 to 100 hPa) under a total hydrogen flow of 8 main. Prior to growth the wet-chemically cleaned Si substrates were thermally treated at 950'C for 15 min in a hydrogen atmosphere in order to remove the native oxide. AsH 3 is introduced during the cool-down phase and then growth was started at 4000C. 10,11 The effect of annealing of the samples was investigated by heating them up to a temperature of 640'C in a phosphine flow. After reaching 640'C the heater was immediately shut off. An atomic-force microscope (AFM) made by TopoMetrix was employed for the characterization of the structures. Figures 1 a to d show AFM images selected from a series of samples obtained for different growth durations from 2 to 30 seconds on (001)Si substrates. Statistical data on the InP islands are given
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