10.1007/s11448-008-2010-8

Abstract

The creation of regular nanostructures of a specific geometry and various compositions on the semiconductor surfaces is of great interest for basic research and is presently the main line in nanotechnology [1,2]. Note that the physical properties of the nanoobjects differ radically from those of their bulk analogs. There are two different technological processes applied in nanostructure formation. First, nanolithography is the most widely developing technique. However, it involves an internal limiting parameter, which, for example, for x-ray nanolithography, amounts to about 50 nm. An alternative, less common method is based on the creation (construction) of a nanostructure from individual atoms or molecules using atomic force microscopy (AFM). However, this individual atomic manipulation cannot be widely used. Therefore, presently, the most promising line is the search and investigation of the self-organization and self-assembly processes of different nanostructures on a solid surface.The self-organization effect is observed, for example, in the growth of quantum dots in InAs/GaAs and InAs/InP systems [3], the Ge and Si quantum dots [4], the CdS quantum dots on the porous Al substrates [5], as well as in the formation of Si and InAs nanowires [6,7] and carbon nanotubes [8,9]. For Group III nitrides, in particular for GaN, these studies are at the initial stage. Recently, the first results on the epitaxial growth of surface nanoobjects in the form of nanowires and pillars were presented [10,11].In this work, we present the data on the creation and analysis of a regular nanostructure of a new nanocomb type formed as a result of the self-organization processes induced by multiple co-adsorptions of the Cs and Ba atoms on the n-GaN surface. The nanostructure has been studied by the methods of AFM, electron microscopy, and photoemission spectroscopy. A high degree of regularity of the structure parameters over the surface has been revealed. A self-organization model is proposed with the inclusion of the lateral interaction of the adsorbed atoms accompanied by the formation of a surface incommensurate phase and its interaction with the Cs + and Ba 2+ ion clusters.An in situ experiment was carried out in a vacuum of P < 1 × 10 -10 Torr at room temperature. The 4-µ mthick n -type sample doped with silicon (3 × 10 17 cm -3 ) was a GaN(0001) epitaxial layer grown on a sapphire substrate by epitaxy from organometallic MOCVD compounds. The sample was pre-annealed directly in a vacuum at about 650 ° C. Atomically pure Cs and Ba were deposited on the sample surface by evaporation from standard sources. The nanostructure was formed as a result of the multilayer co-adsorptions of Cs and Ba followed by the sample annealing at about 600 ° C. The AFM measurements were carried out with the use of a Solver P-47H device in the semiconductor mode and NSG-11 (NT-MDT) probes with the bending radius 10-20 nm.In the in situ investigations of the electron properties of the Cs+Ba/ n -GaN interfaces and the nanostructure formed, threshold pho...