Ba termination of Ge(001) studied with STM

Abstract

We use controlled annealing to tune the interfacial properties of a sub-monolayer and monolayer coverages of Ba atoms deposited on Ge(001), enabling the generation of either of two fundamentally distinct interfacial phases, as revealed by scanning tunneling microscopy. Firstly we identify the two key structural phases associated with this adsorption system, namely on-top adsorption and surface alloy formation, by performing a deposition and annealing experiment at a coverage low enough (∼0.15 ML) that isolated Ba-related features can be individually resolved. Subsequently we investigate the monolayer coverage case, of interest for passivation schemes of future Ge based devices, for which we find that the thermal evaporation of Ba onto a Ge(001) surface at room temperature results in on-top adsorption. This separation (lack of intermixing) between Ba and Ge layers is retained through successive annealing steps to temperatures of 470, 570, 670 and 770 K although a gradual ordering of the Ba layer is observed at 570 K and above, accompanied by a decrease in Ba layer density. Annealing above 770 K produces the 2D surface alloy phase accompanied by strain relief through monolayer height trench formation. An annealing temperature of 1070 K sees a further change in surface morphology but retention of the 2D surface alloy characteristic. These results are discussed in view of their possible implications for future semiconductor integrated circuit technology.

Functionalization of the Si(1 1 1) 7 × 7 substrate with coronene molecules using simple molecular source

“…For this reason, different semiconductor systems are being intensively investigated to solve specific problems, e.g. formation of the metallic contacts [3,4], monoatomic passivation layers [5][6][7][8] or thin insulating layers [9,10]. On the other hand, local surface defects or adsorbed molecules are considered for the controlled nanostructures growth [11][12][13].…”

STM and DFT study on formation and characterization of Ba-incorporated phases on a Ge(001) surface

“…This is because of the structural similarity of the Ge(001) surface to the technologically relevant Si(001) substrate [2,3] and superior electronic properties of Ge compared to Si [1,[4][5][6]. Progress in the field requires, however, and complete knowledge about technologically relevant processes on Ge surfaces such as controlled growth of low Ohmic contacts [7][8][9][10][11], formation of passivation layers [12][13][14][15], or structural and electronic functionalization [16,17].…”

“…The interaction of alkaline-earth metals such as strontium (Sr) or barium (Ba) with the Si(001) and Ge(001) surfaces is fundamental to the controlled formation of high-k surface layers [12][13][14][15]18]. At coverages below 0.5 monolayer (ML) these elements were shown to form two adsorption structures on Si(001) and Ge(001)-namely the on-top and incorporated phases [15,19].…”

“…At coverages below 0.5 monolayer (ML) these elements were shown to form two adsorption structures on Si(001) and Ge(001)-namely the on-top and incorporated phases [15,19]. The on-top phase on Si(001) was observed for the room temperature (RT) adsorption of Ba, Li, or Sr atoms in the form of randomly distributed chains of the adatoms that run across the Si dimer rows [19][20][21][22][23].…”

“…This phase is characterized by the adatom induced 2 × 3 surface reconstruction at coverages up to 1/6 ML [28,30]. It was demonstrated recently that annealing the on-top phase in the * wojciech.koczorowski@put.poznan.pl Ba/Ge(001) adsorption system promotes the incorporation of the Ba adatoms into the substrate and transforms the on-top phase into the incorporated phase [15].…”