Composition of Ge(Si) islands in the growth of Ge on Si(111) by x-ray spectromicroscopy

Abstract

The stoichiometry of Ge∕Si islands grown on Si(111) substrates at temperatures ranging from 460to560°C was investigated by x-ray photoemission electron microscopy (XPEEM). By developing a specific analytical framework, quantitative information on the surface Ge∕Si stoichiometry was extracted from laterally resolved XPEEM Si 2p and Ge 3d spectra, exploiting the chemical sensitivity of the technique. Our data show the existence of a correlation between the base area of the self-assembled islands and their average surface Si content: the larger the lateral dimensions of the 3D structures, the higher their relative Si concentration. The deposition temperature determines the characteristics of this relation, pointing to the thermal activation of kinetic diffusion processes.

Strain-induced Ge segregation on Si at high temperatures

“…Intense Ge-Si intermixing during the Ge growth on Si(1 1 1) surface occurs at the temperatures of 500 1C and higher [8][9][10]. At the growth temperature of 450 1C, deep trenches around Ge islands do not appear in contrast to that observed previously after the growth at 500 1C [15], confirming the absence of considerable Ge-Si intermixing.…”

“…As a result, the amount of Ge which remains in the wetting layer is less than 2 BL [3]. When the growth temperature is 500 1C and higher, the lattice strain causes a significant Ge-Si intermixing [8][9][10]. In the surface morphology, the intermixing manifests itself in the formation of deep trenches along the island perimeters [11][12][13][14].…”

Photoemission electron microscopy with chemical sensitivity: SPELEEM methods and applications

“…14,15 XPEEM was also employed to determine the local stoichiometry of the topmost layers of Ge(Si) islands on Si(111), correlating the island composition to its shape. 16,17 In the following, we report some of the most recent work on chemical imaging, illustrating the methods made available by the SPELEEM.…”

Alloying of self-organized semiconductor 3D islands

“…An example of this kind of composition profile in Ge/Si systems was obtained from XPEEM measurements of Ge islands grown on Si(111) by MBE in the temperature range 400-600 C [26,27]. This technique combines low intrusiveness with excellent elemental sensitivity and allows us to obtain chemical maps of individual islands with a lateral resolution of $25 nm [92].…”

“…Spatially resolving experimental probes allow us in principle to access the nanoscale spectroscopically, which basically yields direct elemental information. Among the most promising tools we mention the transmission or scanning electron microscope combined with electron energy loss spectroscopy or energy dispersive X-ray analysis (TEM or SEM with EELS or EDX) [20][21][22], scanning Auger microscopy (SAM), anomalous X-ray diffraction (AXRD) [23] and X-ray photoemission electron microscopy (XPEEM) (also operated to inspect the near edge X-ray absorption fine structure -NEXAFS) [24][25][26][27]. Other approaches relate local lattice distortions to the composition-dependent strain gradients in the system.…”