Nanometer-scale composition measurements of Ge/Si(100) islands

Abstract

Quantitative, nanometer-scale spatial resolution electron energy-loss spectroscopy (EELS) was used to map the composition of coherent islands grown by molecular-beam epitaxy of pure Ge onto Si(100). The Ge concentration XGe decreased, and the Ge/Si interface became more diffuse as the growth temperature increased from 400 to 700 °C. Integrated island volumes measured by atomic force microscopy (AFM) increased linearly with Ge coverage θGe, with slopes greater than 1. This result confirmed that island growth is faster than the Ge deposition rate due to Si interdiffusion. The linearity of the island volume versus θGe curves implied that XGe was independent of island size. XGe measured by EELS and AFM agree well with each other and correctly predicted the minimum dome size observed at each growth temperature.

Alloying of self-organized semiconductor 3D islands

“…Qualitatively similar experimental results (exhibiting highly alloyed nanostructures, especially in the lower and central parts of the islands) have been also obtained by other authors using different experimental techniques [50,[52][53][54][55][56][57][58].…”

“…The interplay between continuous diffusion and lateral enlargement of the islands would eventually result in the Si-enriched centres. However, several authors have understood the observation of Si-rich cores in particular and of islands with a high degree of Si alloying in general as an indication for the relevance of volume diffusion and stress-driven intermixing processes [57,[59][60][61][62][63]. In these studies the strain energy minimization has been identified as the primary cause in determining the composition profiles.…”

Probing the composition of Ge dots and Si∕Si1−xGex island superlattices

“…Techniques such as x-ray scattering, 3 x-ray absorption, 4 atomic force microscopy, 5 transmission electron microscopy ͑TEM͒, 6 Raman scattering, 7 electron energy-loss spectroscopy ͑EELS͒, 8 and photoluminescence 9 have been used to probe the composition of individual or ensembles of Ge islands and dots. Although most results point to intermixing and an increase in Ge concentration towards the top of the dots, the actual Ge distribution within a single dot has not been fully mapped out without ambiguity.…”

Effect of parameters of Ge(Si)/Si(001) self-assembled islands on their electroluminescence at room temperature

“…1b) at room temperature. Previously [11], it was found that the dome-shaped islands grown at T gr = 600 ° C have the highest PL-signal intensity at room temperature in comparison with the PL signal from islands grown at other temperatures, which is related to the best hole localization in islands grown at T gr = 600 ° C. It is caused by the fact that, on the one hand, an increase in the growth temperature above 600 ° C results in increasing the diffusion of silicon into islands [17,18]. According to the X-ray diffraction analysis, the average Ge content in islands in the investigated structures with d Si = 25 nm decreases from x = (45 ± 3)% to x = (37 ± 3)% when T gr increases from 600 to 650 ° C. The growth of the Si fraction in islands leads to decreasing the valence-band discontinuity at the heterojunction between silicon and the Ge(Si) island, to decreasing the potential-well depth for the holes in the island, and, as a consequence, to the deterioration of their spatial localization.…”