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In situ Control of Si/Ge Growth on Stripe-Patterned Substrates Using Reflection High-Energy Electron Diffraction and Scanning Tunneling Microscopy.

Sanduijav B, Matei DG, Springholz G - Nanoscale Res Lett (2010)

Bottom Line: At 600°C, the ripple onset is shifted toward higher coverages, and at 5.2 monolayers dome islands are formed at the bottom of the stripes.These observations are in excellent agreement with STM images recorded at different Ge coverages.The comparison of the results obtained at different temperature reveals the importance of kinetics on the island formation process on patterned substrates.

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ABSTRACT
Si and Ge growth on the stripe-patterned Si (001) substrates is studied using in situ reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). During Si buffer growth, the evolution of RHEED patterns reveals a rapid change of the stripe morphology from a multifaceted "U" to a single-faceted "V" geometry with {119} sidewall facets. This allows to control the pattern morphology and to stop Si buffer growth once a well-defined stripe geometry is formed. Subsequent Ge growth on "V"-shaped stripes was performed at two different temperatures of 520 and 600°C. At low temperature of 520°C, pronounced sidewall ripples are formed at a critical coverage of 4.1 monolayers as revealed by the appearance of splitted diffraction streaks in RHEED. At 600°C, the ripple onset is shifted toward higher coverages, and at 5.2 monolayers dome islands are formed at the bottom of the stripes. These observations are in excellent agreement with STM images recorded at different Ge coverages. Therefore, RHEED is an efficient tool for in situ control of the growth process on stripe-patterned substrate templates. The comparison of the results obtained at different temperature reveals the importance of kinetics on the island formation process on patterned substrates.

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Left: RHEED patterns during two-step Si buffer layer growth on stripe-patterned Si substrates recorded after 0, 5, 10, and 35 nm Si growth at 450°C and subsequent 2 and 17 nm Si growth at 520°C from (a) to (f), respectively. The {113} and {119} facet spots, as well as the corresponding sidewall inclination angle α (see schematic illustration of Fig. 2) are marked by the arrows and dashed lines. Right: Normalized intensity evolution of the specular spot (purple), the {113} (red), and {119} (blue) facet spots arising from the sidewalls of the stripes plotted as a function of the Si buffer thickness. At 25 nm Si deposition, the substrate temperature increased from 450 to 520°C
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Figure 1: Left: RHEED patterns during two-step Si buffer layer growth on stripe-patterned Si substrates recorded after 0, 5, 10, and 35 nm Si growth at 450°C and subsequent 2 and 17 nm Si growth at 520°C from (a) to (f), respectively. The {113} and {119} facet spots, as well as the corresponding sidewall inclination angle α (see schematic illustration of Fig. 2) are marked by the arrows and dashed lines. Right: Normalized intensity evolution of the specular spot (purple), the {113} (red), and {119} (blue) facet spots arising from the sidewalls of the stripes plotted as a function of the Si buffer thickness. At 25 nm Si deposition, the substrate temperature increased from 450 to 520°C

Mentions: After patterning, the stripes exhibit a nearly rectangular geometry with vertical sidewalls and a depth of 40–50 nm [6]. Due to the surface roughness, etching defects, and residual carbon surface contamination, a spotty RHEED pattern is observed after hydrogen desorption and annealing, as shown by Fig. 1a. During Si buffer growth, the RHEED patterns rapidly evolve as illustrated by the sequence of diffraction patterns displayed in Fig. 1b–1f. Already after 5 nm Si deposition at 450°C, the surface quality drastically improves and the initial 3D diffraction spots completely disappear (see Fig. 1b). Continuation of buffer growth, results in the appearance of faint additional diffraction streaks inclined by 25° to the surface normal, as indicated by the dashed lines in the RHEED pattern of Fig. 1c recorded after 10 nm Si growth. These diffraction streaks arise from electrons specularly reflected from the tilted sidewalls of the stripes. As illustrated schematically in Fig. 2, the tilt angle α of these streaks with respect to the (001) specular spot corresponds exactly to the sidewall tilt angle on the pattern surface. Their appearance thus indicates a rapid flattening of the sidewalls surfaces and a preferential orientation toward {113} surface facets, which are inclined exactly by 25.4° to the (001) substrate orientation. Further Si growth at 450°C up to 25 nm (see Fig. 1d) does not change much the diffractions pattern.


In situ Control of Si/Ge Growth on Stripe-Patterned Substrates Using Reflection High-Energy Electron Diffraction and Scanning Tunneling Microscopy.

Sanduijav B, Matei DG, Springholz G - Nanoscale Res Lett (2010)

Left: RHEED patterns during two-step Si buffer layer growth on stripe-patterned Si substrates recorded after 0, 5, 10, and 35 nm Si growth at 450°C and subsequent 2 and 17 nm Si growth at 520°C from (a) to (f), respectively. The {113} and {119} facet spots, as well as the corresponding sidewall inclination angle α (see schematic illustration of Fig. 2) are marked by the arrows and dashed lines. Right: Normalized intensity evolution of the specular spot (purple), the {113} (red), and {119} (blue) facet spots arising from the sidewalls of the stripes plotted as a function of the Si buffer thickness. At 25 nm Si deposition, the substrate temperature increased from 450 to 520°C
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Figure 1: Left: RHEED patterns during two-step Si buffer layer growth on stripe-patterned Si substrates recorded after 0, 5, 10, and 35 nm Si growth at 450°C and subsequent 2 and 17 nm Si growth at 520°C from (a) to (f), respectively. The {113} and {119} facet spots, as well as the corresponding sidewall inclination angle α (see schematic illustration of Fig. 2) are marked by the arrows and dashed lines. Right: Normalized intensity evolution of the specular spot (purple), the {113} (red), and {119} (blue) facet spots arising from the sidewalls of the stripes plotted as a function of the Si buffer thickness. At 25 nm Si deposition, the substrate temperature increased from 450 to 520°C
Mentions: After patterning, the stripes exhibit a nearly rectangular geometry with vertical sidewalls and a depth of 40–50 nm [6]. Due to the surface roughness, etching defects, and residual carbon surface contamination, a spotty RHEED pattern is observed after hydrogen desorption and annealing, as shown by Fig. 1a. During Si buffer growth, the RHEED patterns rapidly evolve as illustrated by the sequence of diffraction patterns displayed in Fig. 1b–1f. Already after 5 nm Si deposition at 450°C, the surface quality drastically improves and the initial 3D diffraction spots completely disappear (see Fig. 1b). Continuation of buffer growth, results in the appearance of faint additional diffraction streaks inclined by 25° to the surface normal, as indicated by the dashed lines in the RHEED pattern of Fig. 1c recorded after 10 nm Si growth. These diffraction streaks arise from electrons specularly reflected from the tilted sidewalls of the stripes. As illustrated schematically in Fig. 2, the tilt angle α of these streaks with respect to the (001) specular spot corresponds exactly to the sidewall tilt angle on the pattern surface. Their appearance thus indicates a rapid flattening of the sidewalls surfaces and a preferential orientation toward {113} surface facets, which are inclined exactly by 25.4° to the (001) substrate orientation. Further Si growth at 450°C up to 25 nm (see Fig. 1d) does not change much the diffractions pattern.

Bottom Line: At 600°C, the ripple onset is shifted toward higher coverages, and at 5.2 monolayers dome islands are formed at the bottom of the stripes.These observations are in excellent agreement with STM images recorded at different Ge coverages.The comparison of the results obtained at different temperature reveals the importance of kinetics on the island formation process on patterned substrates.

View Article: PubMed Central - HTML - PubMed

ABSTRACT
Si and Ge growth on the stripe-patterned Si (001) substrates is studied using in situ reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). During Si buffer growth, the evolution of RHEED patterns reveals a rapid change of the stripe morphology from a multifaceted "U" to a single-faceted "V" geometry with {119} sidewall facets. This allows to control the pattern morphology and to stop Si buffer growth once a well-defined stripe geometry is formed. Subsequent Ge growth on "V"-shaped stripes was performed at two different temperatures of 520 and 600°C. At low temperature of 520°C, pronounced sidewall ripples are formed at a critical coverage of 4.1 monolayers as revealed by the appearance of splitted diffraction streaks in RHEED. At 600°C, the ripple onset is shifted toward higher coverages, and at 5.2 monolayers dome islands are formed at the bottom of the stripes. These observations are in excellent agreement with STM images recorded at different Ge coverages. Therefore, RHEED is an efficient tool for in situ control of the growth process on stripe-patterned substrate templates. The comparison of the results obtained at different temperature reveals the importance of kinetics on the island formation process on patterned substrates.

No MeSH data available.


Related in: MedlinePlus