Three-dimensional nanostructures on Ge/Si(100) wetting layers: Hillocks and pre-quantum dots
- Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States)
The annealing of sub-critical Ge wetting layers (WL < 3.5 ML) initiates the formation of 3D nanostructures, whose shape and orientation is determined by the WL thickness and thus directly related to the strain energy. The emergence of these nanostructures, hillocks and pre-quantum dots, is studied by scanning tunneling microscopy. A wetting layer deposited at 350 °C is initially rough on the nanometer length-scale and undergoes a progressive transformation and smoothening during annealing at T < 460 °C when vacancy lines and the 2xn reconstruction are observed. The metastable Ge WL then collapses to form 3D nanostructures whose morphology is controlled by the WL thickness: first, the hillocks, with a wedding cake-type structure where the step edges run parallel to the 〈110〉 direction, are formed from thin wetting layers, while {105}-faceted structures, called pre-quantum dots (p-QDs), are formed from thicker layers. The wetting layer thickness and thus the misfit strain energy controls the type of structure. The crossover thickness between the hillock and p-QDs regime is between 1.6 and 2.1 ML. The hillocks have larger lateral dimensions and volumes than p-QDs, and the p-QDs are exceptionally small quantum dots with a lower limit of 10 nm in width. Our work opens a new pathway to the control of nanostructure morphology and size in the elastically strained Ge/Si system.
- OSTI ID:
- 22596731
- Journal Information:
- Journal of Applied Physics, Vol. 119, Issue 20; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ANNEALING
CONTROL
DEPOSITS
LAYERS
LENGTH
MORPHOLOGY
P-TYPE CONDUCTORS
QUANTUM DOTS
SCANNING TUNNELING MICROSCOPY
STRAINS
TEMPERATURE RANGE 0400-1000 K
THICKNESS
THREE-DIMENSIONAL CALCULATIONS
TUNNEL EFFECT
VACANCIES
WIDTH