Formation of Ge Quantum dots by Selective Oxidation of SiGe alloys

1
Formation of Ge Quantum dots by Selective
Oxidation of SiGe alloys for Single-Electron
Devices P. W. Li, W. M. Liao, S. W. Lin, P. S.
Chen1, S. C. Lu1 , and M. J. Tsai1 Department of
Electrical Engineering, National Central
University, ChungLi, Taiwan, R.O.C 320 1
Electronics Research and Service Organization,
ITRI, Hsinchu, Taiwan, R.O.C
Structure

• Si will be preferentially oxidized during
  high-temperature oxidation of Si1-xGex alloys
  while Ge is rejected from the oxide and piles up
  along the SiO2/substrate interface.
• Germanium quantum dots would be formed
  during thermal oxidation of SiGe/Si-on-insulator
• Nano-scale Ge quantum dots (lt10nm)
• Compatible to the prevailing CMOS technology
• Good controllability and reproducibility

SiO2
Si1-xGex8nm
Si32nm
Ge dots
Oxidation
Buried Oxide 375nm
Buried Oxide
Si
Si

• Si1-xGex layer was epitaxially grown on SOI wafer
  (SIMOX).
• Ge dots were formed by thermal oxidation of
  Si1-xGex layer (Ge segregation
  
• and agglomeration).

Ge dots versus thermal oxidation time
Plan-view TEM micrographs of Si0.95Ge0.05 after
11min.25min. oxidation at 900 ?.
Ge precipition
Buried Oxide
Cross-sectional TEM micrographs of Si0.95Ge0.05
after 11min. and 25min.
oxidation at 900 ?.

• Additional thermal oxidation or thermal annealing
  would provide more energy required for Ge atoms
  movement, but too much energy for Ge atoms
  migration and agglomeration will results in
  bigger Ge dots and lower dot density.

Effect of oxidation time on the size and density
of Ge dots formed by thermally oxidized
Si0.95Ge0.05 at 900 oC.
Ge dots versus Ge composition in Si1-xGex
Si0.9Ge0.1
Si0.85Ge0.15
Si0.95Ge0.05
Plan-view TEM micrographs of different Ge
content, 11min. oxidation at 900 ?.

• The reduction of Ge dots size with increasing Ge
  composition in Si1-xGex alloy comes from two
  factors 1. Higher atomic mobility or moving
  speed of Ge atoms. 2. Shorter oxidation time
  required for higher Ge-compositional Si1-xGex to
  be completely oxidized .

Ge dot size and density as a function of Ge
composition in Si1-xGex at 900 oC thermal
oxidation for 11min.
Ge quantum dot Single-Electron devices
Device Structure
Drain
Source
Source
Drain
Ge dots
Buried Oxide
Si
(a) Ge dots formation by selective oxidation of
Si1-xGex and Ge segregation.
(b) SEM micrograph of a narrow wire.
Id-Vg characteristic and transconductance of Ge
SET at Room Temperature.