formation of ge quantum dots by selective oxidation of sige alloys for single-electron devices

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 3201 Electronics Research and Service Organization, ITRI, Hsinchu, Taiwan, R.O.C

Si will be preferentially oxidized during high-temperature oxidation of Si1-xGex alloys while Ge is rejected from the oxide and pile

s 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 (<10nm)

Compatible to the prevailing CMOS technology

Good controllability and reproducibility

Ge pileup along the

SiO2/Si interface

Unconsumed Si Buried Oxide

Ge precipition

Buried Oxide

Ge dots versus thermal oxidation time

Ge dots versus Ge composition in Si1-xGex

15min11min 20min 25min

Plan-view TEM micrographs of Si0.95Ge0.05 after 11min.~25min. oxidation at 900 .℃

Cross-sectional TEM micrographs of Si0.95Ge0.05 after 11min. and 25min. oxidation at 900 .℃

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).

Si0.9Ge0.1 Si0.85Ge0.15Si0.95Ge0.05

Plan-view TEM micrographs of different Ge content, 11min. oxidation at 900 .℃

Ge dot size and density as a function of Ge composition in Si1-xGex

at 900 oC thermal oxidation for 11min.

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.

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 com

pletely oxidized .

Si

Buried OxideGe dots

(a) Ge dots formation by selective oxidation of Si1-xGex and Ge segregation.

(b) SEM micrograph of a narrow wire.

Structure

Ge quantum dot Single-Electron devices

Oxidation

Si

Buried Oxide 375nm

Si

Buried Oxide

Si~32nmSi1-xGex~8nm SiO2

Ge dots

Device Structure

Source

Drain

Drain

Source

Id-Vg characteristic and transconductance of Ge SET at Room Temperature.

Effect of oxidation time on the size and density of Ge dots formed by thermally oxidized Si0.95Ge0.05 at 900 oC.