Chemistry Reference
In-Depth Information
Chapter 10
Formation and Opto-electronic Properties
of Nanostructures on Ultrathin SiO
2
-Covered
Si Surfaces
M. Ichikawa
Abstract
We review a method to form semiconductor nanodots on Si substrates by
using ultrathin Si oxide technology and the results on their opto-electronic prop-
erties. We can form ultrasmall semiconductor nanodots with the size of
∼
5nm
10
12
cm
−
2
on Si surfaces covered with ultrathin SiO
2
and ultrahigh density of
∼
films of
3 nm thickness. We focus on the Ge, GeSn, and GaSb nanodots on Si
substrates and those embedded in Si films. These structures exhibit quantum con-
finement effects and intense luminescence in the energy region of about 0.8 eV. We
also report an application result to grow GaSb thin films on Si substrates covered
with ultrathin SiO
2
films using GaSb nanodots as seeding crystals.
∼
0
.
10.1 Introduction
Quantum confinement effects in semiconductor nanodots lead to the concentra-
tion of continuous electronic density of states into discrete one, the enhancement
of oscillator strengths due to the increase of overlap between electron and hole
wave functions, and the relaxation of carrier momentum conservation. Many stud-
ies have been done for compound and group IV semiconductors since the above
effects contribute to the enhancement of luminescence efficiency from nanodots [
1
].
Especially, in group IV indirect transition semiconductors such as Si or Ge, the
relaxation of momentum conservation is thought to much enhance the luminescence
efficiency [
2
]. This leads to the development of CMOS-compatible integrated opto-
electronic systems.
The Stranski-Krastanov (SK) growth on substrates is a well-known method to
form nanoislands on substrates [
3
]. In this growth, nanoislands are grown on wetting
