Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
The Effect of the Quantum Point Contacts and Impurities on an Electron in the 2D Electron Gas
Engin Cicek 1 , Mustafa Ulas 2 and Afif Siddiki 3,4
1 Department of Physics, Trakya University, 22030 Edirne, Turkey
2 Kirklareli University, Physics Department, Faculty of Arts and Science, Kavakli-Kirklareli, Turkey
3 Istanbul University, Faculty of Sciences, Physics Department, Vezneciler-Istanbul, 34134, Turkey
4 Harvard University, Physics Department, Cambridge, 02138 MA, USA
Abstract— In this work, we investigate the geometrical effects of the single and double quantum point contacts (QPCs) and
impurity effects on a two dimensional electron gas (2DEG) in the AlGaAs/GaAs heterostructure. For a realistic calculation we
take into account the crystal growth parameters and the sample geometries. Next, we solve the three dimensional Poisson
equation using the numerical techniques. We show that the QPC’s shape and impurity properties strongly changes the
distribution of the two dimensional electron gas (2DEG) and the subband energies of the electron which is the located in the
2DEG.
In the last decade, low-dimensional heterostructure
systems such as thin films (2D), wires (1D) and quantum dots
(0D) [1-3] have received a great deal of attention because of
their interesting physical properties [4] and their technological
applications in electronic and optical devices. Fabrication
techniques affect the electronic properties of the sample so
that for a realistic calculations the real sample properties are
taking into account [5].
Here we define a square unit cell, with a surface pattern
(1.5x1.5 m 2 ) where we process three different techniques
(gate, etch and trench gate defined) at the each edge of the
sample in the same direction with 0.5 m. For gate defined
samples we applied -1.8 V to the gates on the surface, whereas
for etch defined samples we etched 62.8 nm from the surface
and for trench gate samples we etch the samples 31.4 nm and
place gates on this plane with a -1.8 V bias. QPCs are located
on the surface with a -1.8 V. The two unlike QPC geometries
(X 2 -X 8 ) are used with three different distances of the QPC’s
tips. A single impurity is set in the heterostructure at various
positions and distances from the 2DEG. To obtain the electron
and potential profiles we solved the electrostatics of the
system in three dimensions with using a code developed on a
fourth order grid, which was successfully applied in previous
studies [6,7]. For a realistic calculation we take into account
the crystal growth parameters, gate patterns, surface images,
densities, QPC and impurity properties explicitly. Our results
can enlighten the experimental structures. In our work, 2DEG
is located 314 nm below the surface and we dope the
heterostructures with two donor layers. The upper donor layer
is 40 nm below the surface and its density is 1.7x10 16 m -2 ,
whereas the other donor layer is located 165 nm below the
surface with a fixed doping surface density of 2.5x10 15 m -2 .
These donor layers are distributed homogeneously. We
compare the electron density distributions and potential
profiles where we create the 2DEG with different techniques
(etching, gate and trench gated defined structures), QPC
shapes and impurity positions.
As a result, the edge properties of the 2DEG is strongly
affected by the shape of the QPC, impurity position and the
which process procedure is used. We can solve the 3D Poisson
equation iteratively and take into account these properties and
wafer properties of the sample. So that we obtain deep insight
of the realistic samples.
a)
b)
Figure: The electron densities of the samples with two different
shape of the QPCs ((a)X 8 shape (b)X 2 shape) for the trench
gated structures with a same QPC distances (100nm). It is clear
from the graphs the X 8 shape QPC is deplete the electrons more
efficiently.
*Corresponding author: engin_cicek79@hotmail.com
[1] H. Akiyama, T. Someya, and H. Sakaki, Phys. Rev. B 53, R10520
(1996).
[2] H. Akiyama, T. Someya, and H. Sakaki, Phys. Rev. B 53, R4229
(1996).
[3]M. Ulas, E. Cicek and S.S. Dalgic, phys. stat. sol. (b) 241, 2968
(2004)
[4] U. Woggon (Ed.), Optical Properties of Semiconductor Quantum
Dots (Springer, Heidelberg, 1997).
[5] S. Arslan, E. Cicek, D. Eksi, S. Aktas, A. Weichselbaum, and A.
Siddiki, Phys. Rev. B 78, 125423(2008).
[6] A. Weichselbaum and S. E. Ulloa, Phys. Rev E 68, 056707
(2003).
[7] A. Weichselbaum and S. E. Ulloa, Phys. Rev B 74, 085318
(2006).
6th Nanoscience and Nanotechnology Conference, zmir, 2010 242