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生长在砷化镓基板上的圆锥形砷化铟量子点的电子状态仿真
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量子点由自由电子局限在半导体表面产生。本例是一个生长在砷化镓基板上的圆锥形砷化铟量子点的电子状态。 仿真文件下载https://download.csdn.net/download/yjw0911/85473360
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2 | CONICAL QUANTUM DOT
This application computes the electronic states for a quantum-dot/wetting-layer system.
It was inspired largely by the work of Dr. M. Willatzen and Dr. R. Melnik (Ref. 1) as well
as B. Lassen.
Introduction
Quantum dots are nanoscale or microscale devices created by confining free electrons in a
3D semiconducting matrix. The tiny islands or droplets of confined “free electrons” (those
with no potential energy) present many interesting electronic properties. They are of
potential importance for applications in quantum computing, biological labeling, and
lasers, to name only a few.
Scientists can create such structures experimentally using the Stranski-Krastanow
molecular beam-epitaxy technique. In that way they obtain 3D confinement regions (the
quantum dots) by growth of a thin layer of material (the wetting layer) onto a
semiconducting matrix. Quantum dots can have many geometries including cylindrical,
conical, or pyramidal. This application studies the electronic states of a conical InAs
quantum dot grown on a GaAs substrate.
To compute the electronic states taken on by the quantum dot/wetting layer assembly
embedded in the GaAs surrounding matrix, you must solve the 1-band Schrödinger
equation in the effective mass approximation:
where h is Planck’s constant, Ψ is the wave function, E is the eigenvalue (energy), and m
e
is the effective electron mass (to account for screening effects).
Model Definition
The model works with the 1-particle stationary Schrödinger equation
h
2
8π
2
---------
∇
1
m
e
r()
---------------
Ψ r()∇
⋅
– Vr()Ψr()+ EΨ r()=
∇
h
2
8π
2
m
---------------
∇Ψ
⋅– VΨ+ EΨ=
3 | CONICAL QUANTUM DOT
It solves this eigenvalue problem for the quantum-dot/wetting-layer system using the
following step potential barrier and effective-mass approximations:
• V = 0 for the InAs quantum dot/wetting layer and V = 0.697 eV for the GaAs
substrate.
• m
e
= 0.023m for InAs and m
e
= 0.067m for GaAs.
Assume the quantum dot has perfect cylindrical symmetry. In that case you can model the
overall structure in 2D as shown in the following figure.
Figure 1: 2D geometry of a perfectly cylindrical quantum dot and wetting layer.
You can now separate the total wave function Ψ into
where is the azimuthal angle. Then rewrite the Schrödinger equation in cylindrical
coordinates as
Dividing this equation by
Ψχzr,()Θϕ()=
ϕ
h
2
8π
2
---------
z∂
∂
1
m
e
-------
z∂
∂χ
1
r
---
r∂
∂
r
m
e
-------
r∂
∂χ
+ Θ–
h
2
8π
2
---------
χ
m
e
r
2
-------------
ϕ
2
2
d
d Θ
– VχΘ+ EχΘ=
仿真文件下载
https://download.csdn.net/download/yjw0911/85473360
4 | CONICAL QUANTUM DOT
and rearranging its terms lead to the two independent equations
(1)
and
(2)
Equation 1 has obvious solutions of the form
where the periodicity condition implies that l, the principal quantum
number, must be an integer. It remains to solve Equation 2, which you can rewrite as
Note that this is an instance of a PDE on coefficient form,
where the nonzero coefficients are
and λ=E
l
.
χ zr,()
m
e
r
2
----------------
Θϕ()
1
Θ
----
ϕ
2
2
d
d Θ
l
2
–=
m
e
– r
2
h
2
8π
2
---------
z∂
∂
1
m
e
-------
z∂
∂χ
l
1
χ
l
---- -
1
r
---
r∂
∂
r
m
e
-------
r∂
∂χ
l
1
χ
l
---- -
+ m
e
r
2
VE–[]+
h
2
8π
------
l
2
–=
Θ ilϕ[]exp=
Θϕ 2π+()Θϕ()=
h
2
8π
2
---------
z∂
∂
1
m
e
-------
z∂
∂χ
l
1
r
---
r∂
∂ r
m
e
-------
r∂
∂χ
l
+–
h
2
8π
2
m
e
----------------- -
l
2
r
2
-----
V+
χ
l
+ E
l
χ
l
,= l Z∈
∇ cu αu– γ+∇–()au β u∇⋅++⋅ d
a
λu=
c
h
2
8π
2
m
e
----------------- -
,= a
h
2
8π
2
m
e
----------------- -
l
2
r
2
-----
V,+= β
r
h
2
8π
2
m
e
----------------- -
1
r
---
,–= d
a
1=
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