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global{}
Global settings simulation domain.
global{
database = "../Syntax/database_nnp.in" #
(obsolete) ==> moved to
database{}
Specify simulation dimension:
simulate1D{} #
simulate2D{} # for a 2D simulation
simulate3D{} # for a 3D simulation
For zinc blende materials
there are three-digit Miller indices.
The Miller indices define a plane. There exists a
vector that is perpendicular to this plane, e.g. in zinc blende blende
materials, the [hkl] vector is always perpendicular to the (hkl) plane.
However, for wurtzite, this is not necessarily
true. For instance, although the [0001] vector is perpendicular to the (0001)
plane, in general is does not hold that the vector that is perpendicular to the
(hkil) plane is defined by [hkil].
Note: For a 1D simulation, the heterostructure is
always grown along the x axis.
For a
2D simulation, always the (x,y) plane is used.
Zincblende
crystal_zb{
x_hkl = [1, 0, 0] #
Specify (hkl) plane perpendicular to x axis: The x axis of the simulation
coordinate system is perpendicular to this hkl plane of the crystal (here:
(1 0 0)).
y_hkl = [0, 1, 0] #
(0 1 0)).
# (0 0 1)) for the z axis are determined automatically.
#
x_hkl = [3, 1, 1] #
x axis of simulation coordinate system is perpendicular to (3 1 1)
plane of crystal coordinate system, i.e. the x axis is along [311] direction.
y_hkl = [0, -1, 1] # (0 -1 1 )
plane of crystal coordinate system, i.e. the y axis is along [0-11] direction.
# [2, -3, -3])
for the z axis are determined automatically, i.e. (2 -3 -3) plane, i.e. the z
axis is along [311] direction.
}
Wurtzite
Usually for wurtzite, the four-digit
Miller-Bravais indices (h k i l)
are used. We also use this notation but omit the
'i' because i = - h - k.
The three integer values (Miller indices) that
are given for x_hkl refer to a
plane and not to a direction. The x direction is then the one that is perpendicular to this plane.
This vector along the x axis has indices that are in general not identical to
the Miller indices in wurtzite.
crystal_wz{
# [0001] axis along x axis
#
x_hkl = [ 0, 0, 1]
# hkil =
( 0, 0, 0, 1)
that define the (hkil)=(0001) plane. Coincidently, the vector [0001] is
pependicular to it.
#
y_hkl = [ 1, 0, 0]
# hkil =
( 1, 0, -1, 0)
that define the (hkil)=(10-10) plane.
}
# (-1 2 -1 0)).
crystal_wz{
# e.g. (10-10) plane is perpendicular to x axis
x_hkl = [ 1, 0, 0]
# hkil =
( 1, 0, -1, 0)
that define the (hkil)=(10-10) plane. The x axis of the simulation coordinate
system is perpendicular to this plane.
y_hkl = [-1, 2, 0]
# hkil =
(-1, 2, -1, 0)
that define the (hkil)=(-12-10) plane. The y axis of the simulation coordinate
system is perpendicular to this plane.
# (0001)).
Coincidently, the vector [0001] is pependicular to it.
#
rotation_c_a_ratio_use_substrate =
yes
# yes) In wurtzite,
the c/a ratio of the two lattice constants 'c' and 'a' is important.
# The ideal one, c/a=sqrt(8/3)=1.63299..., is not the one present in GaN,
AlN or InN, i.e. in real materials.
# For the rotation of the crystal coordinate system to the simulation
coordinate system, a specific c/a ratio has to be assumed.
# By default, we use the one of the substrate material.
# If you want to use the ideal c/a ratio, you have to specify
rotation_c_a_ratio_use_substrate = no.
rotation_c_a_ratio =
1.63299
# rotation_c_a_ratio =
sqrt(8/3) (default).
#
}
x_hkl = [ ., ., .]
#
y_hkl = [ ., ., .]
#
z_hkl = [ ., ., .]
#
Specify substrate (and thus its lattice constant),
i.e. the material on which all layers are grown.
Consequently, all layers are strained with respect to the (unstrained)
substrate.
The substrate is also
necessary to determine the symmetry properties of the k||
integration.
substrate{ # binary
name = "GaAs"
}
or
substrate{ # ternary
name = "Al(x)Ga(1-x)As" #
AlxGa1-xAs
alloy_x = 0.3 #
}
substrate{ # quaternary
name =
"Al(x)Ga(y)In(1-x-y)As" #
AlxGayIn1-x-yAs
alloy_x = 0.3 #
alloy_y = 0.1 #
}
substrate{ # quinternary
name =
"Al(x)Ga(y)In(1-x-y)Sc(1-x-y-z)N" #
alloy_x = 0.3 #
alloy_y = 0.1 #
alloy_z = 0.55 #
}
temperature = 300 #
temperature_dependent_bandgap = yes/no
# yes)
temperature_dependent_lattice = yes/no
#
yes)
This has the consequence that the conduction band offsets are
temperature dependent whereas
the valence band offsets are not temperature dependent.
Due to Varshni formula a correction is calculated
(if necessary interpolated) which is then added to the (interpolated) band gap. For
instance:
Egap (T > 0 K) = Egap (T =
0 K) + Egap,Varshnicorrection(T)
- alpha[AC] * T^2
- alpha[BC] * T^2
- alpha_bow[ABC] * T^2
Egap,Varshnicorrection[AxB1-xC]
= x -------------------------- + (1-x) -------------------------- - x(1-x)
------------------------------------
T + beta[AC]
T + beta[BC]
T + beta_bow[ABC]
Note: For all nextnano versions older than
2019-04-16, the
periodic{} flag was specified within the
grid{} section and not within the
global{} section.
periodic{
#
(optional)
x = yes/no
#
no)
y = yes/no
#
no) (2D or 3D only)
z = yes/no
#
no) (3D only)
}
are solved automatically with periodic boundary
conditions along the appropriate directions.
if the quantum region extends over the whole
simulation region along the relevant direction.
Specify magnetic field:
magnetic_field{
strength = 5.3
# [T] = [Vs / m2]
direction = [3, 1, 1] # (only 3D) orientation of magnetic field vector with respect to (x,y,z) simulation
coordinate system, here: [311]
#
direction must not be
present because the direction is automatically
# set internally to be perpendicular to
the simulation
plane in 2D, i.e. (x,y) plane => [0, 0, 1].
#
direction must not be present because the direction is parallel to the
simulation direction (x).
# Defining magnetic_field{} in the input file results into a different (slower) solver being called.
Thus, omit this section altogether in case no magnetic field is needed.
# Note: The Hall effect for the
drift-diffusion current calculation is not implemented yet.
}
For single-band:
magnetic_field{} is defined, the
Pauli equation
is solved in all 2D and 3D single-band quantum regions instead of the
single-band Schrödinger equation.
although they have the same energy.
Thus, to maximize speed in the absence of magnetic fields, leave magnetic_field{} undefined.
Then the dimension of the matrix from which the eigenfunctions
are calculated has only half the size (and thus only half of the
eigenfunctions have to be calculated), and it is is real instead of Hermitian.
Thus the classical Hall effect is not taken into account.
because the current is proportional to the density.
}
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