nextnano.MSB
Material database
The material parameters that are used by the nextnano.MSB software are
stored in a file called materials.xml .
This XML file can be edited by the users to modify material parameters or to
add further materials.
If you run nextnano.MSB via the
nextnanomat GUI, you can
choose to read in a customized material database as follows:
nextnanomat ==> Tools ==> Options
==> Expert settings ==> Additional arguments passed to
the executable ==> Command line ==> -database "E:\nextnano.MSB\Release-007\Materials_no_Varshni_THz_QCL_NovelDesignPeterGreck.xml"
There are entries for binary compounds like GaAs, AlAs, InP, ..., as well as
for ternary compounds like AlGaAs, InGaAs, ...
<!-- binary compound -->
<Material>
<Name>GaAs</Name>
<ConductionBandOffset
Unit = "eV" >
2.979 </ConductionBandOffset>
<ValenceBandOffset
Unit = "eV" >
1.346 </ValenceBandOffset>
<BandGap
Unit = "eV" >
1.519 </BandGap>
<BandGapAlpha
Unit = "eV/K" >
0.5405e-3 </BandGapAlpha>
<BandGapBeta
Unit = "K" >
204 </BandGapBeta>
<ElectronMass
Unit = "m0" > 0.067 </ElectronMass>
<EpsStatic
> 12.93 </EpsStatic>
<EpsOptic
> 10.10 </EpsOptic>
<LOPhononEnergy
Unit = "eV" >
35e-3 </LOPhononEnergy>
<LOPhononWidth
Unit = "eV" >
3e-3 </LOPhononWidth>
<DeformationPotential
Unit = "eV" >
-9.36 </DeformationPotential>
<MaterialDensity
Unit = "kg/m^3" >
5.3616e3 </MaterialDensity>
<VelocityOfSound
Unit = "m/s" >
4.73e3 </VelocityOfSound>
<AcousticPhononEnergy
Unit = "eV" >
5e-3 </AcousticPhononEnergy>
<Lattice_a
Unit="nm" >
0.56611 </Lattice_a>
<Elastic_c11
Unit="GPa" >
12.5 </Elastic_c11>
<Elastic_c12
Unit="GPa" >
5.34 </Elastic_c12>
<Elastic_c44
Unit="GPa" >
5.42 </Elastic_c44>
<Piezo_e14
Unit="C/m^2" >
-0.015 </Piezo_e14>
</Material>
ConductionBandOffset
[eV] energy
value that defines the position of the conduction band edges on an
absolute energy scale (The zero point of energy is arbitrary.)
It can be used to define a conduction band offset between two different
materials.
ValenceBandOffset
[eV] energy
value that defines the position of the average valence band edge energy Ev,av on an
absolute energy scale (The zero point of energy is arbitrary.)
It can be used to define a valence band offset between two different
materials.
average valence band edge energy: Ev,av = ( Ehh + Elh
+ Eso ) / 3
BandGap
[eV] band gap
at the Gamma point given for T = 0 K
If the band gap is specified here for another temperature, the
Varshni parameters alpha and beta should be set to zero.
BandGapAlpha [eV/K]
Varshni parameter alpha to allow for temperature dependent band gap
BandGapBeta [K]
Varshni parameter beta to allow for temperature dependent band
gap
BandGap , BandGapAlpha , BandGapBeta are not used inside the calculation. They are just needed to output the valence
band edge (which is not used either.)
ElectronMass
[m0] isotropic
effective electron mass of the Gamma conduction band
EpsStatic
[] static dielectric constant,
low frequency dielectric constant epsilon(0)
EpsOptic
[] optical dielectric constant, high frequency dielectric constant
epsilon(infinity)
LOPhononEnergy [eV]
longitudinal optical (LO) phonon energy EOP
(This parameter must not be set to zero as there will be a divison by zero in
this case, see p. 44 of PhD thesis of Peter Greck: NOP = 1 / [
exp(EOP/(kBT)) - 1 ]...
= 1 / (1 - 1) = NAN ("not a number"))
NOP is the phonon distribution and a prefactor of the equation
(eq. (7.5)) where the LO phonon scattering strength is calculated, i.e. if NOP
<< 1, then the LO phonon scattering is rather small.
NOP = 8 * 10- 45 for GaAs at T =
4 K (EOP = 35 meV in GaAs)
NOP = 1.3 * 10- 6 for GaAs at T =
30 K
NOP = 0.000297 for GaAs at T = 50 K
NOP = 0.017524 for GaAs at T = 100 K
NOP = 0.151055 for GaAs at T = 200 K
NOP = 0.348148 for GaAs at T = 300 K
LOPhononWidth [eV]
This is a numerical value that avoids reducing the coupling strength to a
delta function: E + EOP ==>
E +
EOP +- Delta E/2, where Delta E =
LOPhononWidth
The following variables are only relevant for acoustic phonon scattering.
DeformationPotential [eV]
scalar deformation potential - It is used for acoustic phonon scattering.
MaterialDensity
[kg/m^3] material density or mass
density
VelocityOfSound
[m/s] sound velocity
AcousticPhononEnergy [eV]
acoustic phonon energy
The following variables are relevant for strain calculations.
Lattice_a
[nm] lattice
constant a
Elastic_c11
[GPa] elastic
constant c11
Elastic_c12
[GPa] elastic
constant c12
Elastic_c44
[GPa] elastic
constant c44
Piezo_e14
[C/m^2] piezoelectric constant e14
For ternary compounds like AlxGa1-xAs, we have to
specify bowing parameters.
The material parameters in many ternary alloys (AxB1-xC
or CAxB1-x) can be approximated in the form of the usual
quadratic function
TABC = xBAC + (1- x) BBC
- x(1- x)CABC
where CABC is the bowing parameter.
<!-- ternary compounds -->
<Material>
<Name>In(x)Ga(1-x)As</Name>
<Alloy>InAs(x)</Alloy>
<Alloy>GaAs(1-x)</Alloy>
<ValenceBandOffset Unit = "eV" >
-0.38 </ValenceBandOffset>
<BandGap Unit = "eV" >
0.477 </BandGap>
<BandGapAlpha Unit = "eV/K" >
0 </BandGapAlpha>
Currently, the Varshni parameters alpha and beta are
interpolated. It is probably better to interpolate the band gap instead.
<BandGapBeta
Unit = "K" >
0 </BandGapBeta>
<ElectronMass Unit
= "m0" > 0.0091</ElectronMass>
<EpsStatic
> 0 </EpsStatic>
<EpsOptic
> 0 </EpsOptic>
<DeformationPotential
Unit = "eV" >
2.61 </DeformationPotential>
<MaterialDensity
Unit = "kg/m^3" > 0
</MaterialDensity>
<VelocityOfSound
Unit = "m/s" > 0
</VelocityOfSound>
<LOPhononEnergy Unit = "eV" >
0 </LOPhononEnergy>
<LOPhononWidth
Unit = "eV" >
0 </LOPhononWidth>
<AcousticPhononEnergy
Unit = "eV" >
0 </AcousticPhononEnergy>
</Material>
<!-- quaternary compounds -->
<Material>
<Name>In(x)Ga(y)Al(1-x-y)As</Name>
<Alloy>InAs(x)</Alloy>
<Alloy>GaAs(y)</Alloy>
<Alloy>AlAs(1-x-y)</Alloy>
</Material>
It is recommended to use position dependent material parameters, i.e.
for parameters like LO phonon energy, deformation potential, sound velocity,
material density and acoustic phonon energy.
Obviously, the Büttiker probes B(x) depend on position.
But in fact, the
parameters for the wells are the most important ones.
The parameters in the
barriers have only a minor influence.
One can include them in the calculation
but the Büttiker probes in the barriers should not have any significant
influence on the final result.
Back to nextnano.MSB |