Using Materials in PLaSK

Physical properties of geometrical objects are defined by materials. During geometry definition, you assign a particular material or each object. In general, it should be a real material used in the modelled structure, however, it is not necessary. You can create your own material with any properties you want (see Custom Materials).

Getting Materials

PLaSK provides a number of predefined materials. They are stored in the default material database. In GUI, you can simple select them from a list. In Python, you can create them using the plask.material.get() function. The function takes the name of the material as an argument and returns the material object. For example, to create a material object representing gallium arsenide, you can use the following code:

geometry_object.material = plask.material.get('GaAs')

Materials can be simple ones or can be alloys with a variable composition. They may also have doping specified.

Naming Conventions

In PLaSK, names of simple materials are allowed to be arbitrary strings. However, when it comes to alloy names, specific rules apply. They must consist of element names, each accompanied by a composition fraction. The composition fractions for elements within a single group of the periodic table must add up to one. Alternatively, the composition of one element from a group can be omitted, and it will be calculated from the rest of the elements in the group. Valid examples of alloy names include Al(0.2)Ga(0.8)As, Al(0.35)GaAs, Al(0.3)In(0.1)GaAs, and Ga(0.8)InN(0.1)As.

For custom materials, as explained in the sections on custom materials exploration and custom materials in Python, alloy names can include an optional label tag. This tag is placed after the components and separated by an underscore (_). For instance, Al(0.2)GaAs, Al(0.2)Ga(0.80)As_custom, and Al(0.2)Ga(0.80)As_modified represent three distinct materials with the same composition.

Doping in materials can be specified by adding a doping specification after a colon (:). The specification is a string containing the doping element and doping concentration, separated by an equal sign. For example, GaAs:Si=1e18 denotes a GaAs material doped with silicon to a concentration of 1×10¹⁸ cm^-3. It is worth noting that the doping specification can be omitted; in such cases, the material is considered undoped. For example, GaAs represents an undoped GaAs material.

In any case, the used material name, including doping must either exist in PLasK database or must be defined as a custom material. Otherwise, an error will be raised if you try to use it. For example GaAs:Si=1e18 will be recognized as gallium arsenide doped with silicon to a concentration of 1×10¹⁸ cm^-3, but GaAs:N=1e18 will raise an error, because GaAs doped with nitride is not defined in PLaSK database. However, you may define it on your own (see Custom Materials) and then use it.

Materials with modified properties

If you need to define a material with one or more properties changed and consider defining a new material an overkill, you may add [property1=value1 property2=value2] after a material name (with optional space between the material name and [). For example, GaAs [Eg=1.5] will create a material with the same properties as gallium arsenide, but with the band gap set to 1.5 eV.

Material properties

Materials are Python objects of class plask.material.Material. They have a number of methods that return the material properties. These properties may depend on a number of arguments (e.g. most of them depend on temperature). The following table lists all properties and their arguments.

Parameter	Arguments	Unit	Description
A	T	1/s	Monomolecular recombination coefficient
absp	lam, T	cm-1	Absorption coefficient
ac	T	eV	Hydrostatic deformation potential for the conduction band
av	T	eV	Hydrostatic deformation potential for the valence band
B	T	cm3/s	Radiative recombination coefficient
b	T	eV	Shear deformation potential
C	T	cm6/s	Auger recombination coefficient
Ce	T	cm6/s	Auger recombination coefficient for electrons
Ch	T	cm6/s	Auger recombination coefficient for holes
c11	T	GPa	Elastic constant
c12	T	GPa	Elastic constant
c13	T	GPa	Elastic constant
c33	T	GPa	Elastic constant
c44	T	GPa	Elastic constant
CB	T, e, point	eV	Conduction band level
chi	T, e, point	eV	Electron affinity χ
cond	T	S/m	Electrical conductivity
cp	T	J/(kg K)	Specific heat at constant pressure
D	T	cm2/s	Ambipolar diffusion coefficient
dens	T	kg/m3	Density
Dso	T, e	eV	Split-off energy
e13	T	C/m2	Piezoelectric constant
e15	T	C/m2	Piezoelectric constant
e33	T	C/m2	Piezoelectric constant
EactA	T	eV	Acceptor ionization energy
EactD	T	eV	Donor ionization energy
Eg	T, e, point	eV	Energy band gap
eps	T		Static dielectric constant
Eps	lam, T, n		Complex permittivity tensor dependent on the wavelength
lattC	T, x	Å	Lattice constant
Me	T, e, point	m0	Electron effective mass in in-plane (lateral) and cross-plane (vertical) direction
Mh	T, e	m0	Hole effective mass in in-plane (lateral) and cross-plane (vertical) direction
Mhh	T, e	m0	Heavy hole effective mass in in-plane (lateral) and cross-plane (vertical) direction
Mhl	T, e	m0	Light hole effective mass in in-plane (lateral) and cross-plane (vertical) direction
mob	T	cm2/(Vs)	Majority carriers mobilit in in-plane (lateral) and cross-plane (vertical) direction
mobe	T	cm2/(Vs)	Electron mobility in in-plane (lateral) and cross-plane (vertical) direction
mobh	T	cm2/(Vs)	Hole mobility in in-plane (lateral) and cross-plane (vertical) direction
Mso	T, e	m0	Split-off mass
Na		cm-3	Acceptor concentration
Nc	T, e, ``point	cm-3	Effective density of states in the conduction band
Nd		cm-3	Donor concentration
Nf	T	cm-3	Free carrier concentration
Ni	T	cm-3	Intrinsic carrier concentration
Nr	lam, T, n		Complex refractive index
nr	lam, T, n		Real refractive index
Nv	T, e, point	cm-3	Effective density of states in the valance band
Psp	T	C/m2	Spontaneous polarization
taue	T	ns	Monomolecular electrons lifetime
tauh	T	ns	Monomolecular holes lifetime
thermk	T, h	W/(m K)	Thermal conductivity
VB	T, e, point, hole	eV	Valance band level offset
y1			Luttinger parameter
y2			Luttinger parameter
y3			Luttinger parameter

The meaning of parameters arguments is as follows:

Symbol	Description	Unit
T	Temperature	K
lam	Wavelength	nm
e	Lateral strain
x	Lattice parameter
point	Point in the Brillouin zone. '*' means minimum bandgap.
hole	Hole type. 'H' means heavy hole, 'L' means light hole.
h	Layer thickness	µm
n	Injected carriers concentration	cm-3

Material Parameters Preview in GUI