template

Template

This folder contains template Comsol files to work with comsolkit.

General

A template file defines domains and materials, etc.

Since comsolkit is tag driven, some tags should be consistent in the template file (They are usually consitant anyway):

• The electrostatic physics feature should have the tag 'es'
• The study feature used for comsolkit should have the tag 'std'
• The stationary study feature should have the tag 'stat'
• The potential is obtained by evaluating the expression 'mod1.V'

When there are more then one geometry features (root feature containing the whole geometry tree), the first in the list is used.

Parameter driven template

It is a good idea to define parts of a template, that might change depending on the situation using parameters (accessed by set_param() or get_param() in comsolkit).

There are particularly four parameters that are recommended: origin_x, origin_y, l_domain, w_domain. The function comsolkit.GateLayoutModel.choose_domain_region() prints commands you can use to set them. They define the domain region, where the model is typically solved. See template_GaAs.mph section for more details.

template_GaAs.mph

A simple two block template, suspended in a infinite elements elepsoid.

Parameters

• l_domain: Length of domains
• w_domain: Width of domains
• t_vac: Thickness of upper domain (default: 500)
• t_hetero: Thickness of lower domain (default: 500)
• origin_x, origin_y: Coordinates of lower left point of domains (x,y)
• epsilon_vac: Dielectric constant of upper domain (default: 1)
• epsilon_hetero: Dielectric constant of lower domain (default: 13)
• t_2DEG: Depth of the 2DEG (default: -100)
• charge_density: Surface charge density at the 2DEG (default: 0)

Schematic

          (side view)
     ---------------------   /\
    |                     |  ||
    |     epsilon_vac     | t_vac     (upper domain)
    |                     |  ||
     ---------------------   \/ /\    (boundary at z=0)
    |                     |     ||
    |                     |     ||
     ---------------------      ||    (t_2DEG depth)
    |                     |     ||
    |    epsilon_hetero   |  t_hetero (lower domain)
    |                     |     ||
     ---------------------      \/

          (top view)
     ---------------------     /\
    |                     |    ||
    |                     |    ||
    |                     | w_domain
    |                     |    ||
    |                     |    ||
  x,+---------------------     \/
    y origin
     <------l_domain----->

template_GaAs_basic_comsol44.mph

Same as template_GaAs.mph but can be opened with comsol 4.4. It does not contain an infinite elements ellipsoid surrounding the two blocks.

Create template from scratch

It is possible to create a template just with LiveLink commands. The code below will recreate template_GaAs.mph (but without an infinite elements ellipsoid surrounding the two blocks).

%% Import/create
import com.comsol.model.*
import com.comsol.model.util.*

model = ModelUtil.create('Model');
geom1 = model.geom.create('geom1', 3);
geom1.lengthUnit('nm');

%% Parameters
model.param.set('t_2DEG', '-100', 'zPosition of the 2DEG');
model.param.set('chargeDensity', '0', 'Surface charge density of 2DEG');
model.param.set('epsilon_hetero', '13', 'Dielectric constant of lower domain');
model.param.set('epsilon_vac', '1', 'Dielectric constant of upper domain');
model.param.set('l_domain', '3000', 'Length of domain');
model.param.set('origin_x', '30000', 'Origin of domain corner');
model.param.set('origin_y', '23400', 'Origin of domain corner');
model.param.set('t_hetero', '500', 'Height of lower domain');
model.param.set('t_vac', '500', 'Height of upper domain');
model.param.set('w_domain', '1200', 'Width of domain');
model.param.set('infinit_thickness', '100', 'Thickness of the infinite element layers');

%% Geometry
blk1 = geom1.feature.create('blk1', 'Block');
blk1.set('size', {'l_domain', 'w_domain', 't_vac'});
blk1.set('pos', {'origin_x', 'origin_y', '0'});
%blk1.set('createselection', 'on');
blk1.name('Vacuum');
blk2 = geom1.feature.create('blk2', 'Block');
blk2.set('size', {'l_domain', 'w_domain', 't_hetero'});
blk2.set('pos', {'origin_x', 'origin_y', '-t_hetero'});
%blk2.set('createselection', 'on');
blk2.setIndex('layer', 't_hetero+t_2DEG', 0);
blk2.name('Hetero');
geom1.run;

%% Selections
box1 = model.selection.create('box1', 'Box');
box1.set('zmin', 't_2DEG');
box1.set('zmax', 't_2DEG');
box1.set('entitydim', '2');
box1.set('condition', 'inside');
box1.name('2DEG');

box2 = model.selection.create('box2', 'Box');
box2.set('zmin', '0');
box2.set('condition', 'inside');
box2.name('Vacuum');

box3 = model.selection.create('box3', 'Box');
box3.set('zmax', '0');
box3.set('condition', 'inside');
box3.name('Hetero');

%% Materials
mat1 = model.material.create('mat1');
mat1.materialModel('def').set('relpermittivity', {'epsilon_hetero'});
mat1.selection.named('box3');
mat1.name('Heterostruct');
mat2 = model.material.create('mat2');
mat2.materialModel('def').set('relpermittivity', {'epsilon_vac'});
mat2.selection.named('box2');
mat2.name('Vacuum');

%% Physics
es = model.physics.create('es', 'Electrostatics', 'geom1');
es.feature.create('sfcd1', 'SurfaceChargeDensity', 2);
es.feature('sfcd1').set('rhoqs', 'chargeDensity');
es.feature('sfcd1').selection.named('box1');

%% Mesh
mesh1 = model.mesh.create('mesh1', 'geom1');
mesh1.feature.create('ftet', 'FreeTet');
mesh1.feature('size').set('hauto', 3);
mesh1.run;

%% Study
std = model.study.create('std');
std.feature.create('stat', 'Stationary');