This video is taken from the CHARGE 100 course on Lumerical University.

## Transcript

In this unit we explore various simulation modes supported by the CHARGE solver.

The system of equations solved for a charge transport simulation allow both steady-state

and time-varying solutions.

In steady state, the time dependent terms of the equations become zero.

Steady-state simulations can be used to examine the system’s behavior at a fixed operating

point and are also useful when extracting small-signal parameters for a component for

instance for frequency response analysis.

The sources and boundary conditions are specified for a particular operating point and the steady-state

response of the system will be obtained by the solver.

Results may include a current-voltage plot such as the one shown here.

Alternatively, by specifying an initial condition for the carrier density and electrostatic

potential, the equations can be solved in a sequence of discrete times.

The time-dependent behavior of the component can then be used to directly evaluate its

transient response or extract its large-signal AC parameters.

For example, as illustrated here, the change in the response of the system as a function

of time can be simulated using this mode.

Users may be interested in simulation of frequency dependent characteristics of a system.

This is possible by using the small signal AC or SSAC mode of the CHARGE solver.

The small signal analysis is a computationally effective way of resolving the frequency domain

response of a semiconductor device to small perturbations where linear approximations

of the equations become valid.

For large signal response when the behavior of the semiconductor device is non-linear,

a full time-domain simulation should be performed.

For instance, as shown here, the frequency dependent capacitance of a diode can be easily

simulated.

Later in the course, we will walk you through some simple simulation examples for all the

solver modes mentioned in this unit.

In addition to the different modes offered by the CHARGE solver, the temperature dependence

of a semiconductor device performance and behavior can be considered by the CHARGE solver.

By default, CHARGE solver simulations are ISOTHERMAL.

This is a simulation mode with a uniform temperature applied to the entire simulation domain.

In this mode, temperature-dependent material properties are calculated for the adjusted

simulation temperature which by default is set to room temperature.

In addition, a NON-ISOTHERMAL simulation mode is also available which allows a spatially

varying non-uniform temperature map added to a region specified by the user.

This means that temperature-dependent material properties are locally varied across the simulation

domain based on the provided spatial temperature profile.

In this mode, Heat generation or loss is not calculated and therefore the temperature profile

remains unchanged during the simulation.

The most realistic temperature-dependent charge transport simulation mode offered by the CHARGE

solver is the COUPLED mode.

This is a self-consistent CHARGE and HEAT coupled simulation mode that solves a coupled

system of charge transport and heat transport equations.

This mode can be used to account for self-heating effects in semiconductor devices and their

influence on the performance.

Note that in this mode the HEAT solver runs in the background along with the CHARGE solver

and therefore requires a license for the HEAT solver on top of the CHARGE solver license.

Temperature dependent charge transport simulations are beyond the scope of this course and will

not be covered.