Parameter definitions for "poisson"
It's probably useful to look first at the special features page. You may also want to look at one of the general help files, Sliders, or
Graphs.
Inputs
- SLIDERS
- Nd: donor concentration, per centimeter^3, on the n-side of the pn-junction. (Restricted to positive values.)
- Na: acceptor concentration, per centimeter^3, on the p-side of the pn-junction. (Restricted to positive values.)
- E_gap: semiconductor energy gap, in electron-volts. (Restricted to positive values.)
- V_applied: external voltage, in volts, applied to the device: defines the difference in chemical potential at the two ends of the device. For the pn-junction, the forward bias is limited to one-half of (energy gap)/e.
- Ni: doping concentration, per centimeter^3, for the MIS diode: (Nd for the n-type choice and Na for the p-type choice of material). (Restricted to positive values.)
- N_int: interface trap density, per (centimeter^2)*(electron-volt), at the insulator-semiconductor interface in the MIS-diode. The surface is neutral when the chemical potential at the interface is midgap. (Restricted to positive values.)
- Dins: thickness, in centimeters, of the insulator in the MIS-diode. (Restricted to positive values.)
- MENUS
- device: "poisson" provides simulation of either:
- pn junction: the pn-junction, or
- MIS diode: the metal-insulator-semiconductor diode.
- solution: for the pn-junction, the densities and energies may be calculated in two ways (only the 'exact' algorithm is used for the MIS diode):
- 'exact': with only the assumption of the chemical potential being well within the gap; or
- approx.: an approximate scheme in which the carrier densities are assumed to change abruptly from equilibrium value to zero on entering the carrier depletion zone.
- TOGGLES
- autoscale: defeats the autoscaling of the graphs: useful in keeping scales fixed while following systematic variations induced by parameter changes. (Autoscaling can also be defeated by framing the whole, or a portion, of a graph with a zoom. See Graphs.)
- BUTTONS
- copy densities: copies the densities graph for further manipulation. See Graphs.
- copy energies: copies the energies graph for further manipulation. See Graphs.
- presets: Takes you to a tear-off menu with which you may select the presets. For more details, see the preset item in the miscellaneous help file.
- configure: provides opportunity to change more parameters than you will ever need:
- A_metal: work function, in electron-volts, for transfer of an electron from the metal to the conduction band of the insulator. (Restricted to positive values.)
- A_semi: conduction band offset, in electron-volts, of the insulator with respect to the semiconductor. (Restricted to positive values.)
- step size: adjusts the step size, as a percentage of the departure of the band edge from the bulk value (or of 3kT for the MIS diode), in the numerical integrations. Coarser steps imply less accurate and faster calculation. (Restricted to positive values.)
- energy cutoff: energy departure from the bulk value at which the numerical integration is halted. A larger cutoff implies less accurate and faster calculation. (Restricted to positive values.)
- spike width: an arbitrary constant, in centimeters, which is divided into surface charge densities on the metal surface and at the insulator-semiconductor interface to convert them to a volume density of a magnitude that allows representation on the densities graph. (Restricted to positive values.)
- dielectric constant--insulator: dimensionless constant. (Restricted to positive values.)
- dielectric constant--semiconductor: dimensionless constant. (Restricted to positive values.)
- revert: updates the listed configure parameters to the current values (which may have been changed by a preset command).
- close: closes the configure window.
- help: Opens the help system which you have already found!
- quit: Terminates "poisson".
Outputs
- DISPLAYS
- upper: electron (in red) and hole (in blue) densities, per centimeter^3, as a function of position. The black curve is the total charge density, divided by the magnitude of the electronic charge, to convert it to a signed number density. For the MIS-diode, spikes at the two sides of the insulator represent sheet charge densities, again normalized by e, at the metal surface and from the interface states at the insulator-semiconductor interface. The numerical value of the sheet density is obtained from the spike height times the arbitrary spike width, which is set in the configure menu.
- lower: the conduction band edges are shown in red for the semiconductor(s) and insulator (MIS-diode), and the valence band of the semiconductor(s) in blue. Doping impurity levels are indicated by dashed black lines. The chemical potential mu is shown in green, and is different at the two ends of the device if a voltage is applied.
- READOUTS
All charge densities are normalized to number densities by dividing by e, giving units of number per centimeter^2
- Qgate: charge density at the metal-insulator interface. (MIS-diode only)
- Qint: charge density associated with the states at the insulator-semiconductor interface. (MIS-diode only)
- Qinv: charge associated with minority carriers in an inversion channel. (MIS-diode only)
- Qdepl: for the MIS-diode, the charge associated with majority carriers, in either depletion or accumulation, plus impurity doping. For the pn-junction, the depletion layer charge on either side of the junction..
- Qtot: for the MIS-diode, the sum of the four terms above, Qtot, should be zero. Thus, Qtot is a measure of accuracy of the integrations.