DC Characteristics of a MESFET

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DC Characteristics of a MESFET

This model compares the current-voltage characteristics of a MESFET using the majority carrier only formulation.

MOSFETs and MESFETs (metal-semiconductor field-effect transistor) work very similarly. In a MESFET, the gate forms a rectifying junction that controls the opening of the channel by varying the depletion width of the junction.

In this model we simulate the response of a n-doped GaAs MESFET to different drain and gate voltages. For a n-doped material the electron concentration is expected to be orders of magnitude larger than the hole concentration. Accordingly, it is possible to use the majority carrier option to compute an accurate solution with less degrees of freedom then it would normally be needed using the electrons and holes formulation.

Model Definition

The model compares the effect of the carrier formulation on the solution of a 2D MESFET biased with different gate (0, 1, and 2 V) and drain (from 0 to 10 V) voltages.

The geometry is composed of a block of 4 by 0.5 μm. The Schottky contact (gate) has a length of 1 μm. The source (top left) and drain (top right) have both a length of 0.5 μm. Figure 1 shows the model’s geometry.

Figure 1: Geometry of the modeled MESFET.

Results and Discussion

Figure 2 plots the drain current as a function of the drain voltage for both studies (electrons and holes and majority carrier only). The result is identical. Note that the number of degrees of freedom used for the first study (electrons and holes) is 1.5 times larger than the number of degrees of freedom used for the second study (majority carrier only).

Figure 2: Drain current as a function of the drain voltage for the electrons and holes and for the majority carrier only (asterisk).

Semiconductor_Module/Transistors/mesfet

Modeling Instructions

From the menu, choose .

In the window, click

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In the window, click

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In the tree, select .

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Global Definitions

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In the window, under click .

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In the window for , locate the section.

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In the table, enter the following settings:


Name	Expression	Value	Description
L	1[um]	1E-6 m	Gate length
Wd	4[um]	4E-6 m	Device width
Hd	0.5[um]	5E-7 m	Device height
Ws	1[um]	1E-6 m	Source width
Wdd	1[um]	1E-6 m	Drain width
Vg	0[V]	0 V	Gate voltage
Vd	0[V]	0 V	Drain voltage
Vs	0[V]	0 V	Source voltage
Nd	1e16[1/cm^3]	1E22 1/m³	Doping

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In the window, under click .

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In the window for , locate the section.

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From the list, choose .

Rectangle 1 (r1)

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In the toolbar, click

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In the window for , locate the section.

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In the text field, type Wd.

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In the text field, type Hd.

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Locate the section. In the text field, type -Wd/2.

Add points to define the source, drain and gate contacts.

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In the toolbar, click

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In the window for , locate the section.

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In the text field, type -Wd/2+Ws/2 -L/2 L/2 Wd/2-Ws/2.

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In the text field, type Hd Hd Hd Hd.

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In the toolbar, click

to open the window.

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Go to the window.

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In the tree, select .

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Click in the window toolbar.

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In the toolbar, click

to close the window.

Semiconductor (semi)

Metal Contact 1

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In the window, under right-click and choose .

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In the window for , locate the section.

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From the list, choose .

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Select Boundary 5 only.

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Locate the section. In the V0 text field, type -Vg.

Metal Contact 2

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In the toolbar, click

and choose .

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Select Boundary 3 only.

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In the window for , locate the section.

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In the V0 text field, type Vs.

Metal Contact 3

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In the toolbar, click

and choose .

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Select Boundary 7 only.

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In the window for , locate the section.

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In the V0 text field, type Vd.

Analytic Doping Model 1

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In the toolbar, click

and choose .

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Select Domain 1 only.

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In the window for , locate the section.

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From the list, choose .

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In the ND0 text field, type Nd.

Trap-Assisted Recombination 1

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In the toolbar, click

and choose .

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Select Domain 1 only.

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In the window for , locate the section.

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From the τn list, choose . From the τp list, choose .

Adjust the mesh slightly.

In the window, under right-click and choose .

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In the window for , locate the section.

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From the list, choose .

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In the toolbar, click

to open the window.

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Go to the window.

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Find the subsection. In the tree, select .

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Click in the window toolbar.

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In the toolbar, click

to close the window.

Step 1: Stationary

Set up an auxiliary continuation sweep for the ’Vd’ parameter.

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In the window for , click to expand the section.

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Select the check box.

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In the table, enter the following settings:


Parameter name	Parameter value list	Parameter unit
Vg (Gate voltage)		V

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In the table, enter the following settings:


Parameter name	Parameter value list	Parameter unit
Vg (Gate voltage)	0 1 2	V
Vd (Drain voltage)	range(0,1,10)	V

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From the list, choose .

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From the list, choose .

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In the toolbar, click

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1D Plot Group 4

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In the toolbar, click

and choose .

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In the window for , locate the section.

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From the list, choose .

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Right-click and choose .

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In the window for , click in the upper-right corner of the section. From the menu, choose .

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Locate the section. In the table, enter the following settings:


Expression	Unit	Description
semi.I0_3	A	Electrons and holes

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In the toolbar, click

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1

In the toolbar, click

to open the window.

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Go to the window.

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Find the subsection. In the tree, select .

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Click in the window toolbar.

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In the toolbar, click

to close the window.

Step 1: Stationary

1

In the window for , locate the section.

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Select the check box.

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In the table, enter the following settings:


Parameter name	Parameter value list	Parameter unit
Vg (Gate voltage)		V

5

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In the table, enter the following settings:


Parameter name	Parameter value list	Parameter unit
Vg (Gate voltage)	0 1 2	V
Vd (Drain voltage)	range(0,1,10)	V

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From the list, choose .

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From the list, choose .

Semiconductor (semi)

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In the window, under click .

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In the window for , locate the section.

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From the list, choose .

In the toolbar, click

.

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In the window, under right-click and choose .

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In the window for , locate the section.

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From the list, choose .

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Locate the section. In the table, enter the following settings:


Expression	Unit	Description
semi.I0_3	A	Majority carriers only

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Click to expand the section. Find the subsection. From the list, choose .

1D Plot Group 4

1

In the window, click .

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In the window for , locate the section.

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Select the check box.

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In the associated text field, type Drain voltage (Vd).

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Select the check box.

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In the associated text field, type Terminal current (A).

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In the toolbar, click

.