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Chalmers Heterostructure Barrier Varactor Diode Model: CHAL_HBV

Symbol

Summary

The HBV diode is a unipolar device which consists of a symmetric layer structure. An undoped high band gap material (barrier) is sandwiched between two moderately n-doped, low band gap materials. The barrier prevents electron transport through the structure. When the diode is biased a depleted region builds up, causing a nonlinear capacitance voltage characteristic. For more information about the HBV's, see [1] .

An epitaxial layer structure of an N-barrier HBV is shown in the following figure.

Equivalent Circuit

The model of the HBV consists of a parasitic series resistance in series with a shunt- connected voltage dependent capacitance and conductance. L and Cp model parasitic elements, for example the airbridge and pad-to-pad capacitance.

Parameters

Name Description Unit Type Default
ID Element ID Text 1
A Device area um^2 HBV1
b Barrier thickness nm 0.02
s Undoped spacer layer thickness nm 0.0035
epsb Dielectric constant in the barrier material F/m 9.6e-11
epsd Dielectric constant in the modulation layer F/m 1.13e-10
1 Length of the modulation layer nm 250
N Number of barriers   4
Nd Doping concentration in the modulation layer m^-3 8e22
Rs Parasitic series resistance 10
T Device temperature K 26.85
a An empirical constant (I-V) A/(m^2K^2) 170
E0 An empirical constant (I-V) V/m 4.2e6
Fib An empirical constant (I-V) eV 0.17
Cp Parasitic pad-to-pad capacitance pF 0
L Series inductance (to model airbridge inductance) nH 0

Implementation Details

C-V Characteristic

An accurate quasi-empirical expression for the C-V characteristic of a homogeneously doped HBV is described in [2].

The voltage across the nonlinear capacitor is expressed as a function of its charge as:

where Q is the charge stored in the HBV and LD is the extrinsic Debye length:

The C-V characteristic for an HBV is symmetrical and the following figure shows the C-V characteristic for a typical HBV with the Chalmers model.

I/V Characteristic

The following figure shows the current density versus applied voltage for a typical AlGaAsHBV.

The current through the heterojunction barrier as a function of temperature and voltage can be described as:

where Eb is the electric field in the barrier and is expressed as a function of the voltage across the capacitor [2] as:

This IV-model is accurate when the thermionic emission dominates. To neglect the influence of leakage current, set a=0.

Layout

This element does not have an assigned layout cell. You can assign artwork cells to any element. See “Assigning Artwork Cells to Layout of Schematic Elements” for details.

References

[1] J. Stake, "Varactors," in Modern Microwave and RF Handbook, M.Golio, Ed.: CRC press, 2001.

[2] L.Dillner, J.Stake, and E.Kollberg, "Modeling of the heterostructure barrier varactor diode," presented at Int. Semiconductor Device Symp., Charlottesville, December 1997.

[3] J.Stake, L.Dillner, S.H.Jones, C.M.Mann, J.Thornton, J.R.Jones, W.L.Bishop, and E.L.Kollberg, "Effects of self-heating on planar heterostructure barrier varactor diodes," IEEE Transaction on Electron Devices, Vol.45, No.11, pp.2298-2303, 1998

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