first time user guide to pn junction v1.31 - nanohub
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Network for Computational Nanotechnology (NCN) UC Berkeley, Univ.of Illinois, Norfolk State, Northwestern, Purdue, UTEP
First Time User Guide toPN Junction V1.31
Saumitra R Mehrotra*, Ben Haley & Gerhard Klimeck
Network for Computational Nanotechnology (NCN) Electrical and Computer Engineering
http://nanohub.org/resources/229 *[email protected]
Saumitra R Mehrotra
Outline
Introduction What is a PN Junction? Working of a PN Junction.
What can be simulated by in PN Junction Lab? What if you just hit “Simulate”? Examples
What if the doping is changed? What if the intrinsic region is included (e.g. PIN diode)?
Limitation/Comments References
Saumitra R Mehrotra
What is a PN Junction?
• A PN junction is a device formed by combining p-type ( doped with B,Al) and n-type (doped with P,As,Sb) semiconductors together in close contact.
• PN junction can basically work in two modes, » forward bias mode (as shown below: positive terminal connected to p
-region and negative terminal connected to n region) » reverse bias mode ( negative terminal connected to p-region and
positive terminal connected to n region)
PN junction device
Saumitra R Mehrotra
Working of a PN junction
Refer https://nanohub.org/resources/68 for a detailed discussion on operation of PN junction.
Forward Bias
Reverse Bias
Zener or Avalanche Breakdown
Voltage
Current I-V characteristic of a PN junction diode.
• PN junction diode acts as a rectifier as seen in the IV characteristic.
• Certain current flows in forward bias mode.
• Negligible current flows in reverse bias mode until zener or avalanche breakdown happens.
Saumitra R Mehrotra
What can be simulated in PN junction lab?
PN junction device structure
Specify P-type region length. (More number of nodes lead to higher resolution but also more compute time)
Specify N-type region length
Specify intrinsic region length
Specify doping level for P-type and N-type region.
Saumitra R Mehrotra
What can be simulated in PN junction lab?
PN junction material definition
Specify the material to be simulated (Si,Ge,GaAs)
Specify intrinsic minority carrier lifetime (s).
Saumitra R Mehrotra
What can be simulated in PN junction lab?
PN junction environment definition
Specify temperature (K).
Specify applied voltage and number of steps.
Saumitra R Mehrotra
What can be simulated in PN junction lab?
PN junction output plots
Default settings will simulate : PN junction diode in forward bias mode with, 1µm long P-type and N-type regions doped at 1e17 cm3.
Saumitra R Mehrotra
What if you just hit simulate?
• IV characteristic for PN junction in forward bias mode in default settings.
Knee voltage
• Current increases slightly till Knee Voltage*.
• Beyond it current rises exponentially.
*Refer https://nanohub.org/resources/68 for a detailed discussion on operation of PN junction.
Saumitra R Mehrotra
What if you just hit simulate?
• C ∝ d –1 [1]&[2] where, C : capacitance across PN junction
& d : depletion width* (insulating region
at the junction where carriers have diffused away or have been swept by the electric field.)
• Increasing bias decreasing depletion width Increasing Capacitance
C-V characteristic for PN junction in forward bias mode in default settings.
*Refer https://nanohub.org/resources/68 for a detailed discussion on operation of PN junction.
Saumitra R Mehrotra
What if you just hit simulate?
Built in charge, electric field and potential at equilibrium.
Built in charge
Built in electric field
N-region P-region
P-region N-region
Built in potential, Vbi= 0.834V
Saumitra R Mehrotra
What if you just hit simulate?
Built in charge, electric field and potential at forward bias Va=0.6V
Decreasing charge with applied bias due to thinning of depletion width.
P-region N-region
N-region P-region Decreasing electric field with applied bias due to thinning of depletion width.
Potential difference Vbi-Va= 0.234V
Positive bias at P side reduces the barrier leading to increase in diode current.
Increased diffusion of electrons across the barrier lowered by Va.
Saumitra R Mehrotra
What if doping is changed?
Doping= 1e16 cm3
Doping= 1e18 cm3
• Increasing doping leads to increasing built in potential, Vbi [1],[2].
Na : P region doping level (cm-3).
Nd : N region doping level (cm-3).
ni : Intrinsic carrier density (cm-3).
KbT : Thermal voltage (= 0.0259 V).
= Vbi
On changing doping for both n-type and p-type regions from 1e16 cm3 to 1e18 cm3.
Saumitra R Mehrotra
What if intrinsic region is included i.e PIN diode? On introducing an intrinsic region of length 0.2 µm with default setting.
Increased depletion width (d) due to addition of intrinsic region as seen in energy band diagram.
Junction Capacitance, Cj ∝ d-1
shows a decrease as seen in CV characteristic.
PIN diode (bold)
PN diode (light)
Saumitra R Mehrotra
Limitations/Comments
• Large physical dimensions (>10um) might lead to non convergence or large compute time.
• More nodes might be required for better convergence in some cases i.e. high doping in PN junction.
• PN junction currently performs steady state simulations only, no time dependent simulations are possible.
• Contacts during the simulation are considered to be ohmic (i.e. Current-Voltage,I-V curve is linear and symmetric).
Saumitra R Mehrotra
References PN junction theory • [1] PN junction OPERATION : https://nanohub.org/resources/68 • [2] “Semiconductor Device Fundamentals”, by R.F. Pierret
PADRE • [3] Dragica Vasileska; Gerhard Klimeck (2006), "Padre," DOI: 10254/
nanohub-r941.3. • [4] PADRE MANUAL :
http://nanohub.org/resource_files/tools/padre/doc/ index.html
Please report any comment/review at the following link, • https://nanohub.org/resources/pntoy/reviews If you reference this work in a publication, please cite as follows: • Matteo Mannino; Dragica Vasileska; Michael McLennan; Xufeng Wang; Gerhard Klimeck
(2005), "PN Junction Lab," DOI: 10254/nanohub-r229.9.