Lab 6 – Parameter Extraction For Diodes
ELEC361 – Lab 6 – Parameter Extraction Procedures For Diodes
I.S. 21 April 2010
Introduction To Diode Parameters
Early "Point Contact" Semiconductor Diode Construction
Early Selenium Rectifiers & Small Signal Diodes
ac
+
Conection 1
Semiconductor Compound
Connection 2
Mounting Holes
240 Vac
ac
Wire Probe
Metal Base Plate
Early Selenium
Signal Diodes
Germanium Junction Diodes
Germanium Point Contact Diode
Si Planar Junction Diode Construction
Glass Case
Anode
Glass Body
Recombination
Anode
Site For Hole
And ElectronSiO Insulation
Pairs
Ge
Tunsten
Wire Contact
N-Germanium Crystal
Metal Base Connection
Cathode
As -
Holes
Boron Doped
Ge
+
As -
A
K
- Electron
Flow
Electrons
Sealing
Base
(Side View)
Metal Contact + Current
Flow
P Diffused Semiconductor
(Holes)
N Type Substrate
Diode Junction Formed
From P and N Doped
Semiconductor
Metal Base Contact
Cathode
According to the semiconductor junction diode diffusion model, the following I-V
model should predict diode current for any applied voltage within realistic limits
 q v 


I {v}= I s ⋅  e η k T − 1 




where
I {v} ≡ Diode current caused by applied voltage v in Amps
I s ≡ Diode " saturation " current in Amps
q ≡ Electron charge in Coloumbs (1.602 ⋅10 −19 C )
…(1)
k ≡ Boltzmann' s constant in Joules per degree Kelvin ( k ≅ 1 .381 ⋅10 − 23 J K −1 )
T ≡ Diode temperatur e in degrees Kelvin (T ≅ 298 K at room temperatur e )
η ≡ " Ideality factor " or " Emission coefficien t " − usually 1 ≤ η ≤ 2
v ≡ Voltage applied across the diode junction in Volts
We may consider an additional series resistance parameter Rs caused by the bulk
semiconductor resistance connecting the active diode junction to the outside world.
This would modify the actual voltage reaching the active junction as
 q (v − I {v}⋅ R ) 
s


− 1
I {v}= I s ⋅  e η k T




…(2)
Unfortunately, the predicted diode current I{v} is now dependent both on the applied
external voltage v and the diode’s output current I{v}. Therefore, extracting the
diode’s model parameters Is, η and Rs may require some thought! One approach might
be to consider v{I} instead
q
…(3)
v = 1 ⋅ Log e  I + 1  + I ⋅ Rs where g ≡
η kT
g

Is
This approach removes self-referenced dependency but might bias extracted
parameters towards a “best fit” voltage model rather than a “best fit” current one.
These lab 6 exercises will focus on data acquisition for semiconductor diodes. It will
also include 3-terminal BJT measurement. The next lab 7 will then analyse collected
data for parameter extraction and interpretation. Prior to this analysis, some
preliminary data interpretation would be advisable.
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Lab 6 – Parameter Extraction For Diodes
2. Data Collection Tasks
2.1. Semiconductor Diode Data Measurement
The ELVIS II platform measures I-V two-terminal devices. Run the two-terminal
analysis component and obtain a baseline offset current measurement for the
instrument using an appropriate voltage range (e.g. 0 V to 3.0 V) in 10 mV steps. Use
the “coarse sensitivity” setting – this allows currents to be measured up to 40 mA.
Save this data file to disk with an appropriate file name.
Connect a 1N4148 silicon junction diode to the platform in its forward bias direction.
Obtain an I{v} sweep. Save this data to disk with an appropriate file name.
Repeat the exercise with the medium sensitivity setting using appropriate settings.
Repeat the exercise with the highest sensitivity setting (lowest current range)
Replace the 1N4148 diode with a LED (red or other colour). Repeat all previous
exercises using appropriate instrument settings and file names.
Replace the LED with a Germanium point contact diode. Repeat all previous
measurement exercises.
This data will be analysed in the next lab so it is advisable to use file names that
convey enough information to allow any repeat measurements under identical
conditions if required.
2.2. Bipolar Junction Transistor (BJT) Data Measurement
Connect a BC54* BJT to the 3-terminal port on ELVIS II. Run a 3-terminal
measurement on the device and obtain five Ic of Vce traces using appropriate settings
(e.g. 0 < Ic < 40 mA and 0 < Vce < 5 V). Can you explain the data you observe in
terms of semiconductor physics? What is the approximate HFE? What is the
approximate collector resistance (∆Ic / ∆Vce) for each base bias current? What is the
approximate “Early Voltage”? Save the data to disk with an appropriate file name.
Repeat the exercise with the BJT operated in the reverse direction (i.e. swap collector
and emitter).
Now use the Function Generator to exercise the BJT collector voltage using a slow
triangle wave. Use a series resistor and measure the voltage across it using channel
AI_0 differential channel. Also measure the device Vce using channel AI_1. Use the
ELVIS II power supply to provide base bias through an appropriate resistor. Use five
base bias settings. Record all data for analysis and interpretation in next week’s Lab.
Again, it is advisable to use sensible file names to allow previous measurements to be
revisited if needed.
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