<< Chapter < Page Chapter >> Page >

The surface recombination velocity parameter not only affects the base current, it also affects the base current in all of the operating regions. Therefore, it is a powerful parameter to approximately match the base current and gain throughout the full operating range. In some cases, the base current may be less affected in the very high and very low injection regions by changes in the surface recombination velocity, and adding some scope to fine tuning the profile of the base current versus base-emitter voltage curve.

It is important to define the poly-emitter as an electrode so it can define the interfacial surface recombination velocity, VSURFN and VSURFP, using the CONTACT statement. This is in contrast to the MOSFET calibration text where we strongly advise you not to define the polygate as an electrode. Be sure not to get these two confused. The parameter that activates the recombination velocity is SURF.REC, which is also in the CONTACT statement. For example, an NPN BJT statement would be:


A lower value of recombination velocity, VSURFP, will reduce the base current and increase the gain, hfe. The reverse is also true.

7.9.3: Tuning the Collector Current – All Regions

Figure 7.43 shows the parameter that affects the collector current over the entire range is the intrinsic base resistance. The base resistance is primarily determined by the dose of the base implant(s). An increase in the base implant dose will decrease the intrinsic base resistance and decrease the collector current in all injection regions. In some cases, however, the collector current may be affected a little in the very high injection region, giving scope for fine tuning the profile of collector current versus base- emitter voltage.

Figure 7.43: Effect of base doping profile on low injection base current in BJT

If the pinched or intrinsic base sheet resistance is a measured parameter, the simplest way to match measured and simulated data is to make slight changes to the base implant dose so that the simulated dose is not outside the expected error in actual implanted dose in conjunction with the error in percentage activation.

In some designs, where the base contact is close to the collector contact or the base contact is the substrate or is generally wide, the collector current can also influence all current injection regions by specifying a surface recombination velocity at the base contact. For a typical design with a buried n+ collector and surface contacts, the surface recombination velocity at the base contact may have little affect on the collector current.

7.9.4: The Base Current Profile – Medium Injection

In ATLAS, there are two major parameters that have a significant affect on the base current in the medium injection regime. These parameters are the Poly-emitter Work Function and the Bandgap Narrowing Effect. These parameters are described below.

Poly-emitter work function

If the poly-emitter is described as N.POLYSILICON in the CONTACT statement for an NPN device, as already described, the Poly-emitter Work Function is then set to 4.17 V and is correct for saturation doped n++ polysilicon. But if the poly-emitter is not saturation-doped, the work function will differ from this ideal and have a pronounced affect on the base current and current gain in the medium injection regime as shown in Figure 7.44. The work function of the poly-gate can vary from 4.17 V for n++ poly-silicon to (4.17 V + Eg) for p++ polysilicon, depending on the position of the Fermi-Energy. Changing the work function of the poly-emitter by just 0.1 V from 4.17 V to 4.27 V can often reduce the current gain in half in the medium injection regime, so it’s very important to assign the correct value. The CONTACT statement below assigns a work function of 4.27 eV to the poly-emitter, while keeping the other parameters the same as before.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Solid state physics and devices-the harbinger of third wave of civilization. OpenStax CNX. Sep 15, 2014 Download for free at http://legacy.cnx.org/content/col11170/1.89
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Solid state physics and devices-the harbinger of third wave of civilization' conversation and receive update notifications?