What is the Best Strategy to Prepare EDC for GATE Exam?
Hi guys today I’ll be sharing my strategy for how to prepare for Electronic Devices and Circuits for GATE . It’s one of the easiest subject from GATE point of view the only hard part is to memorize all the formulae from various topics apart from that it’s the least time consuming subject in respect to the weightage it shows in GATE exam . EDC cousrse basically provides you with understanding of device physics which also forms a base for various circuit analysis and design courses.
In recent year level of question as well as the weightage of EDC in GATE exam has increased,from last 4 year anlaysis the minimum weightage seen for this subject was 6 and maximum was 12 in 2018 and 2017 it was one of the highest weighted subject and most of the toppers scored full marks in this subject .
Good knowledege of this subject can also help you after GATE in interviews of various IIT’s and PSU .If someone is looking forward to do specialization in Microelectronics this is one of the core subjects of this field ,where you will further learn in depth about device physics and after masters you can start your carrer as device engineer , a good device engineer are very higly paid.
Here I have mentioned the GATE syllabus and i have divide it in parts and in next section i’ll pick out each part and discuss what to prepare and important topics for GATE
- Semiconductor Physics:
Energy bands in intrinsic and extrinsic silicon, Carrier transport: diffusion current, drift current, mobility and resistivity, Generation and recombination of carriers ,Poisson and continuity equations.
P-N junction, Zener diode.
BJT, MOS capacitor, MOSFET .
- Photovoltaic devices
LED, photo diode and solar cell .
- Integrated circuit fabrication process:
oxidation, diffusion, ion implantation, photolithography and twin-tub CMOS process.
SYLLABUS DESCRIPTION AND PREPRATION STRATERGY
I would recommend you to give around 10 to 13 days for EDC in which you’ll have to cover theory, previous year GATE paper questions and solve some extra material for question practice . First of all, before starting this topic all of you should have basic idea about semiconductor, metals, and insulators, how are they classified, band model and bond model, direct and indirect band gap materials.
1). SEMICONDUCTOR PHYSICS (2-3 days)
This topic is some what between easy and moderate level ,but very important as it forms the basics for your further topics . Most of the parts are easy but few parts which are tricky and from which you can expect good level of questions are –
Enerdy band digram.
Graded impurity distribution.
Carrier generation and recombination.
This topic deals with semiconductor physics(particularly silicon) basically to study about properties of the semiconductor.
Silicon crystal structure ,no of valence electron ,Energy band gap etc. Graph related question can be sometime tricky so one should have good understanding of theory to answer those.
In intrinsic semiconductor study about its eletrical property like conductivity and it’s variation with temperature then mobility variation with temperature , velocity saturation at high electric field and understand graph of µ vs T and σ vs T Vd (drift velocity)vs E.
Then calculation position of intrinsic fermi level , calculation of electrons n and hole concentration p ,calculation of intrinsic concentration,mass action law ,charge neutrality, graph of ni vs T and ln(σ ) vs 1/T Once your’e done with intrinsic semiconductor Physic slightly modifies for extrinsic semicoductor calculation ,extra parts that you should know is compensated doping , non degenartive and degenerative semiconductor,variation in nature of semiconductor with temperature.
in carrier transport you should learn about drift and diffusion current density and their expression for n type and p type ,diffusion constant and mobility, life time of carrier, diffusion length ,Einstein relation.
Graded impurity distribution is very important topic in this you shoul learn about non uniform doping ,relation between doping profile and Electric field ,plot of electric field for different doping profile ,current density at equilibrium,good level numerical and graphical question can be framed from it.
Hall effect mechanism , hall coefficient for n type p type and intrinsic semiconductor,hall voltage and it’s application are important, formula based question can be asked from this.
Enerdy band digram is one of the most important and hard topic in EDC if you don’t understand it future topics can be really difficult for you as it forms the base for understanding other devices ,you should learn variation of energy band with applied voltage ,calculation of electric field from slope of band digram and fermi level variation for equilibrium case (also for non -equilibrium but not in detail).
In Carrier generation and recombination process you should learn about phonon(thermal) geneneration and photo(light) generation, expression for excess charge carrier due to light excitation and net recombination rate at steady state.
Poisson and continuity equation is same as in EMT you should learn about Minority carrier continuity equation this equation helps you to sove various problem on steady state injenction in semiconductor due to different excitation.
After learning this topics you can easily analyze physics of any device .
2). Diodes (2 days)
In diode Band Digrams can be difficulty to understand and calculation of Diode parameter like depletion width ,junction potential.
As a pre requisite you should have a good understanding of electrostatic which you can cover from EMT.
In GATE most question are asked from Step graded pn junction so you should know how to plot charge density profile for step graded pn juction and to derive plot for Electric field from it and Potential plot from Electric field and your Energy band diagram is just an inversion of your potential plot.
Charge density →Electric field →Potential plot →Energy band diagram
you should should be very clear about how to draw plot for all these not only for step graded but for any profile and to derive the above parameter.
In last few years many questions are asked from Juction law in diode and flow of charge carrier through drift and diffusion which can confuse you
Diode capcitance in reverse and forward bais for abrupt and linear junction are also important and break down mechanism in diode and there relation with doping concentration and temperature.
Transient in diode can be a hard part some time syou can expect good question from diode switching.
You should also give some time to schottky diode ,One sided pn junction and understand metal semiconductor junction this helps you to study MOS capcacitor
3).Transistor ( 3 days )
BJT (half day)
This is very small and easy topic in EDC as most of the theory you cover in Anlaog circuits some extra things that you might find difficult can be Band digrams in equilibrium and diiferent baising region.
You should study Early effect and it effect on various parameter and punch through then you should cover breakdown in BJT in different junction and relation between breakdown Vceo and Vcbo.
You should also cover topic like minority carrier distribution in different operating region , BJT time delay factor and its cut off frequency, Ebers Moll model.
MOS CAPACITOR(2 days)
This is one of the most important topic in EDC it’s basically like studying OPAM in Analog ckt. This topics will require time to understand and many tricky questionss can be asked from this topic . Most of the students finds it very difficult to learn. First you should start with basic working of MOS capacitor in all three regime accumulation , depletion, and inversion and then you should study it’s band diagram in all the three region then you should start with C-V curve of MOS in this you should know the concept of surface potential , flat band voltage and threshold voltage. For studying flatband voltage Vfb you should understand the concept of workfunction for metal and semiconductor then you should study about trapped oxide charges and finally the complete expression for Vfb in term of bothFor threshold voltage Vt you should study the expression for depletion charge , surface potential at Vt. Depletion width in the semiconductor is calculated by doing one sided pn juction calculation. You should also study the calculation of inversion layer charge density. Then you should learn expression for capacitance in a different region (Cox , Cdep and Cinv) and in the inversion region, you should analyze both LFCV and HFCV curve. Finally you should study fixed oxide and interface traps charge and their effect on the C-V curve.
MOSFET (half day )
Again most of the MOSFET theory you cover in analog but prior to MOSFET, you study MOS capacitor which forms the base for MOSFET .
You should study various short channel effect in MOSFET which cause variation in its parameter and you should study variation in threshold voltage with variation in a parameter like length , oxide thickness , substrate doping etc.
You should study all the operating region of MOSFET and solve a problem related to finding operation region of different MOSFET in ckt and graph as well the expression of gm with respect to Vgs , Id .
4) PHOTOVOLTAIC DEVICES (1 DAY)
very easy and can be covered in no time, you should study about direct bandgap semiconductor and reaction between Eg and λ relation between material bandgap and cut in voltage and parameter like extraction efficiency , internal radiative efficiency and external efficiency.
In this you should learn about it’s working , operation region and parameter like photo current, dark current, Respositivity and expression for sensitivity and quantum effiency
It’s is the most important photovoltaic device with respect to GATE and can be some times hard for some students to learn , you learn it’s working and it’s I-V graph basically there are 4 parameter you should know Voc, Isc, Conversion efficiency and fill factor.
5)Integrated circuit fabrication process(half day)
these topics are very easy but most students don’t find proper material to study these topic .
- oxidation – study about wet and dry oxidation basically how much temprature is required and quality of oxide produce
- diffusion and ion implantation- both are used for the same purpose but study what is their specific application and temperature require to perform both and concept of annealing
- photolithography – In this you should cover topic likemasking, Photoresist , etching.
- twin-tub CMOS process – you should study all the steps required and in order for fabriaction.
This topic might come for one marks you can refer any device book for these process.
BOOKS TO BE USED
1). SEMICONDUCTOR PHYSICS and DEVICES 4e – DONALD A NEAMEN
This book is one of the best book for EDC it’s little hard to understand but once you’ll study this completely I can assure you that you won’t be losing any marks in EDC it cover every topic except fabrication process,many of it’s excersice question are directly given in GATE exam one should definetly refer this book for good understanding of EDC . DIODE, TRANSISTOR, PHOTOVOLTAIC DEVICES can be directly referred from this book GATE related every aspect is covered.
2). SOLID STATE ELECTRONIC DEVICES – BEN G STREETMAN
This book is also a really good book some what easier to understand and cover most of the syllabus for EDC in the gate.
REFERENCE MATERIAL: for refrence, you can use nptel , PDF are availabel for devices courses with really good content