HIGH SPEED DEVICES AND CIRCUITS Assignment Questions 1) Why Silicon Semiconductors are widely used in the VLSI applications? Hint: Refer Video on Introduction to Basic Concepts 2) What are the parameters for high speed circuits? Hint: Refer Video on Requirements for high speed circuits, devices and materials 3) Briefly explain the chemical properties and stability of silicon semiconductor materials. Hint: Refer Video on Classification and properties of semiconductor devices 4) How are compound semiconductors classified? Hint: Refer Video on Classification and properties of semiconductor devices 5) Briefly explain about Binary compound semiconductors. Hint: Refer Video on Classification and properties of semiconductor devices 6) Explain the ternary compound semiconductors with energy band gap versus lattice constant diagram? 7) Explain about the ternary compound semiconductor Gallium arsenide phosphide (GaAs (1-y) P y ).What are its applications? 8) Explain about the ternary compound semiconductor Gallium indium arsenide (Ga x In (1-x) As).What are its applications? 9) What is epitaxy? 10) How a diode can be fabricated using Gallium indium arsenide (Ga 0.47 In 0.53 As)? 11) Explain about the ternary compound semiconductor Aluminium gallium arsenide (Al x Ga (1- x) As) 12) What are the applications of Aluminium gallium arsenide when grown on gallium arsenide (GaAs) (i.e. the AlGaAs/GaAs hetrostructure)? Page 1 of 7
13) Briefly explain the crystal structure of Gallium Arsenide. Hint: Refer Video on Crystal structures in GaAs 14) Explain about the truncation of Gallium Arsenide unit cell by 100 and 110 planes. Hint: Refer Video on Crystal structures in GaAs 15) Explain about the truncation of Gallium Arsenide unit cell by 111 plane. Hint: Refer Video on Crystal structures in GaAs 16) What happens when the impurities from group-ii of the periodic table is added to the Gallium Arsenide (GaAs)? Which is the most popular p-type impurity added to GaAs? 17) What happens when the impurities from group-vi of the periodic table is added to the Gallium Arsenide (GaAs)? Which is the most popular n-type impurity added to GaAs? 18) What is an acceptor and donor impurity? 19) What are the three steps involved in GaAs technology for high speed devices? 20) Why a semi insulating GaAs substrate is required in GaAs technology for high speed devices? 21) What are the different ways to get semi insulating GaAs substrate? 22) How a semi insulating GaAs substrate is obtained using Chromium? 23) What are the various steps involved in the semi insulating GaAs substrate growth by liquid encapsulated Czochralsky method? 24) Explain about the EL 2 doped semi insulating GaAs substrate? 25) What are the basic requirements for the epitaxy of GaAs? 26) On what basis the different epitaxial techniques for GaAs are classified? Mention the different techniques? 27) What is vapour-phase epitaxy? On what basis the vapour phase epitaxy of GaAs is classified? What are they? Page 2 of 7
28) Briefly explain about the Halide process of GaAs epitaxial layer growth. 29) Briefly explain about the Hydride process of GaAs epitaxial layer growth. 30) Briefly explain about the Metal organic Chemical vapour deposition (MOCVD) or Organ metallic Chemical Vapour Deposition (OMCVD) process of GaAs epitaxial layer growth. 31) What are the advantages of Metal organic Chemical vapour deposition (MOCVD) compared with halide and hydride process? 32) Briefly explain about Molecular Beam Epitaxy. 33) What are the drawbacks of Molecular Beam Epitaxy. 34) What is the drawback of Knudsen-type effusion cells in Molecular Beam Epitaxy (MBE)? What is the alternative for that? 35) What is gas source MBE (Molecular Beam Epitaxy) and Metal Organic MBE (MOMBE) systems? 36) What is Liquid phase epitaxy? What are its advantages? 37) What are the different approaches used for GaAs device fabrication? Hint: Refer video on GaAs and InP Devices for Microelectronics 38) Explain about the C-V (Capacitance-voltage) characteristics of GaAs MOS capacitors. Hint: Refer video on GaAs and InP Devices for Microelectronics 39) Can the MOSFETs be realized with GaAs and InP? If yes, how they are realized and if no, why they cannot be realized? 40) What are the different contacts made by the metal with semiconductor? Briefly describe them. Page 3 of 7
41) Briefly explain about the rectifying contact of a metal with n-type semiconductor under thermal equilibrium condition. 42) Briefly explain about the rectifying contact of a metal with n-type semiconductor when forward biased. 43) Briefly explain about the rectifying contact of a metal with n-type semiconductor when reverse biased. 44) When does a metal-semiconductor make an ohmic contact and when it makes a rectifying contact? 45) Briefly explain about the ohmic contact of a metal with n-type semiconductor under different conditions: a) Thermal equilibrium b) Forward biased c) Reverse biased 45) Briefly explain about the metal contact on p-type semiconductor with Φ m (Work function of metal) < Φ s (Work function of semiconductor) under different conditions a) Thermal equilibrium b) Forward biased c) Reverse biased 46) Explain the I-V characteristics of metal- semiconductor contact on p-type semiconductor. 47) Explain the I-V characteristics of metal- semiconductor contact on n-type semiconductor. 48) Derive the expression for barrier height (Φ Bn ). 49) Is it easy or difficult to make ohmic contacts on n-type GaAs and other high band gap materials? Why? Hint: Refer video on Ohmic contacts on semiconductor (continued) Page 4 of 7
50) Briefly explain how to make an Ohmic contact on n- type GaAs. Hint: Refer video on Ohmic contacts on semiconductor (continued) 51) How an ohmic contact is made on p-type GaAs? Hint: Refer video on Ohmic contacts on semiconductor (continued) 52) How an ohmic contact is made on n-type and p-type InP? 53) Briefly explain the effect of interface state density (D it ) on Semiconductor surface layer. 54) Briefly explain the I-V characteristics of Schottky Barrier Diode on n-type semiconductor. Hint: Refer video on Fermi Level Pinning and I-V characteristics of Schottky Barrier Diode 55) What are the different mechanisms by which the electrons are transferred from semiconductor to metal? 56) Compare the I-V characteristics of GaAs and Silicon Schottky Diodes 57) Compare the Schottky Barrier Diode with the pn-junction diode. 58) What are the benefits of Schottky Barrier Diode? 59) Which are the Conduction mechanisms that give rise to Non-Ideal characteristics of Schottky Barrier Diode? 60) Briefly explain the Image Force lowering of the barrier effect in Schottky Barrier Diode. 61) Briefly explain the Quantum mechanical tunnelling effect in Schottky Barrier Diode. 62) Briefly explain the Insulating interfacial layer effect in Schottky Barrier Diode. 63) How the Quantum mechanical tunnelling and Image Force lowering of the barrier effect can be reduced? Briefly explain them. Page 5 of 7
64) Derive the expression for intrinsic Transconductance (g mo ). Hint: Refer video on MESFET: Effects of velocity saturation and velocity field characteristics 65) Briefly explain the velocity field characteristics of electrons in GaAs. Hint: Refer video on MESFET: Effects of velocity saturation and velocity field characteristics 66) Explain the I-V characteristics of metal- semiconductor contact on p-type semiconductor. 67) Explain the I-V characteristics of metal- semiconductor contact on n-type semiconductor. 68) Derive the expression for barrier height (Φ Bn ). 69) Is it easy or difficult to make ohmic contacts on n-type GaAs and other high band gap materials? Why? 70) Briefly explain how to make an Ohmic contact on n- type GaAs. 71) How an ohmic contact is made on p-type GaAs? 72) How an ohmic contact is made on n-type and p-type InP? 73) Can Indium arsenide be used in manufacturing of HEMTs (High electron mobility transistors)? If yes why it is used, if no why it cannot be used? 74) Briefly explain the cross Section of Indium Phosphide Based HEMT structure (AlInAs/GaInAs/InP). 75) Which are the different types of Indium Phosphide Based HEMT systems? Mention the applications of each of them. 76) Briefly explain the pulse/delta/ planar doped GaAs HEMT.What is its benefits? Page 6 of 7
78) Briefly explain the cross Section of Pseudomorphic HEMT. Hint: Refer video on Pseudomorphic HEMT and Heterojunction Bipolar Transistors 79) What is strained layer epitaxy? Briefly explain it? Hint: Refer video on Pseudomorphic HEMT and Heterojunction Bipolar Transistors 80) List the merits of Bipolar junction transistors? Hint: Refer video on Heterojunction Bipolar Transistors 81) What are the factors affected when the base width of the BJT is reduced in order to increase the speed? How it can be overcome? Hint: Refer video on Heterojunction Bipolar Transistors 82) What are the effects of increasing the doping concentration in the base region? Hint: Refer video on Heterojunction Bipolar Transistors Page 7 of 7