# 0.19 Even semester2014-midsemester examination answers  (Page 2/3)

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1. XIV. What does the above Table refer to ? Describe the meaning of the terms entered in the boxes ? Answer: The angle between the Primary Flat of the Si Wafer and the Secondary Flat of the Si Wafer is ‘α’. Type tells if Si-Wafer is N-Type or P-Type. Orientation gives the cleavage plane Orientation in Miller Indices.[1/6+1/6+1/6=1/2Point]

XV. What do the different terms refer to in the above Integral Equation? Answer: N(E)=density of states per unit volume per unit energy, P(E) →Fermi-Dirac Statistics or the probability of occupancy at energy E by Fermions. dE → elemental energy, m*→effective mass of electron in the conduction band.X 0 →Fermi Level in Metal with respect to the bottom edge of the Conduction Band i.e.X 0 =E F - E C .[1/10+1/10+1/10+1/10+1/10=1/2 Points]

XVI.

In the adjacent equation and in Question XV, X 0 is the same parameter. What is this parameter. Answer: X 0 =E F - E C .[1/2 Point]

XVII.

What are the different parameters and what are their units ? Answer: E g is Band-Gap in eV and λ is the wavelength of the photon emitted accompanying the radiative transition from Conduction Band to the Valence Band.[1/4+1/4=1/2]

XVIII. Define the parameters and give the units ?

Semiconductor E g n i ε r (DC) ? ρ i (300K) N C N V
Si 1.12 1×10 10 11.7 5×10 22 /cc 3.2×10 5 3.2×10 19 /cc 1.8×10 19 /cc
Ge 0.67 2×10 13 16.2 4.4×10 22 /cc 48 1×10 19 /cc 5×10 18 /cc
GaAs 1.424 2.1×10 6 12.9 4.42×10 22 /cc 3.3×10 8 4.7×10 17 /cc 7×10 18 /cc

Answers: E g (eV) , n i (#/cc), ε r (DC) rel.permittivity (Dimensionless ), #density of atoms in the crystal , ρ i (300K) Intrinsic Resistivity in Ω-cm, N C _ Effective Density of States at E C, N V _ Effective Density of States at E V [1/14+1/14+1/14+1/14+1/14+1/14+1/14=1/7]

XIX.

Define the terms and give the units. v = 10 7 cm/s. What is this velocity. Answers: v drift = electric drift velocity(m/s), μ(mobility) (cm 2 /(V-s)), q=electric charge(Coulombs), τ scattering (Mean Free Path or Relaxation Time)(sec),m* e =effective mass of electron(Kg)[1/28,1/28,1/28,1/28,1/28,1/28,1/28, 1/28,1/28,1/28,1/28,1/28,1/28,1/28,=1/2]

XX.

This rule is called Matthiessen’s Rule. Define the parameter and give the units of the parameter. Answers:μ effective ,→ effective mobility, μ imp ,→mobility due to impurity scattering, μ lattice ,→mobility due to lattice scattering, cm 2 /(V-s), [1/8+1/8+1/8+1/8=1/2]

XXI.

What are these power laws. Answers: lattice scattering inverse 3/2 power law , impurity scattering 3/2 power law [1/4+1/4=1/2 points]

XXII. σ = qμn Define the terms and give the units. Answers: σ →conductivity(Siemens/cm), q→electronic charge(Coulomb),μ→mobility(cm 2 /(V-s),n→conducting electron number density[1/16+1/16+1/16+1/16+1/16+1/16+1/16+1/16=1/2 Points]

XXIII. What special information is given by this Table.

Metal Au Cu Ni Pt
Effective Mass/Free Mass of electron 1.1 1.01 28 13

Answers: Ni and Pt are heavy Fermionic Metals [1/4+1/4=1/2]

XXIV. What is the basic difference about electron transport reflected by the Table below ?

Element E F τ(femtosec) L(Angstrom) W F v e 1 (×10 5 m/s)
Li 4.7 9 90 9.96
Na 3.1 31 250 2.3 8.08
K 2.1 44 293 2.2 6.55
Cu 7.0 27 328 12.15
Ag 5.5 41 441.6 10.77
Ge E V +E G /2 2217 2106 1.16
Si E V +E G /2 767.6 729 1.16
GaAs E V +E G /2 4890 4645.5 1.16