21. The energy is ______ when the electron is _____ to the nucleus.
Closer, Greater
Greater, Closer
Lesser, Closer
Closer, Lesser
Answer: A
The closer the electron is to the nucleus the greater is the holding influence of the nucleus and the greater is the energy required for the electron to break loose and become free.
22. The ____ electrons are said to be stronger than the ______
A. outer orbit, Inner orbit
B. Inner orbit, Outer Orbit
C. Both are same
D. None of the above
Answer: A
Outer orbit electrons are said to be stronger than inner orbit electrons because of their ability to break loose from the parent atom. These are called valence electrons.
23. Gallium arsenide is made up of
A. single element
B. compound of two elements
C. compound of three elements
D. compound of four elements
Answer: B
Gallium arsenide is a compound semiconductor that is defined as a compound of two elements whereas silicon is a single element semiconductor.
24. Gallium has ______ valence electrons.
A. two
B. three
C. four
D. five
Answer: B
Gallium has three valence electrons and arsenic has five valence electrons. These two are combined to form gallium arsenide.
25. Gallium arsenide is a
A. binary semiconductor
B. trinary semiconductor
C. ternary semiconductor
D. unary semiconductor
Answer: A
Gallium arsenide is a binary semiconductor and high temperatures should be avoided which might result in dissociation of the surface.
26. Addition of impurities is essential for creating switching devices.
A. true
B. false
Answer: A
It is necessary to introduce impurities into the semi-insulating GaAs to facilitate the creation of switching devices.
27. The behavior of the switching element is decided by
A. selection of impurity
B. concentration density
C. selection of impurity & concentration density
D. none of the mentioned
Answer: C
The selection of the impurity and its concentration density determines the behavior of the switching element.
The switching element is normally a pair of MOSFET transistors, one an N-channel device, the other a P-channel device.
28. ______ elements can act as either donors or acceptors.
A. group II
B. group III
C. group IV
D. group V
Answer: C
Group IV elements such as silicon can act as either donors (on Ga sites) or as acceptors (on As sites).
29. Which element is smaller?
A. arsenic
B. gallium
C. silicon
D. aluminum
Answer: A
Arsenic is smaller than gallium and silicon. The covalent radius of Ga is 1.26 Armstrong unit whereas for As is 1.18 Armstrong unit.
30. ______ is used as the dopant for the formation of n-type material.
A. aluminum
B. arsenic
C. silicon
D. gallium
Answer: C
Group IV impurities tend to occupy gallium sites. Silicon is used as the dopant for the formation of n-type material.
31. Increase in positive charge ___________ the effective nuclear charge.
A. increases
B. decreases
C. exponentially increases
D. does not affect
Answer: A
An increase in the positive charge of the nucleus results in an increase in the effective nuclear charge thereby increasing the effective atomic radius.
32. ___________ is used for the formation of p-type material.
A. beryllium
B. magnesium
C. beryllium and magnesium
D. aluminum
Answer: C
Group II elements such as beryllium and magnesium can be used for the formation of p-type materials.
33. Which is the lightest p-type dopant?
A. beryllium
B. magnesium
C. silicon
D. arsenic
Answer: A
Beryllium is the lightest p-type dopant for GaAs, deep implantation of the dopant atoms can be accomplished with less lattice damage.
34. _______ influences the properties of GaAs field-effect transistor.
A. length dependency
B. structural dependency
C. material dependency
D. orientation dependency
Answer: D
Orientation dependency influences the properties of GaAs field-effect transistors. Factors like etching of the crystal, ion implantation, and passivation introduce the concept of orientation dependency.
35. The ion is steered ________ of the lattice.
A. up the open directions
B. down the open directions
C. up the closed directions
D. down the closed directions
Answer: B
When a high-energy ion enters a single crystal lattice, the ion is steered down the open directions of the lattice. This steering is called axial channeling.
36. If the equivalent direction is not used ______ will be increased.
A. ion concentration
B. steering angle
C. area coverage
D. depth distribution
Answer: D
If a random equivalent direction is not used during ion implantation, the depth distribution will be greater than those predicted by range statistics which are used to establish penetration depth.
37. Electrons become hot in gallium arsenide when the energy of
A. lower valley electrons decreases
B. lower valley electrons rises
C. higher valley electrons decreases
D. higher valley electrons rises
Answer: B
In gallium arsenide, when the energy of lower valley electrons rises sufficiently at a higher electric field, the electrons become hot.
38. When electrons become hot, drift velocity
A. increases
B. decreases
C. remains the same
D. does not depend on drift velocity
Answer: B
When electrons become hot, there will be a reduction in the number of high mobility electrons and hence a decrease in drift velocity.
39. ______ is a direct gap material with a valence bond maximum.
A. silicon
B. gallium oxide
C. gallium arsenide
D. silicon arsenide
Answer: C
Gallium arsenide is a direct gap material with a valence bond maximum and conduction band minimum.
40. Narrow valleys correspond to
A. electrons with lower mass state
B. protons with lower mass state
C. electrons with a higher mass state
D. protons with higher mass state
Answer: A
Valleys with band structures that are narrow and sharply curved correspond to electrons with a low effective mass state while valleys that are wide are characterized by larger effective masses.
