VLSI Multiple Choice Questions on “Doping Process of GA-1”.
1. Addition of impurities is essential for creating switching devices.
A. true
B. false
Answer: A
Clarification: It is necessary to introduce impurities into the semi-insulating GaAs to facilitate the creating of switching devices.
2. The behaviour 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
Clarification: Selection of the impurity and its concentration density determines the behaviour of the switching element.
3. ______ elements can act as either donors or acceptors.
A. group II
B. group III
C. group IV
D. group V
Answer: C
Clarification: Group IV elements such as silicon can act as either donor (on Ga sites) or as acceptors (on As sites).
4. Which element is smaller?
A. arsenic
B. gallium
C. silicon
D. aluminium
Answer: A
Clarification: 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.
5. ______ is used as the dopant for the formation of n-type material.
A. aluminum
B. arsenic
C. silicon
D. gallium
Answer: C
Clarification: Group IV impurities tend to occupy gallium sites. Silicon is used as the dopant for the formation of n-type material.
6. Increase in positive charge ___________ the effective nuclear charge.
A. increases
B. decreases
C. exponentially increases
D. does not affect
Answer: A
Clarification: Increase in positive charge of the nucleus results in an increase in the effective nuclear charge thereby increasing the effective atomic radius.
7. ___________ is used for the formation of p-type material.
A. beryllium
B. magnesium
C. beryllium and magnesium
D. aluminium
Answer: C
Clarification: Group II elements such as beryllium and magnesium can be used for the formation of p-type materials.
8. Which is the lightest p-type dopant?
A. beryllium
B. magnesium
C. silicon
D. arsenic
Answer: A
Clarification: Beryllium is the lightest p-type dopant for GaAs, deep implantation of the dopant atoms can be accomplished with less lattic damage.
9. _______ influences the properties of GaAs field affect transistor.
A. length dependency
B. structural dependency
C. material dependency
D. orientation dependency
Answer: D
Clarification: Orientation dependency influences the properties of GaAs field effect transistors. Factors like etching of the crystal, ion implantation and passivation introduces the concept of orientation dependency.
10. 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
Clarification: 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.
11. If equivalent direction is not used ______ will be increased.
A. ion concentration
B. steering angle
C. area coverage
D. depth distribution
Answer: D
Clarification: 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.
12. 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
Clarification: In gallium arsenide, when the energy of lower valley electrons rises sufficiently at a higher electric field, the electrons become hot.
13. When electrons become hot, drift velocity
A. increases
B. decreases
C. remains the same
D. does not depend on drift velocity
Answer: B
Clarification: When electrons becomes hot, there will be a reduction in the number of high mobility electrons and hence decrease in drift velocity.