Question

semi-conductor diode is constructed by placing an n-type semi-conductor together with a p-type semi-conductor.  When the n and p sides are first brought together, electrons in the [1. (A) valence, (B) condition, (C) heavy metal] band of the [2. (A) n, (B) p] side fall into the holes in the [3. (A) valence, (B) condition, (C) heavy metal] band of the

[4. (A) n (B) p] side, creating a depletion zone (a region of [5. (A) increased, (B) decreased, (C) unchanged] resistivity).

When a battery is connected to the diode so that its positive terminal is connected to the n-side and negative terminal is connected to the p-side, the depletion zone [6. (A) becomes narrower, (B) become wider, (C) remains unchanged], causing the resistance of the diode to [7. (A) increase, (B) decrease, (C) remain the same].  The diode in this case is [8. (A) forward, (B) reverse, (C) transverse] biased.

When a battery is connected to the diode so that its positive terminal is connected to the p-side and negative terminal is connected to the n-side, the depletion zone [9. (A) becomes narrower, (B) becomes wider, (C) remain unchanged], causing the resistance of the diode to [10. (A) increase, (B) decrease, (C) remain the same].  The diode in this case is [11. (A) forward, (B) reverse, (C) transverse] biased.

When the diode is forward biased and the battery voltage is increased to the barrier voltage, the depletion zone [12. (A) takes over the entire diode, (B) disappears completely, (C) returns to its original size].  A modest increase in the applied voltage beyond the barrier voltage will cause the current to [13. (A) decrease, (B) not change, (C) increase slightly, (D) increase greatly], giving the resistance characteristic curve of the diode its shape.

Answer 1

1A, 2A,3B (It's conduction band not condition band), 4B,5A,6B, 7A,8B,9A,10B,11A,12B,13D.

Edit: The explanations for the answers are below.

In n-type (n stands for negative here) the extra electron is present in the valence shell of the dopants in the the lattice of the semiconductor so valence Band.

In p-type (p stands for positive here) an electron is missing in the valence shell of the dopants in the lattice of the semiconductor leading to them forming holes which lie in the conduction Band as conduction happens when it gets filled.

Depletion layer forms when the majority charge in one semiconductor diffuses into the adjoining one. Thus forming a barrier of depletion potential which stops further diffusion.

When the positive of the external voltage is connceted to p-type (where charge carriers i.e. holes are positive as they are charecterised by absense of an electron) and negative to the n-side (where charge carriers i.e. free electrons are negative as they are charecterised by presense of an extra electron) then the diode is forward bias and vice versa for reverse bias.

In forward bias the depletion voltage is opposite to the applied voltage therefore forward bias leads to decrease of depletion layer and when the forward bias voltage is equal to the depletion voltage. The depletion layer all but vanishes and subsequently there is no barrier to conduction and hence the current increases greatly.