Conductivity of a semiconductor material increases byI. increasing temperature.II. increasing the surface area.III. decreasing the density of charge carriers.IV. doping with small amounts of impurities.

Explanation

The correct answer is Option B: I and IV. Conductivity in semiconductors increases with temperature because thermal energy excites more electrons into the conduction band, thus increasing the number of charge carriers. Doping with small amounts of impurities introduces additional charge carriers (electrons or holes), which enhances conductivity.Option A is incorrect because although increasing temperature increases conductivity, decreasing the density of charge carriers would reduce conductivity. Option C is incorrect as increasing surface area does not directly affect conductivity, and decreasing the density of charge carriers would reduce it. Option D is incorrect because increasing surface area does not directly enhance conductivity, even though doping does.