problem 1    

The mobility of free electrons and holes for pure silicon are 0.13 and 0.05 m²/V-S respectively. Find the intrinsic conductivity for silicon. Supposing ni = 1.5x 10¹⁶/cm³ at room temperature.

Use the relation: σ = q.n_i (µ_n + µ_p)

problem 2    

The mobility of free electrons and holes in pure germanium are 0.38 and 0.18 m2/V_-s. Find the intrinsic conductivity for germanium. Supposing n_i = 2.5x 1019/m3 at room temperature.

Use the relation: σ = q.ni (µ_n + µ_p)

problem 3    

A specimen of silicon is 0.2 mm long and has a cross-section of 0.2 x 0.2 mm. One volt connected across this bar results in a current of 8 mA. Supposing that the current is because of electrons, find out (a) concentrations of free electrons and (b) the drift velocity. The room temperature value of mobility is: µn = 1300 cm²/V-S

problem 4     

In a germanium sample, a donor impurity is added to the extent of 1 atom per 10⁸ germanium atoms. Show that the resistivity of the germanium sample drops to 3.7 ohm-cm.
Given: µn = 3800 cm²/V-S and µ_p = 1800 cm²/V-S and n_i = 2.5x 10¹³/cm³ at room temperature, Nger = 4.41x 10²² /cm³

problem 5     

An N-type semiconductor has a resistivity of 20 x 10^-2 ohm-m. The mobility of the electrons through a separate experiment was found to be 100 x 10^-4 m²/V-S. Find the electron concentration in this material.