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GATE 2023 EDC Champion Quiz 4

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Question 1

Two GaAs wafers, one n-type and one p-type, are uniformly doped such that N_D (wafer 1) = N_A (wafer 2) ≥ n_i , which wafer will exhibit the larger resistivity?

Question 2

For a silicon diode with long P and N regions, the accepter and donor impurity concentrations are 1 x 10¹⁷ cm^–3 and 1 × 10¹⁵ cm^–3, respectively. The lifetimes of electrons in P region and holes in N region are both 100 µs. The electron and hole diffusion coefficients are 49 cm²/s and 36 cm²/s, respectively. Assume kT/q = 26 mV, the intrinsic earner concentration is 1× 10¹⁰ cm^–3, and q = 1.6 × 10^–19 C. When a forward voltage of 208 mV is applied across the diode, the hole current density (in nA/cm²) injected from P region to N region is ______.

Question 3

The electron concentration in a sample of uniformly doped n-type silicon at 300 K varies linearly from 10¹⁷/cm³ to at x = 0 to 6 × 10¹⁶ /cm³ at x = 2 µm. Assume a situation that electrons are supplied to keep this concentration gradient constant with time. If the electronic charge is 1.6 × 10^-19coulomb and the diffusion constant D_n = 35 cm²/s, the current density in the silicon if no electric field is present?

Question 4

A silicon diode, with N_A=10¹⁷cm^-3 and N_D = 5 × 10¹⁷ cm^-3 , is forward biased with V_a = 0.05 V. Assume that the intrinsic concentration of silicon is n_i = 1.08 ×10¹⁰ cm^-3. What are the minority carrier concentrations ∆n_p(x_p) and ∆ p_n(x_n) at the edge of transition region?

Question 5

The transistor in the circuit shown below has the parameter

mA/V². V_T = -2 V, drain current = 0.5 mA.(neglect channel length modulation)

The value of C_C such that the lower 3 dB frequency is 20 Hz is

Question 6

The built-in potential of an abrupt p-n junction is 0.75 V. If its junction capacitance (Q) at a reverse bias (V_R) of 1.25 V is 5 pF, the value of C_J (in pF) when V_R = 7.25 V is________.