GATE EC Electronic Devices questions

In a semiconductor device, the Fermi-energy level is $0.35 \; \mathrm{eV}$ above the valence band energy. The effective density of states in the valence band at $T=300 \mathrm{~K}$ is $1 \times 10^{19} \mathrm{~cm}^{-3}$. The thermal equilibrium hole concentration in silicon at $400 \mathrm{~K}$ is ____________ $\times 10^{13} \mathrm{~cm}^{-3}$ …

Consider a long rectangular bar of direct bandgap $p-$type semiconductor. The equilibrium hole density is $10^{17} \; \text{cm}^{-3}$ and the intrinsic carrier concentration is $10^{10} \; \text{cm}^{-3}.$ Electron and hole diffusion lengths are $2 \; \mu\text{m}$ and $1 \; \mu\text{m},$ respectively. The left side of the bar $(x = 0)$ is …

In a non-degenerate bulk semiconductor with electron density $n = 10^{16} \; \text{cm}^{-3},$ the value of $E_{c} – E_{Fn} = 200 \; \text{meV},$ where $E_{c}$ and $E_{Fn}$ denote the bottom of the conduction band energy and electron Fermi level energy, respectively. Assume thermal voltage as $26 \; \text{meV}$ and the intrinsic carrier …

Select the $\text{CORRECT}$ statement(s) regarding semiconductor devices.

A $p-$type semiconductor with zero electric field is under illumination (low level injection) in steady state condition. Excess minority carrier density is zero at $x = \pm 2l_{n},$ where $l_{n} = 10 ^{-4} \; \text{cm}$ is the diffusion length of electrons. Assume electronic charge, $q = – 1.6 \times 10^{-19} \; \text{C.}$ The profiles of …

​​​​​​A bar of silicon is doped with boron concentration of $10^{16} \text{cm}^{-3}$ and assumed to be fully ionized. It is exposed to light such that electron-hole pairs are generated throughout the volume of the bar at the rate of $10^{20} \text{cm}^{-3} s^{-1}$. If the recombination lifetime is $100 \;\mu s$, intrinsic carrier concentration of …

The energy band diagram of a $\text{p-type}$ semiconductor bar of length $L$ under equilibrium condition (i.e.. the Fermi energy level $E_{F}$ is constant) is shown in the figure. The valance band $E_{V}$ is sloped since doping is non-uniform along the bar. The difference between the energy levels of the valence band at the two edges of the bar is …

A silicon $P-N$ junction is shown in the figure. The doping in the $P$ region is $5\times10^{16}\:cm^{-3}$ and doping in the $N$ region is $10\times10^{16}\:cm^{-3}$. The parameters given are Built-in voltage $\left ( \Phi _{\text{bi}} \right )$ = $0.8\:V$ Electron charge $(q)$ = $1.6\times10^{-19} C\:$ Vacuum permittivity …

Consider the recombination process via bulk traps in a forward biased $pn$ homojunction diode. The maximum recombination rate is $U_{\text{max}}$. If the electron and the hole capture cross-sections are equal, which one of the following is $\text{FALSE}$?

A one-sided abrupt $pn$ junction diode has a depletion capacitance $C_{D}$ of $50$ $\text{pF}$ at a reverse bias of $0.2 V$. The plot of $1/C^{2}_{D}$ versus the applied voltage $V$ for this diode is a straight line as shown in the figure below. The slope of the plot is ___________ $\times 10^{20}F^{-2}V^{-1}$.

A $pn$ junction solar cell of area $1.0\:cm^{2}$, illuminated uniformly with $100\:mW\:cm^{-2}$, has the following parameters: Efficiency $= 15\%$, open circuit voltage $= 0.7\:V$, fill factor $= 0.8$, and thickness $=200 \mu m$. The charge of an electron is $1.6\times 10^{-19}C$. The average optical generation rate (in $cm^{-3} s^{-1}$) is

An enhancement $\text{MOSFET}$ of threshold voltage $3\:V$ is being used in the sample and hold circuit given below. Assume that the substrate of the $\text{MOS}$ device is connected to $-10\:V$. If the input voltage $V_{1}$ lies between $\pm 10\:V,$ the minimum and the maximum values of $V_{G}$ required for proper sampling and holding …

Which one of the following options describes correctly the equilibrium band diagram at $T=300\:K$ of a Silicon $pnn^{+}\:\:p^{++}$ configuration shown in the figure?

The correct circuit representation of the structure shown in the figure is

The figure shows the high-frequency C-V curve of a MOS capacitor $(\text{at}\: T=300\: K)$ with $\Phi_{ms}= 0\: V$ and no oxide charges. The flat-band, inversion, and accumulation conditions are represented, respectively, by the points

What is the electric flux $\left(\int \vec{E}.d \hat{a}\right)$ through a quarter-cylinder of height $H$ (as shown in the figure) due to an infinitely long line charge along the axis of the cylinder with a charge density of $Q?$

A standard CMOS inverter is designed with equal rise and fall times $(\beta_{n}=\beta_{p}).$ If the width of the pMOS transistor in the inverter is increased, what would be the effect on the LOW noise margin $NM_{L}$ and the HIGH noise margin $NM_{H}$?

The quantum efficiency $(\eta)$ and responsivity $(R)$ at wavelength $\lambda \:(\text{in}\: \mu m)$ in a p-i-n photodetector are related by

Two identical copper wires $W1$ and $W2$ placed in parallel as shown in the figure, carry currents $I$ and $2I$, respectively, in opposite directions. If the two wires are separated by a distance of $4r$, then the magnitude of the magnetic field $\overrightarrow{B}$ between the wires at a distance $r$ from $W1$ is

In the circuit shown, the breakdown voltage and the maximum current of the Zener diode are $20\:V$ and $60\:mA$, respectively. The values of $R_{1}$ and $R_{L}$ are $200\: \Omega$ and $1\:k\Omega,$ respectively. What is the range of $V_{i}$ that will maintain the Zener diode in the ‘on’ state?