GATE EC Electronic Devices questions

A piece of silicon is doped uniformly with phosphorous with a doping concentration of $10^{16}/cm^{3}.$ The expected value of mobility versus doping concentration for silicon assuming full dopant ionization is shown below. The charge of an electron is $1.6 \times 10^{-19} \:C.$ The conductivity $\text{(in S } cm^{-1})$ of the silicon sample at …

A dc voltage of $10\: V$ is applied across an $n$-type silicon bar having a rectangular cross-section and a length of $1\:cm$ as shown in figure. The donor doping concentration $N_{D}$ and the mobility of electrons $\mu_{n}$ are $10^{16} cm^{-3}$ and $1000\: cm^{2} V^{-1} s^{-1},$ respectively. The average time $(\text{in}\: \mu s)$ taken by …

In a MOS capacitor with an oxide layer thickness of $10\: nm,$ the maximum depletion layer thickness is $100\: nm.$ The permittivities of the semiconductor and the oxide layer are $\varepsilon_{s}$ and $\varepsilon_{ox}$ respectively. Assuming $\varepsilon_{s}/\varepsilon_{ox} = 3,$ the ratio of the maximum capacitance to the minimum capacitance of …

The energy band diagram and the electron density profile $n(x)$ in a semiconductor are shown in the figures. Assume that $n(x) = 10^{15}e^{\left(\dfrac{q\alpha x}{kT}\right)}\:cm^{-3} ,$ with $\alpha = 0.1\:V/cm$ and $x$ expressed in cm. Given $\dfrac{kT}{q} = 0.026\;V,D_{n} = 36\:cm^{2}s^{-1},$ and $\dfrac{D}{\mu} = \dfrac{kT}{q}.$ The electron …

In the circuit shown, the current $I$ flowing through the $50\;\Omega$ resistor will be zero if the value of capacitor $C (\text{in}\: \mu F)$ is ______.

The electric field profile in the depletion region of a p-n junction in equilibrium is shown in the figure. Which one of the following statements is NOT TRUE?

A coaxial capacitor of inner radius $1\: mm$ and outer radius $5\: mm$ has a capacitance per unit length of $172\: pF/m.$ If the ratio of outer radius to inner radius is doubled, the capacitance per unit length $\text{(in}\: pF/m)$ is ________.

When the optical power incident on a photodiode is $10\:\mu W$ and the responsivity is $0.8\: A/ W,$ the photocurrent generated $(\text{in} \:\mu A)$ is_______.

In the figure, assume that the forward voltage drops of the $PN$ diode $D_{1}$ and Schottky diode $D_{2}$ are $0.7\: V$ and $0.3\: V,$ respectively. If ON denotes conducting state of the diode and OFF denotes non-conducting state of the diode, then in the circuit,

In the circuit shown in the figure, the value of capacitor $C\:(\text{in}\: mF)$ needed to have critically damped response $i(t)$ is ____.

The doping concentrations on the $p$-side and $n$-side of a silicon diode are $1\times 10^{16}\:cm^{-3}$ and $1\times 10^{17}\:cm^{-3},$ respectively. A forward bias of $0.3\:V$ is applied to the diode. At $T = 300\:K,$ the intrinsic carrier concentration of silicon $n_{i} = 1.5\times 10^{10}\:cm^{-3}$ and $\dfrac{kT}{q} = 26\:mV.$ The …

In the figure shown, the ideal switch has been open for a long time. If it is closed at t = 0, then the magnitude of the current (in mA) through the $4k \Omega$ resistor at $t= 0^{+}$ is ________.

A silicon bar is doped with donor impurities $N_{D}= 2.25 \times 10^{15} \text{atoms} / cm^{3}$. Given the intrinsic carrier concentration of silicon at $T = 300 \: K$ is $n_{i}= 1.5 \times 10^{10} cm^{-3}.$ Assuming complete impurity ionization, the equilibrium electron and hole concentrations are

In CMOS technology, shallow P-well or N-well regions can be formed using

In the figure shown, the capacitor is initially uncharged. Which one of the following expressions describes the current $I(t)$ (in mA) for $t > 0$?

Assume electronic charge $q= 1.6 \times 10^{-19} \: C$, $kT/q=25 \: mV$ and electron mobility $\mu_{n}= 1000cm^{2}/ V-s$. If the concentration gradient of electrons injected into a $P$-type silicon sample is $1 \times 10^{21}/cm^{4}$, the magnitude of electron diffusion current density (in $A/cm^{2}$) is _________ .

Consider an abrupt PN junction (at $T = 300 K$) shown in the figure. The depletion region width $X_{n}$ on the $N$-side of the junction is $0.2 \mu m$ and the permittivity of silicon $( \varepsilon _{gi} )$ is $1.044 \times 10^{-12} \: F/cm$. At the junction, the approximate value of the peak electric field (in $kV/cm$) is ___________.

When a silicon diode having a doping concentration of $N_{A}= 9\times 10^{16}cm^{-3}$ on $p$-side and $N_{D}= 1 \times 10^{16}cm^{-3}$ on $n$-side is reverse biased, the total depletion width is found to be $3 \mu$. Given that the permittivity of silicon is $1.04 \times 10^{-12}$ F/cm, the depletion width on the p-side and the maximum electric …

For the n-channel MOS transistor shown in the figure, the threshold voltage $V_{Th}$ is $0.8$ V. Neglect channel length modulation effects. When the drain voltage $V_{D}= 1.6 V,$ the drain current $I_{D}$ was found to be $0.5$ mA. If $V_{D}$is adjusted to be $2$ V by changing the values of R and $V_{DD}$, the new value of $I_{D}$ (in mA) is

A series $RC$ circuit is connected to a $DC$ voltage source at time $t= 0$. The relation between the source voltage $V_{s},$ the resistance $R$, the capacitance $C$, and the current $i(t)$ is given below. $V_{s}= R \: i(t)+\frac{1}{c}\int ^{t}_{o}i(u)du$. Which one of the following represents the current $i(t)$?