Basic Semiconductor Physics Practice Questions

A small percentage of impurity is added to an intrinsic semiconductor at 300 K. Which one of the following statements is true for the energy band diagram shown in the following figure?

The figure below shows the doping distribution in a p-type semiconductor in log scale. The magnitude of the electric field (in kV/cm) in the semiconductor due to non uniform doping is _________

A silicon sample is uniformly doped with donor type impurities with a concentration of $10^{16} /cm^{3}$ . The electron and hole mobilities in the sample are 1200 $cm^{2}/V-s$ and 400 $cm^{2}$ /V-s respectively. Assume complete ionization of impurities. The charge of an electron is $1.6 \times 10^{-19}$ C. The resistivity of the sample (in $\Omega$ -cm) is ____________.

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 (in $\mu s$ ) taken by the electrons to move from one end of the bar to other end is ________.

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( in S $cm^{-1}$ ) of the silicon sample at 300 K is _______.

The energy band diagram and the electron density profile n(x) in a semiconductor are shown in the figures. Assume that $n(x)=10^{15}e^{(\frac{qax}{kT})}cm^{-3}$ , with $\alpha$ = 0.1 V/cm and x expressed in cm. Given $\frac{kT}{q}$ = 0.026V, $D_{n}=36 cm^{2}s^{-1}, and \frac{D}{\mu}=\frac{kT}{q}$ . The electron current density (in A/ $cm^{2}$ ) at x = 0 is

An n-type silicon sample is uniformly illuminated with light which generates $10^{20}$ electron-hole pairs per $cm^{3}$ per second. The minority carrier lifetime in the sample is 1 $\mu s$ . In the steady state, the hole concentration in the sample is approximately $10^{x}$ , where x is an integer. The value of x is ___.

The cut-off wavelength (in $\mu$ m) of light that can be used for intrinsic excitation of a semiconductor material of bandgap $E_{g}$ = 1.1 eV is _____.

In the figure, $ln(\rho _{i}$ ) is plotted as a function of 1/T , where $\rho _{i}$ is the intrinsic resistivity of silicon, T is the temperature, and the plot is almost linear. The slope of the line can be used to estimate

At T = 300 K, the band gap and the intrinsic carrier concentration of GaAs are 1.42 eV and $10^{6}cm^{-3}$ , respectively. In order to generate electron hole pairs in GaAs, which one of the wavelength $(\lambda _{C})$ ranges of incident radiation, is most suitable ? (Given that : Plank's constant is $6.62 \times 10^{-34}$ J-s, velocity of light is $3 \times 10^{10} cm/s$ and charge of electron is $1.6*10^{-19}$ C)

A thin P-type silicon sample is uniformly illuminated with light which generates excess carriers. The recombination rate is directly proportional to

An N -type semiconductor having uniform doping is biased as shown in the figure. If $E_{C}$ is the lowest energy level of the conduction band, $E_{V}$ is the highest energy level of the valance band and $E_{F}$ is the Fermi level, which one of the following represents the energy band diagram for the biased N -type semiconductor ?

A silicon bar is doped with donor impurities $N_{D}=2.25\times10^{15} atom/cm^{3}$ . Given the intrinsic carrier concentration of silicon at T = 300 K is $n_{i}=1.5\times10^{10}cm^{-3}$ . Assuming complete impurity ionization, the equilibrium election and hole concentrations are

Assume electronic charge $q=1.6 \times 10^{-19}C$ , kT/q=25mV 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 a silicon sample doped with $N_{D}=1\times10^{15}/cm^{3}$ donor atoms. Assume that the intrinsic carrier concentration $n_{i}=1.5\times10^{10}/cm^{3}$ . If the sample is additionally doped with $N_{A}=1\times10^{18}/cm^{3}$ acceptor atoms, the approximate number of electrons/ $cm^{3}$ in the sample, at T = 300 K, will be _____.

At T = 300 K, the hole mobility of a semiconductor $\mu _{P}=500 cm^{2}/V-s$ and $\frac{KT}{q}=26mV$ . The hole diffusion constant $D_{P} \; \in \; cm^{2}/s$ is _____.

When a silicon diode having a doping concentration of $N_{A}=9\times10^{16}cm^{-3}$ on p -side and $N_{D}=1\times10^{16}cm^{-3}$ on n-side is reverse biased, the total depletion width is found to be 3 $\mu$ m. Given that the permittivity of silicon is $1.04\times10^{-12}$ F/cm, the depletion width on the p-side and the maximum electric field in the depletion region, respectively, are

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=300K, the intrinsic carrier concentration of silicon $n_{i}=1.5 \times 10^{16}cm^{-3}$ and $\frac{KT}{q}=26mV$ . The electron concentration at the edge of the depletion region on the p-side is

Drift current in the semiconductors depends upon