Basic Semiconductor Physics Practice Questions

In an n-type silicon crystal at room temperature, which of the following can have a concentration of $4 \times 10^{19}cm^{-3}$ ?

Which of the following is true?

Silicon is doped with boron to a concentration of $4 \times 10^{17}$ atoms/ $cm^{3}$ . Assume the intrinsic carrier concentration of silicon to be $1.5 \times 10^{10}/cm^{3}$ and the value of kT/q to be 25 mV at 300 K. Compared to undopped silicon, the fermi level of doped silicon

The electron and hole concentrations in an intrinsic semiconductor are $n_{i}$ per $cm^{3}$ at 300 K. Now, if acceptor impurities are introduced with a concentration of $N_{A}$ per $cm^{3}$ (where $N_{A}\gt \gt n_{i}$ ), the electron concentration per $cm^{3}$ at 300 K will be

Under low level injection assumption, the injected minority carrier current for an extrinsic semiconductor is essentially the

The majority carriers in an n-type semiconductor have an average drift velocity v in a direction perpendicular to a uniform magnetic field B. The electric field E induced due to Hall effect acts in the direction

A heavily doped n-type semiconductor has the following data: Hole-electron ratio :0.4 Doping concentration : $4.2 \times 10^{8}$ atoms/ $m^{3}$ Intrinsic concentration : $1.5 \times 10^{4}$ atoms/ $m^{3}$ The ratio of conductance of the n-type semiconductor to that of the intrinsic semiconductor of same material and ate same temperature is given by

The concentration of minority carriers in an extrinsic semiconductor under equilibrium is

The primary reason for the widespread use of Silicon in semiconductor device technology is

A Silicon sample A is doped with $10^{18}$ atoms/ $cm^{3}$ of boron. Another sample B of identical dimension is doped with $10^{18}$ atoms/ $cm^{3}$ phosphorus. The ratio of electron to hole mobility is 3. The ratio of conductivity of the sample A to B is

The bandgap of Silicon at room temperature is

The impurity commonly used for realizing the base region of a silicon n - p - n transistor is

The resistivity of a uniformly doped n-type silicon sample is 0.5 $\Omega$ - mc. If the electron mobility ( $\mu_{n}$ ) is 1250 $cm^{2}$ /V-sec and the charge of an electron is $1.6\times 10^{-19}$ Coulomb, the donor impurity concentration ( $N_{D}$ ) in the sample is

The neutral base width of a bipolar transistor, biased in the active region, is 0.5 $\mu$ m. The maximum electron concentration and the diffusion constant in the base are $10^{14}/cm^{3}$ and $D_{n}=25 cm^{2}$ /sec respectively. Assuming negligible recombination in the base, the collector current density is (the electron charge is $1.6\times 10^{-19}$ - Coulomb)

The longest wavelength that can be absorbed by silicon, which has the bandgap of 1.12 eV, is 1.1 $\mu$ m. If the longest wavelength that can be absorbed by another material is 0.87 $\mu$ m, then bandgap of this material is

The Bandgap of silicon at 300 K is

An n-type silicon bar 0.1 cm long and 100 $\mu m^{2}$ in cross-sectional area has a majority carrier concentration of $5\times 10^{20}/m^{2}$ and the carrier mobility is 0.13 $m^{2}/V-s$ at 300 K. If the charge of an electron is $1.6\times 10^{-19}$ coulomb, then the resistance of the bar is

The electron concentration in a sample of uniformly doped n-type silicon at 300 K varies linearly from $10^{17}/cm^{3}$ at x = 0 to $6\times 10^{16}/cm^{3}$ at x = 2 $\mu m$ . Assume a situation that electrons are supplied to keep this concentration gradient constant with time. If electronic charge is $1.6\times 10^{-19}$ coulomb and the diffusion constant $D_{n}=35$ $cm^{2}/s$ , the current density in the silicon, if no electric field is present, is