Out of the following impurities, which impurity is not a trivalent?

Doping of a semiconductor (with small impurity atoms) generally changes the resistivity as follows.

The electron mobility in $N$-type germanium is $3900 \ cm^2/V \cdot s$ and its conductivity is $6.24 \ mho/cm$. If the effect of holes is negligible,what is the impurity concentration?

$A$ transistor is a/an

$A$ crystal of intrinsic silicon at room temperature has a carrier concentration of $1.6 \times 10^{16} / m^3$. If the donor concentration level is $4.8 \times 10^{20} / m^3$, then the concentration of holes in the semiconductor is

Which of the following statements is correct for an $n$-type semiconductor?