In a $P$-type semiconductor, the acceptor level is $57 \text{ meV}$ above the valence band. What is the maximum wavelength of light (in $\mathring{A}$) required to create a hole?

$A$ $N-$ type semiconductor is

When a small amount of antimony impurity is added to a germanium crystal,what happens?

For extrinsic semiconductors,when the doping level is increased:

For a pure $Si$ crystal at $300 \ K$,the electron $(n_e)$ and hole $(n_h)$ concentrations are equal,being $1.5 \times 10^{16} \ m^{-3}$. On doping with Indium,the hole concentration increases to $4.5 \times 10^{22} \ m^{-3}$. Calculate the new electron concentration $(n_e)$ in the doped $Si$.

$A$ potential difference of $2.5 \,V$ is applied across the faces of a germanium crystal plate. The face area of the crystal is $1 \,cm^2$ and its thickness is $1.0 \,mm$. The free electron concentration in germanium is $2 \times 10^{19} \,m^{-3}$ and the electron and hole mobilities are $0.33 \,m^2/V \cdot s$ and $0.17 \,m^2/V \cdot s$ respectively. The current across the plate will be .......... $A$.