Question 11:
moderateThe resistivity of a pure semiconductor is 0.5 Ωm. If the electron and hole mobility be 0.39 m²/V-s and 0.19 m²/V-s respectively then calculate the intrinsic carrier concentration.
Practice NEET Properties of Semiconductors Questions
Question 12:
moderateA Ge specimen is doped with Al. The concentration of acceptor atoms is \[\sim 10^{21} atom/m^{3}\]. Given that the intrinsic concentration of electron hole pairs is \[\sim 10^{19}/m^{3}\], the concentration of electrons in the specimen is :
According to mass action law
\[ n_{e}\times n_{h}= n_{i}^{2} \]
\[ n_{h}=10^{21} ; n_{i}= 10^{19}; n_{e}=n_{i}^{2}/n_{h} = n_{e}= 10^{38}/10^{21}= 10^{17} \]
Question 13:
easyIntrinsic semiconductor is electrically neutral. Extrinsic semiconductor having large number of current carriers would be :
An extrinsic semiconductor with a large number of current carriers is still electrically neutral overall because the total number of positive and negative charges remains balanced.
Question 14:
moderateThe contribution in the total current flowing through a semiconductor due to electrons and holes are 3/4 and 1/4 respectively. If the drift velocity of electrons is 5/2 times that of holes at this temperature, then the ratio of concentration of electrons and holes is :
Current i = neAv
\[ \frac{I_{1}}{I_{2}}= \frac{n_{1}}{n_{2}} * \frac{v_{d1}}{v_{d2}} \]
\[ \frac{3}{1}= \frac{n_{1}}{n_{2}} * \frac{5}{2} \]
\[ \frac{n_{1}}{n_{2}} = \frac{6}{5}Â \]
Question 15:
easyA p-type extrinsic semiconductor is obtained when Germanium is doped with
A p-type semiconductor is created by doping a tetravalent semiconductor (like Ge) with a trivalent impurity such as Boron.
Question 16:
easyThe electron concentration in an \(n\)-type semiconductor is the same as hole concentration in a \(p\)-type semiconductor. An external field (electric) is applied across each of them. Compare the currents in them.
The mobility of electrons (\(mu_e\)) is greater than the mobility of holes (\(mu_h\)). Since current is proportional to mobility for the same carrier concentration and electric field, the current in the \(n\)-type semiconductor is greater than that in the \(p\)-type.
Question 17:
easyA silicon (Si) specimen is doped with aluminium (Al). The concentration of acceptor atoms is \(10^{18}\text{ m}^{-3}\). Given that the intrinsic carrier concentration is \(10^{16}\text{ m}^{-3}\), the concentration of electrons in the specimen is
Formula: \(n_e n_h = n_i^2\). Since the semiconductor is heavily p-doped, \(n_h approx N_a = 10^{18}\text{ m}^{-3}\). Therefore, \(n_e = frac{n_i^2}{n_h} = frac{(10^{16})^2}{10^{18}} = 10^{14}\text{ m}^{-3}\).
Question 18:
easyConsider the following statements:
(a) At 0 K, semiconductor behaves as perfect conductor.
(b) Semiconductors have negative temperature coefficient of resistance.
Choose the correct statement.
At 0 K, semiconductors behave as insulators since no electrons are in the conduction band. The resistance of a semiconductor decreases with increasing temperature, meaning it has a negative temperature coefficient of resistance. Thus, only statement (b) is correct.
Question 19:
easyThe electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than \(6200 A^0\), is incident on it. The band gap in (eV) for the semiconductor is
The band gap is related to the threshold wavelength by the formula \(E_g = \frac{12400}{\lambda in A^0}\text{ eV}\). Substituting \(\lambda = 6200 A^0\), we get \(E_g = \frac{12400}{6200} = 2\text{ eV}\).
Question 20:
easyConsider the following statements
(i) An intrinsic semiconductor will behave as insulator at \(T = 0text{ K}\).
(ii) Doping pure silicon with trivalent impurities gives p-type semiconductors.
(iii) The majority carriers in n-type semiconductors are electrons.
(iv) Solar cell works when it is in forward bias.
The correct statements(s) is/are
At \(T = 0text{ K}\), all electrons are in the valence band, so an intrinsic semiconductor acts as an insulator. Trivalent doping creates p-type, and n-type has majority electron carriers. Solar cells do not require external bias to operate. Thus, statements (i), (ii), and (iii) are correct.