1
GATE ECE 2003
MCQ (Single Correct Answer)
+2
-0.6
The electron concentration in a sample of uniformly doped n-type silicon at 300oK varies linearly from $$10^{17}/cm^3$$ at x = 0 to $$6\times10^{16}/cm^3$$ at x = 2 $$\mu m$$. Assume a situation that electrons are supplied to keep this concentration gradient constant with time.If electronic charge is $$1.6\times10^{-19}\;coulomb$$ and the diffusion constant $$D_n=3\;cm^2/s$$, the current density in the silicon, if no electric field is present is
A
Zero
B
120 A/cm2
C
+1120 A/cm2
D
-1120 A/cm2
2
GATE ECE 2003
MCQ (Single Correct Answer)
+2
-0.6
An n-type silicon bar 0.1 cm long and $$100\;\mu m^2$$ in cross-sectional area has a majority carrier concentration of $$5\times10^{20}/m^3$$ and the carrier mobility is $$0.13\;\;m^2/v-s\;$$ at 300oK. if the charge of an electron is 1.6×10-19 coulomb, then the resistance of the bar is
A
$$10^6\;\Omega$$
B
$$10^4\;\Omega$$
C
$$10^{-1}\;\Omega$$
D
$$10^{-4}\;\Omega$$
3
GATE ECE 1992
MCQ (Single Correct Answer)
+2
-0.6
A semiconductor is irradiated with light such that carriers are uniformly generated throughout its volume. The semiconductor is n-type with $$N_D=10^{19}/cm^3$$. If the excess electron concentration in the steady state id $$\triangle n=10^{15}/cm^3$$ and if $$\tau_p=10\;\mu\;sec$$ [minority carrier life time] the generation rate due to irradiation
A
$$is\;10^{20}\;e-h\;pairs/cm^3/sec$$
B
$$is\;10^{24}\;e-h\;pairs/cm^3/sec$$
C
$$is\;10^{10}\;e-h\;pairs/cm^3/sec$$
D
cannot be determined as the given data is insufficient
4
GATE ECE 1991
MCQ (Single Correct Answer)
+2
-0.6
A silicon sample is uniformly doped with 1016 phosphorous atoms/cm3 and 2 ×1016 boron atoms/cm3. If all the dopants are fully ionized, the material is
A
n-type with carrier concentration of 1016/cm3
B
p-type with carrier concentration of 1016/cm3
C
p-type with carrier concentration of 2 ×1016/cm3
D
n-type with carrier concentration of 2 ×1016/cm3
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