n-type semiconductor. Using this plot, find the width of the forbidden band of the semiconductor and the activation energy of donor
levels.
6.210. The resistivity of an impurity-free semiconductor at room
temperature is p = 50 Q • cm. It becomes equal to pi = 40 Q• cm
when the semiconductor is illuminated with light, and t = 8 ms
after switching off the light source the resistivity becomes equal to
p, = 45 I2-cm. Find the mean lifetime of conduction electrons and
holes.
6.211. In Hall effect measurements a plate of width h = 10 mm
and length 1 = 50 mm made of p-type semiconductor was placed
in a magnetic field with induction B = 5.0 kG. A potential difference V = 10 V was applied across the edges of the plate. In this
case the Hall field is VH = 50 mV and resistivity p = 2.5 52•cm.
Find the concentration of holes and hole mobility.
6.212. In Hall effect measurements in a magnetic field with
induction B = 5.0 kG the transverse electric field strength in an
impurity-free germanium turned out to be rl = 10 times less than
the longitudinal electric field strength. Find the difference in the
mobilities of conduction electrons and holes in the given semiconductor.
6.213. The Hall effect turned out to be not observable in a semiconductor whose conduction electron mobility was 7.1 = 2.0 times
that of the hole mobility. Find the ratio of hole and conduction
electron concentrations in that semiconductor.
6.5. RADIOACTIVITY
• Fundamental law of radioactive decay:
N=Noe —xt.
(6.5a)
• Relation between the decay constant X., the mean lifetime T, and the
half-life T:
1
ln 2
T •
• Specific activity is the activity of a unit mass df a radioisotope.
6.214. Knowing the decay constant X of a nucleus, find:
(a) the probability of decay of the nucleus during the time from 0
to t;
(b) the mean lifetime ti of the nucleus.
6.215. What fraction of the radioactive cobalt nuclei whose halflife is 71.3 days decays during a month?
6.216. How many beta-particles are emitted during one hour by
1.0 p,g of Na24 radionuclide whose half-life is 15 hours?
6.217. To investigate the beta-decay of Mg23 radionuclide, a counter was activated at the moment t = 0. It registered Ni beta-particles by a moment t, = 2.0 s, and by a moment t2 = 3t1 the number
(6.5b)
270
levels.
6.210. The resistivity of an impurity-free semiconductor at room
temperature is p = 50 Q • cm. It becomes equal to pi = 40 Q• cm
when the semiconductor is illuminated with light, and t = 8 ms
after switching off the light source the resistivity becomes equal to
p, = 45 I2-cm. Find the mean lifetime of conduction electrons and
holes.
6.211. In Hall effect measurements a plate of width h = 10 mm
and length 1 = 50 mm made of p-type semiconductor was placed
in a magnetic field with induction B = 5.0 kG. A potential difference V = 10 V was applied across the edges of the plate. In this
case the Hall field is VH = 50 mV and resistivity p = 2.5 52•cm.
Find the concentration of holes and hole mobility.
6.212. In Hall effect measurements in a magnetic field with
induction B = 5.0 kG the transverse electric field strength in an
impurity-free germanium turned out to be rl = 10 times less than
the longitudinal electric field strength. Find the difference in the
mobilities of conduction electrons and holes in the given semiconductor.
6.213. The Hall effect turned out to be not observable in a semiconductor whose conduction electron mobility was 7.1 = 2.0 times
that of the hole mobility. Find the ratio of hole and conduction
electron concentrations in that semiconductor.
6.5. RADIOACTIVITY
• Fundamental law of radioactive decay:
N=Noe —xt.
(6.5a)
• Relation between the decay constant X., the mean lifetime T, and the
half-life T:
1
ln 2
T •
• Specific activity is the activity of a unit mass df a radioisotope.
6.214. Knowing the decay constant X of a nucleus, find:
(a) the probability of decay of the nucleus during the time from 0
to t;
(b) the mean lifetime ti of the nucleus.
6.215. What fraction of the radioactive cobalt nuclei whose halflife is 71.3 days decays during a month?
6.216. How many beta-particles are emitted during one hour by
1.0 p,g of Na24 radionuclide whose half-life is 15 hours?
6.217. To investigate the beta-decay of Mg23 radionuclide, a counter was activated at the moment t = 0. It registered Ni beta-particles by a moment t, = 2.0 s, and by a moment t2 = 3t1 the number
(6.5b)
270