Electrical and Thermal Transport Properties of TlGaSe2 Single ...

Electrical and Thermal Transport Properties of TlGaSe 2… 17
the conduction band. So the width of the forbidden energy gap can be
calculated. It is found to be 2.1 eV. From Fig. 1 the value of σ, at room
temperature equals 1.87×10 -6 (Ω.cm) -1 . Since Hall measurements are
important, Fig. 2 is constructed in the temperature range 248-484 K.
Figure 2 shows the dependence of R H T 3/2 against the temperature. The
positive sign of R H indicates that the majority carriers are holes. It can be
seen from Fig. 2 that the Hall coefficient decreases with the rise in
temperature, but above 400 K it decreases very rapidly. Determination of
the energy gap from Hall data is possible from this relation. The band
width of the energy gap calculated from the slope of the curve in the
intrinsic region was found to be 2.1 eV. The values of the Hall coefficient
and carrier concentration at room temperature are 3.98 × 10 9 cm 3 C –1 and
1.57 × 10 9 cm –3 respectively. The temperature dependence of the Hall
mobility for TlGaSe 2 is shown in Fig. 3. It was found that the exponent n
32
31
ln ( R T ) ( cm
3
.K/C )
3/2
H
30
29
28
27
2.0 2.5 3.0 3.5 4.0 4.5
3
-1
10 / T ( K )
Fig. 2. The dependence of R H T 3/2 against the temperature for TlGaSe 2 single crystal.
in the relation µ
H
α T n (below 330 K) is 1.5 indicating that the scattering
of the carriers is influenced by the impurities, i.e., the impurities play an
important role in this range of temperature. We will be able to say that
the mobility increases with temperature. As temperature decreases, the
mobility due to impurity ion scattering decreases too. In the high
temperature range (T > 330 K), the carrier scattering mechanism is the