Temperature dependence of the electrical conductivity and hall coefficient in 2H‐MoS₂, MoSe₂, WSe₂, and MoTe₂

Abstract

The electrical conductivity and Hall coefficient perpendicular to the c-axis of hexagonal MoS,, MoSe,, and WSe, are measured over the temperature ranges 120 to 117OK and 140 to 820K, respectively. The derived temperature-dependent carrier densities are described by nexp (-E/IcT) for temperatures less than 800 K indicating (thermal) energy gaps of 0.38 eV in n-type MoS,, 0.27 eV in n-type MoSe,, and 0.19 eV in p-type WSe,. Above room temperature the carrier mobilities are given by p -T-a, where a z 1.5 in MoS,, MoSe, and 2.7 in WSe,. The high-temperature (>800 K) thermal activation energies of conduction correspond to energy gaps of 1.27, 0.95, and 1.33 eV in MoS,, MoSe,, and WSe,, respectively. Similar measurements on MoTe, crystals grown by bromine vapour transport demonstrate the effects of included bromine on the low-temperature conduction processes.Es werden die elektrische Leitfahigkeit und der Hall-Koeffizient senkrecht zur c-Ache fiir hexagonales MoS,, Nose, und WSe, im Temperaturbereich 120 bis 1170 K bzw. 140 bis 820 K gemessen. Die abgeleiteten temperaturabhingigen Ladungstragerdichten werden durch n -exp (--E/kT) fiir Temperaturen kleiner als 800 K beschrieben, was (thermische) Energielucken von 0,38 eV in n-leitendem MoS,, 0,27 eV in n-leitendem MoSe,, und 0,19 eV in p-leitendem WSe, ergibt. Oberhalb Raumtemperatur werden die Triigerbeweglichkeiten durch p -T -a gegeben, wobei a = 1,5 in MoS,, MoSe, und 2,7 in WSe, betragt. Die thermischen Aktivierungsenergien der Leitfiihigkeit bei hohen Temperaturen (>SO0 K) entsprechen Energielucken von 1,27, 0,95 und 1,33 eV in MoS,, MoSe, bzw. WSe,. Ahnliche Messungen an MoTe,-Kristallen, die mit Bromdampftransport geziichtet wurden, zeigen den Einflu5 von Bromeinschlussen auf den Leitungsproze5 bei tiefen Temperaturen.

Pressure-induced semiconducting to metallic transition in multilayered molybdenum disulphide

“…From the electronic structure it is possible to calculate s/t as a function of temperature (T) and carrier concentration (n), but it is not possible to calculate s without relaxation time (t). To approximate the relaxation time, we used experimental data from Mahalaway et al 65 The reported experimental electrical conductivity is 0.03 O À 1 cm À 1 at room temperature, which combined with the calculated s/t yield t ¼ 7.5  10 À 14 . We then calculate s as s/t  t.…”

Pressure dependence of the electrical conductivity in 2H‐MoS2 and 2H‐WSe2

“…The small rate of change of conductivity with pressure meant that the isobaric conduct,ivity versus temperature graphs, The WSe, isobaric conductivity versus temperature graphs, Fig. 5, resemble the atmospheric pressure conductivity graphs which, as for MoS,, could be measured over a much wider temperature range [6]. The graphs of Fig.…”

“…Below 800 K the measured activation energies of electrical conduction depend strongly upon the method of crystal growth, consequently conduction at these temperatures hae been attributed to extrinsic processes, particularly since impurities are so readily incorporated between the crystal layers. However, recent measurements on crystals grown directly from the powdered constituents (instead of using the mineral or crystal grown by halogen transport) have given consistent values for the activation eriergy of conduction, corresponding to energy gaps of 0.47 eV in n-type 2H-MoS2 and 0.17 eV in p-type 2H-WSe2 [6]. While these values may correspond to the presence of a specific impurity in each case it is also possible that the energy gaps may be an intrinsic property of the MoS, and WSe, crystals.…”

“…Measurements of the electrical conductivity of 2H-MoS2 over the temperature range 120 to 1170 K at atmospheric pressure [6] have shown that the In a versus T-l graphs are linear over the range 120 to 280 K and over the range 790 to 1170 K giving energy gaps of (0.47 f 0.02) and (1.27 f 0.06) eV, respectively. The In a versus T-l graphs for 2H-MoS2 shown in Fig.…”

“…The measured conductivity a is given by For the n-type MoS, crystals (carrier concentration 6 x 1015 cm-3 at room temperature and pressure) used in these experiments the carrier mobility p a T-3/2 above room temperature [6]. Since p is almost independent of pressure 1221 equations (1) and (2) may be combined to give…”