Electrical and structural characterization of shallow As acceptors in natural p-type 2H-MoS2

Abstract

Hexagonal molybdenite (MoS2) is one of the most promising two-dimensional (2D) semiconductors, known with n-type and p-type conduction, with possible applications in electronic, opto-electronic, and spintronic devices. In this work, highly pure geological samples of 2H-MoS2 were investigated by temperature-dependent electron paramagnetic resonance (EPR) and Hall effect measurements. The low-temperature (<55 K) EPR spectra were consistently explained as holes (S = 1/2) trapped on shallow As acceptors on sulfur sites leading to a four-line hyperfine-split spectrum (75As: I = 3/2, 100%) in axial symmetry and with a concentration of 5(1) ppm (∼2 × 1017 cm−3). Electrical measurements indicate p-type conduction with a free carrier concentration of about 5 × 1017 cm−3 at room temperature and an ionization energy of 52 meV associated with the shallow As acceptors, which is consistent with the ionization energy determined from the hydrogenic model of shallow acceptors in 2H-MoS2. These values are in strong contrast to the unrealistic value of 0.7 meV reported in the literature obtained from the analysis of temperature-dependent EPR measurements. Possible explanations are related to temperature-dependent spin-lattice relaxation effects, affecting strongly EPR line intensities and making impossible their use in obtaining the ionization energy.