Impact of N-plasma and Ga-irradiation on MoS2 layer in molecular beam epitaxy

Pawan Mishra, Malleswararao Tangi, Tien Khee Ng, Mohamed Nejib Hedhili, Dalaver H. Anjum, Mohd Sharizal Alias, Chien Chih Tseng, Lain Jong Li, Boon S. Ooi

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Recent interest in two-dimensional materials has resulted in ultra-thin devices based on the transfer of transition metal dichalcogenides (TMDs) onto other TMDs or III-nitride materials. In this investigation, we realized p-type monolayer (ML) MoS2, and intrinsic GaN/p-type MoS2 heterojunction by the GaN overgrowth on ML-MoS2/c-sapphire using the plasma-assisted molecular beam epitaxy. A systematic nitrogen plasma (N 2) and gallium (Ga) irradiation studies are employed to understand the individual effect on the doping levels of ML-MoS2, which is evaluated by micro-Raman and high-resolution X-Ray photoelectron spectroscopy (HRXPS) measurements. With both methods, p-type doping was attained and was verified by softening and strengthening of characteristics phonon modes E 2 g 1 and A 1 g from Raman spectroscopy. With adequate N 2-irradiation (3 min), respective shift of 1.79 cm-1 for A 1 g and 1.11 cm-1 for E 2 g 1 are obtained while short term Ga-irradiated (30 s) exhibits the shift of 1.51 cm-1 for A 1 g and 0.93 cm-1 for E 2 g 1. Moreover, in HRXPS valence band spectra analysis, the position of valence band maximum measured with respect to the Fermi level is determined to evaluate the type of doping levels in ML-MoS2. The observed values of valance band maximum are reduced to 0.5, and 0.2 eV from the intrinsic value of 1.0 eV for N 2- and Ga-irradiated MoS2 layers, which confirms the p-type doping of ML-MoS2. Further p-type doping is verified by Hall effect measurements. Thus, by GaN overgrowth, we attained the building block of intrinsic GaN/p-type MoS2 heterojunction. Through this work, we have provided the platform for the realization of dissimilar heterostructure via monolithic approach.

Original languageBritish English
Article number012101
JournalApplied Physics Letters
Issue number1
StatePublished - 4 Jan 2017


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