Dear semiconductor physicists,
According to the literature, MoS2 is known as n-type semiconductor while phosphorene (black phosphorus) is known as p-type semiconductor. However, the band structures of both layered-materials, in general, illustrate intrinsic or p-type semiconductoring properties (depends how to define the semiconductor). I would request the researchers/physicists that kindly explain the different semiconducting behaviors of MoS2 and phosphorene in terms of Physics.
The n-type behavior of MoS2 may be due to the non-bonded electrons of Mo. If I am right then what about the band structure in the light of the definition of n-type semiconductor?
But in case of phosphorene, all P atoms are bonded with other three P atoms, no free carriers (either electrons or holes) any more after bonding, then why it is p-type semiconductor?
As we know that the Fermi level pins to the mid of the intrinsic semiconductor, and in case of n-type semiconductor, the Fermi level is greater than that of the intrinsic semiconductor and lies closer to the conduction band than the valence band, while for p-type semiconductors the Fermi level is below the intrinsic Fermi level and lies closer to the valence band than the conduction band. In addition, does the above-mentioned n- and p-type semiconductors definitions are valid for intrinsic n- and p-type semiconductors or not? It would be highly appreciated if the references may also be provided in the support of intrinsic n-type and p-type semiconductors physics.
Thank you!
The n-type conductivity in MoS2 has nothing to do with the d-z2 band as this is essentially non-bonding, localized at Mo and shielded against vacuum and the surface by the Se Atoms with s-p bonding states below the Mo dz2. MoS2 can be n and p type depending on the conditions during crystal growth. I am talking about vacuum cleaved samples!
Both MoS2 and phosphorene are intrinsic semiconductors in the ideal limit, just like Si or GaAs. However, as Dr. Pettenkofer pointed out, during crystal or thin film growth, the material is inevitably doped unintentionally. This is usually due to impurities, or most likely vacancies (e.g., sulfur vacancies for the case of MoS2, making it more n-type).
Sometimes environmental contamination or high temp processes (such as during device fabrication) can also lead to accidental doping and surface Fermi level pinning.
@Tanuj Trivedi could you add some references with your comment on intrinsic semiconducting behavior of MoS2 and black phosphorene, please?
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