biaxial strain

valence band

electronic optical

absorption edge

band structure

Advanced Functional Materials

2D PdSe 2 , a Group 10 noble metal dichalcogenide, has been reported to have a strong thickness‐dependent bandgap energy, ranging from ≈1.6 eV (monolayer) to ≈0.05 eV (bulk) and a high photoresponsivity for bulk samples in the far infrared wavelength range of 10.6 μm. However, a middle bandgap of ≈0.5 eV has been contradictorily reported for bulk PdSe 2 via optical absorption measurements. In this study, detailed electrical transport measurements are conducted to solve this contradiction. The key difference between narrow gap and middle gap semiconductors is the contribution of a depletion layer to the transfer characteristics. Hall measurements reveal intrinsic p ‐type carrier densities of ≈1.9 × 10 18 cm −3 at 300 K and the contribution of the depletion layer to the transfer characteristics for bulk PdSe 2 , suggesting a middle bandgap. Moreover, the maximum depletion width ( W Dm ) is determined from top‐ and back‐gate coupling in dual gate transistors to be ≈17–18 nm. Based on the W Dm – acceptor density diagram, the bandgap of bulk PdSe 2 is quantitatively estimated to be ≈0.3 eV. Although this is not a desirable result from the viewpoint of far infrared material, it helps us to correctly understand the mechanism for the photoresponse of PdSe 2 .

Quantitative Determination of Contradictory Bandgap Values of Bulk PdSe2 from Electrical Transport Properties