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Understanding Negative Photoconductivity Observed in c‐Orientated InN Epitaxial Layer
Author(s) -
Barick Barun Kumar,
Yadav Santosh Kumar,
Dhar Subhabrata
Publication year - 2020
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.202000219
Subject(s) - photoconductivity , electron , epitaxy , layer (electronics) , condensed matter physics , materials science , fermi level , electromotive force , optoelectronics , sapphire , chemistry , nanotechnology , physics , optics , laser , quantum mechanics
The effect of temperature, environmental conditions, and the applied bias on the phototransport properties of InN epitaxial films grown on c‐sapphire substrates is investigated. The study reveals the coexistence of surface photo‐electromotive force (photo‐EMF) and negative photoconductivity (NPC) effects that result in a unique photoresponse, in which not only the magnitude but also the sign of the photoconductivity becomes bias dependent. Like surface photo‐EMF effect, which has been extensively studied in our earlier article [ Appl. Phys. A 2019, 125 , 84], NPC can also be attributed to the accumulation of electrons in a thin layer just below the surface. A theory has been proposed to explain the effect. According to the model, the accumulation layer is ascribed to the electrons stemming from the donor‐like surface states that arise from the attachment of certain adsorbates. Upon illumination, the natural urge to align the quasi‐Fermi level at the two sides of the boundary leads to the rearrangement of the electrons between the accumulation layer and the donor‐like surface states. This rearrangement process can lead to a reduction of the electron concentration in the accumulation layer. It should be noted that the accumulation layer, which can offer high electron mobility due to reduced dimensionality, is expected to dominate the conducting property of the entire film. Photoinduced reduction of electron concentration in the accumulation channel can thus explain the NPC effect observed in these films.