Fabrication of mesa structural n‐type nanocrystalline‐FeSi₂/p‐type Si heterojunction photodiodes by liftoff technique combined with photolithography

Abstract

Mesa structural n‐type nanocrystalline (NC) FeSi2/p‐type Si heterojunctions were fabricated by a liftoff technique combined with photolithography in order to improve the diode performance, particularly to reduce the parasitic capacitance. Their current‐voltage characteristics were experimentally studied in the dark and under illumination using a 1.31 μm laser at room temperature. Their junction capacitance density and leakage current density were evidently reduced as compared with those of the normal structural diodes. The mesa diode exhibits a good rectifying action with a rectification ratio of approximately three orders of magnitude at bias voltages of ±1 V. The photodetection was clearly observed owing to the suppression in the dark current. The estimated detectivity is 2.0 × 109 cm√Hz/W at zero bias, which is an order of magnitude larger than that of the normal structural diodes. This should be because the formation of interface states is reduced accompanied by the interface area reduction. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Enhancement of the Si p-n diode NIR photoresponse by embedding β-FeSi2 nanocrystallites

“…The obtained device specific detectivity at 300 K in zero bias conditions is 1.2 × 10 9  cm × Hz 1/2 /W at a wavelength of 1300 nm. The calculated value exceeds the results for β -FeSi 2 films on average152324 and is inferior in only in comparison with a passivated Si/ β -FeSi 2 heterostructure25.…”

“…3) showed that regardless of the presence of the NCs the value of built-in potential of the Si/ β -FeSi 2 NCs/Si structure along with the reference diode is 0.54 eV, which is in good agreement with the value for a conventional Si p-n junction at room temperature, at the given doping levels of the Si substrate ( N d  = 5 × 10 14  cm −3 ) and epitaxial p -Si layers ( N a  = 1 × 10 14  cm −3 ). Furthermore, on the 1/C 2 curve there is a linear part in the reverse bias range from –30 to –1 V, suggesting that it is due to the reduction of the interface state of the mesa diode15. From the foregoing, one can conclude that embedding of β -FeSi 2 NCs into the depletion region of the Si p-n junction does not cause the formation of a significant amount of interface states.…”

“…At room temperature, the current under illumination is only slightly greater than the dark current, which can be associated with the relatively small amount of the β -FeSi 2 (seven layers with only 0.4 nm of Fe in each) in comparison with the β -FeSi 2 films on Si substrates, which show one order of magnitude difference between dark current and current under illumination1523242526. On the other hand, embedded β -FeSi 2 NCs form mainly scattered layers (Fig.…”

“…The first of these factors is the diffusion of iron atoms into the silicon substrate during β -FeSi 2 formation, which results in deep level formation14, and the second is the existence of dangling bonds in the heterojunction interface and initial β -FeSi 2 layer, which causes the interface states15. In particular, the heterojunction interface between the β -FeSi 2 film and the Si substrate has dangling bonds due to both grain boundaries and a lattice mismatch16.…”

Interface-state density estimation of n-type nanocrystalline FeSi2/p-type Si heterojunctions fabricated by pulsed laser deposition

“…Additionally, β-FeSi 2 grown epitaxially on Si with small lattice mismatches [8][9][10] has an optical absorption coefficient of more than 10 5 cm −1 at 1.2 eV [11][12][13]. Nanocrystalline (NC) FeSi 2 grown on any solid substrate at room temperature possesses semiconducting features close to β-FeSi 2 [14][15][16]. It is comprised of a crystal with diameter range of 3-5 nm [17] and has a larger Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence.…”