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Recently, heterojunctions formed between dissimilar semiconducting materials have been received considerable attention as an elementary building block of photodetectors (PDs) due to their enormous potential of tuning the wavelength selectivity from bandgap limited photoresponsivity in a single band to multiband or broadband. In this work, titania (TiO2) nanorods (NRs) with anatase crystalline structures were synthesized using hydrothermal method and spin coated on p-Si to realize Au/TiO2 NRs/p-Si (lateral) and Au/TiO2 NRs/p-Si/Ag (vertical) heterojunction broadband (BB) PDs. The structural and optical parameters of the prepared TiO2 NRs/p-Si heterojunction were studied using XRD, SEM, EDS, XPS and UV–VIS methods. A direct optical bandgap of 3.22 eV was evaluated using Tauc's method for the TiO2 nanorod (NR) films deposited on quartz substrate. XPS data revealed two strong binding energy (BE) peaks at 464.4 eV and 458.7 eV which correspond to core level spectral lines of Ti2p1/2 and Ti2p3/2, respectively, may arise owing to the interaction of Ti–O–Si bonds. The photoresponse parameters of the prepared two types of BB PDs were evaluated and compared using I–V, responsivity and I–T methods. The vertical structure exhibited betterment in transient responses (@-7 V) due to its reverse bias operation compared to the lateral structure which operated in forward bias (@ 10 V). The Au/TiO2 NRs/p-Si/Ag: vertical BB PD device displayed a peak photoresponsivity of 41 μA/W, detectivity of 4.6 × 108 Jones and rise/fall times of 0.36 s/0.45 s, when compared to Au/TiO2 NRs/p-Si lateral device architecture. This work suggests a simple approach for the development of tunable functionality of inorganic n-TiO2 NRs/p-Si heterojunction-based BB PDs (300–1100 nm) to fit the future necessities of the optoelectronic field. [ABSTRACT FROM AUTHOR]

Recently, heterojunctions-based photodetectors (PDs) with outstanding photosensitivity and fast switching time received substantial attention due to their broadband (BB) photoresponse in various regimes of the electromagnetic spectrum. Still, there is an increasing demand to accomplish BB PDs operating at photovoltaic (self-driven) mode for serving the today's societal energy efficient needs. In this work, Au and NiFe 2 O 4 thin films were deposited onto p-Si substrates to accomplish interdigitated Au/NiFe 2 O 4 /p-Si heterojunction type BB PDs operated in self-powered mode. The structural, optical, morphological and magnetic parameters of the prepared NiFe 2 O 4 thin films as a function of annealing process were studied using XRD, UV–Vis, AFM and XAS/XMCD techniques. Tauc's plot fitted from the UV–Vis absorption data for the as-deposited, 700 °C and 800 °C NiFe 2 O 4 thin films were 4.85, 3.42 and 2.85 eV, respectively. The photodetection parameters of the fabricated interdigitated Au/NiFe 2 O 4 /p-Si BB PDs were analyzed with I–V, photoresponsivity and response (rise/fall) times as a function of annealing process. All the fabricated Au/NiFe 2 O 4 /p-Si BB PD devices with/without annealing process operated in photovoltaic mode (at 0 V). The PD device annealed at 800 °C unveiled better photoresponsivity (12.35 A/W @1060 nm), detectivity (5.9 × 1014 Jones @1060 nm) and rise/fall times (89 ms/185 ms @900 nm) compared to the as-prepared/700 °C annealed PD devices. The reason for this was attributable to the accomplished improvement in crystallinity (XRD), surface morphology (AFM), reduction of bandgap (UV–Vis) and variation of spin/orbital magnetic moments (XAS/XMCD). In this work, we suggest one of the alternative and cost-effective electron beam evaporation method to grow the desired epitaxial NiFe 2 O 4 thin films compared to the other physical vapor deposition approaches such as PLD and ALD to fit the future necessities of optoelectronic field. [ABSTRACT FROM AUTHOR]