Carrier transport mechanism of highly-sensitive niobium doped titanium dioxide/p-Si heterojunction photodiode under illuminations by solar simulated light

Abstract

Nano-crystalline Nb doped anatase TiO2 (NTO) thin film was deposited on p-type Si substrate for fabrication of n-NTO/p-Si heterojunction photodiode using RF magnetron sputtering technique. Rutherford backscattering spectrometry and Raman spectroscopy results suggest the substitutional incorporation of Nb5+ ions in anatase TiO2 lattice, which is evidenced from large stiffening of Eg(1) and softening of B1g Raman modes. The current density-voltage (J-V) characteristics are measured and important diode parameters of n-NTO/p-Si heterojunction diode are determined, such as ideality factor, barrier height, and series resistance. Diode exhibits excellent behavior under dark condition as rectification ratio is found to be ∼7 × 102 with high forward current density ∼1.54 A/cm2 at 5 V. The n-NTO/p-Si heterojunction works as an efficient photodiode in reverse bias under simulated solar light illumination with high contrast ratio ∼225 at −2 V and very high photo responsivity ∼2.7 A/W at −5 V. The high photo responsivity of photodiode is mainly due to the generation of high density electron-hole plasma in NTO depletion region by the absorption of incident UV range photons. Thus n-NTO/p-Si heterojunction diode is suitable device for highly sensitive Ultra-Violet photodiode applications.