Analysis of photodiode and barrier properties of CoPc/n-Ge heterojunction under various illumination wavelengths

Abstract

The present investigation reports the analysis of barrier parameters of the CoPc/n-Ge heterojunction photodiode under varied illumination wavelengths from 500 nm to 1200 nm in steps of 25 nm. The efficiency of this photodiode was also summarized using responsivity, detectivity and quantum efficiency for different illumination wavelengths. The photocurrent seems to be maximum for 850 nm and 1175 nm and shows higher responsivity of 1.72 A/W and 2.38 A/W at 775 nm and 1125 nm wavelength respectively. The quantum efficiency of the photodiode was found to be 275 % at illumination wavelength of 775 nm and 263 % at 1125 nm. For the selective illumination wavelengths (775 nm, 850 nm, 1125 nm and 1175 nm), the electrical properties of the CoPc/n-Ge photodiode were studied. Noticeable variation in the barrier parameters of the photodiode is observed with illumination than compared to dark. Significantly, the series resistance was found to be decreased and shunt resistance is increased with illumination wavelength than compared to dark. Current conduction mechanisms were also investigated in both the forward and reverse bias of the photodiode. The forward current transport processes show that at moderately high bias the current conduction might be associated with TCLC. It is also evidenced from the reverse conduction mechanism that at low reverse voltages PFE is found to be dominant whereas SE is dominant at high reverse voltages. The reduced interface state densities at the CoPc/n-Ge interface were observed under illumination than compared to dark.