Optoelectronic Characteristics of Al2O3/Si Multilayer Structures Fabricated by DC Reactive Sputtering Technique

Abstract

In this work, optoelectronic characteristics of Al₂O₃/Si multilayer structures were presented and analyzed. These structures were prepared by dc reactive sputtering technique with different thicknesses of Al₂O₃ layer (200, 250, and 325 nm). The 200-nm sample showed the highest current levels. The samples with 200 and 250 nm thickness exhibit a much more pronounced photoresponse, while the 325-nm sample shows a higher dark current to begin with. Similarly, the same samples (200 and 250 nm) show remarkably similar behaviors of spectral responsivity (R_λ), both peaking around 0.38 A/W in the NIR region (800-850 nm), while their responsivity is relatively low in the visible range (400-700 nm), but shows a sharp increase beyond 750 nm. This suggests that for these deposition times, the Al₂O₃ layer allows for effective photon absorption in the Si substrate at longer wavelengths. In contrast, the 300-nm sample exhibits significantly lower responsivity values, with the peak responsivity reaching 0.0038 A/W. This drop in responsivity indicates that the thicker Al₂​O₃ layer impedes the photogeneration and collection of carriers. The behaviors of the external quantum efficiency (EQE) and specific detectivity (D^*) were similar to that of the spectral responsivity. The EQE was peaking at ~55-56% around 850 nm, while the specific detectivity was peaking at approximately 0.55×10¹² Jones around 850 nm for both 200 and 250-nm samples.