Indium tin oxid/germanium Schottky photodetectors modulated by ultra-thin dielectric intercalation

Abstract

Germanium (Ge) photodetectorhas been considered as one of the promising optoelectronic devices for optoelectronic integration. So far, most of reported Ge photodetectors with bulk Ge show high dark currents and low responsivities. In this paper, ultra-thin dielectric interlayer-modulated indium tin oxid (ITO)/Ge Schottky photodetectors with high responsivities and low dark currents are investigated, in which the ultra-thin dielectric interlayers are deposited through atomic layer deposition. The characteristics of ITO/Al<sub>2</sub>O<sub>3</sub> (or MoO<sub>3</sub>)/Ge Schottky photodiodes fabricated on bulk Ge wafers with various doping concentrations and Ge epilayer on silicon substrates are comparatively studied. It is found that the 2-nm-thick Al<sub>2</sub>O<sub>3</sub> intercalation between ITO transparent electrode and Ge can effectively enhance the Schottky barrier heights of the photodetectors and trap holes at interface states, rendering their dark currents low and responsivities high. The effective Schottky barrier heights increase from 0.34 eV (ITO/i-Ge) to 0.55 eV (ITO/Al<sub>2</sub>O<sub>3</sub>/i-Ge), and from 0.24 eV (ITO/n-Ge) to 0.56 eV (ITO/Al<sub>2</sub>O<sub>3</sub>/n-Ge). While MoO<sub>3</sub> intercalation between ITO and Ge has no significant effect on the characteristics of all of the photodetectors due to its large electron affinity. The best performance is realized on the ITO/Al<sub>2</sub>O<sub>3</sub>/i-Ge photodetector with a low dark current of 5.91 mA/cm<sup>–2</sup> at –4 V, sharply dropping by two orders of magnitude, compared with that of the ITO/i-Ge photodetector without the Al<sub>2</sub>O<sub>3</sub> interlayer, and the responsivity is significantly improved to 4.11 A/W at 1310 nm. The ITO/Al<sub>2</sub>O<sub>3</sub>/epi-Ge photodetector fabricated on 500 nm Ge epilayer on a silicon substrate also shows the improved performance with a dark current density of 226.70 mA/cm<sup>2</sup> at –3 V and a responsivity of 0.38 A/W at 1310 nm, compared with ITO/epi-Ge photodetector. Finally, experiment studies of single-point infrared images at 1310 nm and 1550 nm are carried out with the ITO/Al<sub>2</sub>O<sub>3</sub>/i-Ge photodetector on a two-dimensional <i>XY</i> displacement platform, which contains 25 pixels and a total detection size of 1750 μm × 1750 μm. The clear and distinguishable images of the infrared spot position are obtained. Consequently, these results suggest that the dielectric interlayer- modulated Schottky photodetectors are competitive in low power consumption and high responsivity, and have great potential applications in the civil field of short wave infrared imaging.