Asymmetrically contacted germanium photodiode using a metal-interlayer-semiconductor-metal structure for extremely...

Area of Science:

• Materials Science
• Optoelectronics
• Semiconductor Physics

Background:

• Germanium (Ge) photodiodes (PD) suffer from high dark current, limiting their application in sensitive optoelectronic devices.
• Metal-semiconductor-metal (MSM) structures are common, but improving dark current suppression is crucial.

Purpose of the Study:

• To propose and investigate a novel germanium (Ge) metal-interlayer-semiconductor-metal (MISM) photodiode (PD) structure.
• To efficiently suppress the dark current of Ge PDs using a specific interlayer material.
• To enhance the performance metrics of Ge-based PDs for low-power, high-sensitivity applications.

Main Methods:

• Fabrication of Ge MISM PDs utilizing a titanium dioxide (TiO2) interlayer.
• Characterization of the electrical and photoresponse properties of the fabricated PDs.
• Analysis of the impact of the TiO2 interlayer on the hole Schottky barrier height and carrier collection.

Main Results:

• Introduction of a TiO2 interlayer in the MISM structure significantly enhances the hole Schottky barrier height.
• Dark current in Ge MISM PDs was reduced by a factor of 8000 with a 7-nm-thick TiO2 interlayer.
• The photocurrent of the MISM PDs remained comparable to traditional Ge metal-semiconductor-metal (MSM) PDs.
• A 6600-fold improvement in the normalized photo-to-dark-current ratio (NPDR) was achieved at 1.55 μm.

Conclusions:

• The proposed Ge MISM PD structure with a TiO2 interlayer effectively suppresses dark current while maintaining comparable photocurrent.
• The enhanced hole Schottky barrier and favorable band offsets contribute to reduced dark current and efficient carrier collection.
• These Ge MISM PDs show significant potential for advanced, low-power, and high-sensitivity optoelectronic systems.