Optoelectronic Characterization of Ge based photodetectors

Infrared photodetectors are ubiquitous in ranging applications, where the distance from the sensor to the target is assessed by either the time delay or the phase shift of the reflected beam compared to the emitted light. Short-wave infrared (SWIR, l=1.4mm...3mm) is a very appealing wavelength range to extend the range and the accuracy of such ranging depth sensors, as this wavelength range has very little atmospheric background light and because the human eye is less sensitive in SWIR than in NIR (near infrared). As the reflected light on the sensor is weak, sensitive detectors with very low dark currents are required. The challenge, however, is that semiconductors sensitive to SWIR, such as Germanium (Ge), have smaller bandgaps than Silicon which result in larger dark currents.

At imec, we are developing Germanium photodiodes in 200 mm or 300 mm process flows with low leakage current, together with optical waveguides into photonic IC’s.

The goal of this position is to characterize material & device characteristics of Ge based photodetectors to better understand the band structure and identify passivation strategies that would enable better Ge photodetectors.  The photodetectors will be tested under various configurations.

Type of work:

60% experimental work, 30% data analysis/modelling, 10% literature review

Expected tasks:

1. Measuring comprehensive electrical properties of the Ge photodiodes and extracting parameters such as dark current, responsivity & EQE
2. Characterization of optical properties of the photodiodes such as PL, PL lifetime
3. Identifying factors detrimental to the opto-electronic properties
4. Rationalizing the characteristics based on diode geometry, design & process steps
5. Helping us develop novel device architectures.