Fabrication and characterization of ultra-fast Si-based detectors for near-infrared wavelengths

Abstract

This thesis presents two different concepts for the fabrication of ultrafast metal-semiconductor-metal (MSM) photodetectors, which are to be used in the near-infrared wavelength regime and which are compatible to silicon processing techniques. To achieve this goal, we have grown Si-Si$_{1-x}$Ge$_{x}$ undulating layer superlattices with x=0.39 and 0.45 by molecular beam epitaxy (MBE) an top of epitaxial implanted COSi$_{2}$ layers and fabricated "vertical" MSM detectors. The devices show a quantum efficiency of 5% for the wavelength of 1320 nm and 0.9 % for 1550 nm. We performed time response measurements, using a Ti:sapphire laser and an optical parametric oscillator which generates ultrafast pulses at infrared wavelengths. An electrical response time of 11.6 ps füll width at half maximum (FWHM) was obtained at a wavelength of 1300 nm. At 1550 nm a response time of 9.4 ps was measured. In a second approach, we have grown pure Ge by MBE an Si(111). The sensitive volumes are 270 nm thick Ge films. Interdigitated Cr metal top electrodes of 1.5 - 3 $\mu$m spacing and identical finger width form Schottky contacts to the Ge film. These detectors show a response time of 12.5 ps füll width at half maximum both at 1300 nm and 1550 nm. The temporal response is limited by the transit time of the carriers between the electrodes