METHOD FOR USING A PHOTODETECTOR HAVING A BANDWIDTH TUNED HONEYCOMB CELL PHOTODIODE STRUCTURE
A photodetector with a bandwidth-tuned cell structure is provided. The photodetector is fabricated from a semiconductor substrate that is heavily doped with a first dopant. A plurality of adjoining cavities is formed in the semiconductor substrate having shared cell walls. A semiconductor well is formed in each cavity, moderately doped with a second dopant opposite in polarity to the first dopant. A layer of oxide is grown overlying the semiconductor wells and an annealing process is performed. Then, metal pillars are formed that extend into each semiconductor well having a central axis aligned with an optical path. A first electrode is connected to the metal pillar of each cell, and a second electrode connected to the semiconductor substrate. The capacitance between the first and second electrodes decreases in response to forming an increased number of semiconductor wells with a reduced diameter, and forming metal pillars with a reduced diameter.
1 . A method for using a photodetector with a bandwidth-tuned cell structure to measure optical signals, the method comprising:
providing a photodetector with a plurality of adjoining photodiode cells formed in a bandwidth-tuned honeycomb structure, where each cell comprises a metal pillar extending into a semiconductor well, having a central axis aligned with an optical path;
accepting a bias voltage between first and second electrodes of the photodetector;
accepting an optical signal;
measuring a higher bandwidth response to forming an increased number of semiconductor wells with a reduced diameter, and forming metal pillars with a reduced diameter.
2 . The method of claim 1 further comprising:
measuring a higher quantum efficiency (QE) in response to forming a decreased number of semiconductor wells with an increased diameter, and forming metal pillars with an increased diameter.
3 . The method of claim 1 wherein providing the photodetector includes providing a photodetector having silicon semiconductor walls, metal pillars having an aspect ratio (L/d) of at least 7:1, where L is defined as a length of the metal pillar and d is defined as a metal pillar diameter at a top surface of the cell well, and a ratio d/d0 of less than 10:1, where d0 is defined as a metal pillar diameter at a bottom surface of the cell well; and,
wherein accepting the optical signal includes accepting an optical signal having a wavelength in a range of about 815 to 875 nanometers (nm).