International Journal of Science, Engineering and TechnologyAuthors: Y C Kamala
Abstract: In 1904 Jagadis Chandra Bose was granted a United States patent for a detector of electrical disturbances in which a metal point pressed on a crystal of galena (lead sulphide, PbS) rectified the currents induced by electromagnetic waves. The device anticipated the semiconductor point-contact diode by several decades, but it was built before any theory of rectifying contacts existed. This paper re-examines Bose’s detector with the physics of the metal–semiconductor (Schottky) barrier. A thermionic-emission model of a metal/PbS point contact is constructed from published material parameters for lead sulphide, and is used to compute the energy-band diagram, current–voltage characteristics, the transition from square-law to linear detection, the intrinsic cut-off frequency and the current responsivity as functions of contact radius, barrier height and doping. The model shows that the very high static permittivity of PbS suppresses tunnelling but enlarges the junction capacitance, so that useful response in Bose’s 12–60 GHz range requires effective contact radii of about one micrometre or less, together with low barrier heights near 0.15–0.20 eV. These results give a physical explanation for the empirical search for a “sensitive spot” that characterised crystal detectors, and they translate into design rules for present-day low-cost sensors: control of effective contact area, engineering of low barriers for zero-bias operation, choice of doping to balance series resistance against tunnelling, and calibration within the square-law regime.
DOI: https://doi.org/10.5281/zenodo.23492295
