Photon-counting solid-state photomultiplier

The solid state photomultiplier is a silicon device capable of continuous detection of individual photons in the wavelength range from 0.4 to 28 μm. Operated with an applied bias near 7 V the device responds to the absorption of an incident photon with a submicrosecond-risetime current pulse with a narrow amplitude distribution well above the electronic readout noise levels. Optimal photon-counting performance occurs between 6 and 10 K and for count rates less than 10¹⁰ counts/s/cm² of detector area. A 60% counting quantum efficiency has been demonstrated at 20 μm, and near 60% was observed in the visible light region. The underlying mechanism involves extremely fast internal charge amplification by impact ionization of impurity-band electrons and results in a pulse for each photoelectrically or thermally induced free carrier. The thermally induced dark pulse rate at 7 K is sufficiently low that background-limited detector performance is obtained at a background of less than 10⁶ photons/cm² s