Michael D. Petroff

Detection of individual 0.4–28 μm wavelength photons via impurity‐impact ionization in a solid‐state photomultiplier

A solid‐state device capable of continuous detection of individual photons in the wavelength range from 0.4 to 28 μm is described. Operated with a dc applied bias, its response to the absorption of incident photons consists of submicrosecond rise time pulses with amplitudes well above the electronic readout noise level. A counting quantum efficiency of over 30% has been demonstrated at a wavelength of 20 μm, and over 50% was observed in the visible‐light region. Optimum photon‐counting performance occurs for temperatures between 6 and 10 K and for count rates less than 1010 counts/s per cm2 of detector area. The operating principle of the device is outlined and its performance characteristics as a photon detector are presented.

Measuring weak scintillations with visible light photon counters

The visible light photon counter (VLPC) is an excellent candidate for scintillating fiber applications, meeting the requirements of high quantum efficiency, high gain with low gain dispersion, and good time resolution. The mechanism of impurity band conduction, on which the device depends, is described. Device operation is outlined, and performance characteristics are presented for a recent design. These characteristics include quantum efficiency, dark count rate, dark current, gain, and their dependence on temperature and operating voltage. Pulse height distribution and excess noise factor are also given, and shown to compare favorably with conventional avalanche photodiodes.

Detection of scintillations in small crystals using VLPCs

This paper addresses the use of Visible Light Photon Counters (VLPCs) for detection of light induced in light arrays of small scintillating crystals for gamma ray imaging. The use of plastic step-index-of-refraction fibers for collecting the scintillation light for detection by a VLPC is examined and data obtained in initial exploratory experiments are discussed. The results are compared with the number of detectable scintillation photons predicted by a model that in essence treats the crystal as an integrating cavity with highly efficient diffuse reflecting surfaces.

The Absorption Cross Section Of As In Si

Infrared absorption cross sections of As in Si near zero Kelvin have recently been measured in two different investigations. The average of the integrals of the cross section over photon wavenumber was 8.64 x 10-13 cm-1. This is nearly equal to the value predicted by the oscillator-strength sum rule. Between 500 and 1000 cm-1, the absorption cross sections reported here agree very well with 0.7 times the currently accepted formula for the photoionization cross section of As in Si. Calibration errors in spreading resistance measurements on epitaxial layers seem to be the cause of the 0.7 multiplicative error in the photoionization formula. Above 1000 cm-1, 0.7 times the value from the formula predicts a larger photoionization cross section than the absorption cross sections reported here. This is apparently caused by the impact ionization of donor electrons from impurity atoms by energetic photoionized electrons.