Maryn G. Stapelbroek

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.

Large-format blocked-impurity-band focal plane arrays for long-wavelength infrared astronomy

Large-format, very-long-wavelength infrared (VLWIR) hybrid focal plane arrays (HFPAs) based on doped-silicon blocked-impurity-band (BIB) detectors have been developed and demonstrated for a variety of astronomy applications. An HFPA consists of a BIB detector array interfaced via indium column interconnects to a matching cryogenic signal processor/multiplexer. Arsenic-doped silicon (Si:As) BIB detector arrays with useful photon response out to nearly 30 micrometers are the most fully developed embodiment of this technology. HFPAs with Si:As BIB arrays have been optimized for low, moderate, and high infrared backgrounds in 128 X 128-pixel formats, and a high-flux 256 X 256-pixel version is under development. For high-flux applications, both the detector array and multiplexer are optimized to handle incident flux densities > 1016 photons cm-2s-1, providing high spatial uniformity, high pixel operability, and background-limited performance down to low frequencies (< 10 Hz). Antimony-doped silicon (Si:Sb) arrays and 128 X 128-pixel Si:Sb HFPAs having response to wavelengths > 40 micrometers have also been demonstrated, primarily for use at low and moderate backgrounds. BIB technology offers producible, low-cost, high-performance focal planes for astronomy in the VLWIR.

Focal planes and mount assemblies for the WIRE program

The wide-field infrared explorer (WIRE) is a small spaceborne cryogenic telescope specifically designed to study the evolution of starburst galaxies. The use of advanced, large format, infrared hybrid focal plane array technology provides a large sensitivity gain over previously flown missions. The hybrid focal plane arrays (HFPAs) used in this instrument are 128 by 128-element arsenic-doped-silicon blocked impurity band infrared detector arrays connected via indium column interconnects to matching cryogenic multiplexers. The WIRE instrument includes two focal plane mount assemblies (FPMAs), each of which includes a HFPA optimized for a particular wavelength band. Details concerning design, fabrication and performance of the critical components of the WIRE FPMAs are described.

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.

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.