Verle W. Aebi

Photon counting III-V hybrid photomultipliers using transmission mode photocathodes

This paper reports on the development of solid-state hybrid photomultiplier tubes using high quantum efficiency, transmission mode, III-V photocathodes. The first strike low-noise gain mechanism in these devices is provided via electron bombardment of a solid-state GaAs Schottky diode. In addition, a second-stage gain is provided by solid-state avalanching within a GaAs Schottky APD (SAPD) anode. A combined gain of 2/spl times/10/sup 4/, adequate for photon counting, is achieved. Device bandwidth, exceeding 1 GHz, is optimized by tailoring the diode anode structure. The combined traits of this device provide high quantum efficiency, large dynamic range, large bandwidth, and adequate gain for photon counting. Photon counting beyond 1 /spl mu/m is feasible for a cooled device. The tube structure, diode anode structure, noise issues and preliminary photon counting results are discussed.

Photon counting 1060-nm hybrid photomultiplier with high quantum efficiency

An ultra-low-noise, high-speed, hybrid photomultiplier tube sensitive from 900 to 1300 nm optical wavelength is described. The device, also known as an intensified photodiode (IPD), uses an active transferred electron (TE) photocathode with the quaternary In/sub .69/Ca/sub .31/As/sub .67/P/sub .33/ photo-absorbing layer and a GaAs Schottky avalanche photodiode (SAPD) anode. The detector has a combined electron bombarded and avalanche gain of over 15000 which is sufficient to overcome preamplifier noise and provide high internal counting efficiency of approximately 85%. At an active cathode bias of 1.5 V the room temperature cathode dark count rate is 6.67/spl times/10/sup 5//s. Cooling reduces this substantially corresponding to a dark current activation energy almost equal to the bandgap of the In/sub .69/Ca/sub .31/As/sub .67/P/sub .33/ layer.

High-quantum-efficiency photomultiplier with fast time response

A novel high performance intensified photodiode (IPD) intended for general use in most applications requiring photomultiplication is described. The IPD has high quantum efficiency and fast time response. The detector is stable and requires a single high voltage power supply to operate. This paper describes the device physics as well as preliminary measurements of D.C. gain, quantum efficiency, and impulse response.

Transferred electron photocathode with greater than 5% quantum efficiency beyond 1 micron

This paper details the status of a program at Varian EOSP to develop high-sensitivity transmission photocathodes which function in the 0.95 - 1.65 micron wavelength range. One goal of the program is to develop a streak tube compatible cathode with greater than 1% quantum efficiency at 1.3 micrometers . Sealed tube results are presented. Measured performance characteristics include: cathode spectral response, room temperature cathode photoresponse stability, dark current, emitted electron energy distributions, photodiode resolution/MTF, and preliminary time response data. Finally, the paper includes a brief review of transferred electron photocathode physics and potential applications.

An Ultra Low‐Temperature Fabricated Poly‐Si TFT with Stacked Composite ECR‐PECVD Gate Oxide

Polycrystalline silicon (poly-Si) thin-film transistors (TFTs) were fabricated with a dual-layer gate dielectric of electron-cyclotron resonance (ECR) oxide and plasma-enhanced chemical vapor deposited (PECVD) oxide, with a maximum process temperature of 150°C, using excimer laser annealing. We demonstrate effective carrier mobilities > 90 cm2/Vs, threshold voltage 35 V. These are the best results reported to date for any TFT technology compatible with polyester substrates.

Transferred electron photocathode with greater than 20% quantum efficiency beyond 1 micron

This paper details the status of a program at Intevac ATD to develop high sensitivity transmission photocathodes which function in the 0.95-1.7 micron wavelength range. The goal of the program is to develop this technology for use with both imaging and nonimaging detectors. Sealed tube results are presented. Measured performance characteristics include: cathode spectral response, dark current, linearity, and the effects of cooling. A brief discussion of planned development, potential applications, and simple modeling illustrating the advantages of the proposed detectors are included.

Negative electron affinity photocathodes as high-performance electron sources-Part 2: Energy spectrum measurements

The energy spectra of electrons emitted from transmission-mode negative electron affinity photocathodes have been measured at high resolution using a parllel-plate retarding technique. The spectra from GaAs photocathodes have a basic structure that varies with temperature, activation layer qualitites, cathode thickness, and illuminating wavelength. A FWHM energy spread of approximately 50meV at room temperature has been achieved. Spectra from a GaAsP cathode show a markedly different structure and a much wider energy spread.

Photocathode development for a 1300-nm streak tube

This paper reports on the status of a program to develop a streak tube compatible photocathode optimized for 1300-nm operation. Performance characteristics will be presented for a Transferred Electron photocathode with greater than 1% quantum efficiency at 1300-nm. Photocathode performance results will also be presented over the 950 - 1700 nm spectral range.

GaAsP photocathode with 40% QE at 550 nm

We have fabricated 18mm format vacuum photodiodes incorporating GaAsP/A1GaAsP photocathodes (Eg 8eV) with P-20 phosphor screens. The photocathode response peaks at approximately 550nm. The quantum efficiency at 550nm is in excess of 55 (electrons per incident photon). The photocathode dark current for these tubes is less than i014 Amps/cm2 at room temperature. We have compared this cathode with the GaAs/AlGaAs photocathode.

Gallium Arsenide Electron Bombarded CCD Technology

Electron Bombarded Charge Coupled Devices (EBCCD) which utilize a high performance Gallium Arsenide (GaAs) photocathode have been fabricated and characterized for performance and tube operating life. The EBCCD utilized an 11 mm diagonal, backside illuminated, frame transfer CCD compatible with RS170 video output. The CCD incorporated lateral anti-blooming structures optimized for backside operation. The EBCCD tube was proximity focused and operated with high gain (greater than 150) at low electron landing voltages (less than 2 kV). The EBCCD was integrated in a gated camera system with fast rise and fall times (less than 50 ns). Predicted operating life in a gated camera system as determined by accelerated tests is in excess of 12,000 hours, limited by photocathode degradation.