The Transferred Electron-Intensified Photo-diode (TE-IPD) is a photomultiplier-like device that provides superior detection capability in the near infra-red. It was developed at Intevac ATD, and the fundamentals of its implementation have been discussed"2'3'4. Under NASA Goddard sponsorship, we have been conducting laboratory tests and evaluations on all aspects of this device, as well as characterizing its potential optical communication and laser radar applications.The TE-IPD can be optimized to have as much as 20% quantum efficiency at 1060 nm, orto provide a nearly flat response of 10 % quantum efficiency out to 1600 nm. The internal ("noiseless") gain can be of order l000x or as much as 20,000x, depending on the choice of anode. We have evaluated all aspects of these variants, including spectral quantum efficiency, dark current as a function of temperature, active cathode area, gain, noise factor and spatial uniformity.We will present detailed laboratory test results and discuss device characterizations for specific system applications in terms of the sensitivity and required signal power at the detector cathode to achieve a given quality of service.A schematic of a generic Transferred Electron photo-cathode Intensified Photo-Diode (TE-IPD) detector, and the electron trajectones within it, is shown in Figure 1 . Photons incident on the photocathode from the left cause electrons to be emitted from it. These electrons are accelerated and focused onto the small anode shown on the right hand side of the figure. This anode could either be a Schottky diode or an avalanche diode (AD). Gain is achieved through the initial electron bombardment gain (impact ionization), as well as gain within the AD when it is the anode.The most important feature of the TE-IPD is the long wavelength sensitivity of its cathode. The most sensitive photocathodes available today are the negative electron affinity (NEA) Ill-V semiconductor photocathodes, whose long wavelength threshold is limited to about 1000-nm by greatly reduced electron surface escape probabilities for semiconductors with bandgaps smaller than 1.25 eV (wavelengths larger than 1000-nm). Work function and surface barrier effects at the vacuum-semiconductor interface limit the successful transport of photo-excited electrons into vacuum. To overcome the surface barrier effects in long wavelength photocathodes, various externally-biased photocathodes have been studied. These photocathodes can, in principle, extend the long wavelength cutoff by lowering the vacuum energy level relative to the Fermi level in the bulk photon-absorbing active layer. A number of p-n junction, MOS, field-emission, and heterojunction biasassisted photocathodes have been proposed and experimentally studied, but none prior to the development of the TE photocathode5 have efficient enough photoemission combined with the required low dark current to be practical. TE photoemission is based on the fact that for certain Ill-V semiconductors such as InP, InGaAsP or InGaAlAs alloys, and GaAs, electrons can ...
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