GaAs photocathode

Other linear focused photomultipliers reported in near-IR fluorescence studies include the Hamamatsu R943-02 52 and the RCA C31034 85 86) both incorporating gallium-arsenide (GaAs) photocathodes. 

Figure 7. Current-potential curves for methanol under Ar and CO2 atmospheres using p-InP and p-GaAs photocathodes.

We thank V. H. Etgens (Paris) and J. P. Contour (Orsay) for providing ZnSe substrates and LaSrMnO samples, respectively. Thanks are also due to Yu. Mamaev (St. Petersburg) for making available strained GaAs photocathodes used as polarized electron sources in some experiments. This work has been partly supported by the Emopean Community through project UE-INTAS 99-125. 

Fig. 8.2 Short-circuit current density of a GaInP2/GaAs photocathode connected to a RUO2 CE in 3 M H2SO4 under 1 sun AM 1.5 G illumination from a tungsten lamp calibrated to a 1.8 eV GaInP2 reference cell. The corresponding STH reaches over 17 %, assuming tip 1...

As the discussion of the semitransparent GaAs photocathode will show, there are a tremendous number of trade-offs involved in the selection of materials parameters for NEA emitters, especially in those for imaging applications. As a result, a large number of variants of a seemingly identical device may become available when more devices are offered commercially, and none of these standard variants may perform as well as a device tailored to a user s specific application. This is similar to the forced choice of high sensitivity, low dark current, or fully extended infrared response in the case of the S-1 phototube. For NEA devices, however, the choices may be of even greater complexity. 

Fig. 5.15. Example multilayer TM GaAs photocathode. The substrate is GaP with a GaAIAs matching layer grown below the GaAs activated layer [5.110]...

One example of a complete TM GaP/GaAlAs/GaAs photocathode, along with its RM and TM response, is shown in Fig. 5.15 [5.110]. The 2eV high-energy cutoff in the TM data is caused by absorption in the GaP. 

These TM sensitivities are factors of five lower than the best reflection mode GaAs at 2000pA/lm, but Allen [5.92] indicates that while reflection mode performance has nearly reached the theoretical limit of 2400pA/lm, transmission mode devices may be expected to climb by a factor of three to about 1200 pA/lm. The transmission mode GaAs photocathode is therefore a realistic, if still undeveloped and difficult to fabricate, imaging retina [5.116]. 

The performance of the HAPD for our application can be further improved through the use of a GaAs photocathode that provides a better match to the detectable Cerenkov spectrum. Devices of this type are currently being fabricated. 

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