Author/Authors :
Togawa، نويسنده , , K and Nakanishi، نويسنده , , T and Baba، نويسنده , , T and Furuta، نويسنده , , F and Horinaka، نويسنده , , H and Ida، نويسنده , , T and Kurihara، نويسنده , , Y and Matsumoto، نويسنده , , H and Matsuyama، نويسنده , , T and Mizuta، نويسنده , , M and Okumi، نويسنده , , S and Omori، نويسنده , , T and Suzuki، نويسنده , , C and Takeuchi، نويسنده , , Y and Wada، نويسنده , , K and Wada، نويسنده , , K and Yoshioka، نويسنده , , M، نويسنده ,
Abstract :
The “surface charge limit (SCL)” phenomenon in negative electron affinity (NEA) photocathodes with GaAs–AlGaAs superlattice and InGaAs–AlGaAs strained-layer superlattice structures has been investigated systematically using a 70 keV polarized electron gun and a nanosecond multi-bunch laser. The space-charge-limited beam with multi-bunch structure (1.6 A peak current, 12 ns bunch width and 15 or 25 ns bunch separation) could be produced from the superlattice photocathodes without suffering the SCL phenomenon. From the experimental results, it has been confirmed that the SCL phenomenon is governed by two physical mechanisms at the NEA surface region, the tunneling of conduction electrons against the surface potential barrier (escaping process) and that of valence holes against the surface band bending barrier (recombination process); these effects can be enhanced using the superlattice structure and heavy p-doping at the surface, respectively. We conclude that a superlattice with heavily p-doped surface is the best photocathode for producing the multi-bunch electron beam required for future linear colliders.
