This photocathode comprises: InP substrate 1; InAs.sub.x2 P.sub.1-x2 (0x1>0.53) light-absorbing layer 3; InAs.sub.x3 P.sub.1-x3 (0 Este fotocátodo compreende: Carcaça 1 do InP; 0 x1 0.53) camada luz-absorvendo 3 de InAs.sub.x2 P.sub.1-x2 (; InAs.sub.x3 P.sub.1-x3 (0