HPD for linear colliders

Hybrid Photo Diode (HPD) is an attractive photodevice with many advantages. The HPD is considered as a candidate photodevice for the calorimetry in future linear collider experiments. HAPD, which uses avalanche photo diode (APD) as the anode is very useful for its much larger gain than usual HPDs. We report results of R&D on Hamamatsu R7110U HAPD.