  Silicon sensors with high time resolution can help particle identification in
the International Linear Collider (ILC). We are studying Low Gain Avalanche
Diodes (LGADs) as a high timing resolution sensor. As a step to develop LGADs,
we are now focusing to characterize Avalanche Photo Diode (APD)s, because the
APDs has the same multiplication structure as LGADs. We studied the
characteristics of APDs with particles from radioisotopes.
