  A hybrid photo-detector (HPD) consisting of a photocathode and a multi-pixel
avalanche diode (MP-AD) was developed a few years ago. Our previous studies
showed that its inherent potential for high resolution photon counting could be
further enhanced by reducing fluctuations in charge loss in the dead layer at
the entrance of the MP-AD. In this paper, we report on the improvement with the
newly developed HPD whose encapsulated MP-AD has a thinner dead layer than
before. It is demonstrated that the new HPD has much better energy resolution,
which enables clearer counting up to nine photoelectrons. Further enhancement
of the photocathode sensitivity of the HPD is also discussed.
