  Operation of semiconductor scintillators requires optically-tight integration
of the photoreceiver system on the surface of the scintillator slab. We have
implemented an efficient and fast quaternary InGaAsP pin photodiode,
epitaxially grown upon the surface of an InP scintillator wafer and sensitive
to InP luminescence. The diode is characterized by an extremely low
room-temperature dark current, about 1 nA/cm2 at the reverse bias of 2 V. The
low leakage makes possible a sensitive readout circuitry even though the diode
has a large area (1 mm/times1 mm) and therefore large capacitance (50 pF).
Results of electrical, optical and radiation testing of the diodes are
presented. Detection of individual \alpha-particles and \gamma-photons is
demonstrated.
