  Radiative efficiency of highly luminescent bulk InP wafers severely degrades
upon heat treatment involved in epitaxial growth of quaternary layers and
fabrication of photodiodes on the surface. This unfortunate property impedes
the use of bulk InP as scintillator material. On the other hand, it is known
that thin epitaxial InP layers, grown by molecular beam epitaxy (MBE) or
metal-organic chemical vapor deposition (MOCVD), do not exhibit any
degradation. These layers, however, are too thin to be useful in scintillators.
The capability of hydride vapor phase epitaxy (HVPE) process to grow thick
bulk-like layers in reasonable time is well known, but the radiative properties
of HVPE InP layers are not known. We have studied radiative properties of 21
micron thick InP layers grown by HVPE and found them comparable to those of
best luminescent bulk InP virgin wafers. In contrast to the bulk wafers, the
radiative efficiency of HVPE layers does not degrade upon heat treatment. This
opens up the possibility of implementing free-standing epitaxial InP
scintillator structures endowed with surface photodiodes for registration of
the scintillation.
