  We observed and studied strong reduction of optical reflection from the
surface of InP wafers after high-temperature annealing. The effect is observed
over a wide range of the incident wavelengths, and in the transparency band of
the material it is accompanied by increasing transmission. The spectral
position of a minimum (almost zero) of the reflection coefficient can be tuned,
by varying the temperature and the time of annealing, in the spectral range
between 0.5 and 6 eV. The effect is explained by the formation of a uniform
oxide layer, whose parameters (thicknesses and average index) are estimated by
detailed modeling.
