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The origin of near infrared absorption spectra in semiconducting CdF2 crystals is reviewed. Good agreement between theoretical calculations and experimental data for CdF2:Gd or Ga gives strong support to the photoionization origin of the near infrared absorption. Lack of an evident “chemical shift” for the different shallow impurities studied indicates the intrinsic nature of the shallow donors responsible for both the infrared absorption and conductivity of CdF2. Arguments are presented for attributing the line spectrum observed in lightly doped CdF2 with phonon replicas of zero‐phonon ls–2p absorption masked by reststrahlen absorption of the host. It is proposed that for systems like semiconducting CdF2 such states should be described in terms of Fano's theory of discrete states degenerate with the continuum.

Schottky diodes on highly conducting CdF2 crystals have been produced with Au and Al metals electrodes. Based upon internal photoemission, capacitance and I(V) measurements, the metal-CdF2 zero-field barrier heights were determined. The average values are 1.45 eV for the Au electrode and 0.82 eV for the Al electrode. The electron affinity of the chemically etched CdF2 was estimated to be 3.6 eV in agreement with the value derived from the measurements of external photoemission, 4.1 eV. The interface properties of the metal-CdF2 system are brief discussed.

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