Abstract: An apparatus, for photo-luminescent analysis of the surface of crystalline silicon, is disclosed, in which the photons emitted from the sample are passed through a two-beam (or two-arm) interferometer, having the usual beamsplitter, fixed mirror, and movable mirror. The interferometer output is directed to a detector which is a germanium photo-diode, cooled in a Dewar, which also cools the initial electronic circuitry to which the detector output is input. Using the disclosed apparatus, methods are available for readily eliminating the negative effect of the electron-hole-dropler phenomenon, and for utilizing the .[.no-photon.]. .Iadd.no-phonon .Iaddend.region of the spectrum to identify otherwise unidentified impurity (or dopant) materials.The questions raised in reexamination request No. 90/001,324, filed Sep. 9, 1987, have been considered and the results thereof are reflected in this reissue patent which constitutes the reexamination certificate required by 35 U.S.C. 307 as provided in 37 CFR 1.570(e).