The photoluminescence spectrum of the layered semiconductor gallium selenide was investigated with a custom-built Raman microscope equipped with a HeNe laser. The spectrum is characterized by three broad and intense bands, which are mainly located to the blue of the laser line. This is interpreted as second-harmonic generation in the laser focus followed by the excitation of electrons into the conduction band and luminescence emission from direct-gap Wannier excitons. The three bands are tentatively ascribed to three crystal modifications of the material. Their lateral intensity distributions were mapped with the confocal microscope. (C) 2002 Elsevier Science B.V. All rights reserved. References: 22
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