Confocal photoluminescence studies on GaSe single crystals

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.