In this paper discussions based on the result of a pump-probe experiment are given on a possibility of application of the emission from Ce doped CaGa2S4 to production of a new laser. Existence of enough gain for laser action was clearly demonstrated from the analysis of the experimental result. Using the phonon-terminated character of this emission, construction of an unique laser having wide wavelength tunability covering violet to green region is thought to be possible. As far as optically pumped lasers are concerned, the only problem to be solved is to grow good single crystals having a suitable size (1×1×1 mm3 or more). In order to realize injection type semiconductor lasers with this material, we have to study conduction type and conductivity control technique together with a suitable epitaxial growth method for obtaining thin films of this material. It is pointed out that Ce doped SrGa2S4 and BaGa2S4 are also strong candidates for construction of similar lasers.

Luminescence characteristics of Ce and Eu co-doped CaGa2S4 have been investigated for the first time. All co-doped samples showed the emission from Eu centers having a peak energy of ∼2.22 eV and they were found to have quantum efficiency values less than 30% for Eu doped sample under 441.6 nm excitation. Thermoluminesence was observed for all co-doped samples. These facts seem to indicate the existence of traps, which may mask the energy transfer from Ce to Eu in co-doped samples. Analyses of the measured transient thermoluminescence (TTL) showed two activation energies, ∼0.2 eV and ∼0.9 eV for most co-doped samples. A model where one trap level participates in two different activation processes is proposed to explain these two activation energies.

The behavior of two shallow bound exciton absorption lines in a magnetic field was investigated for a CuGaS2 single bulk crystal. Upon application of a magnetic field perpendicular to the c-axis, both partially allowed absorption lines split into two components with an apparent g-value of 4. When the temperature was reduced under the applied magnetic field, the lower energy line of each pair decreased in intensity. Such behavior of bound exciton lines, in energy splitting and intensity ratio of split lines under different magnetic fields and at different temperatures, is shown to be consistent with the calculated absorption spectra for excitons bound to neutral centers using known band parameters of CuGaS2. The observed nearly isotropic apparent g-value of around 4, which is the sum of electron and hole g-values, is interpreted in terms of nondegeneracy of the valence band top and larger crystal field splitting compared to spin-orbit splitting for CuGaS2. The good agreement between the calculated and observed features clearly indicates that the binding centers are neutral.

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Site-selective Zn doping for vapor phase eptaxial CuGaS2 layers on GaP substrates was tried by adding Zn vapor to each metal source supply period under completely separated alternate source feeding condition with the sources of CuCl, dietylegalliumchloride, and H2S. For the case of simultaneous Ga and Zn supply, the grown layers were found to be of n-type, while for the case of simultaneous Cu and Zn supply the layers were of p-type. The formation of a p-n homo-junction was demonstrated using these p- and n-type layers, and electroluminescence from this p-n junction was observed under pulsed forward voltage application at 77 K. This is believed to be the first successful report of conduction type control of CuGaS2 by impurity doping.