3元系固溶半導体 (Pb<SUB>1−<I>x</I></SUB>Cd<I><SUB>x</SUB></I>)S<SUB>1−<I>y</I></SUB>の組成<I>x</I>と化学量論的組成からの偏差<I>y</I>の同時制御

Abstract

Attention is recently paid to the new materials for tunable laser diodes, lasing at the wavelength from 2 to 4 μm. The laser diodes are expected as the light source for optical communications in the next generation and also as the real-time IR-photospectrometer for detecting quickly and exactly the kind and the concentration of hydrocarbon pollutants in air such as methane and ethane.Multinary solid solution semiconductors such as ternary (Pb1−xCdx)S1−y and quaternary (Pb1−xCdx) (S1−zSez)1−y are best suited for the above purposes. To realize the continuous laser emission of tunable laser diodes near room temperature, it is necessary that the structure of the diode is a double-heterojunction with a matched lattice parameter and the composition (x, z) of each layer is controlled to a high degree.For this purpose, simultaneous control of the composition (x, z) and the deviation y from stoichiometry is indispensable for each constituent layer.In this study, a new method for simultaneously controlling the composition x and the deviation y from stoichiometry was proposed for the (Pb1−xCdx)S1−y solid solution. That is, the activities of sulfur (PS2) and CdS (aCdS) were controlled independently in the heat-treatment process of the solid solution by providing the respective reservoir chambers in the heat-treatment tube.As a result, it was found that the composition x of the solid solution is seriously effected by the cadmium partial pressures (PCd) dissociated from CdS. From this fact, it was suggested that the deviation y from stoichiometry could also be controlled simultaneously by regulating PS2, keeping PCd to a specific value corresponding to the target composition x.Based on this principle, the diagrams of P(PCd)-x and P(PS2)-T in composition x=0.20 were obtained successfully for this solid solution.In conclusion, the exploited method is applicable to a simultaneous control of other ternary or quaternary solid solutions involving two metallic components.