Comparison study of energy bands and Wannier-Mott excitons in mixed Zn(P $\scriptstyle \sf 1-x$ As $\scriptstyle \sf x$ ) $\scriptstyle \sf 2$ and Zn $\scriptstyle \sf 1-x$ Cd $\scriptstyle \sf x$ P $\scriptstyle \sf 2$ crystals

Abstract

Excitonic absorption, reflection and photoluminescence spectra of mixed Zn(P1-xAsx)2 crystals over the full range of x ( 0 ? x ? 1) and Zn1-xCdxP2 crystals at 0 ? x ? 0.05 have been studied at low temperatures (1.8 K). The decrease of the energy gap in Zn(P1-xAsx)2 at the increase of x occurs slightly sublinearly. The rydbergs of excitonic series in this crystals decrease as well, and the dependences Ry ( x ) for all series are strongly superlinear at small x. In Zn1-xCdxP2 crystals the energy gap and rydbergs decrease at the increase of x (at 0 ? x ? 0.05) as well. The dependences of Eg and Ry on x are considerably stronger in Zn(P1-xAsx)2 than in Zn1-xCdxP2. At the increase of x the half-width of excitonic absorption lines increases monotonically in both type crystals that is evidence of the increasing role of fluctuations of crystal potential.