Second-harmonic generation and birefringence of some ternary pnictide semiconductors

Sergey N. Rashkeev; Sukit Limpijumnong; Walter R. L. Lambrecht

doi:10.1103/PhysRevB.59.2737

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Second-harmonic generation and birefringence of some ternary pnictide semiconductors

Sergey N. Rashkeev, Sukit Limpijumnong, Walter R. L. Lambrecht

DOI 10.1103/PhysRevB.59.2737 · Physical Review B

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Abstract

A first-principles study of the birefringence and the frequency-dependent second-harmonic generation (SHG) coefficients of the ternary pnictide semiconductors with formula ABC2 (A=Zn, Cd; B=Si, Ge; C=As, P) with the chalcopyrite structures was carried out. The zero-frequency limits of χ123(2) were found to be in reasonable agreement with available experimental data for all the considered materials. We found that substitution of P by As, Si by Ge, and Zn by Cd is favorable to get a higher value of χ(2)(0). An analysis of the different contributions shows that the anomalously high value of the zero-frequency SHG in CdGeAs2 appears as a result of a very small interband term in the zero-frequency limit which, contrary to most of the other materials of this class, does not compensate the large intraband contribution. Simple inverse power scaling laws between gaps and χ(2) values are not supported by our results. We find that the (001) oriented 1+1 superlattice structure has significantly lower gaps than the chalcopyrite and correspondingly higher χ(2). However, this smaller gap structure is characterized by a large alternatingly compressive and tensile lateral strain in the layers, which makes it unfavorable. The calculated values of the birefringence for ZnGeP2 and CdGeAs2 are in fair agreement (discrepancies being rather constant and of the order of 10%) with experiment in the frequency range corresponding to the middle of the gap.