Second harmonic generation and birefringence of some ternary pnictide semiconductors

TL;DR

This study uses first-principles calculations to analyze birefringence and second harmonic generation in ternary pnictide semiconductors, revealing complex relationships between band gaps and nonlinear optical responses.

Contribution

It provides the first detailed theoretical analysis of SHG and birefringence in these specific chalcopyrite-structured semiconductors.

Findings

Smaller band gaps tend to correlate with larger SHG responses.

Inverse power laws between gaps and SHG are not observed.

Nonlinear responses result from a delicate balance of intraband and interband effects.

Abstract

A first-principles study of the birefringence and the frequency dependent second harmonic generation (SHG) coefficients of the ternary pnictide semiconductors with formula ABC$_2$ (A = Zn, Cd; B = Si, Ge; C = As, P) with the chalcopyrite structures was carried out. We show that a simple empirical observation that a smaller value of the gap is correlated with larger value of SHG is qualitatively true. However, simple inverse power scaling laws between gaps and SHG were not found. Instead, the real value of the nonlinear response is a result of a very delicate balance between different intraband and interband terms.