We report an experimental study on terahertz (THz) emission from ${\mathrm{Ga}}_{1-x}{\mathrm{In}}_x\mathrm{Sb}$ with $0\le x\le 1$. THz emission is excited by femtosecond near-infrared laser pulses. For this material system THz emission is maximized for an In mole fraction $x\approx 0.5$. The maximum in THz emission occurs as a result of carrier compensation $(N_A\approx N_B)$ for this specific material composition. The THz emission from $n$-type $\mathrm{InSb}$ is twice as large than that from $p$-type $\mathrm{GaSb}$. The THz emission from ${\mathrm{Ga}}_{1-x}{\mathrm{In}}_x\mathrm{Sb}$ is explained according to the photo-Dember model. The ${\mathrm{Ga}}_{1-x}{\mathrm{In}}_x\mathrm{Sb}$ material system enabled the study of the influence of carrier concentrations on the THz emission process in narrow band gap semiconductors. Our study demonstrates the existence of a compromise between the positive effect of high electron temperature provided by narrow band gap materials and the negative effect of a high intrinsic carrier concentration. This compromise dictates the extent to which the band gap in a semiconductor can be reduced in order to enhance the THz emission. This same analysis can be extended to explain why the THz emission from $\mathrm{InSb}$ is lower than that of $\mathrm{InAs}$.

• Received 24 March 2006

DOI:https://doi.org/10.1103/PhysRevB.74.075323