Terahertz Emission Mechanisms in III–V Semiconductors: The Influence of Isoelectronic Dopants

Abstract

The generation of terahertz (THz) radiation by ultrafast optical excitation of III–V semiconductors has been studied extensively in the last three decades. One of the widely used THz sources/detectors is photoconductive antennas (PCAs) based on low-temperature grown GaAs (LT-GaAs). These PCAs have acted as reliable table-top sources of THz radiation required for different applications ranging from spectroscopy to imaging. THz radiation is generated from these semiconductors by transient photocurrents or by the nonlinear optical phenomenon. In the case of low-bandgap semiconductors, like InAs or GaSb, THz emission is mainly due to transient photocurrents. The transient photocurrent arises due to the built-in surface field or due to the difference in the mobility of electrons and holes generated by the intense laser pulse. III–V semiconductors doped with isoelectronic elements like bismuth have shown interesting properties like giant bandgap bowing, (e.g., 80–90 meV/% of Bi in GaAsBi), increase in hole concentration, and giant spin-orbit bowing. In this chapter, we discuss the effect of Bi incorporation on the THz emission and the mechanisms responsible for THz phenomena in two typical III–V semiconductors, viz. GaAs and GaSb. Even though the THz emission mechanism in these two alloys is different, an enhancement in the THz emission efficiency in both the alloys with increased Bi concentration has been reported. We discuss potential applications of these III–V: Bi alloys.