Terahertz Emission Mechanisms in III–V
Semiconductors: The Influence
of Isoelectronic Dopants
Rajeev N. Kini and C. P. Vaisakh
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 lowbandgap 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.
1 Introduction
Semiconductors hold a special place in terahertz science and technology. They are
among the crucial components of terahertz technology ever since the beginning of
investigations in this spectral realm. Ultrafast optical excitation of semiconductors
R. N. Kini (B) · C. P. Vaisakh
Indian Institute of Science Education and Research Thiruvananthapuram (IISER-TVM),
Maruthamala PO, Vithura, Thiruvananthapuram, Kerala, India
e-mail: rajeevkini@iisertvm.ac.in
C. P. Vaisakh
e-mail: vaisakhjayadevan@iisertvm.ac.in
© Springer Nature Singapore Pte Ltd. 2020
A. Biswas et al. (eds.), Emerging Trends in Terahertz Solid-State Physics and Devices,
https://doi.org/10.1007/978-981-15-3235-1_11
169
Semiconductors: The Influence
of Isoelectronic Dopants
Rajeev N. Kini and C. P. Vaisakh
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 lowbandgap 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.
1 Introduction
Semiconductors hold a special place in terahertz science and technology. They are
among the crucial components of terahertz technology ever since the beginning of
investigations in this spectral realm. Ultrafast optical excitation of semiconductors
R. N. Kini (B) · C. P. Vaisakh
Indian Institute of Science Education and Research Thiruvananthapuram (IISER-TVM),
Maruthamala PO, Vithura, Thiruvananthapuram, Kerala, India
e-mail: rajeevkini@iisertvm.ac.in
C. P. Vaisakh
e-mail: vaisakhjayadevan@iisertvm.ac.in
© Springer Nature Singapore Pte Ltd. 2020
A. Biswas et al. (eds.), Emerging Trends in Terahertz Solid-State Physics and Devices,
https://doi.org/10.1007/978-981-15-3235-1_11
169