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Chapter 13:
Wide-Bandgap Semiconductor Quantum Cascade Lasers Operating at Terahertz Frequencies
Abstract
Terahertz lasers spanning 100 GHz to 10 THz of the electromagnetic spectrum offer a technology platform with anticipated applications ranging from detection/imaging of chemico-biological systems to integrated circuits. Terahertz is a non-ionizing radiation that has also found wide application in noninvasive and contactless imaging of obscure or hidden objects with potential use in security communities. For such applications, high-power terahertz sources operating at room temperature (RT) are often preferred but become bulky if implemented using standard optical techniques. Optically pumped terahertz lasers provide power in the range of hundreds of milliwatts, while output is restricted to a few microwatts if terahertz radiation is generated using optical heterodyning. Solid state terahertz lasers provide compactness; however, high-power RT operation still remains a challenge. Shur et al. pioneered terahertz generation using plasma waves formed in 2D electron fluid in the channel of advanced heterostructure field-effect transistors (HFETs). Emission of terahertz radiation has been reported in a GaN HFET with a channel length of 1.5 μm at cryogenic temperatures. Knapp et al. report terahertz generation using InGaAs high-electron-mobility transistors with 60-nm channels. Recently, Fathololoumi et al. were able to generate terahertz radiation at temperatures as high as 199.5 K using the resonant phonon method, and Wade et al. achieved the same at a temperature of 225 K in a high magnetic field. Resonant tunneling diodes (RTDs) and quantum cascade lasers (QCLs) operating at terahertz frequencies offer another technology platform for the generation of terahertz radiation. While RTDs have limited output power, QCLs are suitable candidates for high-power, continuous-wave (CW) terahertz sources operating at RT.
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CHAPTER 13
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