SiC Devices on Different Polytypes: Prospects and Challenges

Abstract

Imaging, broadband communication and high-resolution spectroscopic applications in the midand far-infrared regions have underscored the importance of developing reliable solidstate sources operating in the frequency range from 0.3 Terahertz to 10.0 Terahertz (1000 to 30 μm wavelength). Recent studies suggest that Terahertz (THz) interactions can enable a variety of new applications on the wide range of solids, liquids, gases, including polymers and biological materials such as proteins and tissues. Compared to microwave and MMwave, far-infrared or THz frequency range has significant reduction in the antenna sizes and greater communication bandwidth. Commercial applications comprise thermal imaging, remote chemical sensing, molecular spectroscopy, medical diagnosis and surveillance. Military applications comprise night vision, rifle sight enhancement, missile tracking, space based surveillance and target recognition. Despite the technical advantages, the major challenge today in THz technology is the development of a portable high-power THz source. During the past few years, significant efforts were devoted to search of reliable semiconductor sources at the THz regime. Recently, several solid-state physics research group, the world over, are focusing their research attention in developing semiconductor devices those can generate THz oscillations. A promising concept for THz sources utilizing plasma waves in a gated 2D electron gas (2DEG) was proposed in the early 90-ties. Thereafter, recent experimental observations and theoretical studies have revealed that resonant detection and coherent emission of THz radiation can be effectively induced by excitation of plasma oscillations in the electron channel of Field Effect Transistors (FET). Another promising THz source is the Quantum Cascade Laser (QCL). QCL were first demonstrated in 1994 based on a series of coupled quantum wells constructed using MBE. Although in the mid-infrared region (5< λ < 10 μm) these devices have been in development for more than ten years, it is only recently that the first THz laser has been reported at 4.4 THz. These lasers are made from 1,500 alternating layers of GaAs and AlGaAs and have produced 2.0 mW of peak power (20.0 nW average power). Advances in output power and operating wavelength continue at a rapid pace. Low Temperature Grown (LTG) GaAs photo-mixer can provide up to around 2μW of output power at the frequency of 1.0 THz and their operation frequency can be as high as 5 THz. Of the several available terahertz source technologies, those based on the difference frequency technique are very promising, as they can produce a relatively high power terahertz beam