III-V Nitride Based Novel Solid-State Terahertz Power-Source: Application in Defense and Industry

Introduction

In recent years, the field of Terahertz (THz) science and technology has entered a completely new phase of unprecedented expansion that is generating every growing levels of broad-based international attention. Indeed, the plethora of activities that have arisen recently in both the technology and scientific arenas associated with the THz frequency domain - i.e., between 1 millimeter (300 GHz) and 100 micrometers (3 THz), suggest that the field might be attempting to undergo a dramatic transition that could lead to long-awaited payoffs in a number of application areas. The inherent advantages and potential payoffs of the THz regime for military & security as well as industry relevant applications have long stood as an important driver of interest in this science and technology area. This extremely expansive and spectrally unique portion of the EM spectrum had initial application in space-based communications, upper atmospheric sensing and potentially for short-range terrestrial communications and non-intrusive package screening. However, the very rapid growth in more recent years is arguably most closely linked to the potential payoffs of THz sensing and imaging for an array of military, security and industrial applications. These applications include the spectroscopic-based detection identification and characterization of chemical and biological agents and materials, remote and standoff early-warning for chemical-biological warfare threats, and imaging of concealed weapons and explosives, just to name a few. In addition, THz-regime finds its application possibilities in industry and private-sector areas as food-industry process control, pharmaceutical industry, biological science, medical diagnostics and security screening.

Systems for rapidly emerging applications at THz frequencies thus require reliable high-power sources. In the last few years, the development of suitable sources for this frequency regime is being extensively explored worldwide. There are broadly two technology roadmaps for THz semiconductor devices. Approaching from the lower frequency range in the THz regime, electronic devices such as, Gunn diode, Resonant Tunneling diode (RTD) and nanometer Field Effect Transistors (FET) based on plasma wave have been widely investigated for THz frequency generation. From higher portion of the THz frequency spectrum, the photonics-based device Quantum Cascade Laser (QCL) extends the emission wavelength to Terahertz spectral range. The other approach to THz generation is through femtosecond lasers incident on materials with non-linear optical properties or on photoconductors such as InP. Parametric amplifiers are also being used for the purpose.

All the above efforts are to pursue the effective generation of THz signals. Most of the available THz sources are complex and bulky. QCL, on the other hand, has the advantage of small size, though they require low temperature operation to directly generate THz. Thus it seems that there is lack of availability of small-sized suitable THz source to serve a useful purpose. So, the development of high-power, low-cost and compact semiconductor sources in THz regime has attracted the recent attention of researchers working in this field.