Chapter 1 - THz Solid-State Source Based on IMPATT Devices

Abstract

In recent years, a lot of research interest has been generated for the research and development of terahertz (THz) components, sources, and detectors because of their various applications in astronomy, spectroscopy, bioimaging, biosensing, quality inspection in industrial products, and medical and pharmaceutical research areas. The potentiality of impact avalanche transit time (IMPATT) devices made of different semiconductors particularly the wide bandgap (WBG) semiconductors has been presented in this chapter for operation at THz frequency band. The suitability of IMPATTs based on both normal bandgap (Si, GaAs, InP) and WBG semiconductors (Wz-GaN, 4H-SiC, type IIb diamond) as potential THz sources has been studied by avalanche response time analysis. The design, modelling, and simulation of double-drift region (DDR) IMPATTs based on various semiconductors for operation of these devices at millimetre wave window frequencies (94, 140, 220GHz) and THz frequency frequencies (0.5, 1.0, 1.5THz) have also been presented in this chapter. The avalanche resonance limited frequencies of DDR IMPATTs based on GaN, diamond, and Si IMPATTs are found to be 1.00, 1.50, and 0.50THz, respectively. DDR diamond IMPATTs can be used as potential THz sources to deliver sufficient power at 1.5THz and above. The simulation provides the avalanche resonance limited frequencies of DDR IMPATTs, which is highest for Wz-GaN in THz band. IMPATT devices based on Wz-GaN are found to be without any competition above 1 THz as regard to delivering high power with high conversion efficiency. A quantum drift-diffusion model based on density gradient theory has been presented for accurate large-signal simulation of DDR IMPATT devices based on conventional and WBG semiconductors operating at higher mm-wave and lower THz frequencies. It is observed that the mm-wave and THz performance of DDR IMPATTs based on Wz-GaN, InP, C, 4H-SiC, and Si are affected by quantum phenomena such as quantum confinement, quantum tunneling, etc., arising at certain limiting frequency. The quantum effect on the large-signal properties of IMPATTs will be appreciable if the dimension of the active layer of the device is of the order of de Broglie wavelength of electrons or holes at the design frequencies in mm-wave and THz bands. However, more accurate prediction of large signal power and conversion efficiency of the device can be made due to incorporation of quantum corrections in the drift-diffusion model. In conclusion, the great potential of Wz-GaN and type IIb diamond as base materials of DDR IMPATTs can be explored to experimentally realize these devices for THz operation