Photosensitivity Analysis of Gallium Nitride and Silicon Carbide Terahertz IMPATT Oscillators: Comparison of Theoretical Reliability and Study on Experimental Feasibility

Abstract

Reliability of terahertz-frequency (∼1.0 THz) characteristics of wide-bandgap (WBG) wurtzite (Wz)-GaN-and 4H-SiC-based p ++ nn ++ -type single-drift-region (SDR) impact avalanche transit time (IMPATT) devices (normal and photoilluminated) is compared through a simulation scheme. The simulation experiment reveals that an RF power density of 3.37 × 10 11 W · m −2 (efficiency of 18.2%) at around 1.126 THz may be realized from the optimized unilluminated GaN IMPATT device, whereas the unilluminated 4H-SiC IMPATT device is expected to generate an RF power density of 1.35 × 10 11 W · m −2 (efficiency of 9%) at 1.05 THz. However, the parasitic series resistance reduces the maximum exploitable power density from the terahertz devices. Under optical illumination, additional photogenerated carriers are created in the devices, and these carriers change the admittance and negative resistance properties of the terahertz IMPATT diodes. The performance modulation of the terahertz devices is simulated, and the results are compared in this paper. Under external radiation, the operating frequencies of the GaN-and SiC-based diodes are found to shift upward by 6.0 and 40.0 GHz, respectively, with degradation of maximum output-power density level and device negative resistance. The extensive simulation experiments establish that, although the photosensitivity of the 4H-SiC-based IMPATT device is better than its GaN counterpart, the overall terahertz performance of the unilluminated GaN IMPATT device is far better than the 4H-SiC-based device, particularly in terms of output power and efficiency. The simulation results and the proposed experimental methodology presented here can be used for realizing optically tuned WBG IMPATT oscillators for terahertz communication.

Dynamic properties and avalanche noise analysis of 4H-SiC over wz-GaN based IMPATTs at mm-wave window frequency

“…A SiC IMPATT device can be fabricated on the epiwafer by following the process steps briefly described below [20].…”

Wide-Bandgap III–V nitride based avalanche transit-time diode in Terahertz regime: Studies on the effects of punch through on high frequency characteristics and series resistance of the device

“…For the present analysis, a flat profile SDR (n ++ n p ++ ) structure is considered, where, n ++ and p ++ are highly doped substrates and cap layers, respectively, n is the epi-layer. Experimental values of carrier ionization rates, Monte Carlo simulated temperature dependent (300 K < T < 600 K) values of drift velocity and mobility of charge carriers in hexagonal (Wz)-GaN are considered for the simulation experiment [4,5]. Realistic exponential doping function at the junction as well as at n ++ n contact region has been incorporated in the analysis [4].…”

“…So, in the light of maturity of the fabrication technology and the unique material parameters, GaN appear to be the best choice, overall, for the next decade of device development particularly at THz region. The prospects of hexagonal (Wurtzite) GaN based IMPATT oscillators at THz region were first reported by the authors [4,5]. Reduction of positive series resistance (R S ) of the device is extremely necessary for the practical realization of GaN based THz IMPATT, since at such a high frequency region the device negative resistance becomes small.…”

Influence of the anisotropy on the performance of D-band SiC IMPATT diodes

“…The material parameters which are responsible for heat generation and dissipation in IMPATT diodes limit the output power of conventional Si and GaAs IMPATT diodes at a particular frequency [3]. In order to realize high-power, high-frequency IMPATT sources, wide bandgap semiconductor materials such as SiC and GaN have aroused a lot of interest as an attractive IMPATT diodes material for its high critical field, wide band gap and high thermal conductivity [4][5][6][7][8]. For D-band applications, it is found that 4H-SiC IMPATT diode is capable of generating higher RF power density, while GaN IMPATT diode exhibits better noise behavior [3,9].…”