α-SiC nanoscale transit-time diodes: performance of the photo-irradiated terahertz sources at elevated temperature

Abstract

The effects of elevated junction temperature on the terahertz (THz) frequency characteristics of α-(hexagonal, 4H and 6H) silicon carbide (SiC) based double-drift region (DDR, p ++ p n n ++ type) impact ionization avalanche transit-time (IMPATT) devices are studied and compared for the first time through simulation experiments. This study reveals that at 300 K < T < 600 K, a 4H-SiC IMPATT diode may yield 3.5 W of output power (efficiency (η) ∼ 8.6%) at 1.3 THz, while its 6H-SiC counterpart can deliver 3 W of output power (η = 6.3%) at 1.2 THz. It is interesting to observe that at elevated temperature, the performance of a 6H-SiC IMPATT diode degrades more in comparison with its 4H-SiC counterpart. These comparative analyses reveal the superiority of 4H-SiC diodes over their 6H-SiC counterparts, and thus establish the potential of the former as a high-power THz IMPATT oscillator even in harsh environments. Mobile space charge effects and the effect of positive series resistance on the high-temperature performance of the THz devices are also simulated, and it is found that series resistance reduces the output power level of the diodes by at least 15.0%. Moreover, the effects of increased junction temperature on the photo-sensitivity of top mounted (TM) and flip chip (FC) α-SiC IMPATTs are also investigated using a modified simulation technique. The device operating frequencies, under TM illumination configuration, shifts upward by at least 40.0 GHz, whereas the operating frequency shifts upward by at least 100.0 GHz under FC illumination configuration. The simulation results and the proposed experimental methodology presented here may be used for realizing optically controlled α-SiC transit-time devices for application in THz communication.

Improved performance of Ni/GaN Schottky barrier impact ionization avalanche transit time diode with n-type GaN deep level defects

“…Fourier analysis is performed on the final output wave of the IMPATT diode at the given fundamental frequency. By tuning the equivalent circuit based on non-linear circuit parameters and incorporating Fourier analysis, the non-linear large signal analysis results can be modified [18,25]. Finally the RF output power P RF and the conversion efficiency η is given by: where G is the device negative conductance, V RF is the RF voltage amplitude, and V DC and I DC are the voltage and current, respectively [26].…”

“…Some other parasitic effects (e.g. punch through effect) also need to be considered before the simulation [18]. Previous research showed the effects of different punch-through conditions on the performance characteristics of Si/SiC heterostructure mixed tunnelling and avalanche transit time oscillator, providing more choices when fabricating different type of diodes [25].…”

“…Since the fabrication of p-type GaN is difficult and very low specific contact resistance is essential for the THz operation. However, such a low contact resistance of p-type GaN has not been achieved [8,18]. We use a Schottky contact single drift region (SDR) structure instead of a p-n junction for the GaN IMPATT diode to avoid this technological limitation.…”