En Xia Zhang

AlGaInAs/InP multi-quantum-well continuous-wave Fabry Perot laser diodes are exposed to 1.8 MeV protons at fluences up to 1×10¹³ p/cm². The threshold current increases with fluence, with maximum shift over 180%. Minimal change in slope efficiency is observed. A substantial redshift in emission wavelength is observed at all fluence levels, while the wavelength free spectral range remains constant. The wavelength shift persists even when measured at the same forward current for pre- and post-irradiation conditions, indicating that effects of heating and plasma from the forward current are a second order effect. The series resistance was not significantly affected by radiation exposure. Damage factor analysis reveals a value more than 100 times higher than that of previously studied lasers of these types, indicating high sensitivity to displacement events. For this laser, the dominant mechanism for the radiation-induced wavelength shift is likely a change in group refractive index and gain bandwidth due to radiation-induced defect levels within the bandgap, with minimal contributions from heating. System level and hardness-assurance implications are discussed.

The susceptibility of nanowire FETs (NWFETs) to total ionizing dose (TID) is investigated via technology computer-aided design (TCAD) models that are validated via comparison to experimental studies. The simulated contributions of trapped charge in the gate oxide, spacer, and shallow trench isolation (STI) to performance degradation are compared to the measured TID response of NWFETs to identify the dominant source of TID degradation. Results indicate that degradation in both the gate oxide and the spacer are dominant contributors to degradation in p-type NWFETs, while the spacer is the main contributor for n-type NWFETs. An analysis of the impact of spacer length on the TID response of devices indicates that spacers may become less important in gate-all-around (GAA) technology. Results are compared with previous technology nodes, highlighting the reduced role that STI and spacer dielectrics play in NWFET TID degradation.

We report, for the first time, an experimental investigation of proton radiation-induced effects on a three-section AlGaInAs/InP mode-locked laser diode (MLLD), using 1.8 MeV protons at a fluence of $1\times 10^{12}$ /cm2. Post-irradiation characterization shows stable passive mode-locking operation with improved overall performance. The threshold current increased and slope efficiency decreased due to defect-induced nonradiative recombination and absorption, yet the pulse width remained nearly unchanged at 1.44 ps with an improved time–bandwidth product of 0.438. Optical spectra exhibited a redshift, linewidth broadening, and better optical frequency comb tooth coherency. Fixed-point analysis demonstrated altered dispersion characteristics and enhanced tunability, indicating potential benefits for drift compensation and Doppler shift management in intra-satellite optical links. Multi-tone optical injection locking further confirmed robust post-irradiation performance, with stronger coherency transfer, improved RF sideband suppression (13.9 dB to 34.6 dB), narrower pulses (1.60 ps to 1.44 ps), and reduced time–bandwidth products, albeit requiring slightly higher injection power. These results indicate that this specific three-section MLLDs maintains functionality after proton exposure and exhibits features advantageous for compact, high-coherence comb generation in satellite and deep-space optical communication systems.

Voltage-controlled oscillators (VCOs) are key components in providing periodic signals that are used in RF communications systems for time synchronization and signal processing. However, standalone VCOs can have poor phase noise performance and experience frequency drift; therefore, injection locking can be implemented in a VCO to stabilize these performance metrics. Injection-locked VCOs (ILVCOs) in satellite communications or radar systems can be subject to total-ionizing dose (TID) effects, which could alter the performance of the oscillator. The present work analyzes the effects of TID in a 5 GHz ILVCO using an X-ray source, and demonstrates that the locking range increases and phase noise of the ILVCO improves with total dose. This unexpected result was analyzed using circuit simulations and shows that the negative threshold voltage shifts induced by TID may be posited to the increase of the ratio of injection signal current to oscillator signal current, which may ultimately extend the locking range. Consequently, the increase in the strength of the injection signal due to TID may also lead to the decrease of phase noise. These results suggest that the use of ILVCOs in satellite systems may be favorable as they are TID radiation tolerant compared to standalone oscillators.

Temperature-dependent threshold voltage (VTH) hysteresis and gate leakage current are characterized in commercial AlGaN/GaN HEMTs. Significant peaks in VTH hysteresis are observed at 220 ± 10 K. Gate leakage current increases with increasing temperature for as-processed devices and devices irradiated with 1.8-MeV protons at OFF-state bias, due to Mott hopping. In contrast, gate leakage current for devices irradiated or stressed at ON bias increases strongly with decreasing temperature below 200 K. The increased gate leakage at low temperature and large negative bias in ON-bias stressed and/or irradiated devices is attributed primarily to trap-assisted tunneling through oxygen impurities (ON) in AlGaN. Dehydrogenation of ON–H impurity centers during stress and/or ON-bias irradiation evidently plays a key role in enhanced cryogenic gate leakage at large negative bias in these devices.

On-chip germanium-silicon (Ge-Si) photodiodes are critical elements to advancing the inclusion of silicon photonics in integrated circuit design. Understanding their radiation tolerance is essential for use in instrumentation that are operated in harsh environments, where the benefits of photonic integrated circuits on performance and compactness are increasingly advantageous. Effects of contact configuration and geometry on waveguide-integrated Ge-Si photodiodes under 1.8-MeV proton and 10-keV X-ray irradiation are studied. Modest operating dark current increases up to 35 nA or 4.25 dB result from nonradiative defect center generation and ionization-induced traps. Radiation sensitivities are compared to thermal effects on performance, supporting the relative robustness of Ge-Si photodiodes to radiation. Annealing testing is performed to evaluate interface trap stability due to total ionizing dose, which is dependent on the specific design of the photodiode. The increases to photodiode noise floor are modest overall but are important to design strategies for space and accelerator environments, especially as performance requirements and circuit complexity of integrated photonic technologies increase.

The operability and TID response of 45-nm annular RF SOI nFETs are evaluated and compared with standard layouts. All devices were exposed to 10-keV X-rays, up to a dose of 1 Mrad(SiO2), at both high-gate/low-drain and low-gate/high-drain irradiation conditions. Differences in damage response to DC and small-signal performance between samples are observed as a result of TID-sensitive oxides and their proximity to key transport regions of the devices. Annular FETs are more TID tolerant than standard nFETs, while showing small RF performance tradeoffs as well as lower drive currents and higher threshold voltages. TCAD is used to isolate critical oxides and damage mechanisms in annular and standard layouts to help confirm experimental data and observed damage trends. Taken together, these results suggest that annular FETs represent a valid TID-hardening approach in small-lithography RF SOI CMOS technology platforms for both DC and RF applications.