The integration of efficient, miniaturized group IV lasers into CMOS architecture holds the key to the realization of fully functional photonic-integrated circuits. Despite several years of progress, however, all group IV lasers reported to date exhibit impractically high thresholds owing to their unfavourable bandstructures. Highly strained germanium with its fundamentally altered bandstructure has emerged as a potential low-threshold gain medium, but there has yet to be a successful demonstration of lasing from this seemingly promising material system. Here we demonstrate a low-threshold, compact group IV laser that employs a germanium nanowire under a 1.6% uniaxial tensile strain as the gain medium. The amplified material gain in strained germanium can sufficiently overcome optical losses at 83 K, thus allowing the observation of multimode lasing with an optical pumping threshold density of ~3.0 kW cm⁻². Our demonstration opens new possibilities for group IV lasers for photonic-integrated circuits.

This paper proposes a condition monitoring system for aluminium electrolytic capacitors used as dc-link capacitors in industrial power converters. Electrolytic capacitors are one of the most fragile components of a power converter system because of their wear-out failures and short lifespan. Therefore, the use of condition monitoring systems for aluminium electrolytic capacitors can allow preventive maintenance to be performed, thereby avoiding unexpected shutdown and downtime. The dominant wear-out mechanisms in aluminium electrolytic capacitors are characterized by the increase in equivalent series resistance. Hence, the condition monitoring system proposed in this paper is based on the online estimation of capacitor's equivalent series resistance using the switching frequency components of dc-link capacitor voltage and capacitor current. The equivalent series resistance estimation method is tested using PSpice circuit simulator and validated experimentally using a custom-made inverter. Finally, the equivalent series resistance estimation method is adapted for condition monitoring of capacitors in industrial power converters and the proposed condition monitoring system is implemented in a commercial ac drive system to prove the applicability of proposed method to industrial power converters.

Aluminium electrolytic capacitors are some of the weakest components in a power converter system. Therefore, condition monitoring of capacitors can prevent unexpected system downtime due to capacitor failures. This paper proposes a condition monitoring system for electrolytic capacitors used as dc-link capacitors in front-end rectifier fed three-phase inverters. The proposed methodology is based on equivalent series resistance (ESR) and capacitance estimation using Goertzel algorithm. The ESR is used as the degradation indicator whereas the capacitance value is used as both degradation indicator and temperature-sensitive electrical parameter to estimate core or hotspot temperature. Even though the use of capacitance to estimate hotspot temperature has already been proposed, this paper tackles the practical difficulties associated with capacitor core-temperature estimation using the capacitance and demonstrates a successful implementation strategy for applying this method in power converters to estimate core temperature online. It also introduces a self-calibration procedure to mitigate ageing related errors in temperature estimation. An experimental setup is used to verify the proposed conditioning monitoring system. The experimental results prove the effectiveness and accuracy of the proposed technique.

In this paper, normal incidence vertical $p\text{-}i\text{-}n$ photodetectors on a germanium-on-insulator (GOI) platform were demonstrated. The vertical $p\text{-}i\text{-}n$ structure was realized by ion-implanting boron and arsenic at the bottom and top of the Ge layer, respectively, during the GOI fabrication. Abrupt doping profiles were verified in the transferred high-quality Ge layer. The photodetectors exhibit a dark current density of $\sim 47\mathrm{mA}/{\mathrm{cm}}^2$ at $-1\mathrm{V}$ and an optical responsivity of 0.39 A/W at 1550 nm, which are improved compared with state-of-the-art demonstrated GOI photodetectors. An internal quantum efficiency of $\sim 97\%$ indicates excellent carrier collection efficiency of the device. The photodetectors with mesa diameter of 60 μm exhibit a 3 dB bandwidth of $\sim 1\mathrm{GHz}$, which agrees well with theoretical calculations. The bandwidth is expected to improve to $\sim 32\mathrm{GHz}$ with mesa diameter of 10 μm. This work could be similarly extended to GOI platforms with other intermediate layers and potentially enrich the functional diversity of GOI for near-infrared sensing and communication integrated with Ge CMOS and mid-infrared photonics.

Dark current characteristics of germanium (Ge) vertical p-i-n photodetectors were studied. Ge photodetectors were demonstrated on the germanium-on-insulator (GOI) platforms realized via direct wafer bonding and layer transfer. GOI platforms with two different threading dislocation densities (TDDs) of 3.2 × 10⁶ cm⁻² (low TDD) and 5.2 × 10⁸ cm⁻² (high TDD) were varied via furnace annealing in oxygen ambient. An ultra-low dark current density of 1.12 mA/cm² for epi-Ge photodetectors was obtained for a low TDD Ge photodetector. This is reduced by a factor of 53 in comparison with a high TDD Ge photodetector. A dominant leakage contribution component shifts from bulk leakage to surface leakage as TDD decreases to 3.2 × 10⁶ cm⁻², suggesting that advanced surface passivation is required to further reduce the leakage current. Through an activation energy study, it is revealed that a primary bulk leakage mechanism shifts from Shockley–Read–Hall (SRH) leakage to diffusion leakage in a temperature range of 323–353 K. The surface leakage performed with plasma enhanced chemical vapor deposition-deposited SiO₂ is governed by SRH and trap-assisted tunneling leakage processes. Two orders of magnitude enhancement in the effective carrier lifetime is observed with the reduction in TDD. This work suggests that bulk leakage current density and effective lifetime analysis provide a better understanding of TDD-dependent dark leakage current study.