Thin-film quantum dot photodiode for monolithic infrared image sensors

Imaging in the infrared wavelength range has been fundamental in scientific, military and surveillance applications. Currently, it is a crucial enabler of new industries such as autonomous mobility (for obstacle detection), augmented reality (for eye tracking) and biometrics. Ubiquitous deployment of infrared cameras (on a scale similar to visible cameras) is however prevented by high manufacturing cost and low resolution related to the need of using image sensors based on flip-chip hybridization. One way to enable monolithic integration is by replacing expensive, small-scale III-V-based detector chips with narrow bandgap thin-films compatible with 8- and 12-inch full-wafer processing. This work describes a CMOS-compatible pixel stack based on lead sulfide quantum dots (PbS QD) with tunable absorption peak. Photodiode with a 150-nm thick absorber in an inverted architecture shows dark current of 10(-6) A/cm(2) at 2 V reverse bias and EQE above 20% at 1440 nm wavelength. Optical modeling for top illumination architecture can improve the contact transparency to 70%. Additional cooling (193 K) can improve the sensitivity to 60 dB. This stack can be integrated on a CMOS ROIC, enabling order-of-magnitude cost reduction for infrared sensors

Power harvesting in a helicopter lag damper

In this paper a new power harvesting application is developed and simulated. Power harvesting is chosen within the European Clean Sky project as a solution to powering in-blade health monitoring systems as opposed to installing an elaborate electrical infrastructure to draw power from and transmit signals to the helicopter body. Local generation of power will allow for a ‘plug and play’ rotor blade and signals may be logged or transmitted wirelessly.\ud The lag damper is chosen to be modified as it provides a well defined loading due to the re-gressive damping characteristic. A piezo electric stack is installed inside the damper rod, effec-tively coupled in series with the damper. Due to the well defined peak force generated in the damper the stack geometry requires a very limited margin of safety. Typically the stack geometry must be chosen to prevent excessive voltage build-up as opposed to mechanical overload.\ud Development and simulation of the model is described starting with a simplified blade and piezo element model. Presuming specific flight conditions transient simulations are conducted using various power harvesting circuits and their performance is evaluated. The best performing circuit is further optimized to increase the specific power output. Optimization of the electrical and mechanical domains must be done simultaneously due to the high electro-mechanical cou-pling of the piezo stack. The non-linear electrical properties of the piezo material, most notably the capacitance which may have a large influence, are not yet considered in this study.\ud The power harvesting lag damper provides sufficient power for extensive health monitoring systems within the blade while retaining the functionality and safety of the standard component. For the 8.15m blade radius and 130 knots flight speed under consideration simulations show 7.5 watts of power is generated from a single damper

Characterization and Modeling of the Threshold Voltage Instability in p-Gate GaN HEMTs

The p-gate GaN HEMT is a modern power semiconductor transistor capable of overcoming the switching speed limitation of conventional Silicon-based technologies. However, the GaN HEMT is a fairly new technology that still suffers undesired effects that affect its operation. Nowadays, the most prominent effects are the shift and instability of the threshold voltage Vth, caused by capacitive coupling into the gate stack as well as trapping, accumulation, and depletion of carriers. In this study, an experimental characterization of the Vth behavior is executed and subsequently used to develop a physically-based compact model. For this purpose, a custom setup is developed capable of high-resolution transient measurements for pulse lengths ranging from 100 ns up to 100 s. Utilizing the setup, commercially available state-of-the-art p-gate GaN HEMTs are investigated, showing a Vth shift and instability that appears relevant up to the nominal operation. The experimental results show that the drain-source voltage VDS yields a Vth shift, which, when applied for long durations (e.g., during off-state), leads to an additional Vth instability. The gate-source voltage VGS also yields significant Vth instabilities, which correlate with the VDS-induced effects. Furthermore, the driving conditions causing an impact on Vth appear to also correlate with the devices’ short-circuit capability and degradation. However, no available models cover the Vth behavior, which is necessary to predict their impact and reliability concerns. Consequently, a compact model is developed based on the surface potential for the drain path, extended by the conduction mechanisms covering the gate path. Finally, the Vth shift is modeled based on capacitive coupling into the gate, while for the Vth instabilities, a possible implementation is exemplified for the impact of VDS

The Effects of GaAs substrate miscut on InAs quantum dot optoelectronic properties: Examined by photoreflectance (PR) and deep level transient spectroscopy (DLTS)

In this work, advanced III-V quantum dot (QD) materials are discussed and examined theoretically. The significance of substrate miscut with regards to QD growth is discussed and previous experimental data are examined to show established trends with regards to favorable miscut degree. In order to examine the miscut effect further, multiple testing techniques are presented which characterize material quality as it pertains to optoelectronic device performance, including optical and electrical spectroscopic methods. The optical probing techniques of photoluminescence (PL) and photoreflectance (PR) are used to experimentally characterize the optical properties of GaAs baseline and InAs/GaAs one-layer QD samples. Experimental results reveal conclusive trends concerning QD energetic transitions and material quality as it relates to substrate miscut. Deep level transient spectroscopy (DLTS) was investigated as an experimental method to inspect possible non-radiative defects or other QD defect properties which may contribute to PL signal degradation in miscut samples. Included in the DLTS evaluation section, I-V and C-V analyses are presented to pinpoint deep traps for profiling, as well as obtain general material parameters and trends. The deep defect profiling suggests differences between miscut samples. The behavior of the reduced PL signal, corresponding to reduced radiative-recombination in certain miscut samples, is discussed as related to the compilation of data obtained through optical and electrical probing