Andrei Nitescu

Gain-layer degradation from exposure to radiation limits the use of Low-Gain Avalanche Diodes (LGADs) in high energy particle physics detector experiments. Proper understanding of how the gain-layer is destroyed is not available on a defect level. Only measurements for materials with much lower effective doping concentrations are available. The direct study of the gain-layer is not possible with typical defect spectroscopy measurements like Thermally Stimulated Currents (TSC) and Deep-Level Transient Spectroscopy (DLTS). To combat this problem and gain a better understanding of the processes which degrade LGADs, the Gain-Layer Project was started. This project produced 19050 diodes with various Boron, Phosphorus, Oxygen and Carbon concentrations. The material used is low-resistivity p-type Silicon. The effective doping concentrations are in the order of a LGAD gain-layer. These diodes will serve the defect community in the coming years for various studies. This article introduces this project with detailed descriptions of the diodes, their flavours and their processing, and reports on results from I-V, C-V, SIMS and DLTS measurements on unirradiated diodes.

Layers of HfO ₂ and (Hf,Zr)O ₂ crystalline nano‐particles are synthesized via direct liquid injection atomic layer deposition, and a comprehensive set of structural, chemical, and electrical characterizations is employed to elucidate their phase composition and functional behavior. X‐ray photoelectron spectroscopy revealed a compositional contrast between the films: (Hf,Zr)O ₂ layers contained up to 45% stoichiometric oxide, while pure HfO ₂ films are dominated by sub‐oxides, especially under strongly reducing conditions, in which exclusively sub‐oxide phases and p‐type semiconducting behavior is revealed. Electrical measurements indicated room‐temperature stabilization of polar phases and tetragonal‐to‐orthorhombic phase transition with a Curie temperature near 200 K. FTIR spectroscopy confirmed the presence of tetragonal and orthorhombic HfO ₂ phases, providing insight into minor features observed ≈30° (2θ) in X‐ray diffraction patterns. Notably, devices incorporating an AlN interlayer demonstrated a significant enhancement in pyroelectric performance, suggesting this strategy to advance the pyroelectric performance of HfO ₂ ‐based materials, supporting their development for lead‐free sensor technologies.

The acceptor removal process is the most detrimental effect encountered in irradiated boron-doped silicon. This process is caused by a radiation-induced boron-containing donor (BCD) defect with bistable properties that are reflected in the electrical measurements performed in usual ambient laboratory conditions. In this work, the electronic properties of the BCD defect in its two different configurations (A and B) and the kinetics behind transformations are determined from the variations in the capacitance-voltage characteristics in the 243–308 K temperature range. The changes in the depletion voltage are consistent with the variations in the BCD defect concentration in the A configuration, as measured with the thermally stimulated current technique. The A→B transformation takes place in non-equilibrium conditions when free carriers in excess are injected into the device. B→A reverse transformation occurs when the non-equilibrium free carriers are removed. Energy barriers of 0.36 eV and 0.94 eV are determined for the A→B and B→A configurational transformations, respectively. The determined transformation rates indicate that the defect conversions are accompanied by electron capture for the A→B conversion and by electron emission for the B→A transformation. A configuration coordinate diagram of the BCD defect transformations is proposed.

Embedding electronic and optoelectronic devices in common, daily use objects is a fast developing field of research. New architectures are needed for migrating from the classic wafer- based substrates. Novel types of flexible PMMA/Au/Alq ₃ /LiF/Al structures were obtained starting from electrospun polymer fibers. Thus, using an electrospinning process poly (methyl metacrylate) (PMMA) nanofibers were fabricated. A thin Au layer deposition rendered the fiber array conductive, this being further employed as the anode. The next steps consisted of the thermal evaporation of tris(8-hydroxyquinolinato) aluminum (Alq ₃ ) and aluminum deposition as the cathode. The Au covered PMMA nanofiber layer had a similar behavior with an indium tin oxide film i.e. low sheet resistance 10.6 Ω/sq and high transparency. The low electrode resistivities allow an electron drift mobility of about 10 ^–6 cm ² V ⁻¹ s ⁻¹ at a low applied field, similar to the counterpart structures based on thin films. Concerning the relaxation processes in these structures, the Cole–Cole plots exhibit a slightly deformed semicircle, indicating a more complex equivalent circuit for the processes between metal electrodes and the active layer. This equivalent circuit includes reactance equivalent processes at the anode, cathode, in the active layer and most probably originates from the roughness of the metallic electrodes.