Optical and electrical properties of undoped and doped Ge nanocrystals

Size-dependent photoluminescence characteristics from Ge nanocrystals embedded in different oxide matrices have been studied to demonstrate the light emission in the visible wavelength from quantum-confined charge carriers. On the other hand, the energy transfer mechanism between Er ions and Ge nanocrystals has been exploited to exhibit the emission in the optical fiber communication wavelength range. A broad visible electroluminescence, attributed to electron hole recombination of injected carriers in Ge nanocrystals, has been achieved. Nonvolatile flash-memory devices using Ge nanocrystal floating gates with different tunneling oxides including SiO2, Al2O3, HfO2, and variable oxide thickness [VARIOT] tunnel barrier have been fabricated. An improved charge storage characteristic with enhanced retention time has been achieved for the devices using VARIOT oxide floating gate

The impact of TiW barrier layer thickness dependent transition from electro-chemical metallization memory to valence change memory in ZrO₂ -based resistive switching random access memory devices

The effect of TiW metal barrier layer thickness on voltage-current characteristics of the Cu/TiW/ZrO2/TiN conductive bridge random access memory device was systematically investigated. The change of reset behavior from abrupt decrease to gradual decrease with increasing TiW thickness was observed. Electronic conduction during the forming process was also analyzed to obtain detailed information about the effect of TiW layer thickness on the nature of the conduction phenomenon. The temperature coefficient of resistance of the conductive filament confirms that an electro-chemical metallization (ECM) based conduction was observed in the devices made with a thinner TiW layer. On the other hand, valence change memory (VCM) based conduction was observed with a thick TiW layer. A conduction mechanism is proposed to explain the ECM to VCM conduction transformation phenomenon

Fast, highly flexible, and transparent TaO_x-based environmentally robust memristors for wearable and aerospace applications

Memristor devices that can operate at high speed with high density and nonvolatile capabilities have great potential for the development of high data storage and robust wearable devices. However, in real-time, the performance of memristors is challenged by their instability toward harsh working conditions such as high temperature, extreme humidity, photo irradiation, and mechanical bending. Herein, we introduce a TaOx/AlN-based flexible and transparent memristor device having stable endurance under extreme 2 mm bending (for more than 107 cycles) with an ON/OFF ratio of more than 2 orders of magnitude at 25 ns rapid switching. This device exhibits excellent flexibility under extreme bending conditions (bending radius of 2 mm) even with intense ultraviolet (UV) radiation. A thin AlN insertion layer having low dielectric and high thermal conductivity plays a crucial role in improving the switching stability and device flexibility. In particular, the devices exhibit excellent minimum switching fluctuations under UV irradiation, >106 s nonvolatility retention at high temperature (135 °C), various gas ambient, and damp heat test (humidity 95.5%, 83 °C) because of the indium metal drift during the switching process and high bonding energy of Ta–O. Most importantly, direct observation of indium metal strongly anchored in the TaOx switching layer during the switching process is reported for the first time via transmission electron microscopy, which provides clear insights into the switching phenomenon. Furthermore, the results of electrical and material analyses explain that our facile device design has excellent potential for wearable and aerospace applications