N-doped Device Research Articles

Nitrogen in silicon for room temperature single-electron tunneling devices

Single-electron transistor (SET) has an advanced feature that can be exploited in quantum devices. For practical utilization of such devices, the room-temperature operation is highly essential. Dopant-based single-electron devices are well studied at low temperatures although a few devices are developed for high-temperature operation with certain limitations. Here, we propose and theoretically exhibit that nitrogen (N) donor in silicon is an important candidate for the effective designing of quantum devices. Theoretical calculation of the density of states using the semi-empirical density functional theory method indicates that N-donor in silicon has a deep ground state compared to a phosphorus (P) donor. The N-donor spectrum is explored in nano-silicon structure along with the P-donor. A comparative study of the Bohr radius of N-donor and P-donor is also reported. The simulated current–voltage characteristics confirm that the N-doped device is better suited for SET operation at room temperature.

Improvement on the performance of electrophosphorescent organic light-emitting device employing n-doped bis-4,6-(3,5-di-3-pyridylphenyl)-2-methylpyrimi-dine as electron-transporting layer

Abstract The effects of using Cesium azide as an n-dopant in Bis-4,6-(3,5-di-3-pyridylphenyl)-2-methylpyrimi-dine on the performances of green phosphorescent organic light-emitting device had been studied in detail for the first time. By optimizing the device structure, phosphorescent organic light-emitting device having a maximum current efficiency of 76.4 cd/A and a maximum external quantum efficiency of 21.7% was realized. In particular, the maximum power efficiency and the power efficiency at 100 cd/m2 were as high as 99.9lm/W and 99.4lm/W, respectively, which were better than the parameter on power efficiency of most reported Ir (ppy)3-OLEDs without out-coupling enhancement. Origins of the improvement on device characteristics in the n-doped device were systematically investigated by experimental and theoretical methods and the role of Cesium azide in enhancing the electron conductivity of the n-doped electron-transporting layer was discovered by X-ray photoelectron spectroscopy measurement.

ITO-free large-area top-emission organic light-emitting diode by blade coating

Large-area top-emitting organic light-emitting diodes (TEOLEDs) with multi-layer structure are successfully demonstrated using the solution-processable blade coating on ITO-free substrate. The semitransparent cathode of TEOLED is composed of lithium fluoride (LiF), aluminum (Al) and silver (Ag). The composition of 3nm Al and 10nm Ag has a transmittance of 56% and a sheet resistance of 11Ω/□. It is applied to the green phosphorescence device with an emissive area of 2cm by 2.5cm. The maximum current efficiency is 25.2cd/A with high light-emission uniformity within 10% variation. The large-area TEOLEDs show comparable current efficiency as the small-area devices with an emissive area of 2mm by 2mm (having the same device structure) and better efficiency than traditional large-area bottom-emitting devices. Cesium fluoride (CsF) and n-doped electron transport layer are applied to improve electron injection. At 6V, the luminance is raised from 141cd/m2 to 502cd/m2 and 304cd/m2, respectively. In n-doped device, a simple Al/Ag cathode is used without LiF.

Strong Enhancement of Solar Cell Efficiency Due to Quantum Dots with Built-In Charge

We report a 50% increase in the power conversion efficiency of InAs/GaAs quantum dot solar cells due to n-doping of the interdot space. The n-doped device was compared with GaAs reference cell, undoped, and p-doped devices. We found that the quantum dots with built-in charge (Q-BIC) enhance electron intersubband quantum dot transitions, suppress fast electron capture processes, and preclude deterioration of the open circuit voltage in the n-doped structures. These factors lead to enhanced harvesting and efficient conversion of IR energy in the Q-BIC solar cells.

Si doping in Ge2Sb2Te5 film to reduce the writing current of phase change memory

The characteristics of phase change memory devices in size of several micrometers and with pure Ge2Sb2Te5 (GST), N-doped GST, and Si-doped GST films were investigated and compared with each other. The Si-doped GST device can perform SET and RESET cycles, even if the Si dopant is as small as 4.1 at. %. But the GST and N-doped GST device cannot perform the RESET process, though the SET state resistance of N-doped device is almost the same as that of Si-doped device and larger than that of GST device. In order to explain this phenomenon, the electrical and DSC characteristics of three kinds of films were investigated. Phase separation was found in Si-doped GST films. The reason of the RESET ability of Si-doped GST devices is supposed to be the existence of rich Si phases which act as micro-heaters. Thermal conduction simulations confirmed this supposition and indicate that the separated high resistance phase (rich Si phase) can heat the active volume of device efficiently and reduce the writing current largely.