Fabrication of a bulk silicon p–n homojunction-structured light-emitting diode showing visible electroluminescence at room temperature

We have developed a novel dressed-photon-assisted annealing process, in which the distribution of dopant (boron) domains is modified in a self-organized manner based on the absorption of light having a photon energy higher than the band gap and subsequent stimulated emission. Using this process, we were able to fabricate a bulk silicon p–n homojunction-structured light-emitting diode that showed electroluminescence emission in the visible region at room temperature. A broadband spectrum with three emission peaks at 400 nm, 590 nm, and 620 nm was clearly observed.     

Bulk crystal SiC blue LED with p–n homojunction structure fabricated by dressed-photon-phonon–assisted annealing

To fabricate a high-efficiency light emitting diode using indirect-transition-type bulk crystal SiC having a p–n homojunction structure, annealing was performed using stimulated emission via dressed photons generated at the inhomogeneous domain boundaries of Al dopant sites. This device emitted electroluminescence (EL) due to a two-step transition process via dressed-photon–phonons generated at the inhomogeneous domain boundaries of the Al dopant sites. The EL emission peak wavelength was 480–515 nm when the device was driven by a direct current and 390 nm when driven by a pulsed current. The external quantum efficiency of the EL emission was 1 %, and the internal quantum efficiency was as high as 10 %.     

Mid-infrared photoconductive properties of heavily Bi-doped PbTe p–n homojunction diode grown by liquid-phase epitaxy

We fabricated a heavily Bi-doped (x_Bi ≈ 2 × 10¹⁹ cm⁻³) PbTe p–n homojunction diode that detects mid-infrared wavelengths by the temperature difference method (TDM) under controlled vapor pressure (CVP) liquid phase epitaxy (LPE). The photocurrent density produced by the heavily Bi-doped diode sample is approximately 20 times and 3 times greater than that produced by an undoped and heavily In-doped sample, respectively. By varying the ambient temperature from 15 K to 225 K, the detectable wavelength is tunable from 6.18 μm to 4.20 μm. The peak shift of the detectable wavelength is shorter in the heavily Bi-doped sample than in the undoped sample, consistent with our previously proposed model, in which Bi–Bi nearest donor–acceptor pairs are formed in the heavily Bi-doped PbTe liquid phase epitaxial layer. Current–voltage (I–V) measurements of the heavily Bi-doped diode sample under infrared exposure at 77 K indicated a likely leak in the dark current, arising from the deeper levels. From the dark I–V measurements, the activation energy of the deep level was estimated as 0.067 eV, close to the energy of the deep Tl-doped PbTe acceptor layer. We conclude that the deep level originates from the Tl-doped p-type epitaxial layer.     

Spectral properties of a metal–dielectric sensor structure

Numerical analysis of the spectral characteristics of a two-layer structure is performed in the processes of fabrication, measurement, and application of this structure as a sensor of the refractive index of the external medium. The effect of environmental conditions and parameters of the metal and dielectric layers on the sensor sensitivity is discussed. The results of model calculations are confirmed by experimental studies.     

Evaluating the coupling strength of electron–hole pairs and phonons in a 0.9 μm-wavelength silicon light emitting diode using dressed-photon–phonons

We investigated the coupling strength between electron–hole pairs and phonons in a silicon light emitting diode (Si-LED) fabricated by dressed-photon-assisted annealing. This Si-LED emitted light in the 1.4 eV photon energy (0.9 μm wavelength) band, and phonon sidebands were observed in the emission spectrum. From a comparison with simulation results, these sidebands were found to be due to coupling of electron–hole pairs with LO-mode and TO-mode coherent phonons via dressed-photon–phonons. The value of the Huang–Rhys factor, $S$ , representing the coupling strength between the electron–hole pairs and the phonons was estimated to be $4.08 \pm 0.02$ .     

Spectral properties of a ■-configuration atom driven by a pair of bichromatic fields

The absorption spectrum and the incoherent fluorescence spectrum of the lower transition in an ■-configuration threelevel atomic system driven by a pair of bichromatic fields is investigated. The transmission of the absorption profile from a multipeaked feature to a single-peak feature is identified. Adjusting the relative phase between the two driving fields, the splitting effects of the spectral peaks occur both in the fluorescence and the absorption spectra. Furthermore, phase modulating can dramatically lead to a great suppression of the amplitudes of the whole absorption spectrum. Physically, this effect is attributed to the phase-sensitive nature of the populations and coherence between the atomic states of the system.     

The effects of surface modification on the electrical properties of p–n + junction silicon nanowires grown by an aqueous electroless etching method

Journal of Nanoparticle Research - Applying engineering controls to airborne engineered nanoparticles (ENPs) is critical to prevent environmental releases and worker exposure. This study evaluated...     

An experimental investigation of P–N diode electrical characteristics by soft X-ray annealing method

We present new experimental results for the electrical behaviors of P–N junction diodes irradiated by X-rays. The current–voltage (I–V) characteristics of the P–N junction diodes were measured at room temperature. The reverse and forward current before and after irradiation can be explained relative to the following parameters: carrier generation lifetime (τ_g), ideality factor (n), series resistance (R_s), and sheet resistance (ρ). After irradiation at 40 and 55 keV, a small increment in the diode leakage current was seen, while at 70 keV of exposure, the leakage current was slightly decreased. On the other hand, the forward current was dramatically increased by about three orders of magnitude. In addition, the series resistance of the diodes was confirmed to be positively modified by the use of the soft X-ray annealing method.     

Non-monotonic dependence of current upon i-width in silicon p–i–n diodes

Silicon p–i–n diodes with different i-region widths are fabricated and tested. It is found that the current shows the non-monotonic behavior as a function of i-region width at a bias voltage of 1.0 V. In this paper, an analytical model is presented to explain the non-monotonic behavior, which mainly takes into account the diffusion current and recombination current contributing to the total current. The calculation results indicate that the concentration ratio of p-region to n-region plays a crucial role in the non-monotonic behavior, and the carrier lifetime also has a great influence on this abnormal phenomenon.     

High-efficiency p–i–n organic light-emitting diodes with a novel n-doping electron transport layer

We demonstrate p–i–n organic light-emitting diodes (OLEDs) incorporating an n-doping transport layer which comprises 8-hydroxy-quinolinato lithium (Liq) doped into 4′7-diphyenyl-1,10-phenanthroline (Bphen) as ETL and a p-doping transport layer which includes tetrafluro-tetracyano-quinodimethane (F₄-TCNQ) doped into 4,4′,4″-tris(3-methylphenylphenylamono) triphenylamine (m-MTDATA). In order to examine the improvement in the conductivity of transport layers, hole-only and electron-only devices are fabricated. The current and power efficiency of organic light-emitting diodes have been improved significantly after introducing a novel n-doping (Bphen: 33 wt% Liq) layer as an electron transport layer (ETL) and a p-doping layer composed of m-MTDATA and F₄-TCNQ as a hole transport layer (HTL). Compared with the control device (without doping), the current efficiency and power efficiency of Device C (most efficient) is enhanced by approximately 51% and 89%, respectively, while driving voltage is reduced by 29%. This improvement is attributed to the improved conductivity of the transport layers that leads to the efficient charge balance in the emission zone.     

Memory properties of a Ge nanocrystal MOS device fabricated by pulsed laser deposition

The charge–storage properties of Ge nanocrystal (Nc) memory devices with MOS structure have been studied. The Ge nanocrystals (Ncs) were prepared on a p-Si (100) matrix by means of pulsed laser deposition (PLD) combined with rapid annealing in the presence of Ar gas. The device is characteristic of better switching characteristics (the I _on/I _off>10⁵), low leakage current, which was attributed to the effect of Coulomb blockade preventing injection. A significant threshold-voltage shift of 0.85 V was observed when an operating voltage of 5 V was implemented on the device. The kind of hysteresis behavior in the double sweep suggests that the device has a good electrostatic control over the Ge Nc channel.     

Magnetic properties of Co–Cu nanowire arrays fabricated in different conditions by SC electrodeposition

Magnetic Co–Cu alloy nanowires with low Cu content were prepared by SC electrodeposition in pores of anodic aluminum oxide templates. The as-deposited Co–Cu nanowires, with a diameter of 15 nm, show distinctive magnetic anisotropy as an applied magnetic field parallel to the axis of nanowires. With increase in the molar ratio of Co and Cu, the coercivity along nanowire axis increases and reaches a maximum value of 1977.5 Oe at the Co/Cu molar ratio of 60:1, but the maximum value of coercivity increases to 1743.6 Oe with the decrease of frequency to 2 Hz.     

Optoelectronic properties of bottom gate-defined in-plane monolayer WSe_2 p–n junction

Monolayer transition-metal dichalcogenides(TMDs) are considered to be fantastic building blocks for a wide variety of optical and optoelectronic devices such as sensors, photodetectors, and quantum emitters, owing to their direct band gap,transparency, and mechanical flexibility. The core element of many conventional electronic and optoelectronic devices is the p–n junction, in which the p-and n-types of the semiconductor are formed by chemical doping in different regions.Here, we report a series of optoelectronic studies on a monolayer WSe_2 in-plane p–n photodetector, demonstrating a lowpower dissipation by showing an ambipolar behavior with a reduced threshold voltage by a factor of two compared with the previous results on a lateral electrostatically doped WSe_2 p–n junction. The fabrication of the device is based on a polycarbonates(PC) transfer technique and hence no electron-beam exposure induced damage to the monolayer WSe_2 is expected. Upon optical excitation, the photodetector demonstrates a photoresponsivity of 0.12 mA·W~(-1) and a maximum external quantum efficiency of 0.03%. Our study provides an alternative platform for a flexible and transparent twodimensional photodetector, from which we expect to further promote the development of next-generation optoelectronic devices.     

Photoluminescence of amorphous carbon films fabricated by layer—by—layer hydrogen plasma chemical annealing method

A method in which nanometre-thick film deposition was alternated with hydrogen plasma annealing (layer-by-layer method) was applied to fabricate hydrogenated amorphous carbon films in a conventional plasma-enhanced chemical vapour deposition system.It was found that the hydrogen plasma treatment could decrease the hydrogen concentration in the films and change the sp^2/sp^3 ratio to some extent by chemical etching.Blue photoluminescence was observed at room temperature,as a result of the reduction of sp^2 clusters in the films.     

van der Waals gap-inserted light-emitting p–n heterojunction of ZnO nanorods/graphene/p-GaN film

We report on the electroluminescent (EL) and electrical characteristics of graphene-inserted ZnO nanorods (NRs)/p-GaN heterojunction diode. In a comparative study, ZnO NRs/p-GaN and ZnO NRs/graphene/p-GaN heterojunctions exhibit white and yellow EL emissions, respectively, at reverse bias (rb) voltages. The different EL colors are results of different dichromatic EL peak intensity ratios between 2.25 and 2.8 eV light emissions which are originated from ZnO and p-GaN sides, respectively. The 2.25 eV EL is predominant in both the heterojunctions, because of recombination by numerous electrons tunneled from p-GaN to ZnO across the thin barriers of the staggered broken gap with a large band offset in ZnO/p-GaN and the van der Waals (vdW) gap formed by graphene insertion at ZnO NRs/p-GaN. However, as for the 2.8 eV EL intensity, ZnO NRs/graphene/p-GaN hardly shows the EL emission, whereas ZnO NRs/p-GaN exhibits the substantially strong EL peak. We discuss that the significantly reduced 2.8 eV EL emission of ZnO NRs/graphene/p-GaN is a result of decreased depletion layer thickness at p-GaN side where the recombination events occur for 2.8 eV EL before the reverse bias-driven tunneling because the insertion of graphene (or vdW gap barrier) inhibits the carrier diffusion whose amount determines the depletion thickness when forming the heterojunctions. This study opens a way of suppressing (or enhancing) the specific EL wavelength for the dichromatic EL-emitting heterojunctions simply by inserting atom-thick vdW layer.     

Influence of vacuum annealing on structures and mechanical properties of Al–Ti–N films deposited by multi-arc ion plating

The Al–Ti–N films deposited by multi-arc ion plating have been annealed in vacuum within the range of 700–1100 °C. X-ray diffraction results showed that the structure of the films underwent the formation of coherent c-TiN and c-AlN for the annealing temperatures were up to 900 °C. A new phase AlTi_x (x = 0.50, 0.56, 3) was observed after annealing. The X-ray photoelectron spectroscopy results showed the intensity of Ti–Al bonds decreased as annealing temperatures increased, indicating the decomposition of (Al, Ti)N into c-TiN and c-AlN were at the expense of Ti–Al bonds. Differential scanning calorimetry experiments were used to investigate the dynamic behavior of the films during annealing process and the results showed that the N₂ formed as a consequence of the phase transformation process. The release of the N₂ resulted in the peeling of the films from the substrates. The film exhibited a maximum hardness of 39 GPa after 900 °C annealing due to the formation of coherent c-TiN and c-AlN phases. In addition, we also investigated the influence of vacuum annealing on adhesive strength.