Ultra-Shallow Doping of GaAs with Mg, Cr, Mn and B Using Plasma Stimulated Room-Temperature Diffusion.

It is demonstrated that Mg, Cr, Mn and B can be doped close to GaAs surface by plasma doping without external bias at room temperature (RT). The process only takes a few minutes, and impurity densities in the range of 1018-1021/cm3 can be achieved with doping depths about twenty nanometers. The experiment results are analyzed and the physical mechanism is tentatively explained as follows: during the doping process, impurity ion implantation under plasma sheath voltage takes place, simultaneously, plasma stimulates RT diffusion of impurity atom, which plays the main role in the doping process. The enhanced RT diffusion coefficients of Mg, Cr, Mn and B in GaAs are all in the order of magnitude of 10-15 cm2sec-1. This is reported for the first time among all kinds of plasma assisted doping methods.

Refractive index and extinction coefficient of NH2CH = NH2PbI3 perovskite photovoltaic material.

Very recently, the NH2CH = NH2PbI3 (FAPbI3) perovskite material has attracted considerable attention in fabricating solar cells (SCs). For a photovoltaic material, its refractive index and extinction coefficient, n(λ) and k(λ), as functions of λ, are important to study its optical properties and to estimate the power conversion efficiency potential for the SCs made of it. As far as we know, to date there has been no reports of n(λ) and k(λ) for FAPbI3 material. In this article, with spectroscopic ellipsometry (SE) measurements, the n(λ) and k(λ), as well as E g = 1.45 eV for FAPbI3, are acquired. The fast deposition crystallization (FDC) procedure combined with the slowed down annealing (SDA) process is applied to fabricate smooth and uniform FAPbI3 film on quartz substrate. Several kinds of organic solvents were tried as the second solvent in the FDC procedure, and it is found that when petroleum ether is used, the smallest surface roughness and good FAPbI3 material purity of the FAPbI3 film can be acquired. The k(λ) results for FAPbI3 obtained by SE, calculated from the n(λ) using the Kramers-Kronig relationship, by absorbance, and by first-principles calculations, are compared. The n(λ) and k(λ) for FAPbI3 are also compared with those for CH3NH3PbI3, GaAs and c-Si.

Optical absorption characteristics of nanometer and submicron a-Si:H solar cells with two kinds of nano textures.

The optical absorption properties of a-Si:H have acquired much attention in solar cell(SC) research. In this paper, we studied enhancement of light absorption in the a-Si:H(10%H) SCs with thicknesses from 31.25nm to 2µm and with nano textures of the column-shaped nanohole (CLNH) array and of the cone-shaped nanohole (CNNH) array, via the Finite Difference Time Domain (FDTD) simulation. For a given type of nano texture and film thickness, d, the ultimate efficiency, the ideal efficiency without considering carrier combinations, is optimized over array period, p, and filling fraction, f, and is defined as the optimized ultimate efficiency, η(0). The simulation results demonstrated that: even for the CLNH textured a-Si:H(10%H) SCs as thin as 62.5 nm,η(0) is 19.7%. When the a-Si:H(10%H) SC is thinner than a critical depth of about 250nm, the CLNH texture is more efficient than the CNNH texture, and vice versa. When the thicknesses of SCs are very thin, especially smaller than 100nm, the efficiencies of the a-Si:H(10%H) SCs are evidently higher than those of the c-Si SCs. For example, in the CLNH arrays, when d = 62.5nm, η(0)for the a-Si:H(10%H) SCs is higher than the c-Si SCs by a factor of approximate 2.3.

Ultralow-power complementary metal-oxide-semiconductor inverters constructed on Schottky barrier modified nanowire metal-oxide-semiconductor field-effect-transistors.

We show that the threshold voltages of both n- and p-channel metal-oxide-semiconductor field-effect-transistors (MOSFETs) can be lowered to close to zero by adding extra Schottky contacts on top of nanowires (NWs). Novel complementary metal-oxide-semiconductor (CMOS) inverters are constructed on these Schottky barrier modified n- and p-channel NW MOSFETs. Based on the high performances of the modified n- and p-channel MOSFETs, especially the low threshold voltages, the as-fabricated CMOS inverters have low operating voltage, high voltage gain, and ultra-low static power dissipation.

Highly efficient phosphorescent organic light-emitting diode with a nanometer-thick Ni silicide/polycrystalline p-Si composite anode.

A phosphorescent organic light-emitting diode (PhOLED) with a nanometer-thick (approximately 10 nm) Ni silicide/ polycrystalline p-Si composite anode is reported. The structure of the PhOLED is Al mirror/ glass substrate / Si isolation layer / Ni silicide / polycrystalline p-Si/ V(2)O(5)/ NPB/ CBP: (ppy)(2)Ir(acac)/ Bphen/ Bphen: Cs(2)CO(3)/ Sm/ Au/ BCP. In the composite anode, the Ni-induced polycrystalline p-Si layer injects holes into the V(2)O(5)/ NPB, and the Ni silicide layer reduces the sheet resistance of the composite anode and thus the series resistance of the PhOLED. By adopting various measures for specially optimizing the thickness of the Ni layer, which induces Si crystallization and forms a Ni silicide layer of appropriate thickness, the highest external quantum efficiency and power conversion efficiency have been raised to 26% and 11%, respectively.

1.54 microm electroluminescence from p-Si anode organic light emitting diode with Bphen: Er(DBM)(3)phen as emitter and Bphen as electron transport material.

1.54 microm Si-anode organic light emitting devices with Er(DBM)(3)phen: Bphen and Bphen/Bphen:Cs(2)CO(3) as the emissive and electron transport layers (the devices are referred to as the Bphen-based devices) have been investigated. In comparison with the AlQ-based devices with the same structure but with AlQ:Er(DBM)(3)Phen and AlQ as the emissive and electron transport layers, the maximum EL intensity and maximum power efficiency from the Bphen-based devices increase by a factor of 3 and 2.2, respectively. The optimized p-Si anode resistivity of the Bphen-based device of 10 Omega.cm is significantly lower than that of the AlQ-based device. The NIR EL improvement can be attributed to the energy transfer from Bphen to the Er complex and equilibrium of electron injection from the Sm/Au cathode and hole injection from the p-Si anode at a higher level.

Light emission from nanoscale Si/Si oxide materials.

Most porous Si materials studied have been oxidized in various degrees. The oxidized porous Si comprises of a great quantity of nanoscale Si particles (NSPs) and each of them is covered by a Si oxide layer. The structure and luminescence properties of the NSPs embedded Si oxide and the nanoscale Si/nanoscale SiO2 multilayers are similar to those of the oxidized porous Si. All the three kinds of materials mentioned are called nanoscale Si/Si oxide materials and their photoluminescence and electroluminescence properties especially light emission mechanisms are reviewed in this article. Nanoscale Si/Si oxide materials have been well studied and are believed to be very promising Si based light emitting materials. The very distinct roles of the NSPs and the luminescence centers in Si oxide in the photoluminescence and electroluminescence from the nanoscale Si/Si oxide materials are highlighted.

Enhanced electroluminescence from nanoscale silicon p+ -n junctions made with an anodic aluminum oxide pattern.

An enhancement of the electroluminescence (EL) from nanoscale silicon p(+)-n junctions made with an anodic aluminum oxide (AAO) pattern was demonstrated. The nanoporous AAO pattern with a pore density of 1.4 x 10(10) cm(-2) and a pore diameter of 50 +/- 10 nm was fabricated by the two-step anodic oxidation method on a n-type silicon wafer. The nanoscale AAO patterned Si p(+)-n junctions achieved an EL enhancement factor up to about 5 compared to the unpatterned Si p(+)-n junctions. The enhancement may originate from a reduction of nonradiative recombination due to partial passivation of the Si surface by the AAO pattern and improvement of the light extraction due to surface nanotextures.

Schottky junction photovoltaic devices based on CdS single nanobelts.

Schottky junction photovoltaic (PV) devices were fabricated on single CdS nanobelts (NBs). Au was used as the Schottky contact, and In/Au was used as the ohmic contact to CdS NB. Typically, the Schottky junction exhibits a well-defined rectifying behavior in the dark with a rectification ratio greater than 10(3) at +/- 0.3 V; and the PV device exhibits a clear PV behavior with an open circuit photovoltage of about 0.16 V, a short circuit current of about 23.8 pA, a maximum output power of about 1.6 pW, and a fill factor of 42%. Moreover, the output power can be multiplied by connecting two or more of the Schottky junction PV devices, made on a single CdS NB, in parallel or in series. This study demonstrates that the 1D Schottky junction PV devices, which have the merits of low cost, easy fabrication and material universality, can be an important candidate for power sources in nano-optoelectronic systems.

Light coupling and modulation in coupled nanowire ring-Fabry-Pérot cavity.

CdS nanowire (NW) ring cavities were fabricated and studied for the first time. The rings with radii from 2.1 to 5.9 microm were fabricated by a nanoprobe system installed in a scanning electron microscope. Radius dependent whispering gallery modes (WGMs) were observed. A straight CdS NW with Fabry-Pérot (F-P) cavity structure was fabricated and placed by the side of a NW ring cavity to form a coupled ring-F-P cavity. When the NW ring was excited by a focused laser, a bright green light spot was observed at the output end of the straight NW, indicating that the latter had served as an effect waveguide to couple the light out from the ring cavity. The corresponding light spectrum showed that the WGMs had been modulated. We confirmed that the NW F-P cavity had served as a modulator. Such a coupled cavity has potential application in a nanophotonic system.

1.53 µm photo- and electroluminescence from Er(3+) in erbium silicate.

Si-rich silicon oxide (SRO)/Er-Si-O/SRO multilayers were prepared on p-Si substrates using magnetron sputtering. X-ray diffraction measurements indicate that a mixture of silicates Er(2)Si(2)O(7) and Er(2)SiO(5) was formed after the multilayers were annealed at 1000 and 1150 °C. Strong Er(3+) 1.53 µm photoluminescence (PL) at room temperature has been observed from these multilayers and the full width at half-maximum of the 1.53 µm peak is less than 1.8 nm for the multilayers annealed at 1150 °C. Er(3+) 1.53 µm electroluminescence has been observed from erbium silicate films for the first time.

Combination of passivated Si anode with phosphor doped organic to realize highly efficient Si-based electroluminescence.

Silicon light source plays a key role in silicon optoelectronics, but its realization is an extremely challenging task. Although there are longterm intensive efforts to this topic, the power conversion efficiency (PCE) of the silicon-based electroluminescence is still no more than 1%. In this present report, a highly efficient silicon light source has been achieved. The device structure is p-Si (5 Omegacm)/ SiO2(approximately 2 nm)/ NPB / CBP: (ppy)(2)Ir(acac) / Bphen /Bphen: Cs2CO3 / Sm / Au. The SiO2 passivated Si is the anode having a suitably high hole-injection ability, and CBP: (ppy)(2)Ir(acac) is a highly efficient phosphor doped organic material. The device turn-on voltage is 3.2 V. The maximum luminance efficiency and maximum luminous power efficiency reach 69 cd/A and 62 lm/W, respectively, corresponding to a maximum PCE of 12% and an external quantum efficiency of 17%.

Strong enhancement of Er(3+) 1.54 µm electroluminescence through amorphous Si nanoparticles.

The roles of amorphous Si nanoparticles in light-emitting diodes (LEDs) based on Er-doped Si(1+x)O(2) films (x representing the degree of Si content, and varying widely from 0 to 4.50) have been investigated. In the aspect of the LEDs' electrical performance, it was found that the incorporation of Si nanoparticles facilitates the electrical conductivity of the films by improving the carrier mobility. With x increasing from 0 to 4.50, the mobility increases monotonically up to 5 times. The efficiency of Er(3+) electroluminescence (EL) at 1.54 µm can be enhanced by as much as 160 times when the degree of Si content x is 2.00, coincident with the value at which the rate of mobility increasing versus x slows down. The fact that the maximum of EL efficiency and the slowing down of the rate of increase of mobility occur at the same x value can be explained by coalescence of Si nanoparticles starting at x = 2.

Blueshift of electroluminescence from single n-InP nanowire/p-Si heterojunctions due to the Burstein-Moss effect.

Single-crystalline n-type InP nanowires (NWs) with different electron concentrations were synthesized on Si substrates via the vapor phase transport method. The electrical properties of the InP nanowires were investigated by fabricating and measuring single NW field-effect transistors (FETs). Single InP NW/p(+)-Si heterojunctions were fabricated, and electroluminescence (EL) spectra from them were studied. It was found that both the photoluminescence (PL) spectra of the InP NWs and the EL spectra of the heterojunctions blueshift from 920 to 775 nm when the electron concentrations of the InP NWs increase from 2 × 10(17) to 1.4 × 10(19) cm(-3). The blueshifts can be attributed to the Burstein-Moss effect rather than the quantum confinement effect in the InP NWs. The large blueshifts observed in this study indicate a potential application of InP NWs in nano-multicolour displays.

High-performance logic circuits constructed on single CdS nanowires.

A high-performance NOT logic gate (inverter) was constructed by combining two identical n-channel metal-semiconductor field-effect transistors (MESFETs) made on a single CdS nanowire (NW). The inverter has a voltage gain as high as 83, which is the highest reported so far for inverters made on one-dimensional nanomaterials. The MESFETs used in the inverter circuit show excellent transistor performance, such as high on/off current ratio ( approximately 10(7)), low threshold voltage ( approximately -0.4 V), and low subthreshold swing ( approximately 60 mV/dec). With the assembly of three identical NW MESFETs, NOR and NAND gates have been constructed.

Light extraction efficiency of a top-emission organic light-emitting diode with an Yb/Au double-layer cathode and an opaque Si anode.

We have computed the transmittances of four types of cathode--Yb/Au, Al/Au, Yb/Ag, and Al/Ag double layers--and the light extraction efficiencies of the top-emission organic light-emitting diodes with these cathodes, respectively, based on the characteristic matrix method and the dissipation spectrum model. Computations show that the Yb/Au cathode has a markedly higher transmittance than the other three types of cathode when the Yb and Au thicknesses in the Yb/Au cathode are, respectively, equal to the Al (or Yb) and Au (or Ag) thicknesses in the other three types of cathode. The power lost to the Yb/Au cathode due to the surface plasmon polaritons is the lowest, and hence the device with the Yb/Au cathode has the highest extraction efficiency. The transmittances for the four cathodes are also measured experimentally.

Synthesis and optical properties of ZnTe single-crystalline nanowires.

Single-crystalline ZnTe nanowires with the zincblende structure have been synthesized on silicon (Si) substrates via a vapor phase transport method. The ZnTe (99.99%) powders were used as the source, and 10 nm-thick thermal evaporated gold (Au) film was used as the catalyst. The as-prepared ZnTe nanowires have diameters of 30-80 nm and lengths of more than 10 microm. The products were analyzed by X-ray diffraction, field emission scanning electron microscopy, and high-resolution transmission electron microscopy. Optical properties of these nanowires were investigated by room-temperature Raman scattering spectrum and temperature-dependent photoluminescence measurements. The results show that the as-prepared ZnTe nanowires are of high crystal quality.

Catalyst-free synthesis of well-aligned ZnO nanowires on In0.2Ga0.8N, GaN, and Al0.25Ga0.75N substrates.

Well-aligned ZnO nanowires have been synthesized vertically on In0.2Ga0.8N, GaN, and Al0.25Ga0.75N substrates, using a catalyst-free carbon thermal-reduction vapor phase deposition method for the first time. The as-synthesized nanowires are single crystalline wurtzite structure, and have a growth direction of [0001]. Each nanowire has a smooth surface, and uniform diameter along the growth direction. The average diameter and length of these nanowires are 120-150 nm, and 3-10 )m, respectively. We suggest that the growth mechanism follow a self-catalyzing growth model. Excitonic emission peaked around 385 nm dominates the room-temperature photoluminescence spectra of these nanowires. The room-temperature photoluminescence and Raman scattering spectra show that these nanowires have good optical quality with very less structural defects.

Synthesis of GaN nanotip triangle pyramids on 3C-SiC epilayer/Si substrates via an in situ In-doping technique.

GaN nanotip triangle pyramids were synthesized on 3C-SiC epilayer via an isoelectronic In-doping technique. The synthesis was carried out in a specially designed two-hot-boat chemical vapor deposition system. In (99.999%) and molten Ga (99.99%) with a mass ratio of about 1:4 were used as the source, and pieces of Si (111) wafer covered with 400-500 nm 3C-SiC epilayer were used as the substrates. The products were analyzed by x-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction, Raman spectroscopy, and photoluminescence measurements. Our results show that the as-synthesized GaN pyramids are perfect single crystal with wurtzite structure, which may have potential applications in electronic/photonic devices.

[Photoluminescence from Er-doped silicon-rich silicon oxide film and Er-doped silicon-rich silicon nitride film and its annealing behavior].

Room temperature photoluminescence (PL) with a peak at 1.54 microns was observed from silicon oxide, silicon-rich silicon oxide, silicon nitride and silicon-rich silicon nitride films, all doped with Er and grown by the magnetron sputtering technique. To determine the optimum annealing temperature for the 1.54 microns PL, these films were annealed in the range of 600-1,100 degrees C with an interval of 100 degrees C. Among these four types of films annealed at an identical temperature, the intensity of 1.54 microns PL peak of the Er-doped silicon-rich silicon oxide film was always the strongest one, which arrived at a maximum in 800 degrees C annealing. A 1.38 microns PL band was also observed in each of these four types of films, and which in the silicon-rich silicon oxide or silicon-rich silicon nitride films was found to be correlated with the 1.54 microns PL band in intensity.