Visible-light Electroluminescence Research Articles

GHz Electroluminescence Modulation in Nanoscale Subwavelength Emitters.

We investigate light emission from nanoscale point-sources obtained in hybrid metal-GaAs nanowires embedding two sharp axial Schottky barriers. Devices are obtained via the formation of Ni-rich metallic alloy regions in the nanostructure body thanks to a technique of controlled thermal annealing of Ni/Au electrodes. In agreement with recent findings, visible-light electroluminescence can be observed upon suitable voltage biasing of the junctions. We investigate the time-resolved emission properties of our devices and demonstrate an electrical modulation of light generation up to 1 GHz. We explore different drive configurations and discuss the intrinsic bottlenecks of the present device architecture. Our results demonstrate a novel technique for the realization of fast subwavelength light sources with possible applications in sensing and microscopy beyond the diffraction limit.

Visible-light emission at room temperature in Mn-doped Si light-emitting diodes

We demonstrate Si-based light-emitting diodes that continuously emit reddish-yellow visible light at room temperature by utilizing optical transitions between the p-d hybrid orbitals of Mn atoms doped in Si. Our light-emitting diodes show clear visible-light electroluminescence with two peaks at ${E}_{1}=1.75$ and ${E}_{2}=2.30\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$, corresponding to optical transitions between p-d hybrid orbitals of Mn atoms. The electrons at the p-d hybrid orbitals of Mn in Si are excited by hot holes that are accelerated by an intensive electric field in the depletion layer of reverse biased Si $p\text{\ensuremath{-}}n$ junctions containing a Mn-doped Si (Si:Mn) layer. The observed two peaks at ${E}_{1}=1.75$ and ${E}_{2}=2.30\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ are redshifted and blueshifted by 0.14 eV, respectively, from those of GaAs:Mn or ZnS:Mn. Our observations are consistent with the $p\text{\ensuremath{-}}d$ hybridized electronic structure of Mn atoms doped in Si as predicted by first-principles calculations.

High-field electroluminescence in semiconductor tunnel junctions with a Mn-doped GaAs layer

We investigated high-field electroluminescence (EL) in semiconductor tunnel junctions with a Mn-doped GaAs layer (here, referred to as GaAs:Mn). Besides the band-gap emission of GaAs, the EL spectra show visible light emissions with two peaks at 1.94 eV and 2.19 eV, which are caused by d-d transitions of the Mn atoms excited by hot electrons. The threshold voltages for band-gap and visible light EL in the tunnel junctions with a GaAs:Mn electrode are 1.3 V higher than those of GaAs:Mn excited by hot holes in reserve biased p+-n junctions, which is consistent with the hot carrier transport in the band profiles of these structures. Our EL results at room temperature show that the electron temperature in GaAs:Mn can be as high as ∼700 K for a low input electrical power density of 0.4 W/cm2, while the lattice temperature of the GaAs:Mn layer can be kept at 340 K.

Visible-light electroluminescence in Mn-doped GaAs light-emitting diodes

We observed visible-light electroluminescence (EL) due to d-d transitions in light-emitting diodes with Mn-doped GaAs layers (here, referred to as GaAs:Mn). Besides the band-gap emission of GaAs, the EL spectra show two peaks at 1.89 eV and 2.16 eV, which are exactly the same as 4A2(4F) → 4T1(4G) and 4T1(4G) → 6A1(6S) transitions of Mn atoms doped in ZnS. The temperature dependence and the current-density dependence are consistent with the characteristics of d-d transitions. We explain the observed EL spectra by the p-d hybridized orbitals of the Mn d electrons in GaAs.

Green electroluminescence from Er-doped GaN Schottky barrier diodes

Visible light electroluminescence (EL) has been obtained from Er-doped GaN Schottky barrier diodes. The GaN was grown by molecular beam epitaxy on Si substrates using solid sources (for Ga, and Er) and a plasma source for N2. Al was utilized for both the Schottky (small-area) and ground (large-area) electrodes. Strong green light emission was observed under reverse bias, with weaker emission present under forward bias. The emission spectrum consists of two narrow green lines at 537 and 558 nm and minor peaks at 413 and at 666/672 nm. The green emission lines have been identified as Er transitions from the H11/22 and S3/24 levels to the I15/24 ground state and the blue and red peaks as the H9/22 and F9/24 Er transitions to the same ground state. The reverse bias EL intensity was found to increase linearly with bias current.

Electroluminescence of a-SiC:H multilayer films

Visible-light electroluminescence (EL) of a-SiC:H multilayer light emission diode (LED) has been investigated at the first time. The results show that, the EL intensity of the a-SiC:H LED with a a-SiC:H multilayer active i-layer (LEDM) is several times greater than that of conventional a-SiC:H LED with a single a-SiC:H i-layer (LEDS), and the threshold current is lower, the EL peak positions of LEDM are in the vicinity of 630 nm and 730 nm, the forward EL intensity is one order of magnitude greater than that of reverse. The dependence of the EL intensity on temperature are also investigated.

A study of electroluminescence in a-Si 1−xC x:H and a-Si:H devices with various structures

The electroluminescence in both nin −p a-Si:C:H and pi a-Si:H/ITO structures has been observed directly with naked eyes at room temperature. The former emisson peaks located around 1.94, 1.8 and 1.68ev when x=0.80, 0.75 and 1.28 ev at 300K and 77K. Visible-light electroluminescence of pi a-Si:H/ITO device comes from the short-wave-length tail of the whole spectrum. Therefore the visible EL intensity of the nin −p a-Si:C:H devices is much stronger than that of the pi a-Si:H/ITO devices at room temperature.