Room Temperature Electroluminescence Research Articles

Tensile-strained germanium microdisk electroluminescence.

We report room temperature electroluminescence of tensile-strained germanium microdisks. The strain is transferred into the microdisks using silicon nitride stressors. Carrier injection is achieved with Schottky contacts on n-type doped germanium. We show that a biaxial tensile-strain up to 0.72% can be transferred by optimizing the carrier injection profile. The transferred strain is measured by the electroluminescence spectral red-shift and compared to finite element modeling. We discuss the impact of this strain level to achieve population inversion in germanium.

Room-Temperature Near-Infrared Electroluminescence from Boron-Diffused Silicon Pn-Junction Diodes

Silicon pn junction diodes with different doping concentrations were prepared by boron diffusion into Czochralski (CZ) n-type silicon substrate. Their room-temperature near-infrared electroluminescence (EL) was measured. In the EL spectra of the heavily boron doped diode, a luminescence peak at ~1.6 m (0.78 eV ) was observed besides the band-to-band line (~1.1eV) under the condition of high current injection, while in that of the lightly boron doped diode only the band-to-band line was observed. The intensity of peak at 0.78 eV increases exponentially with current injection with no observable saturation at room temperature. Furthermore, no dislocations were found in the cross-sectional transmission electron microscopy image, and no dislocation-related luminescence was observed in the low-temperature photoluminescence spectra. We deduce the 0.78 eV emission originates from the irradiative recombination in the strain region of diodes caused by the diffusion of large number of boron atoms into silicon crystal lattice.

Enhanced performance in fluorene-free organometal halide perovskite light-emitting diodes using tunable, low electron affinity oxide electron injectors.

Fluorene-free perovskite light-emitting diodes (LEDs) with low turn-on voltages, higher luminance and sharp, color-pure electroluminescence are obtained by replacing the F8 electron injector with ZnO, which is directly deposited onto the CH3NH3PbBr3 perovskite using spatial atmospheric atomic layer deposition. The electron injection barrier can also be reduced by decreasing the ZnO electron affinity through Mg incorporation, leading to lower turn-on voltages.

Nanoheterostructures with InSb quantum dashes inserted in the InAs unipolar matrix

InSb quantum dashes (up to 2.5×109cm-2) were obtained on an InAs(001) substrate by metalorganic vapor phase epitaxy at T=440°C. A change in the geometry of the InSb nanoislands from a quantum dot to a quantum dash was observed in the dependence on growth conditions. The deposited quantum dashes with average lengths, widths and heights of 300nm, 100nm and 30nm, respectively, were strictly self-oriented by the longer side along the [110] direction. A room-temperature electroluminescence has been observed in type II heterostructures based on the InSb quantum dashes inserted in the unipolar n-InAs matrix. The nanoheterostructures exhibited a positive luminescence (3.62μm at 300K) at either forward or reversed bias, which can be ascribed to interfacial recombination transitions of electrons localized on the InAs side across the type II broken-gap InSb/InAs heterointerface to hole levels of the InSb quantum dashes.

Ion-dependent electroluminescence from trivalent rare-earth doped n-ZnO/p-Si heterostructured light-emitting diodes

We have demonstrated rare earths (REs) doped ZnO-based heterojunction light-emitting diodes (LEDs) on p-Si substrates by ultrasonic spray pyrolisis (USP). Room-temperature electroluminescence was clearly observed from reverse-biased n-ZnO:REs/p-Si diodes, which red and blue color emissions were realized from Eu and Tm ions, respectively. The narrow line-width emissions are attributed to the transitions within the shielded 4f levels of the trivalent REs ions that resulting from direct electron impact excitation during reverse bias.

Room Temperature Electroluminescence from Mechanically Formed van der Waals III–VI Homojunctions and Heterojunctions

Room temperature electroluminescence from semiconductor junctions is demonstrated. The junctions are fabricated by the exfoliation and direct mechanical adhesion of InSe and GaSe van der Waals layered crystals. Homojunction diodes formed from layers of p‐ and n‐type InSe exhibit electroluminescence at energies close to the bandgap energy of InSe (Eg = 1.26 eV). In contrast, heterojunction diodes formed by combining layers of p‐type GaSe and n‐type InSe emit photons at lower energies, which is attributed to the generation of spatially indirect excitons and a staggered valence band lineup for the holes at the GaSe/InSe interface. These results demonstrate the technological potential of mechanically formed heterojunctions and homojunctions of direct‐bandgap layered GaSe and InSe compounds with an optical response over an extended wavelength range, from the near‐infrared to the visible spectrum.

Highly-Doped, Highly-Strained Germanium and Schottky Electroluminescent Diodes

We demonstrate that room temperature electroluminescence can be obtained from n-doped germanium layers by using a Schottky contact. The electrical and optical properties of the Schottky device are improved by inserting a thin Al2O3 interfacial barrier. We also show that high active doping of Ge grown on Si can be obtained by molecular beam epitaxy by using a co-doping method with Sb and P. We finally discuss the transfer of tensile strain on microdisk resonators using silicon nitride stressor layers.

UV electroluminescence from p‐ZnO:P/n‐ZnO homojunction diode

The reliability of p-type ZnO thin films obtained by phosphorus implantation, using plasma-immersion ion implantation, followed by rapid thermal annealing is reported. Also reported is the fabrication of a ZnO-based homojunction light-emitting diode. Low-temperature photoluminescence measurements after six months showed a dominant free electron-to-acceptor peak for samples annealed at 900 and 1000°C, confirming the formation of p-type films. Room-temperature electroluminescence spectra for the p-ZnO:P/n-ZnO homojunction diode revealed ultraviolet (UV) emission at 3.18 eV; however, the dominant peak was observed at 1.8 eV because of a deep-level defect peak. Achieving dominant UV emission requires further optimisation of the device structure.

High-temperature interfacial electroluminescence in type-II broken-gap heterostructures based on InSb quantum dashes in n-InAs matrix

Room-temperature electroluminescence is observed for the first time in type-II heterostructures based on InSb quantum dashes embedded in a narrow-gap n-InAs matrix. The heterostructures exhibit positive luminescence at wavelengths in the range 3–4 μm. This is due to the interfacial radiative transitions of electrons from self-consistent quantum wells on the side of InAs matrix layers across the broken-gap type-II InSb/InAs heterointerface to quantum-well hole levels in the InSb quantum dashes, situated in the energy gap of the matrix near the InAs conduction-band bottom.

Schottky electroluminescent diodes with n-doped germanium

n-doped germanium can be used as an active material for the realization of an optical source under electrical pumping. We propose to use Schottky contacts for germanium electroluminescent devices, and we show that carrier injection and electroluminescence in these Schottky devices can be optimized by depositing a thin Al2O3 interfacial layer on top of n-doped germanium. In the latter case, hole injection is optimized due to the drastic decrease of interface trap densities and room-temperature electroluminescence can be observed at small current injection with a higher differential efficiency as compared to the standard Schottky sample.

Near-infrared electroluminescence and photo detection in InGaAs p-i-n microdisks grown by selective area growth on silicon

Microselective-area growth of p-i-n InGaAs disks on (111) silicon by metalorganic chemical vapor deposition is a promising technology for III/V-on-Si integration. As a proof-of-concept, room-temperature electroluminescence is reported from ensembles of p-i-n InGaAs-on-Si micro-disks. The observed spectrum shows peak luminescence at 1.78 μm with a local maxima at 1.65 μm. The disks are also shown to generate a measurable photo current when illuminated by infrared light with less energy than the silicon bandgap energy. This makes these InGaAs-on-Si disks a promising technology for monolithic integration of light sources and detectors with silicon photonics and complementary metal-oxide-semiconductor electronics for optical communication, sensing, and imaging.

Room temperature electroluminescence from n-ZnO:Ga/i-ZnO/p-GaN:Mg heterojunction device grown by PLD

The n-ZnO:Ga/p-GaN:Mg and n-ZnO:Ga/i-ZnO/p-GaN:Mg heterojunction light emitting diodes (LEDs) were fabricated by the pulsed laser deposition (PLD) technique. The blue electroluminescence (EL) of the n-ZnO:Ga/p-GaN:Mg heterojunction LEDs is emitted mainly from the p-GaN layer instead of the n-ZnO:Ga layer, for the reason that the electron injection from n-ZnO:Ga prevailed over the hole injection from p-GaN:Mg due to the higher carrier concentration and carrier mobility in n-ZnO:Ga. On the other hand, the n-ZnO:Ga/i-ZnO/p-GaN:Mg heterojunction LEDs exhibited dominant ultraviolet-blue emission. The reason for this difference is attributed to the inserted undoped i-ZnO layer between n-ZnO:Ga and p-GaN:Mg, in which the holes from p-GaN:Mg and the electrons from n-ZnO:Ga are recombined.

Heterojunction of ZnO nanoparticle/PMMA and its ultraviolet electroluminescence.

A ZnO nanoparticle layer was synthesized by the sol-gel method on ITO glass. Devices with a ZnO nanoparticle layer/polymethylmethacrylate (PMMA) heterojunction structure were then fabricated and the room temperature electroluminescence (EL) spectra were studied. Under DC bias, ultraviolet (UV) EL at 390 nm from the ZnO band edge emission was observed, and defect-related emission of ZnO at 600 and 760 nm were also detected. The EL mechanisms are discussed in terms of the carrier tunneling process.

(Invited) Narrow Linewidth, Highly Efficient, and Integrated Light Emitting Diodes Based on Ge Quantum Dots in Optical Microcavities

Ge self-assembled quantum dots (QDs) grown on Si are promising solution for Si-based light sources due to their emission wavelength in the telecommunication band, capability of electrical injection and CMOS process compatibility. However, as indirect band gap material, their light emission efficiency is still rather low. By embedding Ge QDs into optical microcavities with large Q-factor and small mode volume, the spontaneous emission rate can be enhanced due to the Purcell effect and the light extraction efficiency can also be improved due to the modified cavity mode fields. We have demonstrated strong and sharp resonant photoluminescence peaks from Ge QDs in photonic crystal (PhC) nanocavities and microdisk resonators [1]. For practical application, light emission by electrical injection is desirable. In this abstract, we will review some of our results on electrical injected light emitting diodes (LEDs) based on Ge QDs in microcavities. Electrical injected LEDs were firstly demonstrated by integrating vertical PIN diodes with H3-type PhC cavities [2]. Room-temperature electroluminescence (EL) was successfully observed, but with relatively broad emission peaks. This is due to the large cavity loss induced by the electrical structure. By using lateral PIN diode structure, in which the P+ and N+ regions are located laterally on the PhC slab, while the cavity region is left intrinsic, we achieved intense EL peaks around 1.3 µm with Q-factor of about 260, corresponding to a linewidth of 5 nm [3]. After optimization of PhC nanocavities and electrical structures, the Q-factor of emission peaks increased to 800-1500. The required current for occurrence of resonant peaks was reduced by one order, to 50 µA [4]. The schematic diagram and EL spectra of the device are shown in Fig. 1(a) and 1(b), respectively. Moreover, at injected current of 3 mA, we obtained a measurable output power on the pW order. We also confirmed that the output power was limited by the fabrication process and could be increased further. In order to realize monolithic integration with other photonic devices, waveguide-coupled LEDs are necessary. Waveguide-coupled microdisks containing Ge QDs were fabricated with vertical PIN diodes structures [5], as shown in Fig. 1(c). When there was current injection, light emission from the microdisk was coupled into the waveguide. Sharp resonant peaks around 1.55 µm with Q-factor over 5000 were obtained in the EL spectra collected through the waveguide, as shown in Fig. 1(d). The coupling between the waveguide and microdisk was confirmed by comparing the EL and optical transmission spectra along the waveguide. The LEDs thus can be easily integrated with other waveguide devices. Interestingly, the devices also can be operated as resonant-cavity enhanced photodetectors under reverse bias. Wavelength selective photo-response, with high responsivity and ultra-low dark current around 1.55 µm was also realized [6]. The light emission efficiency of Ge QDs themselves is fundamental to obtain higher intensity. Due to the type-II band lineup of Si/Ge heterostructure, only holes can be well confined in Ge QDs, and there is very weak confinement for electrons. By using n-type doping, extrinsic electrons can be provided and the radiative recombination is expected to be enhanced. In the talk, we will also present some results about light emission enhancement by phosphorus delta-doping between Ge QDs and Si spacers.

Coaxial Multishell (In,Ga)As/GaAs Nanowires for Near-Infrared Emission on Si Substrates

Efficient infrared light emitters integrated on the mature Si technology platform could lead to on-chip optical interconnects as deemed necessary for future generations of ultrafast processors as well as to nanoanalytical functionality. Toward this goal, we demonstrate the use of GaAs-based nanowires as building blocks for the emission of light with micrometer wavelength that are monolithically integrated on Si substrates. Free-standing (In,Ga)As/GaAs coaxial multishell nanowires were grown catalyst-free on Si(111) by molecular beam epitaxy. The emission properties of single radial quantum wells were studied by cathodoluminescence spectroscopy and correlated with the growth kinetics. Controlling the surface diffusivity of In adatoms along the NW side-walls, we improved the spatial homogeneity of the chemical composition along the nanowire axis and thus obtained a narrow emission spectrum. Finally, we fabricated a light-emitting diode consisting of approximately 10(5) nanowires contacted in parallel through the Si substrate. Room-temperature electroluminescence at 985 nm was demonstrated, proving the great potential of this technology.

Non-Lithographic Growth of Core–Shell GaAs Nanowires on Si for Optoelectronic Applications

We demonstrated a nonlithographic method for integrating GaAs nanowire (NW) array-based light-emitting diodes (LEDs) on silicon (Si) substrates. A sub-100 nm hole array on a deposited SiO2 layer was patterned on an entire 2 in. Si wafer based on a sacrificed self-assembled InAs NW array. Then, a core–shell n–p junction GaAs NW array was grown on exposed Si windows via the selective-area growth method. The electrical properties of the core–shell n–p junction GaAs NW has been measured and compared to those of the core–shell junction NWs formed via the self-assembled growth method. Room temperature electroluminescence was successfully observed from the fabricated GaAs NW array-based LEDs. The core–shell junction III–V NW array epitaxially grown on a ubiquitous Si platform could be applied to future low-cost optical devices.

Metal organic chemical vapor deposition growth of high density InAs/Sb:GaAs quantum dots on Ge/Si substrate and its electroluminescence at room temperature

We report on the metal organic chemical vapor deposition (MOCVD) growth of high density InAs/Sb:GaAs quantum dots (QDs) on Ge/Si substrate and its electroluminescence (EL) characteristics at room temperature (RT). High density (above 4 × 1010 cm−2 per layer) QDs with low coalescence emitting in the 1.3 µm band at RT with a full width and half maximum of ∼42 meV were obtained. RT EL at 1.24 µm was observed from a double heterostructure, containing eight-layer stacked InAs/Sb:GaAs QD active region. These results are promising for the realization of monolithically integrated QD laser for silicon photonics application.

Surexpression de l’IL-31 dans une forme sporadique de lichen amyloïde : un lien avec le prurit ?

Radiative recombination of carriers in two kinds of GaxIn1−xP/GaAs double-junction tandem solar cell structures was investigated by using room-temperature electroluminescence (EL) and photoluminescence (PL) techniques. Efficient radiative recombination was observed simultaneously in the top and the bottom subcells in both the samples. By studying the behavior of EL and PL spectra, the radiative recombination intensity ΦEL was demonstrated to be reliant on the material-dependent radiative recombination coefficient, base layer doping concentration and thickness. Furthermore, dependence of ΦEL on substrate misorientation in both the subcells was also evidenced, which was explained in terms of the growth-induced variations in microstructure for the GaInP top cell and in potential barrier profile across the p–n junction for the GaAs bottom cell. Based on these observations, the radiative recombination in the two base layers of the subcells was demonstrated to be the major carrier loss mechanism in the GaxIn1−xP/GaAs double-junction tandem photovoltaic devices and should be suppressed.

Silicon‐silicide quasi‐zero dimensional heterostructures for silicon based photonics, opto‐ and thermoelectronics

AbstractOptimization of growth parameters has permitted to create monolithic nanocomposites with buried nanocrystallites (NCs) of iron and chromium disilicides, polycrystalline nanocomposites with buried Mg2Si NCs and epitaxial MnSi1.74 nanoislands on Si(111) substrate. Grown quasi‐zero dimensional heterostructures with multilayers of β‐FeSi2 NCs atop silicon p‐n junction have demonstrated the range expansion of photoelectrical sensitivity up to 1.8 µm and strong room temperature electroluminescence at 1.2 – 1.6 µm. A new approach to the selective doping of embeddded nanocrystallites inside silicon matrix has been developed on the base of the successive formation of ordered superstructures of metals (Ag, Sb) together with silicide island formation. Nanocomposite layers with n‐ and p‐type conductivity and huge Seebeck coefficient (550‐750 µV/K) in the Si‐p/β‐FeSi2 NCs/Si‐p and Si/Mg2Si NCs/Si‐p and Si/Mg2Si NCs/Si‐n nanocomposites have been created and tested. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Specific features of electroluminescence in heterostructures with InSb quantum dots in an InAs matrix

The electrical and electroluminescence properties of a single narrow-gap heterostructure based on a p-n junction in indium arsenide, containing a single layer of InSb quantum dots in the InAs matrix, are studied. The presence of quantum dots has a significant effect on the shape of the reverse branch of the current-voltage characteristic of the heterostructure. Under reverse bias, the room-temperature electroluminescence spectra of the heterostructure with quantum dots, in addition to a negative-luminescence band with a maximum at the wavelength λ = 3.5 μm, contained a positive-luminescence emission band at 3.8 μm, caused by radiative transitions involving localized states of quantum dots at the type-II InSb/InAs heterointerface.