Gallium Nitride Quantum Dots Research Articles

Photonic Properties of Thin Films Composed of Gallium Nitride Quantum Dots Synthesized by Nonequilibrium Plasma Aerotaxy.

Gallium nitride quantum dots (GaN QDs) are a promising material for optoelectronics, but the synthesis of freestanding GaN QDs remains a challenge. To date, the size-dependent photonic properties of freestanding GaN QDs have not been reported. Here, we examine the photonic properties exhibited by thin films composed of GaN QDs synthesized by nonequilibrium plasma aerotaxy. Each film exhibited two photoluminescence peaks after exposure to ambient air. The first peak was in the ultraviolet spectral region, and the second peak was in the visible region. Both peak positions depended on the QD size. Our findings, supported by transient absorption spectroscopy experiments, suggest that conduction band to valence band recombination was the cause of the ultraviolet photoluminescence and that recombination between the conduction band and an acceptor level was the cause of visible photoluminescence. Furthermore, we show that coating the surface of fresh QDs with Al2O3 suppressed the visible region photoluminescence, corroborating the conclusion that the photoactive defect was caused by oxidation in air.

Oxygen-doped colloidal GaN quantum dots with blue emission

Gallium nitride quantum dots (GaN QDs), as a third-generation semiconductor material, are usually synthesized through a vapor deposition method at an elevated temperature (typically ≥800 °C). Thermal injection method is rarely reported for the synthesis of GaN QDs due to the lack of active precursors and the require of harsh reaction conditions. Here, we report the fabrication of oxygen doped colloidal GaN QDs via rapid thermal injection. By screening the reaction temperature and solvent, well-dispersed GaN QDs with a size of 3.8 nm were obtained in octadecylamine (ODA) at 360 °C. The synthesized GaN QDs show blue emission, the maximum emission wavelength is about 440 nm, and the photoluminescence quantum yield is 14.3%. Furthermore, we reveal the donor-acceptor mechanism of blue emission from GaN QDs. During the growth of GaN QDs, oxygen atoms occupy some nitrogen sites and produce a shallow oxygen donor energy level (ON). A part of the ON can be combined with the adjacent gallium vacancy (VGa) to form a VGa-ON acceptor, whose energy level is about 0.98 eV above the valence band of GaN QDs. The transition of excited electrons from the donor (ON) to the acceptor (VGa-ON) is responsible for the blue emission of GaN QDs.

Electroluminescence from GaN‐Based Quantum Dots

AbstractBulk gallium nitride (GaN) has shown great success in light‐emitting diodes (LEDs), but the use of its counterpart GaN quantum dots (QDs) to obtain electroluminescence has not yet been reported. In this work, the first GaN‐based QLED is demonstrated using Zn‐doped GaN (GaN: Zn) QDs, which is achieved through the combination of trap passivation, energy level adjustment, and morphology engineering. Pure GaN QDs and GaN: Zn QDs are synthesized, and it is found that Zn doping shifts the GaN QD emission from 321 to 377 nm and tunes the highest occupied molecular orbital energy level from 8.6 eV (of original GaN QDs) to 6.9 eV. Multiple washing posttreatment is further developed to improve QD film morphology and size distribution. The optimized GaN: Zn QDs are employed to fabricate solution‐processed LEDs, and the first GaN‐based QLEDs are reported with a maximum quantum efficiency of 0.004%.

Droplet epitaxy of InGaN quantum dots on Si (111) by plasma-assisted molecular beam epitaxy

The droplet epitaxy of indium gallium nitride quantum dots (InGaN QDs), the formation of In–Ga alloy droplets in ultra-high vacuum and then surface nitridation by plasma treatment, is firstly investigated by using plasma-assisted molecular beam epitaxy. During the droplet epitaxy process, in-situ reflection high energy electron diffraction patterns performs the amorphous In–Ga alloy droplets transform to polycrystalline InGaN QDs, which are also confirmed by the characterizations of transmission electron microscopy and X-ray photoelectron spectroscopy. The substrate temperature, In–Ga droplet deposition time, and duration of nitridation are set as parameters to study the growth mechanism of InGaN QDs on Si. Self-assembled InGaN QDs with a density of 1.33 × 1011 cm−2 and an average size of 13.3 ± 3 nm can be obtained at the growth temperature of 350 °C. The photoluminescence emissions of uncapped InGaN QDs in wavelength of the visible red (715 nm) and infrared region (795 and 857 nm) are observed. The formation of high-indium composition of InGaN QDs via droplet epitaxy technique could be applied in long wavelength optoelectronic devices.

Supercritical millifluidic reactor for the synthesis of efficient GaN nanophotocatalysts

Here, we demonstrate the continuous synthesis of gallium nitride (GaN) nanophotocatalysts exhibiting high quantum confinement using a preheated supercritical millireactor. The GaN quantum dots (QDs) are obtained from the direct thermolysis of a single source amido complex precursor (tris(dimethyl)amido gallium(III) dimer), in anhydrous supercritical cyclohexane. The quality of the synthesized QDs is highly dependent on the chemical pathways for the single source precursor thermolysis. Through the use of numerical modeling, we designed a millifluidic reactor allowing a sufficiently high heating rate for a direct precursor thermolysis towards efficient GaN nanoparticles. The as-designed preheated supercritical flow reactor yields highly reproducible GaN QDs (optical properties, crystallite phase and morphology) at high throughput, enabling gram scale production. Eventually, the photocatalytic properties of the GaN QDs were evaluated in a direct photochemical reaction through the degradation of a dye molecule (Methyl Orange). The obtained results demonstrate the higher photocatalytic activity of such photocatalysts compared to the commercially and reference available Degussa P25.

Conductometric nitrogen dioxide gas sensor based on gallium nitride quantum dots film

Gallium nitride (GaN) has some challenges for gas sensing, such as high detection lower limit (LOD) or complicated epitaxy of nanostructures. To address these issues, we exclusively designed a GaN quantum dots (QDs) film to enhance the gas interaction capability which fabricated by metal-organic chemical vapor deposition (MOCVD). The GaN QDs film gas sensor exhibits a low LOD (5 ppb) to nitrogen dioxide (NO2) at room temperature (RT), which has superior gas performance than other GaN-based sensors. The results of morphology and structure characterization manifest that many ultra-small QDs around 2 nm in diameter were stacked to form QDs of larger size, and confirm the existence of vacancies for the GaN QDs film. And the GaN QDs film sensor displays a ultra-high electron mobility of 1237.37 cm2 V−1s−1 at RT, which is greatly beneficial for gas sensing. The sensing mechanisms were analyzed based on its abundant active sites, ultrahigh carrier mobility, high surface energy and chemical activity, grain boundary barrier and good electrical conductivity. Moreover, the sensor processes high selectivity, repeatability, stability and reusability based on MOCVD technology which can realize precise control of structure and morphology, thus this sensor is expected to achieve rapid industrialization.

A Practical and High-Performance Nitrogen Dioxide Gas Sensor that Can Be Rapidly Mass-Produced Based on Gallium Nitride Quantum Dots Film

A Practical and High-Performance Nitrogen Dioxide Gas Sensor that Can Be Rapidly Mass-Produced Based on Gallium Nitride Quantum Dots Film

Ion-induced interdiffusion of surface GaN quantum dots

In the flourishing fields of quantum technology gallium nitride (GaN) quantum dots (QDs) have great appeal by providing high stability and room-temperature operation. Here, we report on the ion implantation of surface GaN QDs grown in the hexagonal crystal structure. An uncapped sample (S1) and two samples capped by 8ML (S2) and 16ML (S3) of AlN are subjected to a 100keV gallium (S1, S2) and a 210keV erbium (S3) ion beam. The fluence ranged from 5×1010cm−2 to 1×1015cm−2 (S1, S2) and from 5×1010cm−2 to 5×1013cm−2 (S3). QD characterization is performed by cathodoluminescence measurements at 77K and atomic force microscopy and scanning electron microscopy.Strong interdiffusion processes upon ion impact at the interfaces are evidenced leading besides other effects to a quenching of the quantum confined Stark effect. Moreover, a model for the QD morphology based on a fluence-dependent diffusion coefficient is developed.

RETRACTED: Growth and characterization of GaN nanoparticles on P-type Si (100) substrate by plasma focus device with nitrogen plasma

A Mather type plasma focus device (PFD) was used to grow semiconductor material gallium nitride nanoparticles on P-type silicon (100) with nitrogen as working gas. Two, four and six amount of plasma focus shots were applied to 3 Silicon substrates, field emission scanning electron microscopy and atomic force microscopy indicated spherical gallium nitride nanoparticles nearly similar to gallium nitride quantum dots on the substrate that was deposited with two shots. Photoluminescence spectrometry shows emission peaks in violet 420 nm (2.95 eV) wavelength in all three samples, additionally as the shots increased small peaks at near ultraviolet 360 nm (3.44 eV) were observed. UV–Vis–NIR shows most reflectance at near ultraviolet for the second sample with four shots, as X-ray diffraction shows only some peaks for the third sample with six shots which indicates the low quality of gallium nitride crystalline formation.

GaN quantum-dots integrated in the gate dielectric of metal-oxide-semiconductor structures for charge-storage applications

Gallium nitride quantum dots (QDs) were investigated as discrete charge storage nodes embedded in the gate dielectric of metal-oxide-semiconductor (MOS) capacitors. The GaN QDs were formed on top of 3.5 nm-thick SiO2/n-Si(001) substrates by radiofrequency plasma-assisted molecular beam deposition. The MOS structures were studied by transmission electron microscopy. Deposition dose was determined as a critical process parameter to obtain two dimensional arrays of discrete QDs. The memory window width, programming speed, and charge retention time were evaluated for GaN QD devices with different deposition doses. All devices showed enhanced electron trapping leading to significant memory windows. Charge retention measurements, at room temperature, revealed that the sample with the lowest concentration of QDs exhibits a low charge loss with a significant extrapolated programming window after 10 yrs. The present study not only demonstrates GaN QD embedded SiO2 structures fabricated by a fully complementary metal oxide semiconductor compatible method but also points out that these structures are promising for the realization of nanofloating gate non-volatile memory devices.

Low-Temperature Synthesis and Characterization of Gallium Nitride Quantum Dots in Ordered Mesoporous Silica

Semiconducting gallium nitride (GaN) quantum dots (QDs) were synthesized at low temperatures (650 °C), using ammonia flow without any organogallium precursor compound, assisted and controlled by an ordered mesoporous silica MCM-41 as host matrix. The final materials exhibit an intense blue shift of the band gap energy compared to the three-dimensional (3D) GaN. MCM-41 hosted GaN QD synthesis is also reported from pyrolysis of an organic precursor, tris(dimethylamido)gallium(III), at 365 °C under ammonia flow, with the largest band gap blue shift reported for such synthesized GaN of 0.6 eV. The QDs, involving inorganic precursor, exhibit an average X-ray diffraction estimated diameter of 12.6 A and crystallize in the zinc blende lattice with cubic symmetry (β-GaN), whereas the hexagonal system is thermodynamically preferred. QDs, based on organic precursor, have hexagonal symmetry (α-GaN, wurtzite structure) with an average diameter of 20.6 A. Spectroscopic and structural characterization of the QD-MCM com...

Electroluminescence from isolated single indium gallium nitride quantum dots up to 150 K

AbstractWe present light emitting diode structures with InGaN quantum dots (QDs) as active material grown by metal‐organic vapor‐phase epitaxy. The devices reveal a threshold voltage of 3.15 V at room temperature, or 8.8 V at 4 K, respectively. At room temperature, the electroluminescence intensity is still as high as 28% of the intensity at 4 K, the emission covering the spectral region from 2.3 to 2.7 eV at 4 K (2.2–2.6 eV at 300 K). Electrically driven luminescence from spectrally isolated single InGaN QDs emitting in the green spectral region is demonstrated with a thermal stability of up to 150 K. These results are an important step towards applications like electrically driven single photon emitters at elevated temperatures, which are desirable as a basis for communication techniques incorporating plastic optical fibers as well as for modern concepts of free space quantum cryptography.

A gallium nitride single-photon source operating at 200 K

Fundamentally secure quantum cryptography has still not seen widespread application owing to the difficulty of generating single photons on demand. Semiconductor quantum-dot structures have recently shown great promise as practical single-photon sources, and devices with integrated optical cavities and electrical-carrier injection have already been demonstrated. However, a significant obstacle for the application of commonly used III-V quantum dots to quantum-information-processing schemes is the requirement of liquid-helium cryogenic temperatures. Epitaxially grown gallium nitride quantum dots embedded in aluminium nitride have the potential for operation at much higher temperatures. Here, we report triggered single-photon emission from gallium nitride quantum dots at temperatures up to 200 K, a temperature easily reachable with thermo-electric cooling. Gallium nitride quantum dots also open a new wavelength region in the blue and near-ultraviolet portions of the spectrum for single-photon sources.

Resistance of group III nitrides irradiated with a 10 keV electron beam; comparison of thecathodoluminescence emission of GaN quantum dots, quantum wells and (Al)GaN epitaxiallayers

We present a comparative study of the in situ modifications induced by a 10 keV electronbeam in gallium nitride (GaN) quantum wells and quantum dots as well as in ELOG(epitaxial laterally overgrown GaN) and AlGaN epilayers. Cathodoluminescence(CL) experiments were performed to investigate the room temperature evolutionof the optical properties as a function of the beam current density. Higher dotresistance is much more apparent when the beam current density is larger than about6 A cm−2. Recombination enhanced diffusion of defects is involved in the degradation of the CLsignal. The two serial mechanisms inferred to be present in the degradation process aredescribed.

Degradation of gallium nitride quantum dots under 10keV electron-beam injection at low and high excitation densities

The time evolution of gallium nitride quantum dots luminescence has been recorded in situ in a scanning electron microscope. Electrons of 10keV were injected in a stationary spot in a scanning electron microscope during 30min. Two different regimes were evidenced depending on the beam current density. At low density, the cathodoluminescence (CL) intensity decreased rapidly and a dark spot appeared. At high beam density, the CL intensity decrease was slower, and a dark ring centered on the beam injection location was formed. All the results are coherently interpreted by an enhanced diffusion of nonradiative defects promoted by nonradiative recombinations.

Temperature Dependent Photoluminescence of MBE Grown Gallium Nitride Quantum Dots

We report on the growth and optical properties of gallium nitride quantum dots (QDs) grown by plasma-assisted molecular beam epitaxy. We have observed strong photoluminescence (PL) from the QDs from 8 to 750 K. Atomic force microscopy studies demonstrate that the QDs have diameters of (30 ± 5) nm and heights of (3 ± 1) nm. PL from the quantum dots was compared to that of a gallium nitride growth template film to unambiguously demonstrate the contribution of the QDs to the spectra. Integrated PL intensity was observed to remain strong well above 300 K, and we attribute the decrease in the quantum dot PL at higher temperatures to phonon-mediated carrier ionization of deep level.

Synthesis of gallium nitride quantum dots through reactive laser ablation

Nanocrystalline GaN was synthesized through reactive laser ablation of gallium metal in a N2 atmosphere. X-ray diffraction, selected-area electron diffraction, and transmission electron microscopy measurements show that the GaN crystallites are as small as 2 nm in diameter, and follow a log-normal size distribution with a mean particle diameter of 12 nm. Size-selective photoluminescence and photoluminescence excitation spectroscopy reveal a continuous range of blueshifted band-edge emissions and absorptions starting from the bulk value for gallium nitride and continuing to below 300 nm. These results are consistent with a GaN particle size distribution that encompasses regions above and below the excitonic-Bohr radius of GaN, such that the GaN material shows combined bulk and quantum confined optical properties.