Glucose-derived water-soluble crystalline graphene quantum dots (GQDs) with an average diameter as small 1.65 nm (∼5 layers) were prepared by a facile microwave-assisted hydrothermal method. The GQDs exhibits deep ultraviolet (DUV) emission of 4.1 eV, which is the shortest wavelength among all solution-based QDs. exhibit typical excitation wavelength-dependent properties expected in carbon-based dots. However, independent size GQDs. unique optical are attributed to self-passivated layer on...

Material that can emit broad spectral wavelengths covering deep ultraviolet, visible, and near-infrared is highly desirable. It lead to important applications such as broadband modulators, photodetectors, solar cells, bioimaging, fiber communications. However, there currently no material meets desirable requirement. Here, we report the layered structure of nitrogen-doped graphene quantum dots (N-GQDs) which possess emission ranging from 300 >1000 nm. The attributed N-GQDs contains a large...

We report on the fabrication and photovoltaic characteristics of InGaN solar cells by exploiting InGaN/GaN multiple quantum wells (MQWs) with In contents exceeding 0.3, attempting to alleviate a certain degree phase separation issue demonstrate cell operation at wavelengths longer than previous attainments (>420 nm). The fabricated based In0.3Ga0.7N/GaN MQWs exhibit an open circuit voltage about 2 V, fill factor 60%, external efficiency 40% (10%) 420 nm (450

We report the realization and properties of a high-resolution solid-state self-emissive microdisplay based on III-nitride semiconductor micro-size light emitting diodes (µLEDs) capable delivering video graphics images. The luminance level microdisplays is several orders magnitude higher than those liquid crystal organic-LED displays. pixel emission intensity was almost constant over an operational temperature range from 100 to −100 °C. outstanding performance direct attribute semiconductors....

Since their inception, micro-size light emitting diode (µLED) arrays based on III-nitride semiconductors have emerged as a promising technology for range of applications. This paper provides an overview decade progresses realizing µLED high voltage single-chip AC/DC-LEDs without power converters to address the key compatibility issue between LEDs and AC grid infrastructure; high-resolution solid-state self-emissive microdisplays operating in active driving scheme need brightness, efficiency...

This perspective provides an overview of early developments, current status, and remaining challenges microLED (μLED) technology, which was first reported in Applied Physics Letters 2000 [S. X. Jin, J. Li, Z. Y. Lin H. Jiang, "GaN Microdisk Light Emitting Diodes," Appl. Phys. Lett. 76, 631 (2000)]. Today, is recognized as the ultimate display technology one fastest-growing technologies world giants utilize it on a wide range products from large flat panel displays televisions, wearable...

III-nitride wide bandgap semiconductors have contributed on the grandest scale to many technological advances in lighting, displays, and power electronics. Among III-nitrides, BN has another unique application as a solid-state neutron detector material because isotope B-10 is among few elements that an unusually large interaction cross section with thermal neutrons. A record high detection efficiency of 60% been achieved by enriched h-BN detectors 100 μm thickness our group. However, direct...

With a recently developed unique deep ultraviolet picoseconds time-resolved photoluminescence (PL) spectroscopy system and improved growth technique, we are able to determine the detailed band structure near Γ point of wurtzite (WZ) AlN with direct gap 6.12 eV. Combined first-principles calculations show that fundamental optical properties differ drastically from GaN other WZ semiconductors. The discrepancy in energy values obtained previously by different methods is explained terms...

Deep UV photoluminescence spectroscopy has been employed to study the optical properties of AlxGa1−xN alloys (0⩽x⩽1). The emission intensity with polarization E⊥c and degree were found decrease increasing x. This is a consequence fact that dominant band edge in GaN (AlN) E⊥c(E∥c). Our experimental results suggest decreased efficiency related emitters could also be their unique property, i.e., light decreases It thus concluded AlGaN as active layers have very different from InGaN other...

We present results on enhancement of 460 nm blue and 340 UV optical power output in III-nitride light emitting diodes (LEDs) using photonic crystals (PCs) under current injection. Triangular arrays the PCs with diameter/periodicity 300/700 were patterned electron-beam lithography inductively coupled plasma dry etching. The total at 20 mA 300×300 μm2 unpackaged LED chips revealed an increase by 63% 95% for LEDs, respectively, as a result PC formation. Possible ways further improving...

Prototype blue microdisplays have been fabricated from InGaN/GaN quantum wells. The device has a dimension of 0.5×0.5 mm2 and consists 10×10 pixels 12 μm in diameter. Emission properties such as electroluminescence spectra, output power versus forward current (L–I) characteristic, viewing angle, uniformity measured. Due to the unique III-nitride wide-band-gap semiconductors, III nitrides can potentially provide unsurpassed performance, including high-brightness/resolution/contrast,...

Mg-doped AlN epilayers were grown by metalorganic chemical vapor deposition on sapphire substrates. Deep UV picosecond time-resolved photoluminescence (PL) spectroscopy has been employed to study the optical transitions in epilayers. From PL emission spectra and temperature dependence of intensity, a binding energy 0.51 eV for Mg acceptor was determined. Together with previous experimental results, activation AlxGa1−xN as function Al content (x) extrapolated entire composition range. The...

Cubic structured CdS, CdSe, and CdTe, II–VI semiconductor nanoparticles have been synthesized using aqueous solution precipitation at room temperature. The ‘‘as-prepared’’ particles a size of about 30 Å. Thermal annealing causes (a) an increase in particle size; (b) structural transition from the cubic to bulk, hexagonal structure for CdS CdSe; (c) no CdTe. unexpected phase small CdSe may be due either metastability or equilibrium surface effect. latter would imply strong correlation between...

Microdisk light-emitting diodes (μ-LEDs) with diameter of about 12 μm have been fabricated from InGaN/GaN quantum wells. Photolithographic patterning and inductively coupled plasma dry etching employed to fabricate these μ-LED devices. Device characteristics, such as the current–voltage light output power, electroluminescence (EL) spectra measured compared those conventional broad-area LEDs. Our results showed that, for an identical area, efficiencies are enhanced over LEDs due current...

Hexagonal boron nitride (hBN) has emerged as an important material for various device applications and a template graphene electronics. Low-dimensional hBN is expected to possess rich physical properties, similar graphene. The synthesis of wafer-scale semiconducting epitaxial layers with high crystalline quality electrical conductivity control not been achieved but highly desirable. Large area (up 2 in. in diameter) were synthesized by metal organic chemical vapor deposition. P-type was...

We present the growth, fabrication, and photovoltaic characteristics of Inx Ga1−xN/GaN(x∼0.35) multiple quantum well solar cells for concentrator applications. The open circuit voltage, short current density, solar-energy-to-electricity conversion efficiency were found to increase under concentrated sunlight. overall increases from 2.95% 3.03% when concentration 1 30 suns could be enhanced by further improving material quality.

A coherent picture for the band structure near Γ point and associated fundamental optical transitions in wurtzite (WZ) GaN, including electron hole effective masses binding energies of free excitons with different valence bands, has been derived from time-resolved photoluminescence measurements a theoretical calculation based on local density approximation. We also determine radiative recombination lifetimes neutral impurity (donor acceptor) bound WZ GaN compare ratios calculated values...

High quality AlN epilayers were grown on sapphire substrates by metal organic vapor deposition and exploited as active deep ultraviolet (DUV) optoelectronic materials through the demonstration of metal-semiconductor-metal (MSM) photodetectors. DUV photodetectors with peak responsivity at 200nm a very sharp cutoff wavelength 207nm have been attained. The MSM are shown to possess outstanding features that direct attributes fundamental properties AlN, including extremely low dark current, high...

We report on the fabrication of 280-nm AlGaN-based deep-ultraviolet light-emitting diodes (UV LEDs) sapphire substrates with an integrated microlens array. Microlenses a diameter 12μm were fabricated substrate by resist thermal reflow and plasma dry etching. LED devices flip-chip bonded high conductive AlN ceramic submounts to improve dissipation, emitted UV light was extracted through substrates. With array, 55% enhancement in output power at 20-mA dc driving achieved compared same without...

Deep-ultraviolet photoluminescence spectroscopy has been employed to study the temperature and compositional dependence of band gap AlxGa1−xN alloys in range between 10 800 K. Band-edge emission peaks were fitted by Varshni equation obtain coefficients, which increase nonlinearly with x. The values coefficients obtained for GaN AlN binary compounds present are good agreement previously reported values. Based on experimental data, alloy empirically determined entire range.

Deep ultraviolet (UV) photoluminescence (PL) spectroscopy has been employed to study deep impurity transitions in AlxGa1−xN (0⩽x⩽1) epilayers. Two groups of were observed, which are assigned the recombination between shallow donors and two different level acceptors involving cation vacancies (Vcation) Vcation complexes alloys. These acceptor levels pinned energy common alloys (0⩽x⩽1). The related with observed x=0 1, while those only x=0.58 1. This points out fact that formation is more...

Deep ultraviolet photoluminescence spectroscopy was employed to study the impurity transitions in Mg-doped AlGaN alloys. A group of deep level observed AlxGa1−xN alloys, which identified have same origin as previously reported blue line at 2.8eV GaN and assigned recombination electrons bound nitrogen vacancy with three positive charges (VN3+) neutral Mg acceptors. Based on measured activation energies acceptors emission peaks, VN3+ energy levels been deduced for entire alloy range. It is...

Hexagonal boron nitride (hBN) epilayers have been synthesized by metal organic chemical vapor deposition and their dielectric strength, optical absorption, potential as a deep ultraviolet (DUV) detector material studied. Based on the graphene absorption concept, estimated band-edge coefficient of hBN is about 7 × 105/cm, which more than 3 times higher value for wurtzite AlN (∼2 105 /cm). The strength exceeds that greater 4.4 MV/cm based measured result an epilayer released from host sapphire...

A hybrid TiO2−carbon nanofiber hierarchical nanostructure has been fabricated by the metal−organic chemical vapor deposition of a TiO2 layer onto vertically aligned carbon array. As time increases from 10 to 60 min, coating changes particulated conformal ultrathin film nanoneedle-like texture along sidewall nanofibers. X-ray diffraction indicates that form anatase crystals with coherent length over 50 nm, in good agreement transmission electron microscopy images. Photoluminescence spectra...

This paper provides a brief overview on recent advances in tackling the doping and optical polarization issues involved development of high performance deep ultraviolet (DUV) light emitting devices. In particular, developments exploitation novel DUV emitter layer structure based hexagonal boron nitride (hBN) AlGaN p–n junction engineering to potentially overcome intrinsic problem low p-type conductivity (or free hole concentration) Al-rich are summarized. By implementing wide bandgap highly...