Room-temperature ultraviolet lasing in semiconductor nanowire arrays has been demonstrated The self-organized, oriented zinc oxide nanowires grown on sapphire substrates were synthesized with a simple vapor transport and condensation process These wide band-gap semiconductor nanowires form natural laser cavities with diameters varying from 20 to 150 nanometers and lengths up to 10 micrometers Under optical excitation, surface-emitting lasing action was observed at 385 nanometers, with an emission linewidth less than 03 nanometer The chemical flexibility and the one-dimensionality of the nanowires make them ideal miniaturized laser light sources These short-wavelength nanolasers could have myriad applications, including optical computing, information storage, and microanalysis

Room-temperature ultraviolet nanowire nanolasers

Diarylethenes for Memories and Switches

The demand for compact ultraviolet laser devices is increasing, as they are essential in applications such as optical storage, photocatalysis, sterilization, ophthalmic surgery and nanosurgery. Many researchers are devoting considerable effort to finding materials with larger bandgaps than that of GaN. Here we show that hexagonal boron nitride (hBN) is a promising material for such laser devices because it has a direct bandgap in the ultraviolet region. We obtained a pure hBN single crystal under high-pressure and high-temperature conditions, which shows a dominant luminescence peak and a series of s-like exciton absorption bands around 215 nm, proving it to be a direct-bandgap material. Evidence for room-temperature ultraviolet lasing at 215 nm by accelerated electron excitation is provided by the enhancement and narrowing of the longitudinal mode, threshold behaviour of the excitation current dependence of the emission intensity, and a far-field pattern of the transverse mode.

Direct-bandgap properties and evidence for ultraviolet lasing of hexagonal boron nitride single crystal.

InGaN multi-quantum-well (MQW) structure laser diodes (LDs) fabricated from III-V nitride materials were grown by metalorganic chemical vapor deposition on sapphire substrates. The mirror facet for a laser cavity was formed by etching of III-V nitride films without cleaving. As an active layer, the InGaN MQW structure was used. The InGaN MQW LDs produced 215 mW at a forward current of 2.3 A, with a sharp peak of light output at 417 nm that had a full width at half-maximum of 1.6 nm under the pulsed current injection at room temperature. The laser threshold current density was 4 kA/cm2. The emission wavelength is the shortest one ever generated by a semiconductor laser diode.

https://iopscience.iop.org/article/10.1143/JJAP.35.L74/pdf

InGaN-Based Multi-Quantum-Well-Structure Laser Diodes.

Status and future outlook of III-V compound semiconductor visible-spectrum light-emitting diodes (LEDs) are presented. Light extraction techniques are reviewed and extraction efficiencies are quantified in the 60%+ (AlGaInP) and ~80% (InGaN) regimes for state-of-the-art devices. The phosphor-based white LED concept is reviewed and recent performance discussed, showing that high-power white LEDs now approach the 100-lm/W regime. Devices employing multiple phosphors for "warm" white color temperatures (~3000-4000 K) and high color rendering (CRI>80), which provide properties critical for many illumination applications, are discussed. Recent developments in chip design, packaging, and high current performance lead to very high luminance devices (~50 Mcd/m2 white at 1 A forward current in 1times1 mm2 chip) that are suitable for application to automotive forward lighting. A prognosis for future LED performance levels is considered given further improvements in internal quantum efficiency, which to date lag achievements in light extraction efficiency for InGaN LEDs

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Status and Future of High-Power Light-Emitting Diodes for Solid-State Lighting

Superbright green InGaN single quantum well (SQW) structure light-emitting diodes (LEDs) with a luminous intensity of 12 cd were fabricated The luminous intensity of these green InGaN SQW LEDs (12 cd) was about 100 times higher than that of conventional green GaP LEDs (01 cd) The output power, the external quantum efficiency, the peak wavelength and the full width at half-maximum of green SQW LEDs were 3 mW, 63%, 520 nm and 30 nm, respectively, at a forward current of 20 mA The p-AlGaN/InGaN/n-GaN structure of green InGaN SQW LEDs were grown by metalorganic chemical vapor deposition on sapphire subsutrates

https://iopscience.iop.org/article/10.1143/JJAP.34.L1332/pdf

Superbright Green InGaN Single-Quantum-Well-Structure Light-Emitting Diodes

InGaN multi-quantum-well-structure laser diodes with Al0.14Ga0.86N/GaN modulation doped strained-layer superlattice cladding layers grown on an epitaxially laterally overgrown GaN (ELOG) substrate was demonstrated to have a lifetime of more than 1150 h under room-temperature continuous-wave operation. After 4 μm etching of the ELOG substrate, the etch pit density was about 2×108 cm2 in the region of the 4-μm-wide stripe window, but almost zero in the region of the 7-μm-wide SiO2 stripe.

InGaN/GaN/AlGaN-based laser diodes with modulation-doped strained-layer superlattices grown on an epitaxially laterally overgrown GaN substrate

Continuous‐wave (cw) operation of InGaN multi‐quantum‐well structure laser diodes (LDs) was demonstrated at room temperature (RT). The threshold current and voltage of the LD were 130 mA and 8 V, respectively. The threshold carrier density was 9 kA/cm2. The lifetime of the LDs under RT cw operation was 1 s due to large heat generation. Mode hopping of the emission wavelength of the LDs was observed. The average wavelength drift due to temperature increase was 0.066 nm/K between 20 and 70 °C, because of the temperature dependence of the gain profile due to band‐gap narrowing of the InGaN active layer.

Room‐temperature continuous‐wave operation of InGaN multi‐quantum‐well structure laser diodes

InGaN multi-quantum-well-structure laser diodes with Al0.14Ga0.86N/GaN modulation doped strained-layer superlattice cladding layers grown on an epitaxially laterally overgrown GaN substrate were demonstrated to have an estimated lifetime of more than 10000 h under continuous-wave operation at 20° C. Under operation at a high temperature of 50° C, the lifetime was longer than 1000 h. With the operating current increasing to above the threshold, a self-pulsation with a high frequency of 3.5 GHz was observed. The carrier lifetime was estimated to be 1.8 ns from the pulsed modulation of the LDs.

https://iopscience.iop.org/article/10.1143/JJAP.36.L1568/pdf

Takao Yamada

Papers

InGaN-Based Multi-Quantum-Well-Structure Laser Diodes.

Superbright Green InGaN Single-Quantum-Well-Structure Light-Emitting Diodes

InGaN/GaN/AlGaN-based laser diodes with modulation-doped strained-layer superlattices grown on an epitaxially laterally overgrown GaN substrate

Room‐temperature continuous‐wave operation of InGaN multi‐quantum‐well structure laser diodes

InGaN/GaN/AlGaN-Based Laser Diodes with Modulation-Doped Strained-Layer Superlattices