After the invention of lasers, in the past 50 years progress made in laser-based display technology has been very promising, with commercial products awaiting release to the mass market. Compact laser systems, such as edge-emitting diodes, vertical-cavity surface-emitting lasers, and optically pumped semiconductor lasers, are suitable candidates for laser-based displays. Laser speckle is an important concern, as it degrades image quality. Typically, one or multiple speckle reduction techniques are employed in laser displays to reduce speckle contrast. Likewise, laser safety issues need to be carefully evaluated in designing laser displays under different usage scenarios. Laser beam shaping using refractive and diffractive components is an integral part of laser displays, and the requirements depend on the source specifications, modulation technique, and the scanning method being employed in the display. A variety of laser-based displays have been reported, and many products such as pico projectors and laser televisions are commercially available already.

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Laser-based displays: a review

A semiconductor light-emitting device of the invention includes: a semiconductor layer including a light-emitting layer and having a first major surface and a second major surface opposite to the first major surface; a phosphor layer facing to the first major surface; an interconnect layer provided on the second major surface side and including a conductor and an insulator; and a light-blocking member provided on a side surface of the semiconductor layer and being opaque to light emitted from the light-emitting layer.

Semiconductor light-emitting device and method for manufacturing same

The use of III-nitride-based light-emitting diodes (LEDs) is now widespread in applications such as indicator lamps, display panels, backlighting for liquid-crystal display TVs and computer screens, traffic lights, etc. To meet the huge market demand and lower the manufacturing cost, the LED industry is moving fast from 2 inch to 4 inch and recently to 6 inch wafer sizes. Although Al2O3 (sapphire) and SiC remain the dominant substrate materials for the epitaxy of nitride LEDs, the use of large Si substrates attracts great interest because Si wafers are readily available in large diameters at low cost. In addition, such wafers are compatible with existing processing lines for 6 inch and larger wafers commonly used in the electronics industry. During the last decade, much exciting progress has been achieved in improving the performance of GaN-on-Si devices. In this contribution, the status and prospects of III-nitride optoelectronics grown on Si substrates are reviewed. The issues involved in the growth of GaN-based LED structures on Si and possible solutions are outlined, together with a brief introduction to some novel in situ and ex situ monitoring/characterization tools, which are especially useful for the growth of GaN-on-Si structures.

https://iopscience.iop.org/article/10.1088/0034-4885/76/10/106501/pdf

Prospects of III-nitride optoelectronics grown on Si.

In this paper, we report on 1.2-kV-class vertical GaN-based trench metal–oxide–semiconductor field-effect transistors (MOSFETs) on a free-standing GaN substrate with a low specific on-resistance. A redesigned epitaxial layer structure following our previous work with a regular hexagonal trench gate layout enables us to reduce the specific on-resistance to as low as 1.8 mΩcm2 while obtaining a sufficient blocking voltage for 1.2-kV-class operation. Normally-off operation with a threshold voltage of 3.5 V is also demonstrated. To the best of our knowledge, this is the first report on vertical GaN-based MOSFETs with a specific on-resistance of less than 2 mΩcm2.

http://iopscience.iop.org/article/10.7567/APEX.8.054101/pdf

1.8 mΩ·cm2 vertical GaN-based trench metal–oxide–semiconductor field-effect transistors on a free-standing GaN substrate for 1.2-kV-class operation

By doping an organic compound functioning as an electron donor (hereinafter referred to as donor molecules) into an organic compound layer contacting a cathode, donor levels can be formed between respective LUMO (lowest unoccupied molecular orbital) levels between the cathode and the organic compound layer, and therefore electrons can be injected from the cathode, and transmission of the injected electrons can be performed with good efficiency. Further, there are no problems such as excessive energy loss, deterioration of the organic compound layer itself, and the like accompanying electron movement, and therefore an increase in the electron injecting characteristics and a decrease in the driver voltage can both be achieved without depending on the work function of the cathode material.

Light Emitting Device

A p-GaN/AlGaN/GaN based normally-off HEMT device has been demonstrated on a Si substrate. Our p-GaN based device shows not only a high threshold voltage of 3 V but also low gate leakage current. Buffer and device breakdown voltages exceed 1600 V with 5.2 um GaN buffer thickness and specific on-state resistance is 2.9mΩ cm2. The calculated figure of merit is 921 MV2/Ωcm2, which is the highest value reported for the GaN E-mode devices.

1.6kV, 2.9 mΩ cm 2 normally-off p-GaN HEMT device

We report a quantum ringlike toroidal cavity naturally formed in a vertical-cavity-like active microdisk plane due to Rayleigh's band of whispering gallery modes. The $\sqrt{T}$-dependent redshift and a square-law property of microampere-range threshold currents down to $2\ensuremath{\mu}\mathrm{A}$ are consistent with a photonic quantum wire view, due to whispering gallery mode-induced dimensional reduction.

Photonic Quantum Ring

We discuss the influence of V-pits and their energy barrier, originating from its facets of (101¯1) planes, on the luminescence efficiency of InGaN LEDs. Experimental analysis using cathodoluminescence (CL) exhibits that thin facets of V-pits of InGaN quantum wells (QWs) appear to be effective in improving the emission intensity, preventing the injected carriers from recombining non-radiatively with threading dislocations (TDs). Our theoretical calculation based on the self-consistent approach with adopting k⋅p method reveals that higher V-pit energy barrier heights in InGaN QWs more efficiently suppress the non-radiative recombination at TDs, thus enhancing the internal quantum efficiency (IQE).

Influence of V-pits on the efficiency droop in InGaN/GaN quantum wells

We report the effect of V-shaped pit size, inverted hexagonal pits embedded in InGaN multiple quantum well, on the reverse leakage current of InGaN light-emitting diodes (LEDs). It was found that the reverse leakage current of InGaN LEDs with larger V-shaped pits is significantly reduced from 1.80 mA down to 3.84 nA at -30 V by several orders of magnitude. We claim that this improvement is accounted for increased Poole-Frenkel barrier height of carrier trapped at the deep centers via enlarged V-pit formation, consequently resulting in lower reverse current of InGaN LEDs.

Effect of V-Shaped Pit Size on the Reverse Leakage Current of InGaN/GaN Light-Emitting Diodes

A high electron mobility transistor (HEMT) includes a substrate, an HEMT stack spaced apart from the substrate, and a pseudo-insulation layer (PIL) disposed between the substrate and the HEMT stack. The PIL layer includes at least two materials having different phases. The PIL layer defines an empty space that is wider at an intermediate portion than at an entrance of the empty space.

Jun-Youn Kim

Papers

1.6kV, 2.9 mΩ cm 2 normally-off p-GaN HEMT device

Photonic Quantum Ring

Influence of V-pits on the efficiency droop in InGaN/GaN quantum wells

Effect of V-Shaped Pit Size on the Reverse Leakage Current of InGaN/GaN Light-Emitting Diodes

High electron mobility transistor and method of manufacturing the same