RESUMEN
We report a self-induced spatially-coherent dot array consisting of fourteen units of vertical-cavity surface-emitting modes that exhibit spatially uniform spectra. A 47.5 µm total beam width and 0.5° narrow emission are achieved using an oblong cavity enclosed with a flat top mirror, cylindrically curved bottom mirror, and side facet. Notably, terminating the side of the cavity with a perpendicular facet enhances the horizontal propagation, which couples with the vertical resonance in each dot, similar to the case of master lasers in injection-locked lasers that delocalize the modes. Conventional semiconductor lasers, edge-emitting lasers, and vertical-cavity surface-emitting lasers have a Fabry-Pérot cavity; furthermore, emission and resonance are in identical directions, limiting the beam width to micrometers. Though the present structure has the same scheme of propagation, the right-angled facet synchronizes the modes and drastically expands the beam width.
RESUMEN
Violet semipolar (20-2-1) InGaN microcavity light-emitting diodes (MC-LED) with a 200 nm ultra-short cavity length were demonstrated. The emission wavelength was 419 nm with a spectrum width of 20 nm. The external quantum efficiency (EQE) of MC-LED was constant at 0.8% for a forward current from 0.5 to 2 mA with the emitting area of 30×30 µm2. With increasing forward current, the peak wavelength and spectrum width of the emission showed almost no changes. For epitaxial growth, metal-organic chemical vapor deposition (MOCVD) was used. Substrate removal and tunnel-junction with an Ag-based electrode made possible the fabrication of the ultra-short 200 nm thick cavity MC-LED. This is more than a factor of 2 improvement compared to previous MC-LEDs of 450 nm cavity thickness sustaining 5 modes.
RESUMEN
The electrical and optical improvements of AlGaInP micro-light-emitting diodes (µLEDs) using atomic-layer deposition (ALD) sidewall passivation were demonstrated. Due to the high surface recombination velocity and minority carrier diffusion length of the AlGaInP material system, devices without sidewall passivation suffered from high leakage and severe drop in external quantum efficiency (EQE). By employing ALD sidewall treatments, the 20×20 µm2 µLEDs resulted in greater light output power, size-independent leakage current density, and lower ideality factor. The forward current-voltage characteristic was enhanced by using surface pretreatment. Furthermore, ALD sidewall treatments recovered the EQE of the 20×20 µm2 devices more than 150%. This indicated that AlGaInP µLEDs with ALD sidewall treatments can be used as the red emitter for full-color µLED display applications.
RESUMEN
We report III-nitride vertical-cavity surface-emitting lasers (VCSELs) with buried tunnel junction (BTJ) contacts. To form the BTJs, GaN TJ contacts were etched away outside the aperture followed by n-GaN regrowth for current spreading. Under pulsed operation, a BTJ VCSEL with a 14 µm diameter aperture showed a lasing wavelength of 430 nm, a threshold current of â¼20 mA (12 kA/cm2), and a maximum output power of 2.8 mW. Under CW operation, an 8 µm aperture VCSEL showed a differential efficiency of 11% and a peak output power of â¼0.72 mW.
RESUMEN
We successfully demonstrated an electrically injected blue(202¯1¯)semipolar vertical-cavity surface-emitting laser with a 5λ cavity length, an ion implanted aperture, and a dual dielectric DBR design. The peak power under pulsed operation was 1.85 mW, the threshold current was 4.6 kA/cm2 , and the differential efficiency was 2.4% for the mode at 445 nm of a device with a 12 µm aperture. Lasing was achieved up to a 50% duty cycle and the thermal impedance was estimated to be 1800 K/W. The lasing emission was found to be 100% plane polarized along the a-direction.
RESUMEN
We investigated the electrical and optical performances of semipolar (11-22) InGaN green µLEDs with a size ranging from 20 × 20 µm2 to 100 × 100 µm2, grown on a low defect density and large area (11-22) GaN template on patterned sapphire substrate. Atom probe tomography (APT) gave insights on quantum wells (QWs) thickness and indium composition and indicated that no indium clusters were observed in the QWs. The µLEDs showed a small wavelength blueshift of 5 nm, as the current density increased from 5 to 90 A/cm2 and exhibited a size-independent EQE of 2% by sidewall passivation using atomic-layer deposition, followed by an extremely low leakage current of ~0.1 nA at -5 V. Moreover, optical polarization behavior with a polarization ratio of 40% was observed. This work demonstrated long-wavelength µLEDs fabricated on semipolar GaN grown on foreign substrate, which are applicable for a variety of display applications at a low cost.
