Staggered InGaN quantum wells (QWs) grown by metal-organic chemical vapor deposition are demonstrated as improved active region for visible light emitters. Theoretical studies indicate that InGaN QW with step-function-like In content in the quantum well offers significantly improved radiative recombination rate and optical gain in comparison to the conventional type-I InGaN QW. Experimental results of light emitting diode (LED) structure utilizing staggered InGaN QW show good agreement with theory. Polarization band engineering via staggered InGaN quantum well allows enhancement of radiative recombination rate, leading to the improvement of photoluminescence intensity and LED output power.
Improvement of light extraction efficiency of InGaN quantum wells light emitting diodes ͑LEDs͒ using SiO 2 /polystyrene microspheres was demonstrated experimentally. The utilization of SiO 2 /polystyrene microlens arrays on InGaN quantum wells LEDs, deposited via rapid convective deposition, allows the increase of the effective photon escape cone and reduction in the Fresnel reflection. Improvement of output power by 219% for InGaN quantum wells LEDs emitting at peak wavelength of 480 nm with SiO 2 /polystyrene microspheres microlens arrays was demonstrated.
Improvement of light extraction efficiency of InGaN light emitting diodes (LEDs) using polydimethylsiloxane (PDMS) concave microstructures arrays was demonstrated. The size effect of the concave microstructures on the light extraction efficiency of III-Nitride LEDs was studied. Depending on the size of the concave microstructures, ray tracing simulations show that the use of PDMS concave microstructures arrays can lead to increase in light extraction efficiency of InGaN LEDs by 1.5 to 2.0 times. Experiments utilizing 2.0 micron thick PDMS with 1.0 micron diameter of the PDMS concave microstructures arrays demonstrated 1.70 times improvement in light extraction efficiency, which is consistent with improvement of 1.77 times predicted from simulation. The enhancement in light extraction efficiency is attributed to increase in effective photon escape cone due to PDMS concave microstructures arrays.
Articles you may be interested inThermal dependence of the optical gain and threshold current density of GaInNAs/GaAs/AlGaAs quantum well lasers Effect of (1010) crystal orientation on many-body optical gain of wurtzite InGaN/GaN quantum well Type-II InGaN-GaNAs quantum wells ͑QWs͒ with thin dilute-As ͑ϳ3%͒ GaNAs layer are analyzed self-consistently as improved III-nitride gain media for diode lasers. The band structure is calculated by using a six-band k · p formalism, taking into account valence band mixing, strain effect, spontaneous and piezoelectric polarizations, as well as the carrier screening effect. The type-II InGaN-GaNAs QW structure allows large electron-hole wave function overlap by confining the hole wave function in the GaNAs layer of the QW. The findings based on self-consistent analysis indicate that type-II InGaN-GaNAs QW active region results in superior performance for laser diodes, in comparison to that of conventional InGaN QW. Both the spontaneous emission radiative recombination rate and optical gain of type-II InGaN-GaNAs QW structure are significantly enhanced. Reduction in the threshold current density of InGaN-GaNAs QW lasers is also predicted.FIG. 4. ͑Color online͒ Spontaneous emission spectra for type-I In 0.24 Ga 0.76 N QW and type-II In 0.15 Ga 0.85 N-GaN 0.97 As 0.03 QW as increasing carrier density n = ͑1-5͒ ϫ 10 19 cm −3 with self-consistent model calculation.
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