III‐nitride light‐emitting diodes (LEDs) and laser diodes (LDs) are ultimately limited in performance due to parasitic Auger recombination. For LEDs, the consequences are poor efficiencies at high current densities; for LDs, the consequences are high thresholds and limited efficiencies. Here, we present arguments for III‐nitride quantum dots (QDs) as active regions for both LEDs and LDs, to circumvent Auger recombination and achieve efficiencies at higher current densities that are not possible with quantum wells. QD‐based LDs achieve gain and thresholds at lower carrier densities before Auger recombination becomes appreciable. QD‐based LEDs achieve higher efficiencies at higher currents because of higher spontaneous emission rates and reduced Auger recombination. The technical challenge is to control the size distribution and volume of the QDs to realize these benefits. If constructed properly, III‐nitride light‐emitting devices with QD active regions have the potential to outperform quantum well light‐emitting devices, and enable an era of ultra‐efficient solid‐state lighting.
In this Letter, a GaN‐based high‐power (HP) single‐chip (SC) large‐area LED with parallel and series network structure is fabricated. The optical characteristics of the HP‐SC LED is investigated. Driven at 600 mA, the optical output power of the HP‐SC LED chip is measured to be 9.7 W, corresponding to an EQE of 26.4%, which is 19.6% lower than that of the standard small LED cell due to both the lateral light‐extraction efficiency degradation and the self‐heating effect. A statistical analysis was carried out to investigate the yield of the fabricated HP‐SC LEDs, the experimental results agree with the theoretical calculations very well, validating the feasibility of this design on the production yield for the large‐area LEDs.
Solid‐state lighting (SSL) is now the most efficient source of high color quality white light ever created. Nevertheless, the blue InGaN light‐emitting diodes (LEDs) that are the light engine of SSL still have significant performance limitations. Foremost among these is the decrease in efficiency at high input current densities widely known as “efficiency droop.” Efficiency droop limits input power densities, contrary to the desire to produce more photons per unit LED chip area and to make SSL more affordable. Pending a solution to efficiency droop, an alternative device could be a blue laser diode (LD). LDs, operated in stimulated emission, can have high efficiencies at much higher input power densities than LEDs can. In this article, LEDs and LDs for future SSL are explored by comparing: their current state‐of‐the‐art input‐power‐density‐dependent power‐conversion efficiencies; potential improvements both in their peak power‐conversion efficiencies and in the input power densities at which those efficiencies peak; and their economics for practical SSL. 相似文献
Wavelength‐tunable light‐emitting diodes (LEDs) of GaxZn1–xO nanowire arrays are demonstrated by a simple modified chemical vapor deposition heteroepitaxial growth on p‐GaN substrate. As a gallium atom has similar electronegativity and ion radius to a zinc atom, high‐level Ga‐doped GaxZn1–xO nanowire arrays have been fabricated. As the x value gradually increases from 0 to 0.66, the near‐band‐edge emission peak of GaxZn1–xO nanowires shows a significant shift from 378 nm (3.28 eV) to 418 nm (2.96 eV) in room‐temperature photoluminescence (PL) measurement. Importantly, the electroluminescence (EL) emission of GaxZn1–xO nanowire arrays LED continuously shifts with a wider range (∼100 nm), from the ultraviolet (382 nm) to the visible (480 nm) spectral region. The presented work demonstrates the possibility of bandgap engineering of low‐dimensional ZnO nanowires by gallium doping and the potential application for wavelength‐tunable LEDs. 相似文献
High-performance Pb(Zr,Ti)O3, PZT, thin films were synthesized on Si substrates by using low-temperature laser-assisted processes, which combine pulsed laser deposition (PLD), laser lift-off (LLO) and laser-annealing (LA) processes. The PZT films were first grown on sapphire substrates at 400 °C, using Ba(Mg1/3Ta2/3)O3, BMT, as seeding layer, by the PLD process, and were then transferred to Si substrates at room temperature by a LLO transferring process. Utilization of the BMT layer is of critical importance in those processes, since it acted as a nucleation layer for the synthesis of the PZT thin films on the sapphire substrates and, at the same time, served as a sacrificial layer during laser irradiation in the LLO process. After the LLO process, the surfaces of the PZT films were recovered by the LA process for removing the damage induced by the LLO process. A thin BMT (∼30 nm) layer is randomly oriented, resulting in non-textured PZT films with good ferroelectric properties, viz. Pr=20.6 μC/cm2 and Ec=126 kV/cm, whereas a thick BMT (∼100 nm) layer is (100) preferentially oriented, leading to (100)-textured PZT films with markedly better ferroelectric properties, viz. Pr=34.4 μC/cm2 and Ec=360 kV/cm. PACS 81.15.Fg; 77.84.-s 相似文献
Optical pumping conditions for organic solid‐state lasers (OSLs) are discussed with particular emphasis on the use of gallium nitride based light‐emitting diodes (LEDs) as pump sources. LEDs operate in a regime where the pump should be optimized for a short rise time and high peak intensity, whereas fall time and overall pulse duration are less important. Lasers pumped with this approach need to have very low thresholds which can now be routinely created using (one‐dimensional) distributed feedback lasers. In this particular case stripe‐shaped excitation with linearly polarized light is beneficial. Arrays of micron‐sized flip‐chip LEDs have been arranged in an appropriate stripe shape and the array dimensions were chosen such that the divergence of LED emission does not cause a loss in peak intensity. These micro‐LED arrays have successfully been used to pump OSLs with thresholds near 300 W/cm2 (∼9 ns rise time, 35 ns pulse duration), paving the way for compact arrays of indirectly electrically pumped OSLs. 相似文献
Currently, one of the challenges in high‐resolution transmission electron microscopy (TEM) studies of nanomaterials is to make contamination‐free materials in a simple and time‐efficient way. Here, a method is demonstrated that combines nanosecond‐pulsed laser dewetting of thin films with a film float‐off technique to realize nanostructures (NSs) on electron‐transparent substrates in a robust and rapid manner. NSs of metal (Ag) and bimetals (AgCo, AuCo) ranging from 20 to 150 nm are synthesized on thin carbon film deposited on mica substrates. The NS/carbon system is subsequently transferred onto TEM grids by a float‐off process resulting from debonding of the carbon from mica due to their contrasting hydrophobic nature. This process enables the fabrication of different NSs on flexible and electron‐transparent substrates. 相似文献
X‐ray irradiation is shown to trigger the deposition of Cu from solution, at room temperature, on a wide variety of insulating substrates: glass, passivated Si, TiN/Ti/SiO2/Si and photoresists like PMMA and SU‐8. The process is suitable for patterning and the products can be used as seeds for electroplating of thicker overlayers. 相似文献
Efficiency droop, i.e. the loss of efficiency at high operating current, afflicts nitride‐based light‐emitting diodes (LEDs). The droop phenomenon is currently the subject of intense research, as it retards the advancement of solid‐state lighting which is just starting to supplant fluorescent as well as incandescent lighting. Although the technical community does not yet have consented to a single cause of droop, this article provides a summary of the present state of droop research, reviews currently discussed droop mechanisms, and presents a recently developed theoretical model for the efficiency droop. In the theoretical model, carrier leakage out of the active region caused by the asymmetry of the pn junction, specifically the disparity between electron and hole concentrations and mobilities, is discussed in detail. The model is in agreement with the droop's key behaviors not only for GaInN LEDs but also for AlGaInP LEDs. 相似文献