We demonstrate high-efficiency green and yellow-green single-quantum-well light-emitting diodes (LEDs) grown on semipolar (20 21) GaN substrates by metal organic chemical vapor deposition. The output power and external quantum efficiency at a driving current of 20 mA under a pulsed condition with a 10% duty cycle are 9.9 mW and 20.4% for the green LED and 5.7 mW and 12.6% for the yellow-green LED, respectively. The electroluminescence linewidth narrowing, which is related to the band-filling effect caused by potential fluctuations, is not observed.
The first 30-mW-class semipolar blue light-emitting diode (LED) on a free-standing (10 1 1) GaN substrate has been demonstrated by using microscale periodic backside structures. The light extraction efficiency and corresponding output power were greatly enhanced, by up to 2.8-fold (bare chip) compare with conventional devices. At a driving current of 20 mA, the LED showed an output power of 31.1 mW and an external quantum efficiency of 54.7%. Semipolar GaN LED technology is now comparable to commercial c-plane blue LED technology, not only in terms of internal material properties but also in terms of chip processing techniques. # W urtzite (Al,Ga,In)N-based light-emitting diodes (LEDs) have attracted considerable attention since their first demonstration in the early to mid-1990s 1) for their wide applications including traffic signals, full-color displays, backlighting sources for liquidcrystal displays, and general lighting. Although device performance has improved steadily, current commercially available c-plane optoelectronic devices suffer from internal electric fields due to discontinuities in both spontaneous and piezoelectric polarization at the heterointerface. This leads to the separation of electrons and holes in the quantum wells and thus limits the radiative recombination rate. 2-5) On the other hand, devices grown on nonpolar planes such as the (1 100) m-plane and (11 20) a-plane, as well as devices grown on (11 22) and (10 1 1) semipolar planes have been demonstrated with eliminated or reduced polarization fields. [6][7][8][9][10][11][12][13] and are theoretically predicted to have a higher optical gain than c-plane devices, due to their anisotropic band structure. 14) Despite those advantages, however, the output power and efficiency of current semipolar and nonpolar LEDs are still lower than those of the best reported c-plane devices, mainly due to the poor light extraction efficiency ( extr ) compared with their polar counterparts. [15][16][17][18][19] Light extraction efficiency has become the most important limiting factor for the efficiency of LEDs, since the internal quantum efficiency (IQE) of nitride-based LEDs has been greatly improved (more than 80%) 20) by the availability of low-dislocation GaN substrates and advances in metal organic chemical vapor deposition (MOCVD) techniques. The low extr is primarily caused by the low critical angle (23 ) of the light escape cone, due to the large differences between the refractive indices of GaN (n $ 2:5) and air (n ¼ 1). 21) For c-plane devices, both extr and the corresponding output power have been greatly improved by surface roughening methods such as patterned sapphire substrate (PSS) and photoelectrochemical (PEC) etching techniques. [21][22][23][24][25] Semipolar and nonpolar devices, however, still suffer from low light extraction efficiency due to the lack of proper roughening techniques, which have hindered their performance. Recently, Zhong et al. have demonstrated that surface patterning with conical features by inductively coupled pla...
The quantum-confined Stark effect (QCSE) on InGaN-based light-emitting diodes (LEDs) was investigated as a part of the continuing study of exploring differences between photoluminescence (PL) and electroluminescence (EL) characteristics. The luminescence characteristics were related to electrical characteristics of green and amber LEDs by employing the electrical-bias-applied PL technique. By inspecting the band diagram, it has been found that the separation of quasi-Fermi levels, which strongly affects the QCSE, can be quantified and related to the luminescence. In order to compare PL and EL characteristics, attention was paid to the QCSE during the PL and EL measurements. Despite the control of the QCSE, differences were still confirmed between PL and EL characteristics, which have led us to the conclusion to that there are other unrevealed origins for the differences.
Lateral thermoelectric devices were fabricated using c-plane GaN thin films grown on sapphire by MOCVD. The device design is appropriate for on-chip integration for power generation in the 1 V and tens of µA range. The fabricated devices were measured to have a maximum open circuit voltage of 0.3 V with a maximum output power of 2.1 µW (=0.15 V×14 µA) at a relatively small temperature difference (ΔT) of 30 K and an average temperature (Tavg) of 508 K. In addition, the suitability of GaN for high temperature thermoelectric applications was confirmed by measurements at 825 K.
Solid solutions between two isotypic host compounds: GdSr(2)AlO(5) and Sr(3)AlO(4)F; Gd(1-x)Sr(2+x)AlO(5-x)F(x):Ce(3+) (GSAF:Ce(3+)), have been prepared across the complete solid solution range x. Depending on x, the series display considerable optical tunability of emission wavelengths in the range 574 nm to 474 nm, which is attributed to the decreased crystal field splitting arising from increased host ionicity with fluorine addition. Applying the GSAF:Ce(3+) phosphors on InGaN LEDs (lambda (max) = 405 nm and 450 nm) permits white lighting sources to be prepared. The characteristics of these are reported.
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