L. W. Wu

Nitride-based LEDs with 800/spl deg/C grown p-AlInGaN-GaN double-cap layers

GaN-based light-emitting diodes (LEDs) with various p-cap layers were prepared. It was found that surface morphologies of the LEDs with 800/spl deg/C grown cap layers were rough due to the low lateral growth rate of GaN. It was also found that 20-mA forward voltage of the LED with 800/spl deg/C grown p-AlInGaN-GaN double-cap layer was only 3.05 V. Furthermore, it was found that we could achieve a high output power and a long lifetime by using the 800/spl deg/C grown p-AlInGaN-GaN double-cap layer.

White-light emission from InGaN-GaN multiquantum-well light-emitting diodes with Si and Zn codoped active well layer

Si and Zn codoped In/sub x/Ga/sub 1-x/N-GaN multiple-quantum-well (MQW) light-emitting diode (LED) structures were grown by metal-organic vapor phase epitaxy (MOVPE). It was found that we can observe a broad long-wavelength donor-acceptor (D-A) pair related emission at 500 nm/spl sim/560 nm. White light can thus be achieved by the combination of such a long-wavelength D-A pair emission with the InGaN bandedge related blue emission. It was also found that the electroluminescence (EL) spectra of such Si and Zn codoped InGaN-GaN MQW LEDs are very similar to those measured from phosphor-converted white LEDs. That is, we can achieve white light emission without the use of phosphor by properly adjusting the indium composition and the concentrations of the codoped Si and Zn atoms in the active well layers and the amount of injection current.

Nitride-based near-ultraviolet light emitting diodes with meshed p‐GaN

This investigation presents nitride-based near ultraviolet light emitting diodes (LEDs) with a meshed p‐GaN layer. With 20mA injection current, it was found that forward voltages were 3.33 and 3.39V while output powers were 9.0 and 10.6mW for the meshed indium-tin-oxide (ITO) LED and meshed p‐GaN LED, respectively. The larger LED output power is attributed to increased light extraction efficiency.

InGaN/GaN blue light-emitting diodes with self-assembled quantum dots

InGaN/GaN blue light-emitting diodes (LEDs) with multiple quantum dot (MQD) active layers were successfully fabricated by using an interrupted growth method in metal-organic chemical vapour deposition (MOCVD). We have successfully formed nanoscale QDs embedded in quantum wells with a typical 3 nm height and 10 nm lateral dimension. It was found that a huge 68.4 meV blue shift in electroluminescence (EL) peak position as the injection current is increased from 3 to 50 mA for the MQD LED. The large EL blue shift reveals that deep localization of exitons (or carriers) originates from QDs will strengthen the band-filling effect as the injection current increases.

GaN-Based MSM Photodetectors Prepared on Patterned Sapphire Substrates

GaN-based metal-semiconductor-metal ultraviolet photodetectors (PDs) prepared on a patterned sapphire substrate (PSS) and a conventional flat sapphire substrate were both fabricated and characterized. It was found that we can reduce dark leakage current and enhance by about two orders of magnitude by using a PSS. The internal gain of the PDs prepared on a PSS was also much smaller.

Electrical behavior of ZrO2-MgO-Y2O3 solid electrolyte

ZrO2 doped with various compositions of two stabilizers, Y2O3 and MgO, in order to lower sintering temperature and improve the electrical behavior of sintered bodies have been investigated in this study. The results show that densification of Y2O3-ZrO2 system is enhanced by MgO addition. Sintered bodies display a bimodal distribution of grains under proper addition. This research discovers that (YO1.5)0.08(MgO)0.04(ZrO2)0.88 system has high conductivity and responsible oxygen sensitivity. With regard to oxygen sensitivity, the log behavior EMF takes place at 440 and 550° C. Besides, the EMF decreases at a very low oxygen pressure caused by electronic conduction and electrode polarization.

Improved ESD reliability by using a modulation doped Al/sub 0.12/Ga/sub 0.88/N/GaN superlattice in nitride-based LED

Electrostatic discharge (ESD) induced electrical pulse is one of the main reliability concerns of optoelectronic devices. In this paper, a modulation doped Al/sub 0.12/Ga/sub 0.88/N/GaN superlattice are introduced to improve ESD reliability in nitrided-based LEDs. The basic idea of this structure is to spread pulse current when LEDs suffer ESD. The ESD-induced pulse current would be spread laterally in 2D electron gas made by Al/sub 0.12/Ga/sub 0.88/N/GaN heterostructure. Therefore the probability of junction breakdown would be lower.

400nm InGaN/GaN and InGaN/AlGaN multiquantum well light-emitting diodes

400 nm In/sub 0.05/Ga/sub 0.95/N/GaN MQW light emitting diode (LED) structure and In/sub 0.05/Ga/sub 0.95/N/Al/sub 0.1/Ga/sub 0.9/N LED structure were both prepared by organometallic vapor phase epitaxy (OMVPE). It was found that the use of Al/sub 0.1/Ga/sub 0.9/N as the material for barrier layers would not degrade crystal quality of the epitaxial layers. It was also found that the 20 mA electroluminescence (EL) intensity of InGaN/AlGaN multiquantum well (MQW) LED was two times larger than that of the InGaN/GaN MQW LED. The larger maximum output intensity and the fact that maximum output intensity occurred at larger injection current suggest that AlGaN barrier layers can provide a better carrier confinement and effectively reduce leakage current.

Microstructure and properties of Cr/sub 2/O/sub 3/ doped lead titanate piezoceramics

The effect of Cr/sub 2/O/sub 3/ additives (0-0.6 wt.%) on the microstructure and electrical properties of Pb/sub 0.88/Ln/sub 0.08/ (Ti/sub 0.98/Mn/sub 0.02/)O/sub 3/ ceramics, where Ln=Nd, La, is studied. In Nd-modified PT (lead titanate) ceramics, the chromium ions enter into the lattice of the perovskite structure. They behave as a grain growth promoter and accelerate densification in microstructure, and they also act as a hardener which favors higher mechanical quality factor, lower dielectric loss, and lower electrical resistivity. In the La-modified PT ceramics, with increasing Cr/sub 2/O/sub 3/ additives the tetragonality and the Curie temperature remains nearly unchanged. Thus, the chromium ions perhaps tend to mostly segregate at the grain boundaries and to act as grain growth inhibitors and binders, being responsible for increases in porosity, dielectric constant, epsilon /sub 33//sup T/, and electrical resistivity.<<ETX>>

Dielectric and piezoelectric properties of PZT ceramics doped with 4PbO-B/sub 2/O/sub 3/

Piezoelectric materials consisting of Pb(Zr/sub x/Ti/sub 1-x/) O/sub 3/ (x=0.52 and 0.94) and glass powder 4PbO-B/sub 2/O/sub 3/ were studied. It is shown that, if a small amount of 4PbO-B/sub 2/O/sub 3/ glass powder is added to the PZT system, the sintering temperature can be reduced and the dielectric and piezoelectric properties will be enhanced. For PZT (52/48) doped with 0.2 wt.% 4PbO-B/sub 2/O/sub 3/ and sintered at 1150 degrees C for 30 h, the planar coupling factor k/sub p/ is higher than that of plain PZT (52/48). For PZT (94/6) doped with 0.5 wt.% 4PbO-B/sub 2/O/sub 3/, a planar coupling factor and a dielectric constant equal to 0.16 and 330, respectively, can be attained with sintering at 950 degrees C for 30 h.<<ETX>>