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The electron emission characteristics of Si:GaN pyramids are measured using field emission current-voltage (I-V), field emission energy distribution analysis (FEED), field emission electron microscopy (FEEM) and photoemission electron microscopy. Field emission current-voltage (I-V) measurements show an average threshold field value of 7 V/micro-m for an emission current of 10nA. FEED and FEEM measurements also yielded similar results.

The output power of InGaN multiple-quantum-well laser diodes (LDs) emitting at 405 nm wavelength is compared for several Al composition in the AlGaN n-cladding layer. The Al composition has been varied from 2% to 6% to study the effect of n-cladding refractive index on threshold current and slope efficiency of the LDs. As the Al composition in the AlGaN n-cladding layer increases, both threshold current and slope efficiency decrease. This behavior can be explained by the change in optical field distribution with refractive index of the AlGaN n-cladding layer. It is found that the Al composition of ¿4% would be advantageous for achieving more than 100 mW output power and high level of catastrophic optical damage. [ABSTRACT FROM AUTHOR]

An optical loss of GaN-based blue-violet laser diodes (BV-LDs) was measured by taking the intensity decay of edge emitting luminescence with respect to the distance from cleaved edge of a wafer to the position where an excitation laser was focused. Amplified spontaneous emission (ASE) was also investigated by tuning the power of an excitation laser on BV-LD wafers. Measurements were performed on wafers with different thicknesses of InGaN optical confinement layers (OCLs). The threshold power of ASE intensity was minimized at an optimum thickness of InGaN OCL. We also found that optical loss of wafers was determined by absorption of an InGaN layer in thicker OCL structure. From experimental data and fittings, we obtained 40 cm-1 for InGaN absorption at 405 nm. The optical field confined in OCL region was reasonably high enough to affect the overall modal loss in devices. Therefore, the optical losses still remained even though the Mg-doped GaN regions are far enough from the active layers. The crystal quality of an InGaN layer should be an important aspect to improve the performance of BV-LDs. [ABSTRACT FROM AUTHOR]

Comparative analysis of optical characteristics of In0.08Ga0.92N/In0.03Ga0.97N multiquantum well (MQW) laser diode structures grown on freestanding GaN and on sapphire substrates is reported. Higher quantum efficiency, higher thermal activation energy, smaller Stokes-like shift, and shorter radiative lifetime are observed for InGaN MQWs on GaN substrate than those of the same MQWs on sapphire substrate. From time-resolved optical analysis, we find that not only an increase in nonradiative lifetime due to reduced dislocation density but also a decrease in radiative lifetime caused by suppressed piezoelectric field play an important role in enhancing optical properties of InGaN MQWs on GaN substrates. [ABSTRACT FROM AUTHOR]

InGaN optical confinement layers (OCLs) were introduced into blue-violet AlInGaN-based laser diodes (LDs), resulting in the drastic improvements of lasing performance. Comparing with conventional LD structure, the lowest threshold current density of 2.3 kA/cm2 has been achieved by adding 100-nm-thick InGaN OCLs which represented maximum optical confinement factor. Additionally, we observed the high quantum efficiency and the uniform emission intensity distribution of InGaN quantum wells grown on lower InGaN OCL than on typical GaN layer. Upper InGaN OCL can reduce Mg diffusion from p-type layers to InGaN active region by separating the distance between InGaN quantum wells and p-type layers. [ABSTRACT FROM AUTHOR]

InGaN quantum-well (QW) green laser diodes (LDs) with an emission wavelength of 483.7 nm were characterized by controlling the injection pulsewidth. The emission wavelength of LDs showed a large blueshift (> 20 nm) of spontaneous emission peak with increasing injection current below the threshold current. The huge blueshift was ascribed to the deep In localization states and the strong piezoelectric field in the green InGaN QW structure with higher In contents than conventional violet/blue InGaN QWs. However, the lasing wavelength of LDs was slightly redshifted by increasing the injection pulsewidth due to the thermal heating effects. [ABSTRACT FROM AUTHOR]

We demonstrated the long wavelength (485 nm) lasing of InGaN laser diodes under continuous wave condition at room temperature over 10 mW. Two InGaN laser structures were adapted with different indium composition for InGaN optical confinement layers (OCLs) below quantum wells. The blue shift of electroluminescence (EL) was reduced in InGaN laser diodes grown on 3% In concentration in InGaN OCL compared with 1.5% In concentration in InGaN OCL. The EL peak for laser diode with 3% In concentration in InGaN OCL occurs at longer wavelength for all current levels compared to the laser with 1.5% In concentration in InGaN OCL. In addition, the laterally nonuniform InGaN wells grown on 1.5% In concentration in InGaN OCL was verified by the cross-sectional view of InGaN active layer using high-resolution transmission electron microscopy. [ABSTRACT FROM AUTHOR]

Direct comparison of optical properties and carrier dynamics of InGaN multiple quantum well (MQW) laser diode structures grown on pendeo epitaxial (PE)-GaN and sapphire substrates is reported. A strong increase in quantum efficiency and a dramatic reduction in stimulated emission threshold are observed for InGaN MQWs on PE-GaN substrates as compared to MQWs on sapphire substrates. Based on temperature-dependent time-resolved optical analysis, the authors find that a significant increase in nonradiative lifetime due to suppressed dislocation density plays an important role in enhancing optical properties of InGaN MQWs grown on PE-GaN substrates, resulting in radiative-process dominant emission even at room temperature. [ABSTRACT FROM AUTHOR]

The authors analyzed radiative efficiency of InGaN laser diodes (LDs) emitting at 405 nm. Based on semiconductor rate equations, the radiative efficiency is unambiguously determined by the analysis of electroluminescence characteristics. The radiative efficiency exceeds 70% even far below threshold of ∼3 mA at a high temperature of 80 °C. This highly radiative characteristic is attributed to reduced contribution of nonradiative recombination in LDs with low-dislocation-density active material. It is also found that the radiative efficiency is almost independent of threshold current, indicating that nonradiative recombination is not a major factor which determines lasing threshold in 405 nm emitting InGaN LDs having low dislocation density. [ABSTRACT FROM AUTHOR]

We report stable temperature characteristics of threshold current and output power in InGaN blue laser diodes emitting around 450 nm. The threshold current is changed by <3 mA in operation temperature range from 20 to 80 °C, and even negative characteristic temperature is observed in a certain temperature range. This peculiar temperature characteristic is attributed to originate from unique carrier transport properties of InGaN quantum wells with high In composition, which is deduced from the simulation of carrier density and optical gain. In addition, slope efficiency is also maintained well and wall plug efficiency is even improved as temperature increases. [ABSTRACT FROM AUTHOR]

Pd/Ti/Al and Ti/Al Ohmic contact materials on Ga-face and N-face surfaces of n-type GaN were investigated by measuring the contact resistivities with respect to annealing temperatures. Pd/Ti/Al contact showed good Ohmic property in contrast to Ti/Al contact on N-face surface of n-type GaN. Cross-sectional transmission electron microscopy results on samples of as-deposited and annealed at 450 °C for 30 s indicated that Pd played an important role in changing the surface state of N-face surface of n-type GaN and less than 50 Å of Pd was required to obtain the best Ohmic contact property. [ABSTRACT FROM AUTHOR]

AlGaN/GaN multiquantum barriers (MQBs) were introduced into violet AlInGaN laser diodes with an InGaN multiquantum-well structure, resulting in drastic improvements in lasing performance. Comparing with conventional AlGaN single electron blocking layer (EBL), lower threshold current of 32 mA and higher slope efficiency of 1.12 W/A at room temperature has been achieved by using the AlGaN/GaN multiquantum barrier. This improvement implies that p-type AlGaN/GaN MQBs are more effective in suppressing the overflow of electrons than p-type AlGaN single EBL. Effective barrier heights of the MQBs should be higher than the single EBL due to the quantum effect of MQBs and the enhancement of p-type doping efficiency. Additionally, the effect of strain on InGaN multiquantum wells from the single EBL can be reduced by using the AlGaN/GaN MQBs structure. [ABSTRACT FROM AUTHOR]

We report on a promising Rh-based scheme for high-quality ohmic contacts to surface-treated p-GaN:Mg (4×10[sup 17] cm[sup -3]). It is shown that the two-step surface-treated Rh contacts (10 nm) produce a specific contact resistance of 1.7×10[sup -5] Ω cm[sup 2]. It is also shown that the two-step treated Rh/Ni (5/5 nm) and Rh/Au (5/5 nm) contacts yield 6.0×10[sup -5] and 9.3×10[sup -6] Ω cm[sup 2], respectively. Based on the current–voltage measurement, x-ray photoemission spectroscopy, and Auger electron spectroscopy results, the mechanisms for the formation of the nonalloyed Rh-based ohmic contacts is described and discussed. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The effect of crystal polarity on the electrical properties of Ti/Al contacts to n-GaN substrate has been investigated. The Ti/Al contacts prepared on Ga-face n-GaN substrate became ohmic with a contact resistivity of 2×10[sup -5] Ω cm[sup 2] after annealing at temperatures higher than 600 °C for 30 s. On the contrary, the contacts on N-face n-GaN substrate exhibited nonlinear current–voltage curve and high Schottky barrier heights over 1 eV were measured at the same annealing conditions. These results could be explained by opposite piezoelectric-field at GaN/AlN heterostructure resulted from different polarity of the GaN substrate. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An electrically injected InGaN/GaN-based distributed Bragg reflector (DBR) laser was demonstrated. Surface grating was formed on both sides of ridge waveguide by chemically assisted ion beam etching technique. The observed threshold current was 375 mA with threshold voltage of 15.1 V for 500x3 μm[sup 2] devices. The emission of the DBR laser occurred in a single longitudinal mode at a wavelength of 401.3 nm. The ratio of sidemode suppression was found to be more than 13 dB until a current injection of 1 A. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Aim: To evaluate the relationship between dental calcification and skeletal maturity and to identify the tooth with the highest correlation with skeletal maturity index in Korean children., Materials: For 447 children (205 boys and 242 girls) aged between 5 and 13 years, hand-wrist and lateral cephalometric radiographs were taken to assess skeletal maturity by Fishman's skeletal maturity indicators (SMI) and Baccetti's cervical vertebrae maturation (CVM) stages. Dental panoramic radiographs were taken to assess dental maturity of the permanent mandibular canine, first and second premolar, and second molar using the method devised by Dermirjian., Conclusion: Dental calcification stages determined by panoramic radiographs can be clinically used as useful indices to predict skeletal maturity in Korean children.

Odontomas can cause impaction of permanent teeth. During the removal of odontomas associated with an impacted tooth, minimally-invasive surgical approaches are necessary. We present a technical note highlighting easy extraction of a deeply impacted odontoma using a patient-specific computer-aided design/computer-aided manufacturing (CAD/CAM) surgical guide. Its use and advantages are described., (Copyright © 2020 Elsevier Masson SAS. All rights reserved.)

Marsupialization is the conservative treatment for cystic lesion in children. This technique requires maintaining the patency between the cyst and oral cavity to allow spontaneous healing of cystic lesion. There have been various fixation methods for securing the patency. However, the previous fixation methods have limitation of being invasive and inability to retain catheter firmly during the treatment. In this technical note, we adopted a novel and easy fixation method to obtain firm stability of catheter without damage to intraoral tissues during marsupialization technique., (Copyright © 2018 Elsevier Masson SAS. All rights reserved.)