Y.-R. Lee

High-Frequency Modulation of GaAs/AlGaAs LEDs Using Ga-Doped ZnO Current Spreading Layers

In this letter, we report the high-frequency modulation of GaAs/AlGaAs near-infrared (NIR) light-emitting diodes (LEDs) with gallium-doped zinc oxide (GZO) prepared by atomic layer deposition as a current spreading layer. This report analyzes the effects of aperture area of the NIR LEDs on minority carrier lifetime and further investigates the required injection current to achieve the 3-dB frequency bandwidth of 100 MHz. At the same injection current density, the LEDs with different aperture areas always exhibit the same minority carrier lifetime, which is inversely proportional to the square root of current density. It means that the GZO layer plays a good current spreading in the lateral direction from the ohmic contact of NIR LEDs, which shows the lower contact resistance and lower forward voltage.

DLTS Analyses of GaN p-i-n Diodes Grown on Conventional and Patterned Sapphire Substrates

In this letter, we report the electrical characteristics of current-voltage, capacitance-voltage, and deep-level transient spectroscopy on the GaN p-i-n diodes with a 5- μm i-layer, which were grown on the conventional sapphire substrates (CSSs) and patterned sapphire substrates (PSSs) by metal-organic chemical vapor deposition. The GaN p-i-n diodes with PSS exhibit a wider diffusion region in the forward bias, two traps at 0.43 and 0.87 eV above the valence band, and a low trap concentration of ~ 5×1016 cm-3, as compared with the GaN p-i-n diodes with CSS. These results show that the GaN p-i-n diodes grown on PSS have a better quality of epitaxial layers than those grown on CSS.

Coherent trapping of x-ray photons in crystal cavities in the picosecond regime

We report on the trapping of 14keV photons in periods of 1.11–1.67ps by the 12 4 0 backdiffraction in two- and multiplate silicon single-crystal cavities of a few hundred micrometer size. The formation of standing waves inside the cavities ensures better coherence for the x rays. We anticipate that the transmitted x rays through this type of cavities can be used as a quasicoherent x-ray source for probing the dynamic structures of solids, liquids, and biological substances.

Large-Area Planar InGaAs p-i-n Photodiodes With Mg Driven-in by Rapid Thermal Diffusion

Conventional InP/InGaAs/InP heterostructure p-i-n photodiodes (PIN-PDs) are usually fabricated by postgrowth Zn diffusion to form the p-type region. In this letter, we propose a novel method to fabricate the high performance of largearea planar InP/InGaAs/InP PIN-PDs with Mg driven-in process. The Mg driven-in is implemented by spin-on dopant technique using magnesium-silica-film (MgSiOx) source and through the rapid thermal diffusion. The preparation of MgSiOx source carrier as the p-type dopant for InP/InGaAs heterostructure is more time-saving than that of zinc-phosphorous-dopant-coating because the latter needs an additional step of oxygen (O2) plasma to remove a thick resin layer. To improve the responsivity of vertically illuminated PDs, Si/Al2O3 bilayers are deposited as the antireflective coating. The 800-μm-diameter PD with Mg driven-in exhibits a low dark current of 20 pA (or 4 nA/cm2) at -10 mV, a high responsivity of 1.14 A/W at 1550-nm wavelength, an excellent quantum efficiency of 91%, and a good uniformity in the light received area. These characteristics are comparable to those of the PD with Zn driven-in.

Diffraction-Enhanced Beam-Focusing for X-rays in Curved Multi-Plate Crystal Cavity

Unusual x-ray focusing effect is reported for parabolic curved multi-plate x-ray crystal cavities of silicon consisting of compound refractive lenses (CRL). The transmitted beam of the (12 4 0) back reflection near 14.4388 keV from these monolithic silicon crystal devices exhibits extraordinary focusing enhancement, such that the focal length is reduced by as much as 18% for 2-beam and 56% for 24-beam diffraction from the curved crystal cavity. This effect is attributed to the presence of the involved Bragg diffractions, in which the wavevector of the transmitted beam is bent further when traversing several curved crystal surfaces.

Schottky Barrier Height Reduction at Interface Between GZO Transparent Electrode and InP/InGaAs Structure by Zinc Driven-in Step and Nickel Oxide Insertion

In this letter, we report the characteristics of transparent Ga-doped ZnO (GZO) electrodes contacted to the InP/InGaAs epitaxial structure both with and without a NiO_x inserting layer. The GZO films deposited onto the p-InP/InGaAs structure by both radio-frequency sputtering and plasma-mode atomic layer deposition always yield Schottky contact characteristics. The barrier height improvement at the n-GZO/p-InP interface is proposed using dual zinc driven-in steps and a NiO_x insertion layer to realize ohmic characteristics. The high zinc concentration (5-8 × 10¹⁸ cm^-3) is first obtained in the surface of the p-InP window layer via the dual zinc driven-in steps. By inserting a NiO_x layer between the GZO and Au/Cr contact films, the Au/Cr/GZO/NiO_x contact pad for zinc driven-in p-InP window layer and the postannealing process of 430 °C for 180 s exhibits a good ohmic contact behavior and a low specific contact resistance of 3.07 × 10^-4 Ωcm².

Multi-plate crystal cavity with compound refractive lenses

Multi-plate crystal cavities consisting of compound refractive lenses were prepared on silicon wafers by lithographic techniques. The crystallographic orientation of the crystal device is the same as that of the two-plate x-ray resonators reported (Phys. Rev. Lett. 94, 174801, 2005). X-ray (12 4 0) back diffraction from these monolithic silicon crystal devices showed interference fringes due to cavity resonance through the compound refractive lenses (CRL), but with less pronounced amplitudes. The transmitted beam size through this device is reduced by a factor of 5. Detailed analysis on cavity interference and beam suppression are discussed.

Effects of O2 plasma post-treatment on ZnO: Ga thin films grown by H2O-thermal ALD

Transparent conducting oxides have been widely employed in optoelectronic devices using the various deposition methods such as sputtering, thermal evaporator, and e-gun evaporator technologies.1-3 In this work, gallium doped zinc oxide (ZnO:Ga) thin films were grown on glass substrates via H2O-thermal atomic layer deposition (ALD) at different deposition temperatures. ALD-GZO thin films were constituted as a layer-by-layer structure by stacking zinc oxides and gallium oxides. Diethylzinc (DEZ), triethylgallium (TEG) and H2O were used as zinc, gallium precursors and oxygen source, respectively. Furthermore, we investigated the influences of O2 plasma post-treatment power on the surface morphology, electrical and optical property of ZnO:Ga films. As the result of O2 plasma post-treatment, the characteristics of ZnO:Ga films exhibit a smooth surface, low resistivity, high carrier concentration, and high optical transmittance in the visible spectrum. However, the transmittance decreases with O2 plasma power in the near- and mid-infrared regions.

Beam suppression and focusing in multi-plate crystal cavity with compound refractive lenses

Beam suppression and focusing in multi-plate crystal cavity with compound refractive lenses Sung-Yu Chen, Y.-Y. Chang, M.-T. Tang, Yu. Stetsko, M. Yabashi, H.-H. Wu, Y.-R. Lee, B.-Y. Shew, S.-L. Chang National Tsing Hua University, 101, Section 2, Kuang-Fu Road, Hsinchu, Taiwan 30013, R.O.C., Hsinchu, Taiwan, 30013, Taiwan, National Synchrotron Radiation Research Center, Hsinchu, Taiwan, R.O.C. 300, Spring-8/RIKEN Mikazuki, Hyogo, Japan, E-mail:d913303@oz.nthu. edu.tw

Effects of multiple-wave interaction on X-ray fluorescence: a synchrotron experiment

Angular distribution of X-ray fluorescence under three-beam di ffraction condition is investigated using synchrotron radiation for GaAs single-crystals. The fluorescence yield and multiply diffracted intensities as a function of the Bragg angle and the azimuth angle of rotation of a symmetric Bragg primary reflection are measured. It is found that fluorescence yield may increase first then decrease as the azimuth angle moves from the lower angles to higher angles across the exact three-beam diffraction position, or vice versa, depending on the polarization of the incident beam and the triplet phases involved in the diffraction process. However, the corresponding multiple diffraction intensities show almost opposite characteristic to fluorescence. The relationship between fluorescence yield and diffraction intensity is thoroughly examined. A theoretical interpretation, based on the dynamical theory, for the observed behavior is also given.