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We report a low-resistance thermally stable ohmic contact on p-type GaN using a promising contact scheme of Pd/Ni. Specific contact resistance as low as 5.7×10−5 Ω cm2 was obtained from the Pd (30 A)/Ni (70 A) contact annealed at 500 °C under an oxidizing ambient. NiO that formed at the surface prevented Pd atoms from outdiffusing, promoting the formation of Pd gallides, Ga2Pd5 and Ga5Pd. This reaction produces Ga vacancies below the contact, leading to enhancement of the thermal stability as well as reduction of the contact resistivity.

Ohmic contact formation mechanism of Ni on n-type 4H–SiC is proposed by comparing the electrical properties with microstructural change. The ohmic behavior was observed at temperatures higher than 900 °C, but Ni2Si phase, as formerly reported to be responsible for ohmic contact, was formed after annealing at 600 °C. The higher work function of Ni2Si than Ni and the observation of graphite phase on the surface of Ni silicide after annealing at 950 °C support that a number of carbon vacancies were produced below the contact, playing a key role in forming an ohmic contact through the reduction of effective Schottky barrier height for the transport of electrons.

Pd contacts on both n-type and p-type GaN were studied using positron annihilation spectroscopy, and the results were used to interpret the role of Ga vacancies on the band bending below the contacts. The concentration of Ga vacancy in Si-doped GaN was higher than that in the Mg-doped one. In Si-doped GaN, implanted positrons were annihilated at the nearer surface region and the interface of Pd/n-type GaN was detected by positrons clearly shifted toward the surface of Pd. This suggests that Ga vacancies could act as an interface state, pinning the Fermi level at the interface of Pd with GaN, leading to the production of a negative electric field below the interface.

We investigated the structural behavior of the Ni/Au contact on GaN(0001) and found the catalytic role of Au during annealing, using in situ x-ray scattering. The oxidation kinetics of Ni during annealing in air was greatly affected by the presence of Au. The accelerated GaN decomposition and Ni nitride formation during annealing in N2 also provide evidence of the catalytic role of Au. The results suggest that oxidized Ni/Au ohmic contact exhibit better thermal stability than that of the N2 annealed Ni/Au contacts.

Effects of CH4 addition on the etched profiles were studied during the BCl3/H2/Ar inductively coupled plasma reactive ion etching of GaN mesas. It was observed that the sidewall angle increases with the addition of up to 10% CH4 but then decreases with further addition, resulting in a maximum angle of about 86° at the optimum condition, while the etch rate continuously decreases. It was proposed that the improved anisotropy is due to the polymer deposition on the surfaces, which reduces the mask erosion during the etching.

A room-temperature Ti/Al Ohmic contact on n-type GaN was obtained by surface treatment using Cl2 inductively coupled plasma treatment. The specific contact resistivity was dramatically decreased from the Schottky behavior to 9.4×10−6 Ω cm2 by the treatment. The binding energy of the Ga–N bond and the atomic ratio of Ga/N were simultaneously increased after the plasma treatment. This provides evidence that N vacancies, acting as donors for electrons, were produced at the etched surface, resulting in a shift of the Fermi level near to the conduction band. This leads to the reduction in contact resistivity through the decrease of the Schottky barrier for the conduction of electrons.

We demonstrate novel method for improving light extraction efficiency for n-side-up vertical InGaN/GaN light-emitting diodes (V-LEDs) using MgO nano-pyramids and ZnO refractive-index modulation layer. The MgO nano-pyramids structure is successfully fabricated on n-GaN/ZnO surface using electron-beam evaporation. The light output power of n-GaN/ZnO/MgO V-LEDs is enhanced by 49% compare to that of n-GaN V-LEDs. The angular-dependent far-field emission shows the significant increase of side emission for the n-GaN/ZnO/MgO V-LEDs due to the increase of critical angle for total internal reflection as well as the roughened surface by MgO pyramids structure. These experimental results indicate the critical role of surface texturing in improving the light extraction efficiency of the V-LEDs for solid-state lighting.

We present a method of increasing light output power and suppressing efficiency droop in vertical-structure InGaN/GaN MQW LEDs without modifying their epitaxial layers. These improvements are achieved by reducing the quantum-confined Stark effect (QCSE) by reducing piezoelectric polarization that results from compressive stress in the GaN epilayer. This compressive stress is relaxed due to the external stress induced by an electro-plated Ni metal substrate. In simulations, the severe band bending in the InGaN quantum well is reduced and subsequently internal quantum efficiency increases as the piezoelectric polarization is reduced.

The effects of point defects on the electrical activation of Si-implanted GaAs during rapid thermal annealing were investigated using slow positron beam, cross-sectional transmission electron microscopy, and Hall measurements. The increase of the Ga vacancy concentration in the GaAs substrate induced by the SiO/sub 2/ cap layer on the substrate during annealing was observed to decrease the activation efficiency and the number of extrinsic stacking faults via the recombination of interstitials with vacancies. It was found that the efficiency of the carrier creation is not dependent upon the Ga vacancy concentration during the rapid thermal annealing of Si-implanted GaAs. Hence, it is proposed that the electrical activation of Si-implanted GaAs is not due to implantation-induced vacancies but to the self-exchange of interstitial Si atoms with the host Ga substitutional atoms. >

The structural evolution during heteroepitaxial growth of ZnO/sapphire(001) by radio-frequency magnetron sputtering has been studied using real-time synchrotron x-ray scattering. The two-dimensional (2D) ZnO(002) layers grown in the initial stage are highly strained and well aligned to the substrate having a mosaic distribution of 0.01° full width at half maximum (FWHM), in sharp contrast to the reported transition 2D layers grown by molecular-beam epitaxy. With increasing film thickness, the lattice strain is relieved and the poorly aligned (1.25° FWHM) three-dimensional (3D) islands are nucleated on the 2D layers. We attribute the 2D–3D transition to the release of the strain energy stored in the film due to the film/substrate lattice mismatch.

Field emission of diamond film was enhanced after surface treatment using boiling aqua-regia solution. The current generated by the emission of electrons was distinctly increased and the threshold field was reduced from 18.1 to 13.8 V/μm by the treatment. The amount of C–C bonds was decreased, but the O–C one was increased by the treatment. The Fermi level at the treated surface was increased by 2.2 eV. This provides evidence that the enhancement of electron emission originated from the reduction of the work function, caused by the chemisorption of oxygen atoms at the surface of diamond during the aqua regia treatment. Thus, the effective electron affinity changed from positive to negative, leading to the reduction of the potential barrier height and width for electron emission at the surface of diamond.

The effects of impurities, such as Si and Be, on both the creation and the migration of Ga vacancies in annealing of GaAs were investigated by a slow positron beam technique. The results show that vacancies diffuse from the surface during the annealing and one of the dominant types is a monovacancy of Ga, VGa, in Be‐doped GaAs and/or Si‐doped GaAs, while the other is a divacancy of VGa‐VAs in undoped GaAs. In annealing the bilayer structures composed of the Si‐doped layer grown on the Be‐doped layer, it was found that VGa is a major type of defect rather than VGa‐VAs if the Si concentration is higher or lower than the Be one in GaAs, but VGa‐VAs is dominant if the concentrations of the impurities are similar. This proposes that the interaction between Si and Be is stronger than that of VAs‐BeGa and/or VGa‐SiGa. The Ga interstitial IGa is created in the Be‐doped layer where IGa interacts with VGa created from the surface and suppresses the migration of VGa. This supports the validity of the kick‐out mechan...

The slow positron beam technique was applied on undoped and Be‐doped GaAs to study the effects of Be impurities on both creation and migration of Ga vacancies, VGa, during annealing. It is observed that a monovacancy of VGa is created in Be‐doped GaAs to result in enhanced Coulombic interaction between As vacancy, VAs, and Be acceptor, BeGa. In undoped GaAs, the formation of divacancies, VGa‐VAs, is dominant. The migration depth of vacancies is shorter in Be‐doped GaAs than in undoped GaAs. This suggests the existence of Ga interstitials, IGa, in the Be diffused layer which interact with VGa introduced from the surface. Based on these observations, we suggest the kick‐out mechanism for Be diffusion in GaAs.

The effects of deep levels on the transconductance dispersion in an AlGaAs/InGaAs pseudomorphic high electron mobility transistor was interpreted using capacitance deep level transient spectroscopy (DLTS). Transconductance was decreased by 10% in the frequency range of 10 Hz–10 kHz at the negative gate bias, but it was increased at the positive one. In the DLTS spectra, two hole trap-like signals corresponding to surface states were only observed at the negative pulse bias, whereas the DX-center with the activation energy of 0.42±0.01 eV were observed at the positive one. The activation energy agrees well with that obtained from the temperature dependence of the positive transconductance dispersion, 0.39±0.03 eV. These provide evidence that the positive and negative transconductance dispersions are due to the DX center and surface states, respectively.

A self-aligned gate pseudomorphic high-electron-mobility transistor (PHEMT) was developed through nonalloyed PdGe ohmic contact on an n+-GaAs cap layer. The lowest contact resistivity obtained was 1.2×10−7 Ω cm2 at 300 °C. This allows us to change the sequence on the formation of source/drain and gate electrodes in the process of PHEMT fabrication, namely self-aligned gate PHEMT. Performance of the self-aligned gate PHEMT was remarkably pronounced with annealing temperature or the decrease of contact resistivity. This is due to the solid-phase regrowth of highly Ge-doped GaAs below the PdGe contact, which acts to reduce barrier height for electron tunneling.

The change of the Fermi energy level at the interface of Pd/p-type GaN by surface treatment was investigated using positron annihilation spectroscopy, and the results were used to provide interpretation of the electrical properties of the contact. Changes in the positron parameters at the interface in the aqua regia-treated GaN are more pronounced than that in the HCl-treated one. This provides evidence that the surface treatment with aqua regia prior to Pd metal deposition removes surface oxides, resulting in the shift of the Fermi level position from a middle of the bandgap to near the valence band. Thus, the barrier for hole injection from metal to p-type GaN is lowered, subsequent to the decrease of contact resistivity by two orders of magnitude.

The energy levels of surface states at the surface of GaAs were determined through capacitance deep-level transient spectroscopy of GaAs metal–semiconductor field-effect transistor with large gate periphery. Two types of hole-like traps are observed in the spectra. These originate from the surface states at the ungated regions between gate and source/drain electrodes. The activation energies of both surface states are determined to be 0.65±0.07 and 0.88±0.04 eV, which agree well with the energy levels of AsGa+ and AsGa++ within band gap of GaAs, responsible for the Fermi level pinning at the surface.

We report the room-temperature ferromagnetism in transition metals (Co, Ni)-doped 8-hydroxy-quinoline aluminum (Alq3) by thermal coevaporation of high purity metal and Alq3 powders. For 5% Co-doped Alq3, a maximum magnetization of approximately 0.33 microB/Co at 10 K was obtained and ferromagnetic behavior was observed up to 300 K. The Co atoms interact chemically with O atoms and provide electrons to Alq3, forming new states acting as electron trap sites. From this, it is suggested that ferromagnetism may be associated with the strong chemical interaction of Co atoms and Alq3 molecules.

The impurity effects on the creation of Ga vacancies in Si‐doped GaAs grown on a Be‐doped epilayer by molecular‐beam epitaxy were investigated through slow positron beam measurements. Doping of Si impurities enhances the creation of Ga vacancies in GaAs. The experimental results support the theoretical prediction of the creation of Ga vacancies in terms of the change in the Fermi‐level position by the Si doping into GaAs, and also suggest that a Si atom diffuses in GaAs as a neutral complex of SiGa‐VGa rather than that of SiGa‐SiAs. The change in the S parameter distribution at the interface between Si and Be‐doped regions is explained by the Be carryforward phenomenon which occurs during the growth of Si‐doped GaAs on a Be‐doped epilayer.

The trap concentration as a function of the depth from the abraded surface of iron single crystals was investigated by means of positron Doppler broadening. The deformation depth was about 40 μm from the surface when the specimen was mechanically polished on 240-grit SiC paper. The depth of the damaged region is less than 15 μm from the surface when a slurry of 0.3 /xm A1"2O3 particles is used. A mixture of edge and screw dislocations was found in the deformed layer. The two stages in recovery observed upon annealing mechanically polished iron are interpreted as being due to the disappearance of screw components during lower temperature anneals (273 to 473 K). When the number of screw dislocations has fallen considerably, the edge-dislocation dipoles begin to disappear. The activation energies for recovery of screw and edge dislocations are estimated at 30.5 and 103.2 kJ/mol, respectively, using the second-order Li model. Based on these small energies, dislocation dipoles disappear by glide rather than by climb in pure iron. Migration of monovacancies and climb are apparently important with impure iron, since the activation energy is similar to that for vacancy migration.

The depth distributions of vacancy‐type defects in Si+ ‐implanted and thermally activated GaAs were studied by a slow positron beam technique and were compared with the results observed with a transmission electron microscope. In as‐implanted GaAs, the concentration of vacancy‐type defects decreased monotonically with increasing depth below the surface and the generation of point defects was demonstrated by the lattice image of transmission electron microscopy. The vacancy concentration is not dependent upon activation conditions; however, the electrical activation coefficiency obtained from Hall measurements is enhanced with increasing activation annealing time. This indicates that the electrical activation of Si+ ‐implanted GaAs is proceeding by the exchange of interstitial Si with substitutional Ga rather than the recombination of interstitial Si into Ga‐related vacancies. The maximum number of extrinsic‐type stacking faults was observed at 70–80 nm below the surface after the activation annealing, which is compared with that of vacancy‐type defects, at 25–35 nm, obtained by the slow positron beam technique. This discrepancy in both of the damage distributions could originate in different types of defects existing along the depth below the surface, which was discussed with the high‐energy recoil theory.

This paper reviews the principles, impediments, and recent progress in the development of ultrathin flexible Ag electrodes for use in flexible optoelectronic devices. Thin Ag-based electrodes are promising candidates for next-generation flexible transparent electrodes. Thin Ag-based electrodes that have a microcavity structure show the best device performance, but have relatively low optical transmittance (OT) due to reflection and absorption of photons by the thin Ag; this trait causes problems such as spectral narrowing and change of emission color with viewing angle in white organic light-emitting diodes. Thinning the Ag electrode to

Microstructural evidence on the formation of a heavily Ge-doped layer below Pd/Ge-based ohmic contact to AlGaAs/InGaAs pseudomorphic high electron mobility transistor was obtained. The contact resistivity is decreased by two orders of magnitude as InGaAs channel is intermixed. This originates from the formation of Au2Al and Au7Ga2 compounds below the contacts during annealing, via production of group III vacancies. The vacancies play a role in producing free electrons by the incorporation of Ge atoms, resulting in intermixing of InGaAs as well as reduction of contact resistivity.

Ohmic contact to p-type GaN with the lowest contact resistivity was developed by the surface treatment prior to Pd/Au metal deposition. The contact resistivity drastically decreased from 2.9×10−2 to 4.3×10−4 Ω cm2 by the surface treatment using aqua regia. The surface treatment plays a role in removing the surface oxide formed on p-type GaN during epitaxial growth, and subsequently in reducing the barrier height for holes at the interface of Pd/p-type GaN, resulting in the good ohmic contacts to p-type GaN.

Microstructural evidence on direct contact of Au/Ge/Ni/Au ohmic metals to a InGaAs channel in AlGaAs/InGaAs pseudomorphic high electron mobility transistor with an undoped GaAs/AlGaAs cap layer was found using transmission electron microscopy, and the results were used to interpret the electrical properties of the contact. The lowest contact resistivity of 3.8×10−6 Ω cm2, obtained at 420 °C annealing, is due to the penetration of the interfacial compounds, Au2Ga and Au2Al, into the buried InGaAs channel. The direct contact of the compounds to the channel causes the reduction of series resistances between the ohmic compounds and the channel, resulting in the low contact resistivity.

/sup G/aAs power MESFET's with 0.5-/spl mu/m T-shaped gate for Ku-band power applications have been developed using a new self-aligned and optical lithography. It displays a maximum current density of 350 mA/mm, an uniform transconductance of 150 mS/mm and a high gate-to-drain breakdown voltage of 35 V. Both the high breakdown voltage and the uniform transconductance were achieved by the new MESFET design incorporating an undoped GaAs cap and a thick lightly doped active layers. The breakdown voltage is the highest one among the values reported on the power devices. The device exhibits 0.61 W/mm power density and 47% power added efficiency with 9.0 dB associated gain at a drain bias of 12 V and an operation frequency of 12 GHz.

The Pd/Ge/Ti/Au ohmic contact to AlGaAs/InGaAs pseudomorphic high electron mobility transistor was investigated with the etch depth of an undoped GaAs/AlGaAs cap layer. The contact resistivity decreases from 9.5×10−5 to 2.3×10−6 Ω cm2 when the contacts were formed on a n-Al0.23Ga0.77As layer by removing the undoped cap layer. X-ray diffraction results show that the good ohmic contact is due to the formation of Au2Al as well as β-AuGa. Both compounds play a role to create group-III vacancies, followed by the incorporation of Ge into group-III vacancies, namely, creation of free electron below the contact. This results in the considerable elimination of contact resistivity by lowering the effective tunneling barrier.

A state-of-the-art GaAs power MESFET operating at a drain bias of 2.3 V has been developed using the low-high doped channel structure. The device has 0.8-/spl mu/m gate length and 21-mm gate width. The power performance tested at a 2.3 V drain bias under 900 MHz operation frequency was output power of 31.3-dBm with 11.3-dB gain and 69-percent power-added efficiency. A third-order intercept point was evaluated to be 50.7-dBm. A Linearity Figure-of-Merit of 55.6 was recorded for 21-mm-wide FET.

Thermally stable, low‐resistance PdGe‐based ohmic contacts to high–low doped n‐GaAs have been developed. The lowest contact resistance obtained is two times lower than that of previously reported PdGe ohmic contacts. The contacts are thermally stable even after isothermal annealing for 5 h at 400 °C under atmosphere ambient. X‐ray diffraction results and Auger depth profiles show that the good PdGe‐based ohmic contact is due to the formation of both AuGa and TiO compounds. The AuGa compound enhances the creation of more Ga vacancies, followed by the incorporation of Ge into Ga vacancies, and the TiO compound suppresses As outdiffusion from the GaAs substrate, respectively.

High quality GaAs layers with excellent crystal quality and surface morphology were grown on InP substrates (GaAs/InP) using liquid phase epitaxy. Thin GaAs buffer layers heavily doped with Se were utilized to prevent the substrate meltback and the InP substrates patterned with gratings to reduce the dislocation density. Double crystal x‐ray diffraction showed about 230 arcsec full width at half maximum of the (400) reflection, which represents significant improvement compared to the previously reported 350 arcsec of the GaAs/InP layer grown by chemical beam epitaxy using strained superlattice buffer layers.

A state-of-the-art GaAs power MESFET operating at a drain bias of 2.9 V has been developed using the high-low doped channel structure grown by molecular beam epitaxy. The device has 0.6 /spl mu/m gate length and 16 mm gate width. The power performance tested at a 2.9 V drain bias and 900 MHz operation frequency was output power of 31.5 dBm with 11.5 dB gain and 64% power-added efficiency. >

A front-end receiver MMIC for 3.3 V-operating CDMA/AMPS dual-mode hand held phone has been developed using a GaAs MESFET process. The developed MMIC, chip size of which is 1.9/spl times/3.9 mm/sup 2/ shows noise figure of 2.8 dB, power gain of 35/25 dB at the nominal current consumption of 22.5/16.1 mA in CDMA/AMPS modes, respectively.

not Available.

Room temperature ohmic contacts to p- and n-type GaN using surface treatments were applied to the fabrication of GaN blue light emitting diode (LED). The state-of-the-art LED operation of the forward voltage of 3.1 V at the injection current of 20 mA was demonstrated without annealing processes. The surface treatment on p-type GaN using aqua regia solution caused the contact resistivity to decrease by three orders of magnitude. The inductively coupled plasma treatment on n-type GaN resulted in the contact resistivity of ~ 10E-6 ohm-cm2 at as-deposited state. Both treatments allowed the room temperature ohmic contacts to be realized on both substrates. Angle resolved synchrotron x-ray photoelectron spectroscopy was employed to examine the atomic composition at the treated surface. From this, the formation of ohmic contacts was deduced as due to the production of vacancies below the contact, that is, Ga vacancies for p-type contact and N vacancies for n-type one.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We investigated the structural evolution of the Ni/Au contact on GaN(000l) during annealing in N2, using in-situ x-ray diffraction, anomalous x-ray scattering, and high resolution electron microscopy. GaN decomposition occurred mostly along GaN dislocations at temperature higher than 500°C. The decomposed Ga diffused into Au and Ni substitutional positions, and the decomposed nitrogen reacted with Ni, forming Ni4N. Interestingly, Ni4N was grown epitaxially. The epitaxial relationship of the Ni4N, Au, and Ni was identified as M(111)//GaN(0002) and M[1 −1 0]//GaN[1 1 −2 0] (M= Ni4N, Au, and Ni). At dislocation free regions, however, the atomically smooth interface remained intact up to 700 °C. Remarkable improvement of device reliability is expected in the contact on dislocation free regions compared with the contact on dislocations.

Synchrotron radiation-based x-ray photoemission spectroscopy was used to study the Fermi level position within the band gap for thin metal overlayers of Au, Ni, and Ti on n-GaN and p-GaN. The Fermi level position was determined with the measured Fermi edge of the metal on the sample in order to correct for the presence of non-equilibrium effects. There are two different behaviors observed for the three metals studied. For Au and Ti, the surface Fermi positions on n-GaN and p-GaN are roughly 0.5 eV apart within the band gap. For Ni, the n-GaN and p-GaN have a Schottky barrier that forms at the same place at the gap.

Surface pretreatment using Cl2 plasma was applied to n-type GaN and Ti/Al ohmic contacts with resistivity of ~ 10−6 Ω cm2, realized without annealing. Using synchrotron radiation photoemission spectroscopy, it was observed that the Fermi level moved by 0.5 eV toward the conduction band edge and the atomic ratio of Ga/N was increased by the treatment. This suggests that a number of N vacancies were produced at the treated surface and the Fermi level was pinned at the energy level of N vacancies near the conduction band. The N vacancies acting as donors for electrons produced a number of electrons, resulting in the near surface region to be in the degenerate state. Both the shift of Fermi level and the production of electrons at the treated surface lead to the reduction in contact resistivity through the decrease of the effective Schottky barrier for conduction of electrons.

We investigated the structural behavior of the Ni/Au contact on GaN(000l) during annealing in N2, using in-situ x-ray diffraction, anomalous x-ray scattering, and high resolution electron microscopy. Thermally activated atomic mobility caused the two metal atoms, Au and Ni, to interdiffuse during annealing and form solid solutions. At temperature higher than 500°C, GaN decomposition and reactions occurred mostly along GaN dislocations. By decomposed nitrogen reacted with Ni, interestingly, epitaxial Ni4N phase was formed. The epitaxial relationship of the Ni4N, Au, and Ni was identified as M(111)//GaN(0002) and M[0 1 1]//GaN[0211] (M= Ni4N, Au, and Ni).

We applied slow positrons to both as‐etched GaP and (NH4)2Sx‐treated GaP. The results show that the surface of as‐etched GaP is active for the adsorption of oxygen atoms when the etched surface was exposed to air for several minutes before the measurement. On the other hand, the monolayer of chemisorbed sulfur in (NH4)2Sx‐treated GaP is effective to protect the clean surface from the adsorption of the oxygen atoms. The mean diffusion length of positrons in the etched GaP is shorter than that in (NH4)2Sx‐treated GaP. This suggests that the centers for the positron trapping, such as Ga vacancies VGa and/or VGa‐related complexes, are created by the adsorption of oxygen atoms.

Two type of top layers, namely, undoped and Si‐doped GaAs layers, were grown, respectively, on a Be‐doped epilayer by molecular beam epitaxy, and the effects of impurities of Be and Si on the creation of Ga interstitials IGa and Ga vacancies VGa during the annealing of the specimens were investigated by a slow positron beam. The concentration of VGa created from the surface of the undoped GaAs during the annealing decreases drastically when the annealed GaAs was kept at room temperature for one month. This implies that the Be atoms diffusing to the undoped GaAs during the growth and/or the annealing cause the creation of IGa in the undoped layer and it makes the recombination with VGa. On the other hand, no decrease in the concentration of VGa was observed in the Si‐doped GaAs. These support the creation of IGa and of VGa, respectively, in the Be‐diffused GaAs and in Si‐diffused GaAs.

We applied slow positrons to the as‐etched GaAs and/or the (NH4)2Sx‐treated GaAs. The results show that a thin oxide film is easily formed on the surface of as‐etched GaAs as soon as the etched surface is exposed to air for several minutes before the measurement. On the other hand, the monolayer of chemisorbed sulfur atoms in the (NH4)2 Sx‐treated GaAs is effective in protecting the clean surface from the adsorption of oxygen atoms. The mean diffusion length of positrons is not affected by the conditions of the surface treatment. This implies that the centers for the trapping of a positron are not created below the free surface by those treatments.

A three-dimensional indium tin oxide (ITO) nanohelix (NH) array is presented as a multifunctional electrode for bulk heterojunction organic solar cells for simultaneously improving light absorption and charge transport from the active region to the anode. It is shown that the ITO NH array, which is easily fabricated using an oblique-angle-deposition technique, acts as an effective antirefl ection coating as well as a light-scattering layer, resulting in much enhanced light harvesting. Furthermore, the larger interfacial area between the electrode and the active layer, together with the enhanced carrier mobility through highly conductive ITO NH facilitate transport and collection of charge carriers. The optical and electrical improvements enabled by the ITO NH electrode result in a 10% increase in short-circuit current density and power-conversion effi ciency of the solar cells.

Flexible electronics are pliable, thin, light weight, and impact resistant, and have many possible applications. Despite flexible substrates and fabrication methods having been studied in numerous reports, the flexible substrates cannot be used in conventional mass production facilities due to their flexibility. Here, we present an innovative approach to the sacrificial material and fabrication process of flexible organic light-emitting diodes using laser transfer technology. An amorphous gallium oxide (α-GaOx) was used as a sacrificial layer for laser lift-off. The atomic structure of α-GaOx on a near-medium range order was changed owing to oxygen deficiency and local absorption centers in bandgap increased laser ablation as the power density of the electron-beam evaporator was increased. The α-GaOx can be completely melted by laser irradiation, thus allowing the OLEDs to be lifted off the glass substrate. The results suggest that the laser lift-off process can be integrated into high temperature processes for fabricating flexible organic devices.