C. A. Lin

Realization of high-quality HfO{sub 2} on In{sub 0.53}Ga{sub 0.47}As by in-situ atomic-layer-deposition

High {kappa} dielectric of HfAlO/HfO{sub 2} was an in-situ atomic-layer-deposited directly on molecular beam epitaxy grown In{sub 0.53}Ga{sub 0.47}As surface without using pre-treatments or interfacial passivation layers, where HfAlO (HfO{sub 2}:Al{sub 2}O{sub 3} {approx} 4:1) with high re-crystallization temperature was employed as the top oxide layer. The HfAlO ({approx}4.5 nm)/HfO{sub 2} (0.8 nm)/In{sub 0.53}Ga{sub 0.47}As metal oxide semiconductor capacitors have exhibited an oxide/In{sub 0.53}Ga{sub 0.47}As interface free of arsenic-related defective bonding, thermodynamic stability at 800 deg. C, and low leakage current densities of <10{sup -7} A/cm{sup 2} at {+-}1 MV/cm. The interfacial trap density (D{sub it}) spectra in absence of mid-gap peaks were obtained by temperature-dependent capacitance and conductance with D{sub it}s of 2-3 x 10{sup 12} eV{sup -1} cm{sup -2} below and 6-12 x 10{sup 11} eV{sup -1} cm{sup -2} above the mid-gap of In{sub 0.53}Ga{sub 0.47}As, respectively. An equivalent oxide thickness of less than 1 nm has been achieved by reducing the HfAlO thickness to {approx}2.7 nm with the same initial HfO{sub 2} thickness of {approx}0.8 nm.

Effective passivation of In0.2Ga0.8As by HfO2 surpassing Al2O3 via in-situ atomic layer deposition

High κ gate dielectrics of HfO2 and Al2O3 were deposited on molecular beam epitaxy-grown In0.2Ga0.8As pristine surface using in-situ atomic-layer-deposition (ALD) without any surface treatment or passivation layer. The ALD-HfO2/p-In0.2Ga0.8As interface showed notable reduction in the interfacial density of states (Dit), deduced from quasi-static capacitance-voltage and conductance-voltage (G-V) at room temperature and 100 °C. More significantly, the midgap peak commonly observed in the Dit(E) of ALD-oxides/In0.2Ga0.8As is now greatly diminished. The midgap Dit value decreases from ≥15 × 1012 eV−1 cm−2 for ALD-Al2O3 to ∼2–4 × 1012 eV−1 cm−2 for ALD-HfO2. Further, thermal stability at 850 °C was achieved in the HfO2/In0.2Ga0.8As, whereas C-V characteristics of Al2O3/p-In0.2Ga0.8As degraded after the high temperature annealing. From in-situ x-ray photoelectron spectra, the AsOx, which is not the oxidized state from the native oxide, but is an induced state from adsorption of trimethylaluminum and H2O, was fo...

Attainment of low interfacial trap density absent of a large midgap peak in In0.2Ga0.8As by Ga2O3(Gd2O3) passivation

The pronounced high interfacial densities of states (Dit) commonly observed around the midgap energy of dielectric/GaAs interfaces are generally considered the culprit responsible for the poor electrical performance of the corresponding inversion-channel metal-oxide-semiconductor field-effect-transistors. In this work, comprehensive Dit spectra as the function of energy [Dit(E)] inside the In0.2Ga0.8As band gap were constructed by using the quasistatic capacitance-voltage and the temperature-dependent conductance method on n- and p-type ultrahigh vacuum (UHV)-Ga2O3(Gd2O3)/In0.2Ga0.8As and atomic-layer-deposited (ALD)-Al2O3/In0.2Ga0.8As metal-oxide-semiconductor capacitors. Unlike the ALD-Al2O3/In0.2Ga0.8As interface giving a Dit spectrum with a high midgap Dit peak, the UHV-Ga2O3(Gd2O3)/In0.2Ga0.8As interface shows a Dit spectrum that monotonically decreases from the valence band to the conduction band with no discernible midgap peak.The pronounced high interfacial densities of states (Dit) commonly observed around the midgap energy of dielectric/GaAs interfaces are generally considered the culprit responsible for the poor electrical performance of the corresponding inversion-channel metal-oxide-semiconductor field-effect-transistors. In this work, comprehensive Dit spectra as the function of energy [Dit(E)] inside the In0.2Ga0.8As band gap were constructed by using the quasistatic capacitance-voltage and the temperature-dependent conductance method on n- and p-type ultrahigh vacuum (UHV)-Ga2O3(Gd2O3)/In0.2Ga0.8As and atomic-layer-deposited (ALD)-Al2O3/In0.2Ga0.8As metal-oxide-semiconductor capacitors. Unlike the ALD-Al2O3/In0.2Ga0.8As interface giving a Dit spectrum with a high midgap Dit peak, the UHV-Ga2O3(Gd2O3)/In0.2Ga0.8As interface shows a Dit spectrum that monotonically decreases from the valence band to the conduction band with no discernible midgap peak.

High efficiency low color-temperature organic light-emitting diodes with a blend interlayer

Low color temperature (CT) lighting sources are crucial for their low suppression of melatonin secretion, and high power efficiency is essential for energy-saving. This study demonstrates the incorporation of a blend interlayer between emissive layers to improve the device performance of low CT organic light emitting diodes. The resulting devices exhibit a CT much lower than that of incandescent bulbs, which is ∼2500 K with a ∼15 lm W−1 efficiency, and even as low as that of candles, which is ∼2000 K with ∼0.1 lm W−1. The best device fabricated shows an external quantum efficiency of 22.7% and 36 lm W−1 (54 cd A−1) with 1880 K at 100 cd m−2, or 20.8% and 29 lm W−1 (50 cd A−1) with 1940 K at 1000 cd m−2. The high efficiency of the proposed device may be attributed to its interlayer, which helps effectively distribute the entering carriers into the available recombination zones.

Highly efficient orange-red organic light-emitting diode using double emissive layers with stepwise energy-level architecture

This study demonstrates a highly efficient orange-red organic light-emitting diode with a double emissive layer architecture that exhibits a record-breaking power efficiency of 47 lm W−1 at 100 cd m−2, or 32 lm W−1 at 1 000 cd m−2. Two factors may contribute to the high efficiency. First, the device architecture has a stepwise energy-level, leading to a significantly reduced energy-barrier for both hole and electron to transport, revealed by the relatively low driving voltage. Second, employing a hole-transporting host and an electron-transporting host leads to a nearly perfect balanced injection of hole and electron to the emissive zones, indicated by the obtained external quantum efficiency that reaches the 20% theoretical limit.

Nearly non-roll-off high efficiency fluorescent yellow organic light-emitting diodes

This paper demonstrates the employment of a multi-emissive-layer device architecture with smooth cascading energy levels to improve markedly the efficiency, roll-off, and color-stability of a fluorescent yellow organic light-emitting diode. As a tri-emissive layer structure was used in lieu of neat film, for example, the resultant external quantum efficiency was increased from 2.2 and 1.8% to 8.2 and 8.6% between 100 and 1000 cd m−2, while current efficiency increased from 5.8 and 4.6 cd A−1 to 26.5 and 27.2 cd A−1 and efficacy from 4 and 2.4 lm W−1 to 20.6 and 18.3 lm W−1. Moreover, the color stability of the tri-emissive layer structure has become of even higher quality than the neat film counterpart has. The reason why the multi-emissive-layer device exhibits both high efficacy and high color-stability may be attributed to the stepwise energy levels that enable a significant reduction in injection barriers, a wider recombination zone, and a more effective carrier confinement. Additionally, the paired host and guest energy-levels in two of the emissive layers allow excitons to generate on the host to facilitate the occurrence of host-to-guest energy transfer and, thus, high device efficiency. The little roll-off may be due to the different paired host and guest energy-levels in the third emissive layer allowing excitons to generate predominantly on the guest at low voltage, but with increasing excitons generating on the host as the voltage increases, fully utilizing all the possible recombination sites.

High efficiency yellow organic light emitting diodes with a balanced carrier injection co-host structure

We demonstrate herein the design and fabrication of a highly efficient yellow organic light-emitting diode (OLED) with a balanced carrier injection device architecture having a zero electron-injection-barrier host blended with a hole-injection aiding co-host. The resultant yellow OLED showed, at 1000 cd m−2 for example, an efficacy of 59 lm W−1, current efficiency of 71 cd A−1 and external quantum efficiency (EQE) of 23%, with values of 42 lm W−1, 47 cd A−1 and 15% EQE without a co-host. The co-host effect that resulted in very balanced carrier injection was also valid for other yellow OLED devices and their efficiency improvement was also very marked. With the use of a micro-lens, the device efficiency is further improved to 79 lm W−1, 96 cd A−1 and 30% EQE.

High-quality molecular-beam-epitaxy-grown Ga2O3(Gd2O3) on Ge (100): Electrical and chemical characterizations

High-κ dielectric Ga2O3(Gd2O3) (GGO) has been deposited on Ge (100) at room temperature using molecular beam epitaxy. In situ angular-resolved x-ray photoelectron spectroscopy on the GGO/Ge after gate dielectric deposition and 500°C postdeposition annealing has exhibited negligible Ge interdiffusion, thus revealing high thermal stability of the heterostructure. The CF4-plasma treatment on the passivated GGO/Ge has greatly improved the capacitance-voltage characteristics of the metal-oxide-semiconductor capacitors, besides the very low gate leakage current density of 3.2×10−9A∕cm2 at a flat-band voltage +1V. These excellent interfacial characteristics have been achieved without employing any intentional passivation layers.

Engineering of threshold voltages in molecular beam epitaxy-grown Al2O3∕Ga2O3(Gd2O3)∕In0.2Ga0.8As

The metal-oxide-semiconductor (MOS) capacitors of Al2O3∕Ga2O3(Gd2O3) on n- and p-type In0.2Ga0.8As with different metal gates exhibited excellent capacitance-voltage (C-V) characteristics and remarkable thermodynamic stability after rapid thermal annealing up to 850°C. The flat-band voltage (Vfb), flat-band voltage shift (ΔVfb), threshold voltage (Vth), and frequency dispersion of the MOS capacitors with different metal gates were extracted from the C-V curves. The Vth values of Al2O3∕Ga2O3(Gd2O3)∕p-In0.2Ga0.8As were calculated to be about 0.04V (Al gate) and 1.15V (Ni gate) and those of Al2O3∕Ga2O3(Gd2O3)∕n-In0.2Ga0.8As −1.94V (Al gate) and −0.88V (Ni gate). The correlation between flat-band voltage and different metal gates indicates unpinned Fermi levels at the metal/dielectric interfaces.

Organic light-emitting diodes with direct contact-printed red, green, blue, and white light-emitting layers

We demonstrate the feasibility of using direct contact-printing in the fabrication of monochromatic and polychromatic organic light-emitting diodes (OLEDs). Bright devices with red, green, blue, and white contact-printed light-emitting layers with a respective maximum luminance of 29 000, 29 000, 4000, and 18 000 cd/m2 were obtained with sound film integrity by blending a polymeric host into a molecular host. For the red OLED as example, the maximum luminance was decreased from 29 000 to 5000 cd/m2 as only the polymeric host was used, or decreased to 7000 cd/m2 as only the molecular host was used. The markedly improved device performance achieved in the devices with blended hosts may be attributed to the employed polymeric host that contributed a good film-forming character, and the molecular host that contributed a good electroluminescence character.