Jeong Woon Bae

Direct measurement of nanoscale sidewall roughness of optical waveguides using an atomic force microscope

An atomic force microscope (AFM) with an ultrasharp tip was used to directly measure the sidewall profile of InP/InGaAsP waveguide structures etched using an inductively coupled plasma reactive ion etching (ICP-RIE) in Cl2-based plasma. A special staircase pattern was devised to allow AFM tip to access the etched sidewall of the waveguides in the normal direction. Statistical information such as correlation length and rms roughness of the sidewall profile obtained through three-dimensional imaging by AFM has been presented. rms roughness as low as 3.45 nm was measured on the sidewall of 4-μm-deep etched InP/InGaAsP heterostructures.

High-Rate Dry Etching of ZnO in BCl3/CH4/H2 Plasmas

High-rate dry etching characteristics of aluminum-doped zinc oxide (AZO) have been investigated in inductively coupled plasma (ICP) using BCl3/CH4/H2 plasma chemistry. Etch rates were measured as a function of BCl3 flow rate in BCl3/CH4/H2 mixture and dc-bias voltage. Measurement of etch rate, and etched sidewall profile were performed using a stylus profilometer and scanning electron microscopy, respectively. The highest AZO etch rate about 310 nm/min, could be obtained near 80% BCl3 and at dc-bias voltage of -350 V.

C4F8O/O2/N-based Additive Gases for Silicon Nitride Plasma Enhanced Chemical Vapor Deposition Chamber Cleaning with Low Global Warming Potentials

In this study, N2O and NO were added as additive gases to C4F8O/O2 for plasma enhanced chemical vapor deposition (PECVD) silicon nitride chamber cleaning and their effects on the emission properties of perfluorocarbon compounds (PFCs) were investigated. The cleaning rate, destruction and removal efficiencies (DREs), and million metric tons of carbon equivalent (MMTCE) were studied as a function of flow rates of PFCs and additive gases. The use of C4F8O/O2 alone showed the highest cleaning rate and the lowest emission properties at the cleaning condition of 20%C4F8O/80%O2, working pressure of 500 mTorr, and 13.56 MHz rf power of 350 W. By the addition of about 20% NO or 20% N2O to the optimized C4F8O/O2, the additional reduction of MMTCE higher than 50% could be obtained. The addition of NO resulted in lower MMTCE compared to that in the case of the addition of N2O mostly due to the higher silicon nitride cleaning rate in the latter case.

Formation of High Flux Parallel Neutral Beam Using a Three Grid System of Ion Beam during Low Angle Forward Reflection of Ions

The energy and the flux of the ion gun with a three-grid system was compared with those of the ion gun with a two-grid system and the characteristics of the neutral beam sources composed of the ion guns with different grid systems and a reflector for the low angle reflection of the ions were investigated. By using the three-grid system instead of the two-grid system and by applying higher negative voltage to the 2nd grid, a higher ion flux without changing the ion energy could be obtained for the ion gun of the neutral beam source. The three-grid ion gun system generated higher neutral beam fluxes compared to the two-grid ion gun system. This result was confirmed by measuring the etch rates of Si and GaAs with Ar and fluorine neutral beam. Also, using the neutral beam source with the three-grid ion gun, 35nm-width Si patterns could be etched vertically by CF4 gas indicating the formation of a parallel neutral beam.

Micro-racetrack notch filters based on InGaAsP/InP high mesa optical waveguides

Experimental and theoretical investigations were carried out on the spectral responses of micro-racetrack notch filters based on InP/InGaAsP high mesa optical waveguides that were fabricated by utilizing electron beam lithography and inductively-coupled-plasma reactive ion etching (ICP-RIE) technique. The critical factors determining the performance of micro-racetrack resonator-coupled devices were identified to be the optical power coupling efficiency between the bus waveguide and the racetrack resonator and the round-trip loss of the racetrack resonator. These parameters were extracted from the measured spectral responses of three single resonator-coupled waveguide devices with different gap spacings between the bus waveguides and the racetrack resonators, which were 0.2, 0.35, and 0.5 µm. These extracted parameters can be used to uniquely determine the pole and zero locations of the unit racetrack-coupled waveguide filter. The phase responses as well as the magnitude responses of optical filters can be calculated using the uniquely determined pole and zeros. The extracted parameters were used to calculate the spectral responses of a high-order racetrack-coupled device that was designed by cascading the three single racetrack-coupled devices having gap spacings of 0.2, 0.35, and 0.5 µm. The calculated and measured spectral responses of the high-order filters were compared to verify the parameter extraction process. The measured spectral response of the filters matched very well with the theoretically calculated response using the extracted parameters from the first-order racetrack resonator-coupled devices.

Comparative Studies on Low-Resistance Pd-Based Ohmic Contacts on p-GaAsSb

19 cm �3 500 nm thick p-type GaAs0.5Sb0.5. All the ohmic contacts with Pd as a bottom layer exhibited better electrical characteristics than conventional Ti/Pt/Au metallization at as-deposited conditions. It shows that Pd forms a more favorable metal-semiconductor junction with the GaAs0.5Sb0.5 layer compared with Ti. When Ir or Pt was incorporated on top of the bottom Pd layer, ohmic characteristics of Pd/Ir/Au and Pd/Pt/Au were improved by annealing at 250°C by the effect of Ir and Pt with high work function. When Pd/Au, Pd/Ir/Au, and Pd/Pt/Au ohmic metallizations were annealed at temperatures higher than 300°C, gradual degradation of ohmic properties was observed. To improve the thermal properties of the Pd-based ohmic contacts, an Mo layer was inserted beneath the top Au layer as a diffusion-barrier layer. The Pd/Ir/Mo/Au metallization scheme withstood higher annealing temperatures than the ohmic metallizations without the Mo layer. X-ray photoelectron spectroscopy was also carried out to investigate the interactions between the multilayer metallizations and the ternary GaAsSb compound semiconductor. The Mo layer was found to be effective in blocking Au diffusion into the semiconductor layer when it was combined with an Ir layer.

Effect of Indium-Oxide Deposited Using an Oxygen Ion-Beam-Assisted-Deposition to Top-Emitting Organic Light-Emitting Diodes

Indium oxide thin films have potential applications as cathodes in top-emitting organic light-emitting diodes (TEOLEDs). This study examined the characteristics of transparent conducting indium oxide (IO) films deposited by an oxygen ion-beam-assisted-deposition (IBAD) as a function of the applied oxygen ion energy (Va). When TEOLED devices consisting of glass/Ag (100 nm)/ITO (125 nm)/2-TNATA (30 nm)/NPB (15 nm)/Alq3 (55 nm)/LiF (1 nm)/Al (2 nm)/Au (20 nm)/IO (100 nm) were fabricated at a lower Va, a lower turn-on voltage was observed even though the maximum luminance (32,000 cd/m2) was similar one another. A Va of approximately +50 V produced an IO film with a resistivity of 8.5×10-4 Ωcm and a transmittance of 85%. The definition (I–V) characteristics of TEOLED devices with a cathode layer of Al (2 nm)/Au (20 nm)/IO (100 nm) were similar to the device fabricated with Al (2 nm)/Au (20 nm) only.

Effects of Tin Concentration on the Electrical Properties of Room-Temperature Ion-Beam-Assisted-Evaporation-Deposited Indium Oxide Thin Films

Tin-doped indium oxide (ITO) thin films were deposited at room temperature by a dual-oxygen-ion-beam-assisted evaporator system and the effects of doped tin concentrations in the films on the electrical properties of the ITO films were investigated. Doped tin atoms in amorphous ITO films caused extra scattering and structural defects due to the inactivation of tin atoms in the films. Therefore, increasing the tin concentration decreased the conductivity. The lowest resistivity of indium oxide (IO) and ITO obtained was 3.6×10-4 Ω-cm for IO and 4×10-4–7×10-4 Ω-cm for 5–25 wt% SnO2. The mobility and mean free path of these films were 20–63 cm2/Vs and 3.3–7.4 nm, respectively.

Inductively coupled plasma reactive ion etching of ZrO2:H solid electrolyte film in BCl3-based plasmas

Inductively coupled plasma reactive ion etching (ICP-RIE) of ZrO 2 :H solid electrolyte films was investigated using BCl 3 -based plasma. ZrO 2 :H etch rates were studied as a function of the BCl 3 /Ar chemistry, ICP coil power, bias voltage, and working pressure. Scanning electron microscopy and atomic force microscopy were employed to characterize the etch rate and root-mean-square surface roughness of etched samples. It was found that in comparison with Cl 2 -based gas mixtures, pure BCl 3 plasma results in a high etch rate of ZrO 2 :H layer, suggesting an abundance of B and BCI radicals made up of a volatile compound such as B x O y , BCl-O, and Zr-Cl bond. In addition, Auger electron spectroscopy analysis exhibits that the BCl 3 -based etching process produces no change in surface stoichiometry of the ZrO 2 :H films.

Indium-phosphide-based microresonator modulators and wavelength multiplexers

In this paper, we report on the combination of nanofabrication techniques, laterally coupled micro-ring-resonator modulator design, angled multimode interference couplers, and highly efficient InP-based modulator materials, to demonstrate wavelength selective modulators arrays. Wavelength selective modulator permits the modulation of a single optical carrier without the wavelength multiplexing.