C.H. Jeong

Room-temperature GaN vertical-cavity surface-emitting laser operation in an extended cavity scheme

A GaN-based vertical-cavity surface-emitting laser (VCSEL) has been demonstrated in an extended cavity structure. A VCSEL device had a long extended cavity, which consisted of a sapphire substrate as well as a GaN epilayer and had an integrated microlens on one side. High-reflection dielectric mirrors were deposited on both sides of the laser cavity. The laser was optically pumped and operated at room temperature. The VCSEL device lased at a low threshold excitation intensity of 160 kW/cm2. In contrast to a conventional microcavity-VCSEL structure, the VCSEL operated in multiple longitudinal modes with mode spacing consistent with its physical thickness.

High rate sapphire (Al2O3) etching in inductively coupled plasmas using axial external magnetic field

Abstract BCl3/HBr inductively coupled plasmas magnetized by external magnetic fields was used to achieve high etch rate of sapphires and high etch selectivities over photoresist. The etch characteristics such as etch rates of sapphire and photoresist, etch selectivity over photoresist, plasma density, and etch profiles etc. were investigated as functions of applied external magnetic field strength, working pressure, and dc bias voltage. The obtained highest etch rate of sapphire was approximately 7700 A/min at −800 V of dc bias voltage and 20 Gauss (G) of external magnetic field, when 1400 W of inductive power, 10 mTorr of 90% BCl3/10% HBr were used. The etch selectivities over photoresist were varied from approximately 0.6 to 0.8, where, it increased up to 0.8 with an increasing external magnetic field, however, it decreased with an increasing dc bias voltage.

The Effect of N2 Flow Rate in He/O2/N2 on the Characteristics of Large Area Pin-to-Plate Dielectric Barrier Discharge

In this study, the effects of N2 flow rate in the He/O2/N2 gas mixture on the characteristics of a pin-to-plate dielectric barrier discharge (DBD) having the size of 100 mm ×1000 mm have been investigated for the application to flat panel display processing such as photoresist ashing. The pin-to-plate DBD showed about 70–120% higher photoresist ashing rate at the same applied voltage compared to the conventional DBD. The addition of 3 slm of N2 to He(10 slm)/O2(3 slm) showed the highest photoresist ashing rate of about 580 nm/min for the pin-to-plate DBD at 12 kV of AC voltage. The increase of N2 flow rate in He/O2 gas mixture up to 3 slm appeared to increase the density of N2+ ions and N2 metastables while the oxygen atomic density appeared to decrease continuously. The increase of photoresist ashing rate with the increase of N2 flow rate up to 3 slm was related to the increase of the substrate surface temperature by the increased collision of N2+ ions and N2 metastables with the substrate.

Etch characteristics of SrBi2Ta2O9 (SBT) thin films using magnetized inductively coupled plasmas

Abstract In this study, SrBi 2 Ta 2 O 9 (SBT) thin films were etched using a magnetized inductively coupled plasma (MICP) and their etch characteristics were investigated as a function of Cl 2 /Ar gas mixing ratio, inductive power and bias voltage. The SBT etch rate appeared to show the highest value when Cl 2 concentration in the Cl 2 /Ar mixture was 30%, even though the SBT etch rate remained nearly constant when the Cl 2 concentration in the mixture was higher than 10%. SBT etch rates were also strongly influenced by both inductive power and bias voltage. This result implies that the etching of SBT is dependent upon both ion bombardment and chemical reaction. An etch rate of 150 nm/min could be obtained using 30% Cl 2 /70% Ar, 6.7 Pa of operation pressure, 600 W of inductive power, and −300 V of bias voltage. The etch selectivity of SBT over Pt, and photoresist were less than 0.5 and 1.0∼1.2, respectively, when the Cl 2 was more than 10% in Cl 2 /Ar mixtures. An SBT (200 nm)/Pt (100 nm)/Ti (100 nm) heterostructure was etched using the MICP with 30% Cl 2 /70% Ar mixture, which resulted in an anisotropic etch profile without the formation of sidewall residue.

High-Luminance Top-Emitting Organic Light-Emitting Diodes Using Cs ∕ Al ∕ Au as the Semitransparent Multimetal Cathode

Top-emitting organic light-emitting diodes (TEOLEDs) using an ultrathin cesium (Cs) layer capped with a semitransparent Al/Au layer as an effective, electron-injecting cathode were fabricated by vacuum evaporation. The optical properties of Cs (20 nm)/Al (20 nm)/Au (20 nm) at a wavelength of 520 nm exhibited a transmittance of 59% and a reflectance of 14%. The Cs/Al/Au cathode showed lower power consumption and higher luminance at the same forward bias voltage than the Cs/Al/Ag cathode. Using a tris(8-quinolinolato)aluminum(III) (Alq 3 ) layer as the emissive material, a TEOLED based on the Cs/Al/Au cathode showed a maximum luminance of 66,200 cd/m 2 at 9.8 V. An external quantum efficiency and the power efficiency of 1.6% and 2.1 Im/W, respectively, at a luminance of 1000 cd/m 2 (corresponding to a bias voltage of 6.2 V) was obtained. The good driving performance of this TEOLED was attributed to the excellent optical properties such as high transmittance and efficient-electron injection from the Cs/Al/Au to the adjoining organic layer.

A study of GaN etching characteristics using HBr-based inductively coupled plasmas

Abstract In this study, HBr-based(Cl 2 /HBr, BCl 3 /HBr, and HCl/HBr) inductively coupled plasmas were used to etch GaN selectively over photoresist and its etch characteristics were investigated. The inductive power and dc bias voltage to the substrate were fixed at 1600 W and −150 V, respectively. Among the gas combinations used in this experiment, BCl 3 /HBr showed the highest etch selectivity over photoresist and the etch selectivity of 1.5 with the etch rate of 6400 A/min could be obtained with 40% BCl 3 /60% HBr. Also, the most anisotropic GaN etch profiles could be observed with this gas mixture. The highest etch rate obtained was about 7700 A/min for pure Cl 2 , however, the etch selectivity was lower than 0.6. Optical emission spectroscopy showed that the GaN etch rate and etch selectivity for BCl 3 /HBr were related to the Cl 2 + ions.