Jung-Seung Yang

Blueshift of intersubband transition wavelength in AlN/GaN multiple quantum wells by low temperature metal organic vapor phase epitaxy using pulse injection method

AlN/GaN multiquantum wells (MQWs) were grown at different growth temperatures via a metal organic vapor phase epitaxy (MOVPE) system using a pulse injection method and their intersubband transition (ISBT) properties were investigated. Strong ISBT at 1.58 μm measured at room temperature was realized with MQWs grown at 770 °C and its absorption properties was the best reported in MOVPE system using GaN buffer layer. Clear blueshift of ISB absorption wavelength by lowering growth temperature was observed, which suggests that interdiffusion within MQWs was suppressed at lower growth temperatures.

Strain effects on the intersubband transitions in GaN/AlN multiple quantum wells grown by low-temperature metal organic vapor phase epitaxy with AlGaN interlayer

The strain in low-temperature-grown GaN/AlN multiple quantum wells (MQWs) have been tailored by inserting an AlGaN interlayer between an AlN template and the MQWs, for the purpose of intersubband transition (ISBT) at shorter wavelength (1.52 μm) with smaller full-width at half-maximum (FWHM) (113 meV). The strain in GaN wells, ISBT wavelength and its FWHM were dependent on Al-content in the AlGaN interlayer. The compressive strain in GaN wells shifted ISBT to shorter wavelengths and narrowed absorption peaks. The interlayer with an appropriate Al-content has been proved to be mandatory for achieving strong and short-wavelength ISBT by metal organic vapor phase epitaxy-grown GaN/AlN MQWs.

Intersubband Transition at 1.52 µm in GaN/AlN Multiple Quantum Wells Grown by Metal Organic Vapor Phase Epitaxy

We have achieved the intersubband transition at 1.52 µm in metal organic vapor phase epitaxy (MOVPE) grown 40-period GaN (1.4 nm)/AlN (4.3 nm) multiple quantum wells (MQWs). Two breakthroughs led us to this achievement: (1) the low temperature growth of MQWs at 830 °C on a high-quality AlGaN/AlN template grown at higher temperatures led to excellent GaN/AlN interfaces, and (2) reduction of carbon impurity in the GaN wells by pulse injection method resulted in a carrier density as high as 2×1019 cm-3 in spite of the low temperature growth. A strong absorption peak at 1.52 µm with a full-width at half-maximum of 113 meV was clearly observed at room temperature.

Fabrication of Abrupt AlN/GaN Multi Quantum Wells by Low Temperature Metal Organic Vapor Phase Epitaxy

AlN/GaN multi quantum wells (MQWs) with abrupt interface were grown by metal organic vapor phase epitaxy (MOVPE). It was revealed that the interface abruptness and coherency of AlN/GaN MQWs to AlN buffer layer were improved at lower temperature of 930 °C. We suggest that the inter-diffusion between wells and barriers was suppressed by lowering growth temperature. The surface of MQWs became smooth at lower temperature of 930 °C showing 0.86 nm of root mean square (RMS) value. Therefore, it is strongly suggested that the low temperature growth at 930 °C is essential for the fabrication of abrupt and smooth AlN/GaN MQWs by MOVPE.

Intersubband absorption saturation in AlN-based waveguide with GaN/AlN multiple quantum wells grown by metalorganic vapor phase epitaxy

Intersubband absorption saturation at 1.57 μm wavelength was observed in a 400-μm long Si3N4-rib AlN-based waveguide with GaN/AlN multiple quantum wells (MQWs) fabricated by metalorganic vapor phase epitaxy (MOVPE). The self-saturation measurement was employed using a 1.56-μm short pulse laser which has a temporal width of 0.4 ps (full-width at half-maximum) and a repetition rate of 63 MHz. An intersubband absorption saturation by 5 dB was achieved using a pulse energy of 115 pJ. We have demonstrated the capability of MOVPE-grown GaN/AlN MQWs for intersubband optical devices operated at communication wavelength.Intersubband absorption saturation at 1.57 μm wavelength was observed in a 400-μm long Si3N4-rib AlN-based waveguide with GaN/AlN multiple quantum wells (MQWs) fabricated by metalorganic vapor phase epitaxy (MOVPE). The self-saturation measurement was employed using a 1.56-μm short pulse laser which has a temporal width of 0.4 ps (full-width at half-maximum) and a repetition rate of 63 MHz. An intersubband absorption saturation by 5 dB was achieved using a pulse energy of 115 pJ. We have demonstrated the capability of MOVPE-grown GaN/AlN MQWs for intersubband optical devices operated at communication wavelength.

Low Temperature Metal Organic Vapor Phase Epitaxial Growth of AlN by Pulse Injection Method at 800 °C

High quality AlN layer could be grown at 800 °C by metal organic vapor phase epitaxy (MOVPE) by pulse injection (PI) method in which trimethylaluminium (TMAl) and NH3 are alternately supplied. Crystal quality of AlN layer grown by PI method (PI-AlN) was comparable with AlN layer grown by conventional MOVPE with continuous sources flow sequence (continuous-AlN, C-AlN) at 1240 °C showing similar (0002) symmetric and (1012) skew symmetric full width at half maximum (FWHM) values by high resolution X-ray diffraction (HRXRD). Especially, it is noticeable that best crystal quality was observed when the growth rate was controlled to 1 monolayer/cycle. Moreover, PI method was proved to be effective in improving surface roughness of AlN layer. The root-mean-square (RMS) roughness of PI-AlN layer was 0.9 nm, which is three times smaller than C-AlN layer grown at same temperature with PI-AlN layer.

High-resolution transmission electron microscopy (HRTEM) observation of dislocation structures in AlN thin films

The structure and configuration of threading dislocations (TDs) in AlN films grown on (0001) sapphire by metal–organic vapor phase epitaxy (MOVPE) were characterized by high-resolution transmission electron microscopy (HRTEM). It was found that the TDs formed in the films were mainly the perfect edge dislocations with the Burgers vector of b 1 U3〈112 ¯0〉. The majority of the edge TDs were not randomly formed but densely arranged in lines. The arrays of the edge TDs were mainly observed on the {112 ¯0} and {101 ¯0} planes. These two planes showed different configurations of TDs. TD arrays on both of these planes constituted low-angle boundaries. We suggest that these TDs are introduced to compensate for slight misorientations between the subgrains during the film growth.