Hyung Koun Cho

Generation of misfit dislocations in high indium content InGaN layer grown on GaN

Abstract We have investigated the relaxation of the misfit strain by the formation of misfit dislocations and stacking faults in high indium content In x Ga 1− x N layers grown by metal-organic chemical vapor deposition. The misfit dislocations in the highly mismatched In 0.33 Ga 0.66 N/GaN system are generated not only at the InGaN/GaN interface but also within an InGaN layer. It indicates that the InGaN layer in the interface is partially relaxed and the considerable residual strain is relaxed within the InGaN layer. In addition, we observed that stacking faults formed by stacking order mismatch between sub-grains play the role of a seed in the formation of misfit dislocations within a high indium content In x Ga 1− x N layer.

Strain relaxation behavior of the InGaN/GaN multiple quantum wells observed by transmission electron microscopy

We have investigated the strain relaxation behavior of InGaN/GaN multiple quantum wells (MQWs) with high indium composition using transmission electron microscopy (TEM). We found that the position of the main emission peak in the MQWs with indium content of more than the critical composition is significantly affected by the increase in the number of quantum wells (QWs). From high-resolution TEM (HRTEM) and energy dispersive X-ray spectroscopy (EDX), the redshift by the increase of QW numbers originates from the increase of indium segregation in the MQWs, and dislocations and stacking faults may enhance the formation of the indium segregation.

Influence of GaAs/InAs quasi-monolayer on the structural and optical properties of InAs/GaAs quantum dots

Abstract InAs QDs on strained {GaAs/InAs} quasi-monolayer (QML) with an alternative growth mechanism were grown by molecular beam epitaxy (MBE). The properties of quantum dots (QDs) were investigated by transmission electron microscopy (TEM), photoluminescence (PL), and photoreflectance (PR). TEM images and PR spectra of InAs QDs with strained {GaAs/InAs} QML only show a lack of the wetting layer (WL) compared with conventional InAs QDs sample. The Photoluminescence (PL) emission peak of the InAs QDs with 10 periods strained {GaAs/InAs} QML is red-shifted by 180xa0meV at 10xa0K relative to the reference InAs QDs sample which has no {GaAs/InAs} QML. The InAs QDs with 10 periods {GaAs/InAs} QML also show a strong PL emission with 1.32xa0μm at room temperature. Similar to the various periods of QML in InAs QDs sample, the emission wavelength of InAs QDs changes significantly toward the long wavelength emission.

Observation of inversion domain boundaries in Mg-doped AlGaN layers grown by metalorganic chemical vapor deposition

We have investigated the formation of inversion domain boundaries in Al0.13Ga0.87N layers grown on sapphire substrates by metalorganic chemical vapor deposition using transmission electron microscopy (TEM). We found that the shape of inversion domain boundaries strongly depends on Mg source flow rate in the Mg-doped Al0.13Ga0.87N layers. By increasing the Mg source flow rate, the shape of inversion domain boundaries is changed from the vertical shape to the horizontal shape. In addition, the change of polarity by the horizontal shape inversion domain boundary (IDB) resulted in the inverted rotation of pyramidal shape IDB within the Mg-doped Al0.13Ga0.87N layers.