Doo Soo Kim

Formation and characterization of (Zn1-xMnx)O diluted magnetic semiconductors grown on (0001) Al2O3 substrates

(Zn1-xMnx)O diluted magnetic semiconductors (DMSs) grown on (0001) Al2O3 substrates by radio frequency magnetron sputtering were investigated with the aim of producing a material with a high ferromagnetic transition temperature (Tc). X-ray diffraction, photoluminescence, and Hall-effect measurements showed that the grown (Zn1-xMnx)O thin films were p-type crystalline semiconductors with single phases. Magnetization curve as a function of magnetic field at 5 K indicated that ferromagnetism existed in the (Zn1-xMnx)O thin films, and magnetization curve as a function of temperature showed that the Tc of the (Zn0.93Mn0.07)O thin film was 70 K. These observations can improve the understanding of the increase in Tc for (Zn1-xMnx)O DMSs grown on (0001) Al2O3 substrates.

Highly stable blue-emission in semipolar (11-22) InGaN/GaN multi-quantum well light-emitting diode

We demonstrate highly stable blue-emission on the semipolar (11-22) InGaN/GaN multi-quantum well light-emitting diode (LED) that has been prepared by the direct lateral-overgrowth method. The LED clearly displays bright blue-emission (λ ∼ 441 nm) with the reduced quantum-confined Stark effect. The variation of the emission-wavelength takes place only at the small injection-current range (<10 mA), and the net variation is less than 1.3 nm for wide driving-current ranges (5–100 mA). After the stabilization of light emission, the optical power is linearly increased with increasing the driving-current (1–1.8 mW). Additionally, the LED exhibits the stable light-polarization characteristics.

Investigation of carrier transport properties in semipolar (112¯2) GaN films with low defect density

We report on the anisotropic carrier transport properties of semipolar (112¯2) GaN films with low defect density. We utilized the asymmetric lateral epitaxy to obtain various semipolar (112¯2) GaN films having significantly reduced partial dislocations and basal-plane stacking faults (BPSFs). The directionally dependent carrier transport was observed with the lower sheet resistances (Rsh) along the [11¯00] direction. The Rsh ratios of semipolar (112¯2) GaN films were found to be relatively smaller than those of nonpolar a-plane GaN films, possibly due to low BPSF density and the reduced in-plane electric field induced by BPSF along the [112¯3] direction at wurtzite domain boundaries.

Effect of SiNx interlayer on structural and electrical properties of nonpolar a-plane (11-20) gallium nitrides

We investigated the effects of SiNx interlayers on the structural and electrical properties of nonpolar a-plane (11-20) GaN grown on r-plane (1-102) sapphire substrates by metal–organic chemical vapor deposition (MOCVD). The Nomarski optical microscope images showed that the deposition conditions of the SiNx layer could strongly affect the a-plane GaN surface morphology due to the different SiNx coverage. Basal-plane stacking faults (BSFs) and threading dislocation (TD) densities were reduced in the a-plane GaN samples with high SiNx coverage and multiple SiNx-treated GaN interlayers. These results indicate that TD reduction is associated with an increase in the 3D growth step and with the blocking of TD propagation. From on-axis (11-20) X-ray rocking curve (XRC) measurements, the anisotropy of full width at half maximum (FWHM) can be attributed to the crystal mosaicity due to insertion of different SiNx interlayers. The anisotropy of sheet resistance between the c-and m-axis was also clearly seen in a-plane GaN samples with a high density of defects, which was attributed to the BSFs as scattering centers.