Jinwan Kim

Growth and characterization of high quality AlN using combined structure of low temperature buffer and superlattices for applications in the deep ultraviolet

This study reports on the growth and characterization of AlN/AlxGa1−xN superlattices (SLs) for reduction of threading dislocations to grow high quality AlN layer. Insertion of optimized SLs is shown to effectively reduce the dislocation density, there by resulting in a high crystal quality 2.5-µm-thick AlN layer. It was found that full width at half-maximum (FWHM) of X-ray rocking curves (XRCs) around both (0002) and diffraction were decreased to 230 and 420, respectively. The results of XRC FWHM and dislocation densities from etch pit density (EPD) by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) micrographs are in a good agreement. This high quality and low dislocation density AlN layer is of key importance for high efficiency deep-UV light emitting diodes and power devices.

Self-compensation effect in Si-doped Al0.55Ga0.45N layers for deep ultraviolet applications

The self-compensation effect in Si-doped Al0.55Ga0.45N layers was investigated using different SiH4/III ratios. The degree of compressive strain changed with SiH4 flow rate during growth. With a low SiH4/III ratio of 2.46 × 10−6, compressive strain was increased in comparison with the un-doped case. However, above this SiH4/III ratio, compressive strain decreased from exx = −5.07 × 10−3 to 4.28 × 10−3 when the ratio was increased to 4.1 × 10−5. For higher SiH4/III ratios, the compressive strain again increased, which is attributed to the self-compensation effect of Si atoms. A similar tendency was observed in Photo-luminescence (PL) results. While the UV-to-violet ratio (IUV/IVL) of room-temperature PL remained to be almost constant for SiH4/III ratios below 8.2 × 10−5, IUV/IVL decreased rapidly above this value, as a result of self-compensation of Si atoms. These results were in good agreement with the Hall effect measurements.

Improved carrier injection of AlGaN-based deep ultraviolet light emitting diodes with graded superlattice electron blocking layers

A DUV-LED with a graded superlattice electron blocking layer (GSL-EBL) is demonstrated to show improved carrier injection into the multi-quantum well region. The structures of modified EBLs are designed via simulation. The simulation results show the carrier behavior mechanism of DUV-LEDs with a single EBL (S-EBL), graded EBL (G-EBL), and GSL-EBL. The variation in the energy band diagram around the EBL region indicates that the introduction of GSL-EBL is very effective in enhancing carrier injection. Besides, all DUV-LEDs emitting at 280 nm are grown in the high temperature metal organic chemical deposition system. It is confirmed that the optical power of the DUV-LED with the GSL-EBL is significantly higher than that of the DUV-LED with the S-EBL and G-EBL.