2017, Vol.27, No.6

Journal of the Korean Crystal Growth and Crystal Technology 2023 KCI Impact Factor : 0.19

pISSN : 1225-1429 / eISSN : 2234-5078
https://journal.kci.go.kr/jkcgct

AlN is a promising material for wide band gap and high-frequency electronics device due to its wide bandgap and high thermal conductivity. AlN has advantages as materials for power semiconductors with a larger breakdown field, and a smaller specific on-resistance at high voltage. The growth of a p-type AlN epilayer with high conductivity is important for a manufacturing an AlN-based applications. In this paper, Mg doped AlN epilayers were grown by a mixed-source HVPE. Al and Mg mixture were used as source materials for the growth of Mg-doped AlN epilayers. Mg concentration in the AlN was controlled by modulating the quantity of Mg source in the mixed-source. Surface morphology and crystalline structure of AlN epilayers with different Mg concentrations were characterized by FE-SEM and HR-XRD. XPS spectra of the Mgdoped AlN epilayers demonstrated that Mg was doped successfully into the AlN epilayer by the mixed-source HVPE.

In this paper, GaAs/AlGaAs multi-layer structure was grown by liquid phase epitaxy with graphite sliding boat, which can be used as a device structure of a photocathode image sensor. The multi-layer structure was grown on an n-type GaAs substrate in the sequence as follows: GaAs buffer layer, Zn-doped p-type AlGaAs layer as etching stop layer, Zndoped p-type GaAs layer, and Zn-doped p-type AlGaAs layer. The Characteristics of GaAs/AlGaAs structures were analyzed by using scanning electron microscope (SEM), secondary ion mass spectrometer (SIMS) and hall measurement. The SEM images shows that the p-AlGaAs/p-GaAs/p-AlGaAs multi-layer structure was grown with a mirror-like surface on a whole (1.25 mm × 25 mm) substrate. The Al composition in the AlGaAs layer was approximately 80 %. Also, it was confirmed that the free carrier concentration in the p-GaAs layer can be adjusted to the range of 8 × 10 18 /cm 2 by hall measurement. In the result, it is expected that the p-AlGaAs/p-GaAs/p-AlGaAs multi-layer structure grown by the LPE can be used as a device structure of a photoelectric cathode image sensor.

Films fabricated using atomic layer 2-dimensional nanosheets exhibit various physical properties depending on the size of the nanosheet. This is because the physical properties of the film depend on the interfacial properties between the sheets. Therefore, the synthesis of large-sized nanosheets is very important because it can reduce the dependency of the film on the interfacial properties. In this study, we succeeded in fabricating TiOx nanosheets with atomic layer thickness over micrometer size by using single-crystallized starting material and its chemical exfoliation. In addition, it was revealed that the mechanical agitation speed (the stirring speed of a magnetic bar) during the exfoliation step using the organic material is closely related to the nanosheet size and the colloidal concentration of the nanosheets.