Papers by Keyword: Epilayer

Abstract: A kind of broken carrot defects which are not parallel to the step flow direction are observed on 4H-SiC epilayer surfaces. We use the molten KOH and polishing methods to reveal the structure and source of the broken carrots. It is shown that the broken carrot defects still contain the prismatic stacking fault (SF) and basal plane SF and originate from threading screw dislocation on the substrate. The presence of other substrate threading dislocation can disturb the expansion of prismatic SF. This leads to the appearance of the broken carrot.

Abstract: We have studied the defects on 4H-SiC substrates and epilayers by using molten KOH defect selective etching. It is found that adding Na₂O₂ into molten KOH at the etched temperature enables the revelation of dislocations on n⁺ and semi-insulating substrates, whereas purely molten KOH is sufficient to obtain good etched pattern on p⁺ substrates. Related statistical data on dislocation densities of n⁺, p⁺ and semi-insulating substrates are also presented. The morphological defects commonly observed on the epilayers are finally investigated and it is shown that some important structural features can be revealed by molten KOH method.

Abstract: Optical characterization of molecular-beam-epitaxy-grown ZnO and MgZnO epitaxial layers on sapphire (0001) substrates is presented. The parameters such as carrier recombination time and optical gain coefficient are analyzed. Radiative recombination mechanisms of ZnO in dense quasiparticle system are discussed. The ZnO epilayers even with lower structural quality are tolerable for applications in optoelectronics as light emitters.

Abstract: In this work we report the measurement of minority carrier lifetimes using the time resolved photoluminescence technique. It was found that 4H-SiC homo-epilayers grown using chlorine-based precursors have longer carrier lifetimes if used in conjunction with a tantalum carbide coated (TaC-coated) graphite susceptor rather than a SiC-coated graphite susceptor. Longer carrier lifetimes were obtained by optimal combinations of precursor gases and susceptor type. The controllable variation in lifetime from 250 ns to 9.9 s was demonstrated.

Abstract: Some aspects of the chloride-based CVD growth process have been investigated by using both the approach to add HCl to the standard precursors or/and by using the single molecule precursor methyltrichlorosilane (MTS). The efficiency of the process for different precursors, the growth rate stability and the effect that the Cl/Si-ratio has on the growth have been studied. MTS is showed to be the most efficient precursor; the growth can be hindered by to much chlorine in the gas mixture. The Cl/Si-ratio is also found to be a process parameter that affects the amount of incorporated nitrogen in the epilayers.

Abstract: The chlorinated precursor methyltrichlorosilane (MTS), CH3SiCl3, has been used to grow epitaxial layers of 4H-SiC in a hot wall CVD reactor, with growth rates as high as 170 µm/h at 1600°C. Since MTS contains both silicon and carbon, with the C/Si ratio 1, MTS was used both as single precursor and mixed with silane or ethylene to study the effect of the C/Si and Cl/Si ratios on growth rate and doping of the epitaxial layers. When using only MTS as precursor, the growth rate showed a linear dependence on the MTS molar fraction in the reactor up to about 100 µm/h. The growth rate dropped for C/Si < 1 but was constant for C/Si > 1. Further, the growth rate decreased with lower Cl/Si ratio.

Abstract: The homoepitaxial chloride-based CVD growth is demonstrated on Si-face on-axis 4H-SiC substrates. The use of chloride-based CVD has allowed growth of 100% 4H-SiC epitaxial layers with a growth rate of 20µm/h, thus about seven times higher than with standard precursors. It was also found that chlorine etches preferentially the 3C-SiC inclusions that tends to nucleate on Si-face on-axis substrates. Therefore the Cl/Si ratio is a fundamental process parameter to optimize.

Abstract: In this work, we have investigated the 3C-SiC re-growth on planarized 3C-SiC epitaxial layers, grown on (001)Si, after the application of a chemical mechanical polishing (CMP) process. A specific polishing process was developed for 3C-SiC to achieve a flat, high-quality surface. The interface between the deposited 3C-SiC and the polished 3C-SiC on Si film was studied by TEM characterization to determine if defects appear at this interface. It was observed that no additional defects were nucleated at the interface. The resulting re-grown film roughness, as a function of film thickness, was studied and is reported along with recommendations for future work.