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.
The in-situ p-type doping of 4H-SiC grown on off-oriented (0001) 4H-SiC substrates was performed with trimethylaluminum (TMA) and/or diborane (B2H6) as the dopants. The incorporations of Al and B atoms and their memory effects and the electrical properties of p-type 4H-SiC epilayers were characterized by secondary ion mass spectroscopy (SIMS) and Hall effect measurements, respectively. Both Al- and B-doped 4H-SiC epilayers were p-type conduction. It was shown that the profiles of the incorporated boron and aluminum concentration were in agreement with the designed TMA and B2H6 flow rate diagrams. The maximum hole concentration for the Al doped 4H-SiC was 3.52×1020 cm-3 with Hall mobility of about 1 cm2/Vs and resistivity of 1.6~2.2×10-2 Wcm. The heavily boron-doped 4H-SiC samples were also obtained with B2H6 gas flow rate of 5 sccm, yielding values of 0.328 Wcm for resistivity, 5.3×1018 cm-3 for hole carrier concentration, and 7 cm2/Vs for hole mobility. The doping efficiency of Al in SiC is larger than that of B. The memory effects of Al and B were investigated in undoped 4H-SiC by using SIMS measurement after a few run of doped 4H-SiC growth. It was clearly shown that the memory effect of Al is stronger than that of B. It is suggested that p-type 4H-SiC growth should be carried out in a separate reactor, especially for Al doping, in order to avoid the join contamination on the subsequent n-type growth. 4H-SiC PiN diodes were fabricated by using heavily B doped epilayers. Preliminary results of PiN diodes with blocking voltage of 300 V and forward voltage drop of 3.0 V were obtained.
3C-SiC is a promising material for the development of microelectromechanical systems (MEMS) applications in harsh environments. This paper presents the LPCVD growth of heavily nitrogen doped polycrystalline 3C-SiC films on Si wafers with 2.0 μm-thick silicon dioxide (SiO2) films for resonator applications. The growth has been performed via chemical vapor deposition using SiH4 and C2H4 precursor gases with carrier gas of H2 in a newly developed vertical CVD chamber. NH3 was used as n-type dopant. 3C-SiC films were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), and room temperature Hall Effect measurements. It was shown that there is no voids at the interface between 3C-SiC and SiO2. Undoped 3C-SiC films show n-type conduction with resisitivity, Hall mobility, and carrier concentration at room temperature of about 0.56 ⋅cm, 54 cm2/Vs, and 2.0×1017 cm-3, respectively. The heavily nitrogen doped polycrystalline 3C-SiC with the resisitivity of less than 10-3 ⋅cm was obtained by in-situ doping. Polycrystalline SiC resonators have been fabricated preliminarily on these heavily doped SiC films with thickness of about 2 μm. Resonant frequency of 49.1 KHz was obtained under atmospheric pressure.
Using AlN as a buffer layer, 3C-SiC film has been grown on Si substrate by low pressure chemical vapor deposition (LPCVD). Firstly growth of AlN thin films on Si substrates under varied V/III ratios at 1100oC was investigated and the (002) preferred orientational growth with good crystallinity was obtained at the V/III ratio of 10000. Annealing at 1300oC indicated the surface morphology and crystallinity stability of AlN film. Secondly the 3C-SiC film was grown on Si substrate with AlN buffer layer. Compared to that without AlN buffer layer, the crystal quality of the 3C-SiC film was improved on the AlN/Si substrate, characterized by X-ray diffraction (XRD) and Raman measurements.
Cesium azide (CsN 3 ) doped 2,9-bis(naphthalen-2-yl)-4,7diphenyl-1,10-phenanthroline (NBphen) has been demonstrated as an efficient electron-injection layer (EIL) in this work. Advantageous for its low evaporation temperature and air stability, CsN 3 is employed as an n-dopant to replace the reactive alkali metals or alkali metal compounds. Organic lightemitting diodes utilizing this composite EIL exhibit highly improved current density-luminance-voltage characteristics compared to the control device with LiF. When C545T-doped Alq 3 is used as an emitting layer, a maximum current efficiency of 10.4 cd A À1 can be reached. Our results indicate that this CsN 3 -doped NBphen composite layer has great potential as an alternative EIL in organic electronic devices.
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