ABSTRACT
Electrical and interfacial properties of metal-oxide-semiconductor (MOS) capacitors fabricated using atomic layer deposited bilayer TiO2/Al2O3 films on In0.53Ga0.47As/InP substrates are reported. Vacuum annealing at 350 °C is shown to improve the interface quality. Capacitance-voltage (C-V) characteristics with higher accumulation capacitance, negligible frequency dispersion, small hysteresis and low interface state density (â¼1.5 × 10(11) cm(-2) eV(-1)) have been observed for MOS capacitors. Low frequency (1/f) noise characterization and inelastic electron tunneling spectroscopy (IETS) studies have been performed to determine defects and interface traps and explain the lattice dynamics and trap state generation mechanisms. Both the IETS and 1/f noise studies reveal the spatial locations of the traps near the interface and also the nature of the traps. The IETS study further revealed the dynamic evolution of trap states related to low frequency noise sources in the deposited TiO2/Al2O3 stacks. It is shown that deposition of an ultrathin layer of TiO2 on Al2O3 can effectively control the diffusion of As in the dielectric and the oxidation states of In and Ga at the In0.53Ga0.47As surface.
ABSTRACT
High quality surface passivation on bulk-GaAs substrates and epitaxial-GaAs/Ge (epi-GaAs) layers were achieved by using atomic layer deposited (ALD) titanium aluminum oxide (TiAlO) alloy dielectric. The TiAlO alloy dielectric suppresses the formation of defective native oxide on GaAs layers. X-ray photoelectron spectroscopy (XPS) analysis shows interfacial arsenic oxide (As(x)O(y)) and elemental arsenic (As) were completely removed from the GaAs surface. Energy dispersive X-ray diffraction (EDX) analysis and secondary ion mass spectroscopy (SIMS) analysis showed that TiAlO dielectric is an effective barrier layer for reducing the out-diffusion of elemental atoms, enhancing the electrical properties of bulk-GaAs based metal-oxide-semiconductor (MOS) devices. Moreover, ALD TiAlO alloy dielectric on epi-GaAs with AlGaAs buffer layer realized smooth interface between epi-GaAs layers and TiAlO dielectric, yielding a high quality surface passivation on epi-GaAs layers, much sought-after for high-speed transistor applications on a silicon platform. Presence of a thin AlGaAs buffer layer between epi-GaAs and Ge substrates improved interface quality and gate dielectric quality through the reduction of interfacial layer formation (Ga(x)O(y)) and suppression of elemental out-diffusion (Ga and As). The AlGaAs buffer layer and TiAlO dielectric play a key role to suppress the roughening, interfacial layer formation, and impurity diffusion into the dielectric, which in turn largely enhances the electrical property of the epi-GaAs MOS devices.
ABSTRACT
Withania somnifera (L.) Dunal, a potential medicinal plant used for the treatment of nervous disorders, intestinal infection, leprosy, and cancer, is a perennial herb belonging to Solanaceae and distributed throughout the drier parts of India. Leaf blight disease of this plant generally occurs during March in various districts of South Bengal, India. At the initial stage of infection, symptoms appear as small, light brown spots, gradually becoming irregular, dark brown, concentrically zonate with a diffuse margin, frequently surrounded by light yellow haloes, conspicuous brownish concentric rings in the advance stage of infection. A species of Alternaria was isolated from the lesions. The pathogen was isolated on potato dextrose agar (PDA) media. On PDA, the fungus grew slowly with colonies reaching approximately 35 to 40 mm in diameter in 7 days when incubated at 30°C. Conidiophores arose singly or in groups, straight or flexous, cylindrical, septate, pale to olivaceous brown, as much as 155 µm long, 4 to 5.5 µm thick; conidia were straight, obclavate, pale olivaceous brown, smooth, with up to 15 transverse and rarely 1 or 2 longitudinal or oblique septa and measured 50 to 115 × 5 to 10 µm. Pathogenicity tests were carried out three times on 6-month-old plants (n = 10). Plants were sprayed with a conidial suspension of 105 conidia/ml; control plants were sprayed with sterilized water. Plants were covered with polyethylene bags for 10 days. Disease symptoms appeared after 12 ± 1 day after inoculation. Symptoms on the leaves were similar to those of a naturally occurring diseased plant. The fungal pathogen was consistently reisolated from inoculated plants. The pathogen was identified as Alternaria dianthicola and further confirmed by the Agharkar Research Institute, Pune, India. A literature survey reports the occurrence of some fungal diseases (1), but to our knowledge, this is the first report of A. dianthicola on W. somnifera. References: (1) P. Sinha et al. Page 14 in: Recent Progress in Medicinal Plants. Vol. 6 Diseases and their Management. Sci Tech Publishing LLC, Houston, TX, 2000.
