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16. Dielectics on germanium : electrical and interfacial properties

Author

Tantraviwat, Doldet

Subjects
537.24
Abstract

Over the past decades, the continuous reduction in Si02/Si device dimensions has been approaching its technological and fundamental limits. This opens a possibility of novel channel materials and high-x dielectrics to be implemented for future CMOS field-effect transistors (FETs). Germanium has recently gained a lot of research interest due to its high electron and hole mobilities. Therefore, Si02, Ah03, and Hf02 materials are investigated as potential gate dielectrics for future germanium MOSFETs. Atmospheric pressure chemical vapour deposition technique is used to deposit Si02 on germanium, showing good results. The influence of an aluminium gate is experimentally demonstrated and the device performance of Si02/Ge devices is degraded during thermal treatment. The use of tungsten allows Si02/Ge capacitors to receive higher thermal treatment. Minority carrier lifetime is studied through low temperature capacitance-time measurements. Zerbst plots and linear approximation equation are used to determine carrier generation lifetime. Atomic layer deposition of Ah03 and Hf02 materials are also studied. Direct formation of Ah03 on germanium provides reasonable results. However, degradation of device performance is observed after thermal treatment, implying that a good interface layer is needed. In-situ plasma nitridation and thermal oxidation processes are developed to form GeOxNy and Ge02 interface layers, respectively. A high quality interface between germanium and Ge02 is observed, resulting in good electrical properties of capacitors with a Ge02 interface layer. Germanium MOSFETs are fabricated with Si02, Hf02 and Ah03 gate dielectrics with and without an interface layer. High electron (~1400 cm2N's) and hole mobilities (~540 cm2N•s) are experimentally demonstrated on devices with Si02 gate dielectric. However, low hole mobilities are observed on high-x/Ge transistors with and without GeOxNy interface layer, ~80-100 and ~160 cm2N•s, respectively. Consistent with the results observed on MOS capacitors, it is believed that high interface trap density is responsible for degradation of transistor performance.

Published
2011

23. Simple preparation of nitrogen-doped TiO2 and its performance in selective oxidation of benzyl alcohol and benzylamine under visible light

Author

Japa, Mattawan, Tantraviwat, Doldet, Phasayavan, Witchaya, Nattestad, Andrew, Chen, Jun, Inceesungvorn, Burapat, Japa, Mattawan, Tantraviwat, Doldet, Phasayavan, Witchaya, Nattestad, Andrew, Chen, Jun, and Inceesungvorn, Burapat

Abstract

N-doped TiO2, denoted as T_400, was prepared simply by the facile thermal hydrolysis of TiOSO4 using NH4OH as both a precipitating agent and a nitrogen source. Compared to TiO2 without nitrogen doping, T_400 provides superior photocatalytic activity toward the selective oxidation of benzyl alcohol and benzylamine under visible light irradiation, with > 85 % conversion and > 95 % selectivity to benzaldehyde and N-benzylidenebenzylamine products, respectively. The increased photoactivity of T_400 is ascribed to enhanced visible-light absorption and efficient photogenerated charge transfer and separation as supported by UV–vis DRS, photoelectrochemical and VB-XPS results. The catalyst can tolerate the presence of substituent groups in benzyl alcohol and benzelamine molecules as > 80 % conversion and > 95 % selectivity are still achieved, which expands the scope of substrates and catalyst utilization. Band energy level of N-doped TiO2 compared to that of undoped TiO2 is determined using Mott-Schottky and UV–vis DRS measurements. Possible mechanisms for the formation of benzaldehyde and N-benzylidenebenzylamine over N-doped TiO2 are proposed. This work presents a simple synthesis of N-doped TiO2, using a low-cost and easily handled inorganic titanium salt instead of air/moisture-sensitive alkoxide precursors and reveals its potential application toward photocatalytic synthesis of organic fine chemicals under visible light.

Published
2020

35. Carrier Mobility Variations in Self-Aligned Germanium MOS Transistors

Author

Low, YeeHooi, Tantraviwat, Doldet, Rainey, Paul, Baine, Paul, McNeill, David W., Mitchell, Neil S., Armstrong, Brian M., and Gamble, Harold

Abstract

Tungsten gate germanium MOS transistors have been manufactured on bulk germanium platforms. Hole mobility in the range 450 cm2/Vs has been achieved on bulk germanium, but mobility is reduced during the densification of thinner dielectrics at 600C. This may be due to the formation of volatile GeO at the interface during densification. Low temperature measurements of the thinner dielectric device indicate that lattice scattering is dominant at room temperature for the device where the densification was omitted and the excellent subthreshold slopes at low temperatures also indicate devices of good quality.

Published
2010

36. Electrical Characterization of ALD Al2O3 and HfO2 Films on Germanium

Author

Tantraviwat, Doldet, Low, YeeHooi, Baine, Paul, Mitchell, Neil S., McNeill, David W., Armstrong, Brian M., and Gamble, Harold

Abstract

Al2O3 and HfO2 films were deposited on germanium substrates by atomic layer deposition (ALD) and analyzed by MOS capacitor electrical characterization. In-situ plasma nitridation performed prior to ALD was found to improve the stability of the interface. For Al2O3/GeON/Ge capacitors, a 450degC anneal in nitrogen ambient reduced hysteresis and oxide fixed charge to 90 mV and 1012 cm-2 respectively, with low leakage current density. On the contrary, degradation was observed for un-nitrided Al2O3/Ge capacitors after 300 and 400degC post-metal anneals. HfO2/GeON/Ge capacitors benefitted from a 400degC densification anneal but exhibited degradation after post-metal anneals at temperatures greater than 300degC. This degradation is attributed to the influence of Al electrodes on the HfO2 gate stack. HfO2 is considered to be a suitable material for the gate stack and Al2O3 for the buried dielectric in a GeOI structure.

Published
2010

37. Electrical Characterization of ALD Al2O3and HfO2Films on Germanium

Author

Tantraviwat, Doldet, Low, YeeHooi, Baine, Paul, Mitchell, Neil S., McNeill, David W., Armstrong, Brian M., and Gamble, Harold

Abstract

Al2O3and HfO2films were deposited on germanium substrates by atomic layer deposition (ALD) and analyzed by MOS capacitor electrical characterization. In-situ plasma nitridation performed prior to ALD was found to improve the stability of the interface. For Al2O3/GeON/Ge capacitors, a 450°C anneal in nitrogen ambient reduced hysteresis and oxide fixed charge to 90 mV and 1012cm-2respectively, with low leakage current density. On the contrary, degradation was observed for un-nitrided Al2O3/Ge capacitors after 300 and 400°C post-metal anneals. HfO2/GeON/Ge capacitors benefitted from a 400°C densification anneal but exhibited degradation after post-metal anneals at temperatures greater than 300°C. This degradation is attributed to the influence of Al electrodes on the HfO2gate stack. HfO2is considered to be a suitable material for the gate stack and Al2O3for the buried dielectric in a GeOI structure.

Published
2010
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38. Tuning the Dielectric Constant and Surface Engineering of a BaTiO 3 /Porous PDMS Composite Film for Enhanced Triboelectric Nanogenerator Output Performance.

Author

Tantraviwat D, Ngamyingyoud M, Sripumkhai W, Pattamang P, Rujijanagul G, and Inceesungvorn B

Abstract

In this work, synergistic effects derived from surface engineering and dielectric property tuning were exploited to enhance the output performance of a triboelectric nanogenerator (TENG) based on an inorganic/porous PDMS composite in a contact-separation mode. BaTiO 3 (BT)/porous PDMS films with different BT weight ratios were fabricated and evaluated for triboelectric nanogenerator (TENG) application. Maximum output signals of ca. 2500 V, 150 μA, and a power density of 1.2 W m -2 are achieved from the TENG containing 7 wt % BT, which is the best compromise in terms of surface roughness, dielectric constant, and surface contact area as evidenced by SEM and AFM studies. These electrical signals are 2 times higher than those observed for the TENG without BT. The 7BT/porous PDMS-based TENG also shows high stability without a significant loss of output voltage for at least 24 000 cycles. With this optimized TENG, more than 350 LEDs are lit up and a wireless transmitter is operated within 9 s. This work not only shows the promoting effects from porous surfaces and an optimized dielectric constant but also offers a rapid and template/waste-free fabrication process for porous PDMS composite films toward large-scale production., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

Published
2021
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