| 1. |
- Bergsten, Johan, 1988, et al.
(författare)
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AlGaN/GaN high electron mobility transistors with intentionally doped GaN buffer using propane as carbon precursor
- 2016
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Ingår i: Japanese Journal of Applied Physics. - : IOP Publishing. - 1347-4065 .- 0021-4922. ; 55:5
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Tidskriftsartikel (refereegranskat)abstract
- AlGaN/GaN high electron mobility transistors (HEMTs) fabricated on a heterostructure grown by metalorganic chemical vapor deposition using an alternative method of carbon (C) doping the buffer are characterized. C-doping is achieved by using propane as precursor, as compared to tuning the growth process parameters to control C-incorporation from the gallium precursor. This approach allows for optimization of the GaN growth conditions without compromising material quality to achieve semi-insulating properties. The HEMTs are evaluated in terms of isolation and dispersion. Good isolation with OFF-state currents of 2 x 10(-6)A/mu m, breakdown fields of 70V/mu m, and low drain induced barrier lowering of 0.13mV/V are found. Dispersive effects are examined using pulsed current-voltage measurements. Current collapse and knee walkout effects limit the maximum output power to 1.3W/mm. With further optimization of the C-doping profile and GaN material quality this method should offer a versatile approach to decrease dispersive effects in GaN HEMTs. (C) 2016 The Japan Society of Applied Physics
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| 2. |
- Bergsten, Johan, et al.
(författare)
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AlGaN/GaN high electron mobility transistors with intentionally doped GaN buffer using propane as carbon precursor
- 2016
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Ingår i: Japanese Journal of Applied Physics. - : Institute of Physics Publishing (IOPP). - 0021-4922 .- 1347-4065. ; 55, s. 05FK02-1-05FK02-4
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Tidskriftsartikel (refereegranskat)abstract
- AlGaN/GaN high electron mobility transistors (HEMTs) fabricated on a heterostructure grown by metalorganic chemical vapor deposition using analternative method of carbon (C) doping the buffer are characterized. C-doping is achieved by using propane as precursor, as compared to tuningthe growth process parameters to control C-incorporation from the gallium precursor. This approach allows for optimization of the GaN growthconditions without compromising material quality to achieve semi-insulating properties. The HEMTs are evaluated in terms of isolation anddispersion. Good isolation with OFF-state currents of 2 ' 10%6A/mm, breakdown fields of 70V/μm, and low drain induced barrier lowering of0.13mV/V are found. Dispersive effects are examined using pulsed current–voltage measurements. Current collapse and knee walkout effectslimit the maximum output power to 1.3W/mm. With further optimization of the C-doping profile and GaN material quality this method should offer aversatile approach to decrease dispersive effects in GaN HEMTs.
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| 3. |
- Elamain, Omaima Abubakr, et al.
(författare)
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Polar flexoelectric in-plane and out-of-plane switching in bent core nematic mixtures
- 2016
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Ingår i: Japanese Journal of Applied Physics. - : IOP Publishing. - 0021-4922 .- 1347-4065. ; 55:7
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Tidskriftsartikel (refereegranskat)abstract
- Polar electro-optic response, arising from the coupling between an applied in-plane and out-of-plane dc electric field, respectively, and the flexoelectric polarization of bent core nematic liquid crystal mixtures with hybrid alignment is studied in conventional sandwich cells with homeotropic anchoring at one of the cell substrates and planar at the other. Such a hybrid alignment, however, results in a splay/bend elastic deformation of the nematic giving rise of a flexoelectric polarization. It was found that a pronounced polar electro-optic response, both in-plane and out of plane, took place in the bent core nematic mixtures at very low voltages due to the high flexoelectric polarization in these mixtures, compared with the one observed in calamitic liquid crystals.
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| 4. |
- Hatayama, Tomoaki, et al.
(författare)
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Low-temperature photoluminescence of 8H-SiC homoepitaxial layer
- 2016
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Ingår i: Japanese Journal of Applied Physics. - : IOP PUBLISHING LTD. - 0021-4922 .- 1347-4065. ; 55:2, s. 020303-
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Tidskriftsartikel (refereegranskat)abstract
- Low-temperature photoluminescence of a nitrogen-doped 8H-SiC epilayer homoepitaxially grown by a chemical vapor deposition method is reported. The polytype and stacking sequence of the epilayers were confirmed by transmission electron microscopy analyses. The identification of emission lines is discussed in terms of the temperature dependence of the luminescence spectra. Luminescence related to the free excitons and the nitrogen-bound excitons is observed, which allows the determination of the excitonic bandgap of the 8H-SiC polytype. In addition, the low binding energies found for the nitrogen-bound excitons imply shallow levels for the nitrogen donors. (C) 2016 The Japan Society of Applied Physics
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| 5. |
- Henry, Anne, et al.
(författare)
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Early stages of growth and crystal structure evolution of boron nitride thin films
- 2016
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Ingår i: Japanese Journal of Applied Physics. - : IOP PUBLISHING LTD. - 0021-4922 .- 1347-4065. ; 55:5, s. 05FD06-
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Tidskriftsartikel (refereegranskat)abstract
- A study of the nucleation and crystal structure evolution at the early stages of the growth of sp(2)-BN thin films on 6H-SiC and alpha-Al2O3 substrates is presented. The growth is performed at low pressure and high temperature in a hot wall CVD reactor, using ammonia and triethylboron as precursors, and H-2 as carrier gas. From high-resolution transmission electron microscopy and X-ray thin film diffraction measurements we observe that polytype pure rhombohedral BN (r-BN) is obtained on 6H-SiC substrates. On alpha-Al2O3 an AlN buffer obtained by nitridation is needed to promote the growth of hexagonal BN (h-BN) to a thickness of around 4 nm followed by a transition to r-BN growth. In addition, when r-BN is obtained, triangular features show up in plan-view scanning electron microscopy which are not seen on thin h-BN layers. The formation of BN after already one minute of growth is confirmed by X-ray photoelectron spectroscopy. (C) 2016 The Japan Society of Applied Physics
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| 6. |
- Hirasaki, Takahide, et al.
(författare)
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Investigation of NH3 input partial pressure for N-polarity InGaN growth on GaN substrates by tri-halide vapor phase epitaxy
- 2016
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Ingår i: Japanese Journal of Applied Physics. - : IOP PUBLISHING LTD. - 0021-4922 .- 1347-4065. ; 55:5, s. 05FA01-
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Tidskriftsartikel (refereegranskat)abstract
- The influence of NH3 input partial pressure on N-polarity InGaN grown by tri-halide vapor phase epitaxy was investigated. It was found that surface morphology, solid composition and optical properties were affected by NH3 input partial pressure. As shown in thermodynamic analyses, the indium content increased due to an increase in the driving force for InN deposition caused by increased NH3 input partial pressure. In addition, the deep level emission around 2.1 eV in photoluminescence measurements drastically decreased at higher NH3 input partial pressures. Ab initio calculations and subsequent secondary ion mass spectrometry measurements suggested the reduction of metal-vacancies and/or carbon impurity incorporation in the InGaN layers. (C) 2016 The Japan Society of Applied Physics
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| 7. |
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| 8. |
- Illarionov, Y.Yu., et al.
(författare)
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Bias-temperature instability on the back gate of single-layer double-gated graphene field-effect transistors
- 2016
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Ingår i: Japanese Journal of Applied Physics. - : Institute of Physics (IOP). - 0021-4922 .- 1347-4065. ; 55:4
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Tidskriftsartikel (refereegranskat)abstract
- We study the positive and negative bias-temperature instabilities (PBTI and NBTI) on the back gate of single-layer double-gated graphene fieldeffect transistors (GFETs). By analyzing the resulting degradation at different stress times and oxide fields we show that there is a significant asymmetry between PBTI and NBTI with respect to their dependences on these parameters. Finally, we compare the results obtained on the high-k top gate and SiO2 back gate of the same device and show that SiO2 gate is more stable with respect to BTI.
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| 9. |
- Shan, Bo, et al.
(författare)
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Preparation of graphene/aligned carbon nanotube array composite films for thermal packaging applications
- 2019
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Ingår i: Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes. - : IOP Publishing. - 0021-4922 .- 1347-4065. ; 58
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Tidskriftsartikel (refereegranskat)abstract
- Vertically aligned carbon nanotube arrays (VACNTs) have been successfully achieved by CVD. The carbon nanotubes were almost triple-walled. Furthermore, the graphene/VACNT composite films have been prepared as thermal interface materials, using photolithographic and densification processes. Compared with pure epoxy resin, the longitudinal thermal conductivity of the composite films was obviously improved, which confirmed that VACNTs provided additional longitudinal heat transfer channels in the films. Furthermore, their longitudinal thermal conductivity was largely dependent on the distribution of VACNTs. The transversal thermal conductivity of the composite film with a pattern size of 300 mu m was about seven times higher than that of pure epoxy resin. This indicated that graphene provided additional horizontal heat transfer channels to achieve the enhancement of transversal thermal conductivity in composite films. (C) 2019 The Japan Society of Applied Physics
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| 10. |
- Togashi, Rie, et al.
(författare)
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High rate growth of In2O3 at 1000 degrees C by halide vapor phase epitaxy
- 2016
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Ingår i: Japanese Journal of Applied Physics. - : IOP PUBLISHING LTD. - 0021-4922 .- 1347-4065. ; 55:12
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the first-ever growth of cubic-In2O3 at 1000 degrees C by halide vapor phase epitaxy (HVPE) was achieved, using gaseous InCl and O2 as precursors in a N-2 flow. The growth rates of In2O3 layers on (001) beta-Ga2O3 and (0001) sapphire substrates were 4.1 and 5.1 mu m/h, respectively, even at the high growth temperature applied, which are approximately half the growth rate of beta-Ga2O3 homoepitaxially grown by HVPE at 1000 degrees C. Theoretical thermodynamic analyses were also conducted, and results confirmed the growth of In2O3 at temperatures above 1000 degrees C by HVPE. The as-grown In2O3 layers were light yellow-green in color. The In2O3 layers grown on the (001) beta-Ga2O3 and (0001) sapphire substrates exhibited an optical absorption edge at about 370 nm, in addition to n-type conductivity with electron concentrations of 2.7 x 10(18) and 1.7 x10(18) cm(-3), and electron mobilities of 16.2 and 22.7cm(2)V(-1) s(-1), respectively. (C) 2016 The Japan Society of Applied Physics
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| 11. |
- Togashi, Rie, et al.
(författare)
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Thermal and chemical stabilities of group-III sesquioxides in a flow of either N-2 or H-2
- 2016
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Ingår i: Japanese Journal of Applied Physics. - : IOP PUBLISHING LTD. - 0021-4922 .- 1347-4065. ; 55:12
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Tidskriftsartikel (refereegranskat)abstract
- The thermal and chemical stabilities of group-III sesquioxides (Al2O3, Ga2O3, and In2O3) were comparatively investigated at an atmospheric pressure at heat treatment temperatures ranging from 250 to 1450 degrees C in a flow of either N-2 or H-2. In a flow of N-2, the thermal decomposition of alpha-Al2O3 was not observed at the temperatures investigated, while the decompositions of beta-Ga2O3 and c-In2O3 occurred above 1150 and 1000 degrees C, respectively, with no generation of group-III metal droplets on the surfaces. In contrast, the chemical reactions of alpha-Al2O3, beta-Ga2O3, and c-In2O3 began at low temperatures of 1150, 550, and 300 degrees C in a flow of H-2. Thus, the presence of H-2 in the gas flow significantly promotes the decomposition of group-III sesquioxides. The order of thermal and chemical stabilities (alpha-Al2O3 amp;gt;amp;gt; beta-Ga2O3 amp;gt; c-In2O3) obtained experimentally was verified by thermodynamic analysis, which also clarified dominant decomposition reactions of group-III sesquioxides. (C) 2016 The Japan Society of Applied Physics
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| 12. |
- Togashi, Rie, et al.
(författare)
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Thermal stability of beta-Ga2O3 in mixed flows of H-2 and N-2
- 2015
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Ingår i: Japanese Journal of Applied Physics. - : Japan Society of Applied Physics. - 0021-4922 .- 1347-4065. ; 54:4, s. 041102-
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Tidskriftsartikel (refereegranskat)abstract
- The thermal stability of beta-Ga2O3(010) substrates was investigated at atmospheric pressure between 250 and 1450 degrees C in a flow of either N-2 or a mixture of H-2 and N-2 using a radio-frequency induction furnace. The beta-Ga2O3 surface was found to decompose at and above 1150 degrees C in N-2, while the decomposition of beta-Ga2O3 began at only 350 degrees C in the presence of H-2. Heating beta-Ga2O3 substrates in gas flows containing different molar fractions of H-2 demonstrated that the decomposition was promoted by increasing the H-2 molar fractions. Thermodynamic analysis showed that the dominant reactions are Ga2O3(s) = Ga2O(g) + O-2(g) in N-2 and Ga2O3(s) + 2H(2)(g) = Ga2O(g) = 2H(2)O(g) in a mixed flow of H-2 and N-2. The second-order reaction with respect to H-2 determined for the mixed flows agrees with the experimental results for the dependence of the beta-Ga2O3 decomposition rates on the H-2 molar fraction.
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| 13. |
- Yoshida, Kento, et al.
(författare)
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Dependence of thermal stability of GaN on substrate orientation and off-cut
- 2019
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Ingår i: Japanese Journal of Applied Physics. - : IOP PUBLISHING LTD. - 0021-4922 .- 1347-4065. ; 58
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Tidskriftsartikel (refereegranskat)abstract
- The thermal stability of +/- c- and m-plane GaN substrates and its dependence on the m-plane GaN off-cut angle were investigated at and above 1200 degrees C at atmospheric pressure in flowing N-2 with and without added NH3. It was clarified that decomposition of the +c-plane GaN surface is promoted by the addition of NH3, while decomposition of the -c- and m-plane GaN surfaces is suppressed by added NH3. It was found that -c- and m-plane GaN substrates can be heated at 1300 degrees C with an added NH3 input partial pressure of more than 0.2 atm, which is 100 degrees C higher than for +c-plane GaN substrates. Nevertheless, decomposition of m-plane GaN substrates became noticeable with increase in the off-cut angle of the substrate. It was revealed that the decomposition was better controlled by using m-plane GaN substrates with an off-cut towards [000 (1) over bar] than towards [0001]. (C) 2019 The Japan Society of Applied Physics
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| 14. |
- Zhou, S. X., et al.
(författare)
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Growth and electrical properties of high-quality InGaAsBi thin films using gas source molecular beam epitaxy
- 2017
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Ingår i: Japanese Journal of Applied Physics. - : IOP Publishing. - 1347-4065 .- 0021-4922. ; 56:3
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Tidskriftsartikel (refereegranskat)abstract
- The effects of Bi flux and In/Ga ratio on Bi incorporation and electrical properties of InGaAsBi grown by gas source molecular beam epitaxy were systematically studied. It is found that use of a low In/Ga ratio has an enhancement effect on the incorporation of Bi and its content increases linearly with Bi flux until reach a saturation. Incorporation of Bi induces p-type dopant that compensates the background electron concentration but does not degrade the electron mobility for the Bi content up to 6.2%. Up to 7.5% of Bi incorporation has been confirmed by Rutherford backscattering spectroscopy (RBS) and a maximum electron mobility of 5600 cm(2)& V-1.s(-1) at room temperature was achieved in InGaAsBi with x(Bi) = 6.2%, which is the highest value reported in InGaAsBi with x(Bi) > 5%. (C) 2017 The Japan Society of Applied Physics
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| 15. |
- Zota, Cezar B., et al.
(författare)
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Junctionless tri-gate InGaAs MOSFETs
- 2017
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Ingår i: Japanese Journal of Applied Physics. - 0021-4922. ; 56:12
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate and characterize junctionless tri-gate InGaAs MOSFETs, fabricated using a simplified process with gate lengths down to L g = 25 nm at a nanowire dimension of 7 - 16 nm2. These devices use a single 7-nm-thick In0.80Ga0.20As (N D = 1 - 1019 cm-3) layer as both channel and contacts. The devices show SSsat = 76 mV/dec, peak g m = 1.6 mSm and I ON = 160A/m (at I OFF = 100 nA/m and V DD = 0.5 V), the latter which is the highest reported value for a junctionless FET. We also show that device performance is mainly limited by high parasitic access resistance due to the narrow and thin contact layer.
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