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Journal Articles

Effect of annealing on proton irradiated AlGaN/GaN based micro-Hall sensors

Abderrahmane, A.*; Takahashi, Hiroki*; Tashiro, Tatsuya*; Ko, P. J.*; Okada, Hiroshi*; Sato, Shinichiro; Oshima, Takeshi; Sandhu, A.*

AIP Conference Proceedings 1585, p.123 - 127, 2014/02

 Times Cited Count:1 Percentile:41.94

The effect of annealing at 673 K on irradiated micro-Hall sensors irradiated with protons at 380 keV and fluences of 1$$times 10^{14}$$ cm$$^{-2}$$, 1$$times 10^{15}$$ cm$$^{-2}$$, 1$$times 10^{16}$$ cm$$^{-2}$$ is reported. Cathodoluminescence measurements were carried out at room temperature before and after annealing and showed improvement in the band edge band emission of the GaN layer. After annealing a sensor irradiated by 1$$times 10^{15}$$ cm$$^{-2}$$ the device became operational with improvements in its magnetic sensitivity. All irradiated sensors showed improvement in their electrical characteristics after annealing.

Journal Articles

Partial recovery of the magnetoelectrical properties of AlGaN/GaN-based micro-Hall sensors irradiated with protons

Abderrahmane, A.*; Tashiro, Tatsuya*; Takahashi, Hiroki*; Ko, P. J.*; Okada, Hiroshi*; Sato, Shinichiro; Oshima, Takeshi; Sandhu, A.*

Applied Physics Letters, 104(2), p.023508_1 - 023508_4, 2014/01

 Times Cited Count:4 Percentile:75.8(Physics, Applied)

The effect of annealing on the magnetoelectrical properties of proton-irradiated micro-Hall sensors at an energy of 380 keV and very high proton fluences was studied. Recovery of the electron mobility and a decrease in the sheet resistance of the annealed micro-Hall sensors, as well as an enhancement in their magnetic sensitivity were reported. Trap removal and an improvement in the crystal quality by removing defects were confirmed through current-voltage measurements and Raman spectroscopy, respectively.

Journal Articles

Effect of proton irradiation on AlGaN/GaN micro-Hall sensors

Abderrahmane, A.*; Koide, Shota*; Okada, Hiroshi*; Takahashi, Hiroki*; Sato, Shinichiro; Oshima, Takeshi; Sandhu, A.*

Applied Physics Letters, 102(19), p.193510_1 - 193510_4, 2013/05

 Times Cited Count:6 Percentile:66.67(Physics, Applied)

The magnetoelectric properties of AlGaN/GaN micro-Hall effect sensors were studied after 380 keV proton irradiation. After irradiation the current-voltage measurements, stability of the magnetic sensitivity of the sensors, and the sheet electron density were degraded with a dramatic decrease of the electron mobility at high temperatures. Raman spectroscopy showed a degradation in the crystalline quality of GaN crystal, but there was no change in the strain.

Journal Articles

Synthesis of Al$$_{x}$$Ga$$_{1-x}$$N and InN crystals under high pressures

Saito, Hiroyuki; Utsumi, Wataru; Kaneko, Hiroshi*; Aoki, Katsutoshi

Proceedings of Joint 20th AIRAPT - 43rd EHPRG International Conference on High Pressure Science and Technology (CD-ROM), 4 Pages, 2005/06

We have performed synthesis studies of various III-V nitrides crystals, key materials for optoelectronic and high-power/frequency devices, using a cubic-anvil-type large volume high-pressure apparatus combined with in situ X-ray diffraction. Polly-crystallines of Al$$_{x}$$Ga$$_{1-x}$$N alloys covering a composition range of 0 $$leq$$ x $$leq$$ 1 were synthesized by a solid-phase reaction under high pressure. In situ X-ray diffraction profiles were measured to observe the alloying process, which started at around 800$$^{circ}$$C under 6.0 GPa. Single crystal of Al$$_{0.1}$$Ga$$_{0.9}$$N was also successfully obtained by slow cooling of its melt from 2400$$^{circ}$$C at 6.5 GPa. For InN, its phase diagram was determined under high P-T conditions up to 20GPa and 2000$$^{circ}$$C based on the in situ observations, which demonstrates that 19GPa and 1900$$^{circ}$$C are needed for its congruent melting.

Journal Articles

Single crystal growth of gallium nitride by slow-cooling of its congruent melt under high pressure

Saito, Hiroyuki; Utsumi, Wataru; Kaneko, Hiroshi*; Kiriyama, Koji*; Aoki, Katsutoshi

State-of-the-Art Program on Compound Semiconductors XLI and Nitride and Wide Bandgap Semiconductors for Sensors, Photonics, and Electronics V, p.587 - 592, 2004/10

Single crystals of GaN were successfully synthesized by slowly cooling its stoichiometric melt under high pressure. Applying high pressures above 6.0 GPa prevented decomposition and allowed the congruent melt of GaN at 2220$$^{circ}$$C, which was confirmed by an in situ X-ray diffraction study. Using a cubic-anvil-type, large volume, high-pressure apparatus and a GaN powder as a starting material, single crystal growth was achieved by reducing the temperature from 2400$$^{circ}$$C at 6.5 GPa. The X-ray rocking curve of the recovered sample showed a very narrow line width, less than 30 arcsec, suggesting a low dislocation density. Bulk specimens of Al$$_x$$Ga$$_{1-x}$$N alloys, which covered a composition range of 0$$leq$$x$$leq$$1 were also synthesized under high pressures.

Journal Articles

Synthesis of Al$$_{x}$$Ga$$_{1-x}$$N alloy by solid-phase reaction under high pressure

Saito, Hiroyuki; Utsumi, Wataru; Kaneko, Hiroshi*; Aoki, Katsutoshi

Japanese Journal of Applied Physics, Part 2, 43(7B), p.L981 - L983, 2004/07

 Times Cited Count:4 Percentile:78.74(Physics, Applied)

Bulk specimens of Al$$_{x}$$Ga$$_{1-x}$$N alloys covering a composition range of 0$$leq$$${it x}$$$leq$$1 were synthesized by a solid-phase reaction under high pressure. ${it In situ}$ X-ray diffraction profiles were measured to observe the alloying process, which began at around 800$$^{circ}$$C under 6.0 GPa. SEM observation and X-ray analysis of the recovered specimen indicated a uniform distribution of Al and Ga and continuous variations of the lattice constants against the composition, which implies that a solid solution of AlN and GaN is formed regardless of atomic composition.

Journal Articles

Effects of Al composition on luminescence properties of europium implanted Al$$_{x}$$Ga$$_{1-x}$$N(0$$<$$x$$<$$1)

Nakanishi, Yasuo*; Wakahara, Akihiro*; Okada, Hiroshi*; Yoshida, Akira*; Oshima, Takeshi; Ito, Hisayoshi; Shibata, Tomohiko*; Tanaka, Mitsuhiro*

Physica Status Solidi, 0(7), p.2623 - 2626, 2003/07

In our previous study, it was reported that Eu-doped Nitride semiconductors show luminescence propetires. In this study, we investigate the relationship between luminescence properties and Al composition using Al$$_{x}$$Ga$$_{1-x}$$N(0$$<$$x$$<$$1). Al$$_{x}$$Ga$$_{1-x}$$N were grown using OMVPE. Eu atoms were doped into the samples by ion implantation (200keV). After implantation, the samples were annealed to remove residual damege. Luminescence propreties of the samples were measured using photoluminescence and cathodeluminescence. As a result, luminescence at 621 nm which relates 4f-4f transition were observed for all samples (x=0 to 1). As for intensity, samples with x=0.5 show the strongest luminescence. This result can be interpreted in terms of the internal stress of crystals by the existence of Al atoms.

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