Dr. Ronel Christian I. Roca Profile

Dr. Ronel Christian I. Roca

Assistant Professor at Toyota Technological Institute

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Publications (6)

SPIE Journal Paper | 4 September 2024

Electrical and structural properties of ArF excimer laser activation of Mg-doped GaN small area mesa device

Maria Emma Villamin, Ronel Christian Roca, Itaru Kamiya, Naotaka Iwata

OE, Vol. 63, Issue 09, 096101, (September 2024) https://doi.org/10.1117/12.10.1117/1.OE.63.9.096101

KEYWORDS: Laser irradiation, Annealing, Gallium nitride, Excimer lasers, Atomic force microscopy, Pulsed laser operation, Optical engineering, Magnesium, Laser processing, Semiconducting wafers

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Laser activation annealing using of an Mg-doped GaN four-point probe small mesa device using a 193-nm ArF excimer laser is investigated. Fabricated mesa device has 2-μm-high small mesa structures with In/Au contacts formed using standard semiconductor device process. In our setup, the ArF excimer laser was directed onto the sample using a series of mirrors and was focused through an aspheric lens to the sample, which is mounted on to a movable stage. The mesa device and the laser were aligned while being viewed on the computer monitor screen using a UV CCD camera. This method has several merits: (1) the four-point probe measurement allows accurate resistivity measurement of the GaN layer independently of the contact resistance, (2) utilizing a small area mesa also as the alignment marker during laser annealing ensures that the irradiated area precisely corresponds to the resistivity measurement area, and (3) multiple irradiation-measurement cycles are possible with a single mesa device, which avoids wafer-scale variations. The dependence of the resistivity to the laser fluence and irradiation time were investigated by multiple-irradiation measurement cycles to a single mesa device in combination with atomic force microscopy analysis for surface morphology characterization. Results reveal that laser annealing at 530 mJ/cm2 for 1500 s (at 150 Hz repetition rate) decreases the resistivity from 11.5 (before irradiation) to 5.6 Ω·cm (after irradiation). This value is similar to resistivity achieved by rapid thermal annealing (RTA) at 800°C for 120 s, suggesting successful Mg-doped GaN activation. Results also show stronger dependence on the irradiation time (temporal dependence) than the laser fluence, which may imply that activation mechanism for the laser annealing has a thermal contribution. This is the first report demonstrating ArF laser annealing that achieves a similar degree of activation with conventional RTA using resistivity measurements.

SPIE Journal Paper | 9 July 2024

Optical spin injection and detection in submonolayer InAs/GaAs nanostructures by circularly polarized photoluminescence

Ronel Christian Roca, Itaru Kamiya

JNP, Vol. 18, Issue 03, 036001, (July 2024) https://doi.org/10.1117/12.10.1117/1.JNP.18.036001

KEYWORDS: Nanostructures, Gallium arsenide, Quantum spin, Quantum confinement, Polarization, Indium arsenide, Optical properties, Photoluminescence, Quantum optics experiments, Quantum information applications

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Proceedings Article | 12 March 2024 Presentation + Paper

Optical spin injection and detection in submonolayer InAs/GaAs nanostructures

Ronel Christian Roca, Itaru Kamiya

Proceedings Volume 12874, 1287409 (2024) https://doi.org/10.1117/12.3002062

KEYWORDS: Nanostructures, Gallium arsenide, Polarization, Indium arsenide, Luminescence, Emission wavelengths, Quantum spin, Wave plates, Spin polarization, Optical testing, Quantum dots, Molecular beam epitaxy, Spintronics, Photoluminescence

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Proceedings Article | 8 March 2024 Poster + Paper

ArF excimer laser activation of Mg-doped GaN small area mesa device

Maria Emma Villamin, Ronel Christian Roca, Itaru Kamiya, Naotaka Iwata

Proceedings Volume 12886, 128860F (2024) https://doi.org/10.1117/12.3002082

KEYWORDS: Laser irradiation, Annealing, Gallium nitride, Excimer lasers, Semiconducting wafers, Atomic force microscopy, Ultraviolet radiation, Sapphire, Resistance, Pulsed laser operation

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Proceedings Article | 6 September 2017 Presentation + Paper

Progress in the room temperature operation of GaAs-based lateral-type spin-PD in near-infrared wavelength region

R. Roca, N. Nishizawa, K. Nishibayashi, H. Munekata

Proceedings Volume 10357, 103571C (2017) https://doi.org/10.1117/12.2275577

KEYWORDS: Semiconductors, Electrons, Spintronics, Polarization, Integrated optical circuits, Photonic devices, Heterojunctions, Photodiodes

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Proceedings Article | 8 September 2015 Paper

Spin-photonic devices based on crystalline-AlOx / GaAs for emission and detection of circular polarized light

H. Munekata, M. Aoyama, R. Roca, K. Nishibayashi, N. Nishizawa

Proceedings Volume 9551, 955120 (2015) https://doi.org/10.1117/12.2187003

KEYWORDS: Iron, Switching, Light emitting diodes, Electroluminescence, Crystals, Polarization, Gallium arsenide, Electrodes, Electrons, Spin polarization

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Showing 5 of 6 publications

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