Izak Baranowski

Active tracking system for visible light communication using a GaN-based micro-LED and NRZ-OOK

Visible light communication (VLC) holds the promise of a high-speed wireless network for indoor applications and competes with 5G radio frequency (RF) system. Although the breakthrough of gallium nitride (GaN) based micro-light-emitting-diodes (micro-LEDs) increases the -3dB modulation bandwidth exceptionally from tens of MHz to hundreds of MHz, the light collected onto a fast photo receiver drops dramatically, which determines the signal to noise ratio (SNR) of VLC. To fully implement the practical high data-rate VLC link enabled by a GaN-based micro-LED, it requires focusing optics and a tracking system. In this paper, we demonstrate an active on-chip tracking system for VLC using a GaN-based micro-LED and none-return-to-zero on-off keying (NRZ-OOK). Using this novel technique, the field of view (FOV) was enlarged to 120° and data rates up to 600 Mbps at a bit error rate (BER) of 2.1×10-4 were achieved without manual focusing. This paper demonstrates the establishment of a VLC physical link that shows enhanced communication quality by orders of magnitude, making it optimized for practical communication applications.

Demonstration of AlN Schottky Barrier Diodes With Blocking Voltage Over 1 kV

This letter reports the first demonstration of 1-kV-class AlN Schottky barrier diodes on sapphire substrates by metal organic chemical vapor deposition. The device structure mimics the silicon-on-insulator (SOI) technology, consisting of thin <inline-formula> <tex-math notation=LaTeX>

Ultra-low turn-on voltage and on-resistance vertical GaN-on-GaN Schottky power diodes with high mobility double drift layers

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Reliability analysis of InGaN/GaN multi-quantum-well solar cells under thermal stress

</tex-math></inline-formula>-AlN epilayer as the device active region and thick resistive AlN underlayer as the insulator. At room temperature, the devices show outstanding performances with a low turn-ON voltage of 1.2 V, a high ON/OFF ratio of <inline-formula> <tex-math notation=LaTeX>

Low loss GaN waveguides at the visible spectral wavelengths for integrated photonics applications

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Characterizations of the nonlinear optical properties for (010) and (2- 01) beta-phase gallium oxide

</tex-math></inline-formula>, a low ideality factor of 5.5, and a low reverse leakage current below 1 nA. The devices also exhibit excellent thermal stability over 500 K owing to the ultra-wide bandgap of AlN. The breakdown voltage of the devices can be further improved by employing field plate, edge termination technologies, and optimizing the SOI-like device structure. This letter presents a cost-effective route to high performance AlN-based Schottky barrier diodes for high-power, high-voltage, and high-temperature applications.

Energy band engineering of InGaN/GaN multi-quantum-well solar cells via AlGaN electron- and hole-blocking layers

This letter reports the implementation of double-drift-layer (DDL) design into GaN vertical Schottky barrier diodes (SBDs) grown on free-standing GaN substrates. This design balances the trade-off between desirable forward turn-on characteristics and high reverse breakdown capability, providing optimal overall device performances for power switching applications. With a well-controlled metalorganic chemical vapor deposition process, the doping concentration of the top drift layer was reduced, which served to suppress the peak electric field at the metal/GaN interface and increase the breakdown voltages of the SBDs. The bottom drift layer was moderately doped to achieve low on-resistance to reduce power losses. At forward bias, the devices exhibited a record low turn-on voltage of 0.59u2009V, an ultra-low on-resistance of 1.65 mΩu2009cm2, a near unity ideality factor of 1.04, a high on/off ratio of ∼1010, and a high electron mobility of 1045.2u2009cm2/(Vu2009s). Detailed comparisons with conventional single-drift-layer (S...

InGaN-based solar cells for space applications

We investigate the thermal stability of InGaN solar cells under thermal stress at elevated temperatures from 400u2009°C to 500u2009°C. High Resolution X-Ray Diffraction analysis reveals that material quality of InGaN/GaN did not degrade after thermal stress. The external quantum efficiency characteristics of solar cells were well-maintained at all temperatures, which demonstrates the thermal robustness of InGaN materials. Analysis of current density–voltage (J–V) curves shows that the degradation of conversion efficiency of solar cells is mainly caused by the decrease in open-circuit voltage (Voc), while short-circuit current (Jsc) and fill factor remain almost constant. The decrease in Voc after thermal stress is attributed to the compromised metal contacts. Transmission line method results further confirmed that p-type contacts became Schottky-like after thermal stress. The Arrhenius model was employed to estimate the failure lifetime of InGaN solar cells at different temperatures. These results suggest that wh...

A Comparative Study on the Electrical Properties of Vertical (

We perform comprehensive studies on the fundamental loss mechanisms in III-nitride waveguides in the visible spectral region. Theoretical analysis shows that free carrier loss dominates for GaN under low photon power injection. When optical power increases, the two photon absorption loss becomes important and eventually dominates when photon energy above half-bandgap of GaN. When the dimensions of the waveguides reduce, the sidewall scattering loss will start to dominate. To verify the theoretical results, a high performance GaN-on-sapphire waveguide was fabricated and characterized. Experimental results are consistent with the theoretical findings, showing that under high power injection the optical loss changed significantly for GaN waveguides. A low optical loss ~2 dB/cm was achieved on the GaN waveguide, which is the lowest value ever reported for the visible spectral range. The results and fabrication processes developed in this work pave the way for the development of III-nitride integrated photonics in the visible and potentially ultraviolet spectral range for nonlinear optics and quantum photonics applications.

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We report, for the first time, the characterizations on optical nonlinearities of beta-phase gallium oxide (β-Ga2O3), where both (010) β-Ga2O3 and (2¯01) β-Ga2O3 were examined for two-photon absorption coefficient, Kerr nonlinear refractive index, and their polarization dependence. The wavelength dependence of two-photo absorption coefficient and Kerr nonlinear refractive index were also estimated by a widely used analytical model. β-Ga2O3 exhibits a two photon absorption (TPA) coefficient of 1.2 cm/GW for (010) β-Ga2O3 and 0.6 cm/GW for (2¯01) β-Ga2O3. The Kerr nonlinear refractive index is -2.1 × 10-15 cm2/W for (010) β-Ga2O3 and -2.9 × 10-15 cm2/W for (2¯01) β-Ga2O3. In addition, β-Ga2O3 shows stronger in-plane nonlinear optical anisotropy on (2¯01) plane than on (010) plane. Compared with GaN, TPA coefficient of β-Ga2O3 is 20 times smaller, and the Kerr nonlinear refractive index of β-Ga2O3 is also found to be 4-5 times smaller. These results indicate that β-Ga2O3 have the potential for ultra-low loss waveguides and ultra-stable resonators and integrated photonics, especially in UV and visible wavelength spectral range.