京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20384号 / 工博第4321号 / 新制||工||1670(附属図書館) / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 川上 養一, 教授 野田 進, 教授 山田 啓文 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

In this work, we propose a model to address the challenge of droop in internal quantum efficiency in InGaN/GaN Multiple Quantum Well LEDs. Efficiency droop limits the performance of high brightness LEDs as they operate at currents greater than 350mA. The efficiency droop is a multi-physics problem posed by various entities such as (1) dislocation recombination, (2) Auger recombination in active region, (3) non-radiative recombination, and (4) current overflow in the active region. This work aims at reducing the droop associated with non-radiative recombination by engineering the quantum well barrier thickness and materials. The goals are three-fold, namely: (1) To explore the role of barriers in determining the droop in internal quantum efficiency and to justify the use of multiple barriers to increase the carrier density and reduce the leakage current thereby increase the radiative recombination at higher current densities ; (2) Propose optimum barrier specifications such as number, material combination, and thickness for downscaling the efficiency droop, and thereby improving the device efficiency; and (3) Finally, obtain improved efficiency by engineering the barrier in a realistically-sized device by considering the effects of long-range strain fields in the device.

In the global context of increasing oil prices and public concern regarding the safety of nuclear plants, renewable forms of energy are called upon to play a major role in tomorrow’s energy market. Among the various forms of renewable energies, solar power holds the greatest potential for development. Despite the constant improvement of photovoltaic technologies over the past few year, these technologies are rapidly approaching the theoretic performance limits. New ideas and materials are required to overcome this bottleneck and to take full advantage of solar power. With a band-gap energy spanning the full solar spectrum, and an absorption coefficient ten times higher than competing materials, indium gallium nitride alloys are amongst the most promising solar-cell materials. Nevertheless, fundamental issues related to the fabrication and doping of InGaN alloys still hamper the development of InGaN-based photovoltaics. In the present thesis, conducted within the framework of the ANR project NewPVonGlass, the growth of InGaN alloys suitable for photovoltaics using metalorganic vapor-phase epi- taxy (MOVPE) is studied. A combination of several cutting-edge characterization tools is employed to determine the fundamental mechanism that govern the growth of InGaN. Based on the results of this study, an innovative procedure that allows the growth of hig-quality InGaN epitaxial layers is demonstrated and is used for the fabrication of InGaN-based solar cells.

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In this thesis I will discuss the development, construction and testing of a sub-Kelvin Q-band electron paramagnetic resonance (EPR) spectrometer and optically detected magnetic resonance (ODMR) of wide bandgap semiconductors at Q-band. The sub-Kelvin EPR spectrometer was developed to be integrated into a standard commercial system. Characterisation of the cryogenics and microwave components of the spectrometer will be discussed as well as the design and adaptations made to enable EPR experiments to be performed below 1 K. A waveguide thermal break design, previously only used in detectors for the cosmic microwave background radiation, was optimised using ANSYS High frequency structure simulator (HFSS) to operate at Q-band and was built and tested in this spectrometer. The sub-Kelvin EPR spectra of Cr3+ in Al2O3 and [Cr12O9(OH)3(O2CCMe3)15] were obtained. The resonant cavity of the spectrometer was also successfully tested at room temperature, with a pulsed microwave bridge, paving the way for further development of the system to enable sub-Kelvin pulsed EPR. A home-built Q-band ODMR spectrometer was used to investigate the wide band gap semiconductors ZnO and InGaN/GaN multiple quantum wells (MQWs). The ZnO was a natural crystal, and used to characterise the spectrometer. ODMR from a green c-plane InGaN/GaN MQW was studied to probe the method of carrier localisation in the QW. It was shown qualitatively that the ODMR results support current theories for carrier localisation mechanisms, but the noise on these measurements needs to be reduced to provide quantitative support.

Design, fabrication and characterization of III-Nitride pn junction devices Jae Boum Limb 94 pages Directed by Dr. Russell D. Dupuis This dissertation describes an investigation of three types of III-nitride (AlInGaN) based p-n junction devices that were grown by metalorganic chemical vapor deposition (MOCVD). The three types of devices are Ultra-Violet (UV) avalanche photodiodes (APDs), green light emitting diodes (LEDs), and p-i-n rectifiers. For avalanche photodiodes, a material growth on low-dislocation density GaN substrates, processed with low-damage etching receipes and high quality dielectric passivations, were proposed. Using this technology, GaN APDs with optical gains greater than 3000, and AlGaN APDs showing true avalanche gains have been demonstrated. For green LEDs, the use of InGaN:Mg as the p-layer, rather than employing the conventional GaN:Mg has been proposed. Green LEDs with p-InGaN have shown higher emission intensities and lower diode series resistances compared to LEDs with p-GaN. Using p-InGaN layers, LEDs emitting at green and longer wavelengths have been realized. For p-i-n rectifiers, design, fabrication and characterization of device structures using the conventional mesa-etch configuration, as well as the full-vertical method have been proposed. High breakdown devices with low on-resistances have been achieved. Specific details on device structures, fabrication methods, and characterization results are discussed.

¡@¡@A high efficient packaging technique was proposed for power InGaN light emitting diodes( LEDs ).In this approach , sub-mounts based on Si bench technology were used to provide a fact heat conducting channel between the LEDs and the cases.Two different structures of the Si sub-mounts were used, namely, a conventional Si block and a Si block with a copper-filled V-groove. ¡@¡@The thermal resistance of the two different sub-mounts were measured and compared. For a 45mil power LED biased at 1W, thermal resistance of 12.77¢J/W and 18.79¢J/W were measured for the Si sub-mount and the Si sub-mount with copper-filled V-groove. We believe the better thermal resistance of the sub-mount with copper-filled V-groove is due to high thermal conductivity of the copper.

This thesis used TCSPC (Time-Correlated Single Photon Counting) apparatus to study the time-resolve photoluminescence (TRPL) of InGaN multi-quantum-well light emission diode and the photoluminescence of Zn1-xMgxSe properties at different Mg concentration. We obtained the activation energy form Arrhenius Plot, internal quantum efficiency (IQE), the radiative lifetime, and the radiative recombination critical at 180K of In0.25Ga0.75N multi-quantum well LED. Furthermore, the variation of PL peak location and FWHM with Mg concentration of Zn1-xMgxSe thin film with x=0.1¡B0.25¡B0.34¡B0.37¡B0.4¡B0.42 are observed.

In this thesis, we investigate the optical properties of m-plane InGaN/GaN multiple quantum well grown by metal organic vapor phase epitaxy. The optical spectroscopies we employed are photoluminescence (PL), polarized PL, power-dependent PL, photoluminescence excitation (PLE), polarized PLE, and Raman scattering. From the blue shift of E2 mode in Raman spectrum, we find that the epitaxial layers are under compressive stress. The PL spectrum at 10 K is dominated by the emission band peaked at 433 nm. We found the optical emission possesses the polarization anisotropy. The degree of polarization is about 80% at room temperature. It is found that the degree of polarization decreases with increasing temperature, which may be explained by carrier population effect. In addition, two major contributions to the PLE spectrum detected for the emission band have identified. Finally, the absence of quantum confined Stark effect is confirmed by power-dependent PL measurements.

InN has been grown on GaN with a thin intermediate layer of InGaN by metalorganic chemical vapor deposition (MOCVD) to further enhance indium incorporation in subsequent InGaN layer. Trimethylindium (TMI) and ammonia (NH₃) were used as the source for InN growth and transmission electron microscopy (TEM) confirmed the presence of pyramid-like structure of InN. A layer of InGaN subsequently grown on top of these InN pyramids shows a red-shift of ~20 nm relative to InGaN layer grown directly on GaN using the same growth condition. However, there is no significant pits reduction. An alternative method to enhance indium incorporation is to grow the InN by adding a small amount of trimethygallium (TMG) into the TMI and NH₃ flow. This method provides a seed layer for the InN growth and it gives a higher density of InN pyramids. X-ray diffraction (XRD) measurement of this sample shows a high indium incorporation to give InGaN with x~0.26 as compared to x~0.22 for sample grown without TMG flow in the InN layer. / Singapore-MIT Alliance (SMA)