Nitrure de gallium

Résumé

Le nitrure de gallium est un à gap direct de à . De formule chimique GaN, c'est un matériau très dur de structure cristalline de type wurtzite (système hexagonal , ) avec pour paramètres et . Il cristallise également dans le système cubique avec la structure blende (polymorphe ) selon le groupe d'espace (). Il s'agit d'un semiconducteur à large bande interdite couramment utilisé pour la fabrication de diodes électroluminescentes () bleues et dont les propriétés électroniques et optiques permettent le développement d'applications optoélectroniques, hautes fréquences et d'électronique de puissance. Le GaN est ainsi le matériau permettant de produire des diodes laser violettes (longueur d'onde de ) sans devoir recourir à un doublage de fréquence non linéaire. Il est également étudié dans le cadre du développement de la technologie 5G. Le nitrure de gallium est peu sensible aux rayonnements ionisants, comme généralement les au

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The international actions against global warming demands reductions in carbon emission and more efficient use of energy. Energy efficiency in the conversion and use of electricity, as an important form of energy in the modern life, has strong environmental and economical impacts. Power electronic devices determining roles in the overall system efficiency in many applications such as power converters and inverters. Gallium Nitride (GaN) devices have emerged as an superior alternative to the silicon devices and enabled unprecedented efficiencies. GaN-based high electron-mobility transistors (HEMTs) offer excellent characteristics such as high switching speed, low switching and conduction losses, small device size and high power density capabilities. However, such significant increases in the power density and the reduction of device size comes at the price of dramatic increases in the heat fluxes and appearance of hot spots in the device footprint that cannot be addressed using conventional methods. The integration of diamond and GaN has been highly pursued for thermal management purposes as well as combining their exceptional complementary properties for power electronics applications and novel semiconductor heterostructures. In this thesis, we discuss the key hindrances towards realisation of diamond on GaN substrates and devices, and we propose novel solutions for improving the feasibility of diamond-on-GaN integration for efficient thermal management of hot spots in GaN devices and development of diamond devices integrated with GaN devices in the same chip.The growth of diamond on GaN is challenging due to the high lattice and thermal expansion mismatches. The weak adhesion of diamond to GaN and high residual stresses after the deposition often result in the diamond film delamination or development of cracks, which prevents the subsequent device fabrication. In this thesis, a new seed dibbling method is presented for seeding and growing high-quality diamond films on cost-effective GaN-on-Si substrates, which result in significantly larger diamond grains and lower residual stresses (as low as 0.2 GPa) compared to conventional methods. Moreover, the excellent adhesion obtained by this method enabled a reliable polishing of the as-grown diamond films on GaN-on-Si without any delamination, resulting in smooth diamond-on-GaN substrates with sub-nanometer roughness. The high temperature hot spots in GaN devices are addressed by the near-junction heat spreaders using diamond films deposited on GaN. An analytical model for the heat spreading is presented to analyse the performance and optimize the heat spreaders, considering the geometry and thermal conductivity of the heat spreader and the substrate. Experimental demonstration of diamond heat spreaders on vertical GaN diodes together with the thermal characterization of their behaviour shows significant reduction of thermal spreading resistances, hot spot temperatures and temperature gradients from the device footprint, which highlights the impact of such heat spreaders for the thermal management of high power density GaN devices.The diamond films deposited on GaN were also used to demonstrate high-performance diamond transistors integrated on AlGaN/GaN-on-Si substrates with characteristics such as high breakdown voltage, high current density, and high on/off ratio, which opens many new possibilities for the development of power ICs with complementary logics, gate drivers and power

EPFL2021

Chargement

Intrinsic Polarization Super Junctions: Design of Single and Multichannel GaN Structures

Catherine Erine, Elison de Nazareth Matioli, Amirmohammad Miran Zadeh, Luca Nela

Super junctions (SJs) have enabled unprecedented performance in Silicon power devices, which could be further improved by applying this concept to wide bandgap semiconductors like gallium nitride (GaN). Currently, polarization super junctions (PSJs) are the most promising candidates for GaN SJs. Yet, until now, p-type doping of the GaN cap layer was required to ensure the presence of a 2-D hole gas (2DHG), and the proper charge matching between the 2DHG and 2-D electron gas (2DEG), which is fundamental to the operation of SJs. This approach, however, requires precise control of the p-GaN doping level, which is very challenging and has hindered the demonstration of high-performance PSJs. Besides, while PSJs are particularly promising for multichannel structures aimed at reducing the sheet resistance, achieving proper charge matching combined with large electron density for all the buried channels is challenging. Here, we propose a simple and robust platform for intrinsic PSJs (i-PSJs) that enables excellent charge matching for a wide range of structures, without relying on doping. We show that surface donor states are the origin of charge mismatch and provide a strategy to minimize their impact. Simulated devices based on this structure show optimal carrier depletion with a flat electric field profile in the whole drift region. Finally, we extend this concept to multichannel i-PSJ structures. We demonstrate a much-reduced sheet resistance down to 58 Ω /sq and present a robust strategy to achieve charge balance, which enables reducing the on-resistance without degrading the off-state performance, thus greatly improving the device figure-of-merit.

2022

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, ,

It is the most exciting time for power electronics in decades. The combination of new applications, such as microinverters, electric vehicles and solid state lighting, with the new opportunities brought by wide bandgap semiconductors is expected to significantly increase the reach and impact of power electronics. This paper describes some of the recent advances on developing power devices based on Gallium Nitride (GaN), the key design constrains, and the process to take a new device material and structure from the research laboratory of universities to full commercialization. © 2015 IEEE.

IEEE2015

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EPFL2021