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Epitaxie de composés semiconducteurs borés (III-B)-N pour applications en Hyperfréquence et optoelectronique – GABORE

Submission summary

Wide Band Gap semiconductors, such as GaN and related alloys ( GaAlN, InAlN, InGaN), exhibit many attractive properties far beyond the capabilities of Si and GaAs : the unique combination of the wide band gap, the high breakdown field the high saturation velocity and the ability to form high quality Ga(In)AlN/Ga(In)N/GaN heterostructures with good transport properties make them ideal candidates for high power, high frequency applications. All these materials have direct band gaps which range from 0.7eV for InN to 6.1eV for AlN. Therefore they are also promising materials for optoelectronic devices, such as light emitting diodes (LEDs) and laser diodes operating throughout ultra violet to green visible region. One of the more limiting aspects of these GaN based materials is their relatively poor crystal quality, due to the necessity of heteroepitaxy. Sapphire(0001), silicon carbide (4H-SiC or 6H-SiC) and silicon (111) are the most common substrates for GaN epitaxy, but each suffers from large lattice constant mismatches (16%, 3.5% and 17%, respectively). Lattice mismatch and thermal strain present in nitride heterostructures on SiC, Si and Sapphire lead to high residual strain and an increase in dislocations within the epitaxial layers, which may have a critical impact on the reliability of the associated devices. A promising new approach to increasing the flexibility of nitride alloy compounds is the introduction of Boron. It may be possible to reduce or eliminate the lattice constant mismatch by adding boron to GaN or AlN, thereby forming BxGa1-xN or BxAl1-xN alloys. The boron aluminium gallium nitride (BGaAlN) quaternary system may be lattice matched to both Silicon Carbide (6H-SiC) and AlN substrates. The estimated band gap energy (Eg) of the BGaAlN lattice matched to 6H-SiC is in the range of 3.8eV (B0.15Ga0.83N) to 6.2eV ( B0.05Al0.95N), and the corresponding wavelengths lie between 340 and 200nm. On the other hand, the lattice matching of BAlGaN to AlN necessitates a lower boron composition than that to 6H-SiC, with an estimated Eg between 3.6eV and 6.2eV. These boron nitride based films are very useful for many applications due to their unique properties such as high thermal conductivity, hardness, excellent chemical stability and optical transparency over a wide spectral range. Moreover, SiC substrates offer many advantages in addition to lattice matching to boron–nitride based materials, such as a high thermal conductivity and in particular a thermal expansion coefficient nearly identical to that of AlN. As a consequence, the B(GaAl)N/AlN/SiC quaternary system is a promising material system for high power high frequency electronic devices and light-emitting devices in the UV to deep-UV spectral region. Some groups have already studied crystal growth in the BAlGaN system. The BGaN ternary system, for example, has previously been grown by molecular beam epitaxy (MBE) and low pressure metallorganic vapor phase deposition (LP-MOCVD) [1,2]. Room temperature PL emission from the strain controlled (BAlGaN/AlN)/SiC MQW structure was reported at 250nm [3]. Some physical parameters were estimated theoretically, including band offset and refractive indices of BGaN and BAlN, band gap energy, effective mass and optical gain of BGaN. These characteristics show clearly the interest of these new materials for device applications envision in this study. Nevertheless more investigation is required for better understanding and control of the growth of these boron nitride materials. The proposed project aims to : - develop the processing technology by MOCVD to grow these new materials: BGaN, BAlN and BGaAlN on SiC and AlN substrates. - evaluate the materials quality of B(Ga,Al)N alloys - understand the basic physical properties of these new materials - evaluate the boron nitride material and heterostructures for device applications. B(Ga)AlN/AlN/SiC HEMT will be taken as demonstrator. Our studies will include the following sub-projects: • SP1: Epitaxial growth of new semiconductor materials BAlN, BGaN and BAlGaN on GaN, SiC and AlN substrates • SP2: Characterisation and understanding the basic physical proprieties associated to the mechanisms of growth of III-N-B based materials • SP3 : Charge transport modelling in BGaAlN-based heterostructures and device simulations (GT-CNRS, IEMN) • SP4: Device processing and test structure characterisation By the end of this project we expect to have qualitative and quantitative number of elements related to the material quality/concept of structures that will be directly relevant to evaluate B(Ga,Al)N/AlN/SiC devices technology compared to GaAlN/GaN/SiC ones. [1] A. Polyakov et al , J. Electron Mater. 26, 237 (1997) [2] C.H. Wei et al , J. Electron Mater vol.29 N° 4 (2000) [3] T. Takano et al, Journal of Crystal growth 237-239 (2002)

Project coordination

Abdallah OUGAZZADEN (Organisme de recherche)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

Help of the ANR 435,000 euros
Beginning and duration of the scientific project: - 36 Months

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