Claire Richtarch

Study of extended-defect formation in Ge and Si after H ion implantation

Extended defects formed after hydrogen implantation into Si and Ge (100) substrates and subsequent thermal anneals were investigated by transmission electron microscopy. The majority of the extended defects formed in both materials were platelet-like structures lying on {100} and {111} planes. We found {100} platelets not only parallel but also perpendicular to the surface. In Ge wafers, high density of {311} defects and nanobubbles with the average size of 2 nm were observed. The difference between two materials can be attributed to the weaker strength of Ge–H bond.

AlGaN / GaN HEMT Structures Grown on SiCOI Wafers Obtained by the Smart CutTM Technology

SiCOI (SiC On Insulator) composite substrates obtained by the Smart-Cut TM process are alternative possible substrates for epitaxial growth of Wide Band Gap (WBG) materials such as GaN and GaN alloys. Similar to bonded SOI structure, the SiCOI structures basically comprises a thin film of single SiC crystal bonded onto a substrate such as, for instance, silicon. Additionally to the well known insulation properties, SiCOI substrates have proven to be adapted to the growth of high quality GaN layers. This first study has proven compatibility of SiCOI structures for single layer GaN MBE growth. We present here lastest results of AlGaN / GaN HEMT structures grown by MBE with NH3 as nitrogen precursor onto SiCOI (on silicon) structure realised by Smart Cut TM. First of all, complete SiCOI structure realisation will be described and typical physical characterization results will be presented for this kind of substrate. Then, MBE epitaxy set-up and growth parameters for HEMT structure will be detailed, including specific buffer layer stack description. Finally, physical and electrical characterisation results for epi-layers and HEMT structure will be presented. Those results show strong compatibility of the SiCOI structure for MBE epitaxy of GaN based HEMT structure and demonstrate the interest of the Smart Cut TM approach to build composite substrates, like SiCOI, for hetero-epitaxy application. Introduction III-Nitride materials and related devices are clearly identified as a major research field for lighting and high power high frequency applications. Since few years, important progresses have been done for GaN based blue, UV and white LED (Light Emitting Diode), and market for those products is growing really fast. Many promising results have been already published about nitride based high frequency and high power devices, like HFET (Hetero-junction Field Effect Transistor), showing real interest in using nitride based devices for those applications. Nevertheless, many challenges are still across the road leading to optimized devices, and many of those challenges are linked to GaN material quality. Obtaining high quality low dislocation density GaN material is difficult. High growth rate techniques like HVPE [1] or high pressure high temperature with nitrogen atmosphere and liquid gallium [2] have been used to get low density dislocation GaN substrate, but until now, the size of GaN crystal obtained is too small to be used as standard substrate for device realization. Thin film hetero-epitaxy is therefore the most popular way to get GaN based structures. MOCVD and MBE are the most used techniques to grow GaN and alloys thin films onto sapphire, 6H or 4H silicon carbide or silicon (111) substrates. To overcome difficulties of hetero-epitaxy, numerous growth techniques have been developed [3], like use of low temperature AlN or GaN buffer layer onto sapphire substrate for instance. Although those techniques allow realization of GaN based structures compatible with device building, with good final characteristics, material quality improvement is still a major challenge to reach devices with optimized behavior, good reliability and longer Materials Science Forum Online: 2004-06-15 ISSN: 1662-9752, Vols. 457-460, pp 1621-1624 doi:10.4028/www.scientific.net/MSF.457-460.1621

Fracture in Hydrogen‐Implanted Germanium

We have studied the mechanism of fracture in hydrogen‐implanted Ge. First, the as‐implanted Ge state and its evolution during subsequent annealing were characterized via TEM and FTIR‐MIR spectroscopy. Results showed that the extended defects formation and growth follow the same basic mechanism in Ge as in Si, which is the reference material. Nevertheless, the global damage level in the implanted Ge layer is higher compared to Si. Second, the fracture step was studied via the fracture kinetics analysis, SIMS and AFM on the transferred layer. An activation energy comparable to the reported data from blistering studies was obtained. Just like in Si, the Cmax of H in Ge measured via SIMS was found to decrease during the fracture anneal. This decrease is associated with the formation of gaseous H2 that pressurizes the internal cavities and then contributes to the fracture. Finally, a high roughness of the Ge transferred layer was measured, which results from the large thickness of the implantation damaged zone.

Metal Bonding in SiC Based Substrates

QuaSiC TM substrates can be obtained by transferring a single crystal SiC layer onto a poly SiC substrate using the Smart Cut TM technology. The structure evolution of metal bonding (W-Si silicide) layer has been investigated by Transmission Electron Microscopy and X-ray diffraction. Results indicate that the metal bonding film is made of W5Si3. The film is discontinuous and strained. Annealing releases stress at least partially.