Materials Science Forum Vol. 711

Abstract: AlGaN/GaN high electron mobility transistors (HEMTs) have shown outstanding improvements in performance and reliability, becoming the leading option for power applications in the 1-40 GHz range. However, the presence of traps and defects in the hetero-structure are strongly correlated to the tolerance of the fabrication process. New powerful models designed to overcome limitations associated with the Process Variability (PV) may be part of the exploitation outcome. This work describes a methodology useful to characterize the effects of PV on AlGaN/GaN HEMTs performance, by deriving Process Compact Model (PCM) from systematic TCAD simulations. The device under examination is an Al_0.26Ga_0.74N/GaN HEMT and the selected critical process parameters are: molar fraction of the first AlGaN layer, AlGaN layer thickness, source-gate and drain-gate distance, field plate extension, gate height and width, recessed effect under the gate contact.

Abstract: Today microwave market has identified GaN-HEMT technology as a strategic enabling technology for next generation MMICs to be implemented in high performance RF sub-assemblies such as T/R Modules, Solid State Power Transmitters, Compact Receivers, High Speed Communications. To allow commercial market entry of GaN technology, a tradeoff between high RF performance and low cost is mandatory and a possible solution is represented by GaN-on-Silicon substrate. In this scenario the evaluation of FETs RF performance and losses of passive components are demanding to understand the feasibility of GaN MMIC on Si. Following such approach, in SELEX Sistemi Integrati a 4 inches GaN-on-Si wafer containing discrete active devices and passive components has been fabricated with the 50μm Si thickness. RF FETs performance demonstrates an output power of 4W/mm @ 3GHz, while passive components characterization exhibits similar behavior of GaN SiC passive elements up to C Band.

Abstract: MOS SiO₂/GaN structures were fabricated with different surface preparation and different PECVD processes for the dielectric thin film deposition (ECR-PECVD and ICP-PECVD in continuous and pulsed modes). On the basis of C-V curves, the surface preparation steps, involving chemical etching with BOE, UV-Ozone oxidation and oxygen plasma oxidation, were compared in terms of resulting effective charge and interface trap density. A good SiO₂/GaN interface quality was achieved for N-type MOS capacitances obtained both with continuousICPPECVD and ECR-PECVD deposition of the SiO₂ dielectric. However, the interface quality is greatly reduced for MOS capacitors fabricated on P-type GaN.

Abstract: We present the growth and characterization of epitaxial Graphene on the (000-1) and (11-20) planes. In both cases, the growth was carried out in a RF furnace, by implementing our technique of confined atmosphere, covering the SiC substrate with a graphitic cap during the growth. The grown material was investigated by means of AFM, SEM, Raman spectroscopy and magneto transport. Contrary to the (0001) face, in both faces (000-1) and (11-20), almost free standing Graphene monolayers of very high quality are grown. These Graphene sheet are uniform, continuous, almost strain-free and lightly doped. In both faces, Hall bars were fabricated and Shubnikov-de Haas oscillations typical of Graphene, as well as the Half Integer Quantum Hall Effect are observed.

Abstract: By conducting a heteroepitaxy of a 3C-SiC film on a Si substrate and by annealing its surface in a UHV ambient, epitaxial graphene can be formed on such 3C-SiC virtual substrates. While the growth on the Si-terminated 3C-SiC(111)/Si (111) surface is known to proceed in a similar manner as on the Si-terminated 6H-SiC(0001) surface, successful growth of graphene on 3C-SiC(100)/Si (100) and 3C-SiC(110)/Si (110) surfaces remains puzzling. We have carried out detailed cross-sectional transmission-electron-microscopy observations on these systems to find out that (111)-facets may play crucial roles in the initiation of graphene on these surfaces. This observation also accounts for the absence of the interface layer at the graphene/SiC in these orientations.

Abstract: Biosensor diagnostics based on bio-functionalized semiconductor devices are an important development in ultrasensitive sensors for early detection of disease biomarkers. Electrochemical devices using chemically modified graphene (CMG) channels are excellent candidates for nanobiosensors. This paper presents the development of novel antibody functionalized epitaxial graphene devices for bio-sensing applications. Epitaxial graphene has been grown on silicon carbide (SiC) substrates under high vacuum and high temperature conditions (1200 – 1700°C). A generic electrochemical surface functionalisation chemistry, which can be used to attach a variety of “bio-receptors” to graphitic surfaces, has been developed. The attached bio-receptors are capable of specific and selective interaction with disease biomarkers. When a target biomarker molecule interacts with the “bio-receptor” functionalized surface, the charge density at that surface is affected. This change can be detected as an electrical signal from the biosensor, enabling highly sensitive (nM) detection of biomarker analytes. This paper reports the fabrication of graphene channel sensors for detection of disease biomarkers.

Abstract: We have grown graphene on 6H-SiC(0001) and 3C-SiC(111)/Si (111) using propane-hydrogen CVD. This contribution studies the effects of pressure on graphene growth and on its structural properties studied through low energy electron diffraction. We show that varying pressure allows to control the formation of graphene on a (6√3×6√3)-R30° interface reconstruction (low pressure) or graphene with in-plane rotational disorder (high pressure) on both 6H-SiC(0001) and 3C-SiC(111). The effects of the SiC morphology before graphene growth are discussed in order to explain the differences observed between polytypes.