Abstract: In this work, both ‘‘Schottky to Schottky’’ structure (STS) and pseudo-vertical Schottky barrier diode (pv-SBD) have been processed on GaN heteroepitaxially grown on sapphire or silicon by metal organic chemical vapor deposition (MOCVD) and characterized physically and electrically. Ni and Ti/Al were used to obtain respectively Schottky and Ohmic contacts using rapid thermal annealing (RTA). Adequate passivation steps and insertion of a resistive guard ring were also implemented in pv-SBD. The STS results, presented in this paper, evidence the impact of the substrate on the growth as well as all the progresses that have been done on GaN material quality. Furthermore, we demonstrate that high quality Schottky diodes can be obtained on GaN grown on sapphire by MOCVD. Indeed, ideality factors of 1.09 as well as a barrier height of 1.06 eV were obtained on pv-SBD devices that have a breakdown voltage over 600 V.
Abstract: To face silicon limits, gallium nitride (GaN) exhibits major interests for optoelectronics and power electronic devices. Nevertheless, several challenges have to be overcome, with local doping by ion implantation as a major one. It requires development of reliable characterization tools able to provide electrical information with nanoscale resolution. In this work, Atomic Force Microscopy (AFM) combined to its Scanning Capacitance Microscopy (SCM) mode was used for surface damages quantification and nanoscale dopant profiling. GaN samples have been implanted with Si in order to obtain a box-like profile and annealed above 1000°C under nitrogen with AlN protective cap layer. SCM measurements have led to reliable and quantitative dopant electrical activity measurements thank to calibration sample. Moreover, a good agreement, in terms of depth and shape, has been obtained between SCMand SIMS profiles. This work has evidenced that a high activation rate of implanted Si can be achieved using rapid thermal annealing.
Abstract: In this work we analyze the static behavior of cantilevers elaborated on the basis of
3C-SiC thin films grown by chemical vapor deposition on (100) and (111) oriented silicon
substrates. A direct microscope observation of cantilever bending indicates the opposite sign of
stress gradient (respectively negative and positive) for both film orientations. The correlation of this
observation with the commonly admitted nature of intrinsic stress for each orientation (respectively
compressive and tensile) leads us to an unexpected conclusion: instead of relaxing, the absolute
value of the intrinsic stress increases from the interface to the layer surface. We propose an
analytical model that could explain this phenomenon.
Abstract: For electronic devices, good ohmic contacts are required. To achieve such contacts, the semiconductor layer has to be highly doped. The only method available to locally dope the SiC is to implant dopants in the epilayer through a mask. In this work, non-intentionally doped 3C-SiC epilayers were implanted using nitrogen or phosphorus at different energies and subsequently annealed at temperatures between 1150 °C and 1350 C in order to form n+ implanted layers. Different techniques such as Fourier Transformed InfraRed spectroscopy (FTIR), Secondary Ion Mass Spectroscopy (SIMS) and Transmission Electron Microscopy (TEM) were used to characterize implanted 3C-SiC epilayers subsequently to the different annealing steps. Then, Ti-Ni contacts were carried out and the specific contact resistance (Ïc) was determined by using circular Transfer Length Method (c-TLM) patterns. Ïc values were investigated as a function of implanted species and contact annealing conditions, and compared to those obtained for highly doped 3C-SiC epilayers. As expected, pc value is highly sensitive to post-implantation annealing. This work demonstrates that low resistance values can be achieved using nitrogen or phosphorus implantation at room temperature hence enabling device processing.
Abstract: In this contribution we recapitulate the state of the art of silicon carbide and related materials polishing. Since the demonstration (by Vicente et al) of an ultimate preparation of Si-face ï¡-SiC wafers some important progresses were made in the field of surface preparation of silicon carbide and related materials. This concerns the industrial, high output treatments of substrates of increasing size, as well as the research studies of the feasibility of new preparation approaches for wide band gap materials. We also discuss the problems related to the polishing of the polycrystalline material and to the planarization of epilayers.
Abstract: 3C-SiC, the only polytype which can be heteroepitaxially grown on large diameter silicon substrates, is a promising material to achieve power Schottky diodes. To carry out such diodes, high quality ohmic contacts are required. In this work, ohmic contacts were investigated on in situ highly n-doped 3C-SiC epilayers grown on (100) cheap silicon substrates. Different metals such as nickel, titanium, aluminum and gold were used to carry out the contacts. Classical circular Transfert Length Method (c-TLM) structures were prepared to evaluate the specific contact resistance. Ni and Ti-Ni contacts were annealed between 950° C and 1050° C while Al and Ti-Au contacts were annealed between 300° C and 600° C. The specific contact resistance was then determined by using c-TLM patterns. For each investigated contact, the best specific contact resistance values obtained are lower than 2×10−5·cm2, even consecutively to a low temperature annealing.
Abstract: In this work, non-intentionally doped 3C-SiC epilayers were implanted using phosphorus at different energies and subsequently annealed at temperatures between 1100°C and 1350°C in order to form n+ implanted layers. Different techniques such as Fourier Transformed InfraRed spectroscopy (FTIR) and Secondary Ion Mass Spectroscopy (SIMS) were used to characterize implanted 3C-SiC epilayers after the different annealing steps. Successively, metal layers were sputtered in order to form the contacts. The specific contact resistance (ñC) was determined by using circular Transfer Length Method (c-TLM) patterns. Specific contact resistance values were investigated as a function of doping and contact annealing conditions and compared to those obtained for highly doped 3C-SiC epilayers. As expected, ñC value is highly sensitive to post-implantation annealing and metal contact annealing. This work demonstrates that low resistance values can be achieved using phosphorus implantation and, hence, enabling device processing.
