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Generic Technical Issues Associated with Materials for High-Temperatures...
Pages 39-50

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From page 39...
... ELECTRICAL CONTACTS The requirements for high-quality contacts for hightemperature electronic devices are similar to their lowtemperature counterparts, but these contacts may be more prone to degradation at their elevated temperatures of operation. Therefore, studies on the mechanisms of intermetallic and metal semiconductor reactions, interdiffusion reactions, and electrical changes as a function of time will be critical to projecting device stability and reliability.
From page 40...
... (1994) speculates on the nature of the low-resistance contacts to GaN Two possible mechanisms for low-resistance 40 contacts are discussed: low-barrier Schottky contacts coupled with intermediate or graded bandgap interfaces and tunneling.
From page 41...
... On the upper end, the observed hole concentration became nonlinear as a function of TEA flow above 10~9 cm~3 In general, [background nitrogen causes unintentionally doped crystals to be e-type. In the best 6H-SiC samples ( < colt cm~~ nitrogens, background carrier concentrations , _, ~1A ~.
From page 42...
... (1993) , at GE, have demonstrated improved diode characteristics using boron-implanted 6H-SiC at high temperature with a post-annealing.
From page 43...
... As for silicon, oxidation rates and oxide quality will vary according to the SiC polytype, the crystal orientation, defect density, doping level, and the nature of the oxidation conditions (i.e., whether carried out under wet or dry ambient conditions)
From page 44...
... Other work has found that sweeping from accumulation to inversion in real time required heating the substrate to 860 °C (Morkoc et al., 1994~. The extensive characterization of oxide samples revealed interface trap states between mid-10 cm~~ evil and 10~2 cm~~ eve, with lower trap densities for dry compared with wet oxidation, but comparable emission time constants (a ps)
From page 45...
... Furthermore, although the initial applications of dry etching to the wide bandgap materials have met with success, much more work remains in order to delineate the basic mechanisms, the rate-limiting steps, the quality of the etch surface, the possibility of etch-induced damage, etc. Etching of SiC Successful reactive-ion etching (RIE)
From page 46...
... Temperature-dependent etch-rate studies would help to more clearly reveal the rate-limiting steps in current dryetching approaches and would also give a better idea of the ultimate etch rates and profiles achievable. In a manner similar to forming selective GaAs to AlGaAs etch processes, the addition of excess fluorine to a gas composition will provide high selectivity of etching GaN with respect to A1N (Pearson et al., 19931.
From page 47...
... The reliability of heterojunction devices such as SISFETS will similarly depend on the nature of the interface; interface roughness and interface state densities will affect device mobilities and increase device noise, as well as long-term performance. YIELD 47 High yield in device and circuit manufacturing requires high-quality substrates and wide process margins.
From page 48...
... In summary, process yield is dependent on the critical defect density and the chip area. The next phase of research and development on high-temperature semiconductors must identify the critical defects and improve materials and processes to reduce their density to economically tolerable levels.
From page 49...
... re-evaluation of known failure mechanisms in a hightemperature applications context and (2) identification and remediation of new failure modes in these new materials systems and environments.


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