Molybdenum (Mo)/4H-silicon carbide (SiC) Schottky barrier diodes have been fabricated with a phosphorus pentoxide (P 2 O 5 ) surface passivation treatment performed on the SiC surface prior to metallization. Compared to the untreated diodes, the P 2 O 5 -treated diodes were found to have a lower Schottky barrier height by 0.11 eV and a lower leakage current by two to three orders of magnitude. Physical characterization of the P 2 O 5 -treated Mo/SiC interfaces revealed that there are two primary causes for the improvement in electrical performance. First, transmission electron microscopy imaging showed that nanopits filled with silicon dioxide had formed at the surface after the P 2 O 5 treatment that terminates potential leakage paths. Second, secondary ion mass spectroscopy revealed a high concentration of phosphorus atoms near the interface. While only a fraction of these are active, a small increase in doping at the interface is responsible for the reduction in barrier height. Comparisons were made between the P 2 O 5 pretreatment and oxygen (O 2 ) and nitrous oxide (N 2 O) pretreatments that do not form the same nanopits and do not reduce leakage current. X-ray photoelectron spectroscopy shows that SiC beneath the deposited P 2 O 5 oxide retains a Si-rich interface unlike the N 2 O and O 2 treatments that consume SiC and trap carbon at the interface. Finally, after annealing, the Mo/SiC interface forms almost no silicide, leaving the enhancement to the subsurface in place, explaining why the P 2 O 5 treatment has had no effect on nickel-or titanium-SiC contacts.

We have studied the mechanisms underpinning effective surface passivation of silicon with hafnium oxide (HfO 2 ) thin films grown via atomic layer deposition (ALD). Plasma-enhanced ALD with O 2 plasma and a tetrakis(dimethylamido)hafnium precursor was used to deposit 12 nm thick HfO 2 films at 200 °C on high-lifetime 5 Ωcm n-type Czochralski silicon wafers. The passivation was activated by postdeposition annealing, with 30 min in air at 475 °C found to be the most effective. High-resolution grazing incidence X-ray diffraction measurements revealed the film crystallized between 325 and 375 °C, and this coincided with the onset of good passivation. Once crystallized, the level of passivation continued to increase with higher annealing temperatures, exhibiting a peak at 475 °C and yielding surface recombination velocities of <5 cm s −1 at 5 × 10 14 cm −3 injection. A steady decrease in effective lifetime was then observed for activation temperatures >475 °C. By superacid repassivation, we demonstrated this reduction in lifetime was not because of a decrease in the bulk lifetime, but rather because of changes in the passivating films themselves. Kelvin probe measurements showed the films are negatively charged. Corona charging experiments showed the charge magnitude is of order 10 12 qcm −2 and that the reduced passivation above 475 °C was mainly because of a loss of chemical passivation. Our study, therefore, demonstrates the development of highly charged HfO 2 films and quantifies their benefits as a standalone passivating film for silicon-based solar cells.

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