Effect of low thermal budget annealing on surface passivation of silicon by ALD based aluminum oxide films.

Thermal ALD deposited Al2O3 films on silicon show a marked difference in surface passivation quality as a function of annealing time (using a rapid thermal process). An effective and quality passivation is realized in short anneal duration (∼100 s) in nitrogen ambient which is reflected in the low surface recombination velocity (SRV <10 cm s(-1)). The deduced values are close to the best reported SRV obtained by the high thermal budget process (with annealing time between 10-30 min), conventionally used for improved surface passivation. Both as-deposited and low thermal budget annealed films show the presence of positive fixed charges and this is never been reported in the literature before. The role of field and chemical passivation is investigated in terms of fixed charge and interface defect densities. Further, the importance of the annealing step sequence in the MIS structure fabrication protocol is also investigated from the view point of its effect on the nature of fixed charges.

High pressure growth of nanocrystalline silicon films.

Nanocrystalline silicon thin films were grown using gaseous mixture of 5% silane (SiH4) diluted in hydrogen (H2) and argon (Ar) in a radio frequency (13.56 MHz) plasma enhanced chemical vapor deposition technique. These films were deposited as a function of pressure and were characterized using AFM, Laser Raman, UV-VIS transmission, photoluminescence and electrical conductivity techniques. AFM micrographs shows that these films contain nanocrystallites of 30-60 nm size. Laser Raman peaks at 520 cm(-1) and photoluminescence peaks at 2.75 and 2.85 eV have been observed. The crystalline fraction in these films was varied from 30% to 80% with the variation of deposition pressure from 2 Torr to 8 Torr. There is an optimum pressure of 4 Torr where the maximum growth of nanocrystalline phases was observed. It has been found that nanocrystallites in these film enhanced the optical band gap and electrical conductivity. Also a voltage-current (V-I) probe was used to evaluate the various electrical parameters of the plasma used to deposit the nc-Si:H films for the present investigation. Growth via a SiH3 precursor, diffusion of hydrogen in the sub-surface and argon etching of weak bonds are some of the processes that may be involved in the nano crystallization process.

Morphological observation of Y and T junctions in nanostructured boron nitride thin films.

Formations of Y and T nano junctions have been observed in boron nitride films deposited on silicon substrates by plasma chemical reaction of diborane (B2H6 diluted in hydrogen) and ammonia (NH3) gases using dual frequency (microwave/radio) plasma enhanced chemical vapor deposition technique without any intentional heating of the substrates. It has been observed that these nano junctions form at a critical feed gas ratio of ammonia and diborane. We have investigated the effect of gas feed ratio R (=NH3/B2H6) in the plasma reaction chamber, keeping all other deposition parameters constant, on the morphology of boron nitride films. The deposited films are characterized by SEM, AFM, TEM and Laser Raman. For gas feed ratio, R < 100, octahedron and cubic morphologies have been observed in BN films and on increasing R to >100, size of the crystallites reduces to nanometer level. In some of our BN samples deposited at a critical value of gas ratio (R = 400), uniform Y and T junctions having bamboo like morphologies, in nanometer level, have been observed, which we wish to emphasis here as an interesting and newer observation in boron nitride films deposited by the dual frequency PECVD technique. This change in morphology exhibited by varying gas feed ratio is mainly due to excess nitrogen ions in the plasma.