Papers by Author: Robert P. Devaty

Abstract: We present relative recovery data for six proteins diffusing through porous silicon carbide membranes having a hybrid columnar/dendritic morphology. These membranes are promising candidates for implantable biosensors. The results are interpreted using an effective medium model.

Abstract: Brillouin spectra have been recorded for a series of supported films of p-type porous 6H-SiC with a branched morphology and porosities in the range from 30% to 58%. Complex spectra comprising up to 7 identifiable components were observed in some cases. An effective medium model is being developed as an aid in interpreting the spectra, and preliminary results are presented.

Abstract: The effects of initial surface morphology on the early stages of porous SiC formation under highly biased photoelectrochemical etching conditions are discussed. We etched both Si-face and C-face polished n-type 6H SiC with different surface finishes prepared either by mechanical polishing or by chemical mechanical polishing at NOVASiC. For both Si-face and C-face porous SiC samples, a variety of surface and cross sectional porous morphologies, due to different surface finishes, are observed. The proposed explanation is based on the spatial distribution of holes at the interface of the SiC and electrolyte inside the semiconductor.

Abstract: A hybrid columnar and dendritic porous structure has been developed in n-type 6H SiC using photoelectrochemical etching with proper control of the applied voltage and current density. The diameter of the formed columnar pores is around 200-500 nm. A possible formation mechanism due to the spatial distribution of holes and the HF concentration gradient in the pores is proposed. A self-supporting film with this morphology is a promising candidate for protein dialysis.

Abstract: The morphology and atomic structure of 4H-SiC(1102) and 4H-SiC(1102) surfaces, i.e. the surfaces found in the triangular channels of porous 4H-SiC, have been investigated using AFM, LEED and AES. After hydrogen etching the surfaces show steps parallel and perpendicular to the caxis, yet drastically different morphologies for the two isomorphic orientations. Both surfaces immediately display a sharp LEED pattern. Together with the presence of oxygen in the AES spectra this indicates the development of an ordered oxide. Both surfaces show an oxygen free, well ordered surface after Si deposition and annealing.

Abstract: Ab initio supercell calculations have been carried out to investigate the doping of phosphorus in chemical vapor deposited (CVD) SiC layers. CVD conditions have been simulated by using the appropriate chemical potentials for hydrogen and phosphorus (P). We found that the most abundant defect is P at Si-site followed by P at C-site. The calculated concentrations of the P-donors and free carriers in CVD grown SiC agree with the experimental results.

Abstract: New lines are observed in the photoluminescence of 6H and 4H SiC epitaxial layers grown in cold wall CVD reactors and doped with phosphorus. These lines are associated with neutral phosphorus donor four particle bound exciton complexes with the phosphorus substituting on both the carbon and silicon sublattices. Assignments are made for the (h) hexagonal and (k) cubic sites of the phosphorus donor substituting on the two SiC sublattices.

Abstract: Hot-wall chemical vapor deposition has been used to epitaxially grow SiC layers on porous n-type 4H-SiC substrates. The growth was carried out at different speeds on porous layers of two different thicknesses. The quality of the SiC films was evaluated by X-ray diffraction and photoluminescence techniques. Based on the measurements, both the growth speed and the thickness of the porous layer buried underneath the epilayers do not appear to influence the structural integrity of the films. The intensity of the near bandedge low temperature photoluminescence appears stronger by a factor of two in films grown on porous layers.

Abstract: A set of four lightly p-type 6H SiC boule samples was implanted with H or He and annealed in isochronal stages from 950°C to 1500°C. Differences in the hydrogen, DI and DII low temperature photoluminescence spectra are observed and compared. Surprisingly, the hydrogen spectrum appears after a 1300°C anneal in the He implanted samples. A number of unidentified damage lines are also reported.

Abstract: A brief historical development of porous SiC and GaN is given. SEM images of nine porous morphologies in 4H, 6H and 3C SiC are shown along with anodization details. Similarly, two porous GaN morphologies are presented. Applications and future prospects are discussed.