Tadeusz T. Piotrowski

Sleepwalking episodes are preceded by arousal-related activation in the cingulate motor area: EEG current density imaging

OBJECTIVE To investigate local arousal fluctuations in adults who received ICSD-2 diagnosis of somnambulism. METHODS EEG neuroimaging (eLORETA) was utilized to compare current density distribution for 4s epochs immediately preceding sleepwalking episode (from -4.0 s to 0 s) to the distribution during earlier 4s epochs (from -8.0 s to -4.0 s) in 20 EEG segments from 15 patients. RESULTS Comparisons between eLORETA images revealed significant (t>4.52; p<0.05) brain activations before onset of sleepwalking, with greater current density within beta 3 frequency range (24-30 Hz) in Brodmann areas 33 and 24. CONCLUSIONS Sleepwalking motor events are associated with arousal-related activation of cingulate motor area. SIGNIFICANCE These results support the notion of blurred boundaries between wakefulness and NREM sleep in sleepwalking.

Design and fabrication of GaSb/InGaAsSb/AlGaAsSb mid-IR photodetectors

The paper reports on the design and fabrication of LPE-grown (formula available in paper) heterojunction photodetectors operating in the 2-2.4 micrometers wavelength region. Experiments on LPE growth of high-x- content quaternaries as well as optimization of device processing has been carried out. LPE growth at Tapproximately equals 530DEGC enabled obtaining lattice matched heterostructures with 19% indium in the active layer In (formula available in paper) and photodetectors with (lambda) co=2.25micrometers . By increasing the temperature of epitaxial growth to 590DEGC In (formula available in paper)heterostructures (with 23%indium content suitable for photodetectors with (lambda) co=2.35 micrometers have been obtained. Mesa-type photodiodes were fabricated by RIE in Ccl (formula available in paper) plasma and passivated electrochemically in (formula available in paper). These devices are characterized by differential resistance up to (formula available in paper) and the detectivity in the range (formula available in paper), in dependence on the photodiode active area cutoff wavelength.

Chemical processing of GaSb related to surface preparation and patterning

The effects of various chemical treatments on (100) GaSb surface with the aim to develop procedures of polishing of GaSb substrates, surface preparation prior to LPE growth, metal and dielectric deposition, fabrication of patterns have been examined. We show that chemomechanical polishing in Br2 - ethylene glycol followed by anodic oxidation and oxide removal enables to fabricate damage free GaSb surface with the roughness of about 1.5 nm. Surface treatment in 30 HCL-1HNO3 followed by 5%HCL etch gives the best results for surface cleaning prior to metal deposition. The optimum pre-epitaxial treatment includes the use of 1M Na2S solution and H2 anneal. For features patterning 60HCL-1H2O2-1H2O enables etching at rate of approximately 4 micrometers /min, however, to achieve highly anisotropic etching of small size features the use of Ccl4/H2 plasma is the most suitable.

Oxidation Process of SiC by RTP Technique

The kinetics of 4H-SiC thermal oxidation by RTP technique and the properties of thin thermal oxide was reported. The thickness of the thermal oxide was determined by spectroscopic ellipsometry and confirmed by electrical measurements. The conductance method was applied to analyse the surface states parameters. The lifetime, density and cross-section of the surface traps were extracted for as-fabricated MOS capacitors and after thermal annealing processes.

Fabrication of GaSb Microlenses by Photo and E-Beam Lithography and Dry Etching

Fabrication of surface-relief microstructures in GaSb for application in mid-infrared optoelectronic devices is described. Photo- and e-beam lithography was used to define patterns on GaSb surfaces. Ar/O2 sputter etching and RIE in BCl3-based plasma were applied to transfer preshaped master into the GaSb substrate. Circular microlenses with an aspect ratio (height to diameter) 0.4/10 µm and circular gratings with 0.4 µm linewidth / 1 µm period and 1.7 µm depth have been demonstrated.

Technology and properties of GaAlAsSb layers grown on GaSb substrates

LPE growth of Ga1-xAlxAsySb1-y on (100) GaSb substrates has been investigated for wide range of aluminum content in the melt, xAl1=0.01 - 0.06, various growth temperatures, and various amount of supersaturation. Epilayers were characterized by means of XRD, TEM, EPXMA, and SIMS. It has been found that LPE growth at Tapproximately equals 5300C produces good quality Ga1-xAlxAsySb1-y layers with Al content in the solid up to x equals0.24 and latice mismatch (delta) a/a not exceeding 5*10-4. As for the growth of higher aluminum content alloys at higher temperatures Tequals590 - 6000C, good results have been obtained unless the Al content in the melt does not exceed xAl1equals0.02 giving perfectly matched Ga1- xAlxAsySb1-y epilayers with Al content in the solid by up to x equals0.3. By introducing an interlayer, either of the lattice matched Ga0.91In0.09As0.08Sb0.92 or Ga0.70Al0.30As0.03Sb0.97, LPE growth from the melt with Al content up to xAl1equals0.06 becomes possible and enables fabrication of Ga1-xAlxAsySb1-y layers with Al content in the solid as high as xequals0.62. Ga1-xAlxAsySb1-y layers obtained from the melt with xAl1equals0.04 were characterized by lattice mismatch (Delta) a/aequals(8-9)-10-4, an increase of (Delta) a/a to 2.2*10-3 was observed for epilayers obtained from the melt with xAl1equals0.06.

AgTe/ZrB2/Au multilayer metallization for improved ohmic contacts to n-GaSb

We report on the silver based metallization for improved ohmic contacts to n-GaSb. Ag(Te), Ag(Te)/Cr/Au and Ag(Te)/ZrB2/Au multilayers were sputtered on (100)GaSb. Ohmic contacts were thermally formed by annealing at temperatures in range 250°C - 400°C. RBS, XRD and TEM were used to evaluate the thermal stability of the metallization and changes in the morphology. Silver recrystallization in the Ag(Te) film of the Ag(Te)/ZrB2/Au metallization was observed after heat treatments. We found that the depth of Ag penetration depends mainly on the silver film thickness and only weakly on temperature. Only the cubic silver phase of the Ag(Te, Ga, Sb) solid solution was detected in the silver film, which seems to be stable up to 400°C. The Ag(Te)/ZrB2/Au metallization exhibited an excellent thermal stability and a minimum contact resistivity of 3 x 10-5 Ωcm2 after annealing at 300°C for 3 min.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.