Suseendran Jayachandran | IMEC - Academia.edu (original) (raw)

Papers by Suseendran Jayachandran

ECS Journal of Solid State Science and Technology, 2016

We perform a systematic study on the growth of epitaxial Silicon–Oxygen superlattices (SLs) and i... more We perform a systematic study on the growth of epitaxial Silicon–Oxygen superlattices (SLs) and investigate the impact ofstructural properties on the electrical performance. Si layers and O atomic layers (ALs) are deposited using SiH4 and O3 reactions respectively. Although the deposition of O ALs and epitaxial Si thereon, i.e. 1st period of Si–O SL is well documented, the controlled deposition in maintaining the overall crystalline quality of SL is stilla challenge. This is due to inability to limit the O layer to sub-AL content (1AL = 6.7 × 1014 at/cm2) at higher periods (≥2). The Si surface prior to O AL deposition is chemically modified with H-passivation and sub-AL O-contentis achieved. This ensures minimum structural distortions, enabling epitaxial ordering of Si and hence the epitaxial Si–O SLup to 5-periods. No SiOx clusters are detected and O layers are stable at Si deposition temperature. Electrically, donor defects increase with Si–Operiods and partially reduced with forming gas anneal. The presence of defects and increased roughness during the growth,degrade the mobility due to coulomb and surface scattering respectively. It can be circumvented by optimizing SL parametersand other process integration parameters subjected for future research.status: publishe

and many others for a fun filled social life at Leuven. Gokul, Hari, Marissa and Ravi are few of ... more and many others for a fun filled social life at Leuven. Gokul, Hari, Marissa and Ravi are few of my close friends, where we all live together like a family. Thanks guys. Last but not least, I would like to thank my parents and my brother for bearing my absence for the past 6 years. I am being the first person in our family to hold a PhD degree, which comes at the expense of their numerous sacrifices. A poor and cute girl, my wife (Saranya) kept cooking mouth watering dishes whenever I am back home. She always wishes me to stay next to her at all times, but it was hard during the last phase of my PhD. I would like to thank her for tolerating me. I love you all and thanks for everything.

Bulletin of the American Physical Society, Mar 5, 2015

4 at 500C. We discuss the structural and electronic properties calculated with density functional... more 4 at 500C. We discuss the structural and electronic properties calculated with density functional theory and give an overview of the most promising Si superlattices in terms of anticipated mobility enhancement. We report on the electrical device characteristics of 2D nanolattice Schottky diodes, MOS capacitors and MOSFETs. We discuss the impact of defectivity on electrical characteristics and the impact of the 2D nanolattices on MOSFET carrier mobility.

Physica Status Solidi B-basic Solid State Physics, Oct 7, 2016

The presence of deep levels in a silicon-oxygen (Si-O) superlattice (SL) deposited on p-type sili... more The presence of deep levels in a silicon-oxygen (Si-O) superlattice (SL) deposited on p-type silicon substrates has been investigated by deep-level transient spectroscopy (DLTS) on thermally evaporated Cr Schottky barriers (SBs). The SLs have been fabricated with different thicknesses of the silicon interlayers, formed by chemical vapor deposition. It is shown that a broad band of hole traps is present near the surface of the SB, which is associated with the SL. In addition, the activation energy corresponding with the peak maximum shifts to higher values with respect to the valence band and gives rise to a higher trap concentration with increasing silicon interlayer thickness. It is proposed that these states are associated with the structural defects found in similar SL structures, that is, with the epitaxial quality and not with the Si-O bonds in the atomic layers. The change in the DLT-spectra with silicon thickness could be related with the transformation of the structural defects from small selfinterstitial clusters to stacking faults.

Applied Surface Science, Oct 1, 2016

Abstract The epitaxial growth of Si layers on Si substrates in the presence of O atoms is general... more Abstract The epitaxial growth of Si layers on Si substrates in the presence of O atoms is generally considered a challenge, as O atoms degrade the epitaxial quality by generating defects. Here, we investigate the growth mechanisms for Si epitaxy on O atomic layers (ALs) with different O-contents and structures. O ALs are deposited by ozone (O3) or oxygen (O2) exposure on H-terminated Si at 50 °C and 300 °C respectively. Epitaxial Si is deposited by chemical vapor deposition using silane (SiH4) at 500 °C. After O3 exposure, the O atoms are uniformly distributed in Si-Si dimer/back bonds. This O layer still allows epitaxial seeding of Si. The epitaxial quality is enhanced by lowering the surface distortions due to O atoms and by decreasing the arrival rate of SiH4 reactants, allowing more time for surface diffusion. After O2 exposure, the O atoms are present in the form of SiOx clusters. Regions of hydrogen-terminated Si remain present between the SiOx clusters. The epitaxial seeding of Si in these structures is realized on H-Si regions, and an epitaxial layer grows by a lateral overgrowth mechanism. A breakdown in the epitaxial ordering occurs at a critical Si thickness, presumably by accumulation of surface roughness.

Photonic Integrated Circuits (PICs) in the visible wavelength range have been extensively used fo... more Photonic Integrated Circuits (PICs) in the visible wavelength range have been extensively used for life science applications. Silicon Nitride has been the most widely used material, as it allows to fabricate low loss waveguides with the refractive index ranging from 1.9 to 2.1. For downscaling of PICs, many investigations into Titanium Oxide (TiO2) have been studied. The refractive index of TiO2 ranges from 2.3 to 2.6. Despite a high refractive index, TiO2 tends to crystallize at temperatures above 300oC, limiting its potential for CMOS compatible fabrication. In addition, the presence of oxygen vacancies in TiO2 results into photon absorption in the visible range, leading to high propagation losses. We investigate Niobium Oxide (Nb2O5) as an alternative waveguide material, focusing on material and optical properties for light propagation in the visible wavelength range. Physical vapor deposition of the Nb target in Oxygen atmosphere results in stoichiometric Nb2O5. On a 200mm wafer, a 90nm Nb2O5 is deposited on 2.3µm bottom clad (SiO2). The extracted refractive index is above 2.3, while the extinction coefficient is 0 for visible wavelengths. From X-ray diffraction, the as-deposited layers were amorphous, while the surface roughness was below 0.3 nm. Waveguides were patterned using 193 nm lithography and etched using chlorine based chemistry. In the visible range, optical losses for un-cladded waveguides were below 5 dB/cm, comparable to our in-house SiN platform. There were no significant changes in optical losses after 400oC anneal, signifying its potential for improved propagation after top-cladding deposition.

Applied Surface Science, 2015

Epitaxial Si-O superlattices consist of alternating periods of crystalline Si layers and atomic l... more Epitaxial Si-O superlattices consist of alternating periods of crystalline Si layers and atomic layers of oxygen (O) with interesting electronic and optical properties. To understand the fundamentals of Si epitaxy on O atomic layers, we investigate the O surface species that can allow epitaxial Si chemical vapor deposition using silane. The surface reaction of ozone on H-terminated Si(100) is used for the O deposition. The oxygen content is controlled precisely at and near the atomic layer level and has a critical impact on the subsequent Si deposition. There exists only a small window of O-contents, i.e. 0.7-0.9 atomic layers, for which the epitaxial deposition of Si can be realized. At these low O-contents, the O atoms are incorporated in the Si-Si dimers or back bonds (-OSiH), with the surface Si atoms mainly in the 1+ oxidation state, as indicated by infrared spectroscopy. This surface enables epitaxial seeding of Si. For O-contents higher than one atomic layer, the additional O atoms are incorporated in the Si-Si back bonds as well as in the Si-H bonds, where hydroxyl groups (-Si-OH) are created. In this case, the Si deposition thereon becomes completely amorphous.

Electrically active defects in silicon-based epitaxial layers on silicon substrates have been stu... more Electrically active defects in silicon-based epitaxial layers on silicon substrates have been studied by Deep-Level Transient Spectroscopy (DLTS). Several aspects have been investigated, like, the impact of the pre-epi cleaning conditions and the effect of a post-deposition anneal on the deep-level properties. It is shown that the pre-cleaning thermal budget has a strong influence on the defects at the substrate/epi layer interface. At the same time, a post-deposition Forming Gas Anneal can passivate to a large extent the active defect states. Finally, it is shown that application of a post-deposition anneal increases the out-diffusion of carbon from a Si:C stressor layer into the p-type CZ substrate.

ECS Solid State Letters, Sep 5, 2013

Endothelin-1 (ET-1) is an endogenously expressed potent peptide vasoconstrictor. There is growing... more Endothelin-1 (ET-1) is an endogenously expressed potent peptide vasoconstrictor. There is growing evidence that ET-1 plays a role in the pain signaling system and triggers overt nociception in humans. The underlying neuronal pathways are still a matter of great debate. In the present study, we applied an intradermal ET-1 sensitization model to induce mechanical hyperalgesia in healthy subjects. Functional magnetic resonance imaging (fMRI) was used to tease out the cortical regions associated with the processing of ET-1-induced punctate hyperalgesia, as compared to a nonnoxious mechanical stimulation of the contralateral arm. Von Frey hair testing revealed the presence of increased responsiveness to punctate stimulation in all subjects. Activational patterns between nonpainful control stimulation and hyperalgesic stimulation were compared. Two major observations were made: (1) all cortical areas that showed activation during the control stimulation were also present during hyperalgesic stimulation, but in addition, some areas showed bilateral activation only during hyperalgesic stimulation, and (2) some brain areas showed significantly higher signal changes during hyperalgesic stimulation. Our findings suggest that injection of ET-1 leads to a state of punctate hyperalgesia, which in turn causes the activation of multiple brain regions. This indicates that ET-1 activates an extended neuronal pathway.

Physica status solidi, May 13, 2016

In this paper, the deep levels found by Deep-Level Transient Spectroscopy in Si-O superlattices o... more In this paper, the deep levels found by Deep-Level Transient Spectroscopy in Si-O superlattices on p-type silicon substrates are compared with the band of near mid-gap hole traps typically observed at the Si/SiO2 interface. In addition, the impact of a post-deposition Forming Gas Annealing is investigated. A large similarity between the two material systems is reported, which indicates that similar silicon-oxygen bonds may be responsible for the deep hole traps. TEM cross section of a two layer Si-O superlattice on a ptype silicon substrate.

Semiconductor Science and Technology, Dec 21, 2015

This work reports on the deep levels observed in Pt/Al2O3/p-type Si metal-oxide-semiconductor cap... more This work reports on the deep levels observed in Pt/Al2O3/p-type Si metal-oxide-semiconductor capacitors containing a silicon-oxygen superlattice (SL) by deep-level transient spectroscopy. It is shown that the presence of the SL gives rise to a broad band of hole traps occurring around the silicon mid gap, which is absent in reference samples with a silicon epitaxial layer. In addition, the density of states of the deep layers roughly scales with the number of SL periods for the as- deposited samples. Annealing in a forming gas atmosphere reduces the maximum concentration significantly, while the peak energy position shifts from close-to mid-gap towards the valence band edge. Based on the flat-band voltage shift of the Capacitance-Voltage characteristics it is inferred that positive charge is introduced by the oxygen atomic layers in the SL, indicating the donor nature of the underlying hole traps. In some cases, a minor peak associated with P-b dangling bond centers at the Si/SiO2 interface has been observed as well.

8th International Conference on Silicon Epitaxy and Heterostructures - ICSI-8, 2013

2016 China Semiconductor Technology International Conference (CSTIC), 2016