rajeev singh - Academia.edu (original) (raw)

Papers by rajeev singh

Materials Science in Semiconductor Processing, 2005

Strained silicon devices provide for an enhanced carrier mobility compared to that of unstrained ... more Strained silicon devices provide for an enhanced carrier mobility compared to that of unstrained silicon devices of identical dimensions. The device performance gets even better when using strained silicon on insulator material. We report experimental procedures based on wafer bonding, smart cutting and selective chemical etching to obtain thin strained silicon ($15 nm) on insulator wafers. The starting material is an 8 00 wafer with pseudomorphically grown strained silicon on a so-called virtual substrate as realized by epitaxial chemical vapor deposition of relaxed SiGe (grown with a grading rate of 10% Ge in the SiGe-alloy per 1 mm layer deposition) on a Si(0 0 1) substrate. The starting and bonded wafers are characterized: (i) structurally using transmission electron microscopy, (ii) topographically, using atomic force microscopy and (iii) the strain is quantified using UV-Raman spectroscopy. r

Materials Science and Engineering B-advanced Functional Solid-state Materials, 2006

Tensile strained Si (sSi) layers were epitaxially deposited onto fully relaxed Si 0.78 Ge 0.22 (S... more Tensile strained Si (sSi) layers were epitaxially deposited onto fully relaxed Si 0.78 Ge 0.22 (SiGe) epitaxial layers (4 m) on silicon substrates. Periodic arrays of 150 nm × 150 nm and 150 nm × 750 nm pillars with a height of 100 nm were fabricated into the sSi and SiGe layers by electronbeam lithography and subsequent reactive ion etching. The strain in the patterned and unpatterned samples was analyzed using high-resolution UV micro-Raman spectroscopy. The 325 nm excitation line used probes strain in Si close to the surface (penetration depth of ∼9 nm). The Raman measurements revealed that the nano-patterning yields a relaxation of strain of ∼33% in the large pillars and ∼53% in the small pillars of the ∼0.95% initial strain in the unpatterned sSi layer.

Journal of Electronic Materials, 2008

The thermoelectric properties of ErAs:InGaAlAs were characterized by variable-temperature measure... more The thermoelectric properties of ErAs:InGaAlAs were characterized by variable-temperature measurements of thermal conductivity, electrical conductivity, and Seebeck coefficient from 300 K to 600 K, which shows that the ZT(¼ a 2 rT=j, where a; r; j; and T are the Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature, respectively) of the material is greater than 1 at 600 K. Power generator modules of segmented elements of 300 lm Bi 2 Te 3 and 50 lm thickness ErAs:(InGaAs) 1-x (InAlAs) x were fabricated and characterized. The segmented element is 1 mm · 1 mm in area, and each segment can work at different temperature ranges. An output power up to 5.5 W and an open-circuit voltage over 10 V were measured. Theoretical calculations were carried out and the results indicate that the performance of the thermoelectric generator modules can be improved further by improving the thermoelectric properties of the element material, and reducing the electrical and thermal parasitic losses.

Applied Physics Letters, 2006

We report a wafer scale approach for the fabrication of thin-film power generators composed of ar... more We report a wafer scale approach for the fabrication of thin-film power generators composed of arrays of 400 p and n type ErAs: InGaAs/ InGaAlAs superlattice thermoelectric elements. The elements incorporate ErAs metallic nanoparticles into the semiconductor superlattice structure to provide charge carriers and create scattering centers for phonons. p-and n-type ErAs: InGaAs/ InGaAlAs superlattices with a total thickness of 5 m were grown on InP substrate using molecular beam epitaxy. The cross-plane Seebeck coefficients and cross-plane thermal conductivity of the superlattice were measured using test pattern devices and the 3 method, respectively. Four hundred element power generators were fabricated from these 5 m thick, 200 m ϫ 200 m in area superlattice elements. The output power was over 0.7 mW for an external resistor of 100 ⍀ with a 30 K temperature difference drop across the generator. We discuss the limitations to the generator performance and provide suggestions for improvements.

Seebeck coefficient is one of the key parameters to evaluate the performance of thermoelectric co... more Seebeck coefficient is one of the key parameters to evaluate the performance of thermoelectric coolers. However, it is very difficult to directly measure Seebeck coefficient perpendicular to thin film devices because of the difficulty of creating a temperature gradient and measuring localized temperature and voltage change simultaneously. In this paper, a novel method is described and it is used to measure the Seebeck coefficient of SiGe superlattice material perpendicular to the layers 1 . Successful measurement was achieved by integrating a thin film metal wire as a temperature sensor and heat source on top of the SiGe superlattice micro coolers. Extensive thermoreflectance imaging characterization was performed to ensure uniform temperature distribution on top of the thin film device. Details of the experimental set-up and measurement technique are discussed. By analyzing the measured thermoelectric voltage for various device sizes and superlattice thickness, Seebeck coefficient of the superlattice material perpendicular to the layers is deduced.

Journal of The Serbian Chemical Society, 2002

Page 1. J.Serb.Che.Soc. 67(7)507521(2002) UDC 546.824+546.137-32:66.061+620.168. 3 JSCS 2972 O... more Page 1. J.Serb.Che.Soc. 67(7)507521(2002) UDC 546.824+546.137-32:66.061+620.168. 3 JSCS 2972 Original scientific paper Extraction and separation of titanium(IV) with D2EHPA and PC-88A from aqueous perchloric acid solutions ...