Engineering topics

Bhat, Ishwara B.

Publications and source records attributed to Bhat, Ishwara B..

4 records

DOE OSTI2018

Growth of epitaxial CdTe thin films on amorphous substrates using single crystal graphene buffer

Traditionally, a high-quality CdTe film can only be grown on a single crystal substrate with a small lattice mismatch. We report the epitaxy of CdTe films on monolayer single crystal graphene buffered amorphous SiO 2 /Si(100) substrates, despite a 86% lattice mismatch between CdTe(111) and graphene. X-ray pole figure, electron backscatter diffraction mapping and transmission electron microscopy all confirm that the epitaxial CdTe films are composed of two domains: the primary and the Σ3 twin. The crystal quality of films is shown to improve as the post-deposition annealing temperature increases. However, the rotational misalignment in CdTe remains large even after annealing. Through density functional theory calculations on the charge transfer distribution at the interface of CdTe and graphene, it is found that the interface is dominated by the weak van der Waals interaction, which explains the large spread of in-plane orientation in CdTe films. Furthermore, the rotational misalignment in graphene itself is also confirmed to produce the large in-plane orientation spread in CdTe films. Although imperfect in epitaxy quality, this work demonstrates that monolayer single crystal graphene can buffer amorphous substrates for growing epitaxial films, and hence hints an opportunity for developing advanced thin film devices using graphene as a template.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Selective, electrochemical etching of a semiconductor

Methods for facilitating fabricating semiconductor structures are provided which include: providing a multilayer structure including a semiconductor layer, the semiconductor layer including a dopant and having an increased conductivity; selectively increasing, using electrochemical processing, porosity of the semiconductor layer, at least in part, the selectively increasing porosity utilizing the increased conductivity of the semiconductor layer; and removing, at least in part, the semiconductor layer with the selectively increased porosity from the multilayer structure. By way of example, the selectively increasing porosity may include selectively, anodically oxidizing, at least in part, the semiconductor layer of the multilayer structure.

42 ENGINEERING↗

DOE OSTI2017

Capacitance reduction for pillar structured devices

In one embodiment, an apparatus includes: a first layer including a n+ dopant or p+ dopant; an intrinsic layer formed above the first layer, the intrinsic layer including a planar portion and pillars extending above the planar portion, cavity regions being defined between the pillars; and a second layer deposited on a periphery of the pillars thereby forming coated pillars, the second layer being substantially absent on the planar portion of the intrinsic layer between the coated pillars. The second layer includes an n+ dopant when the first layer includes a p+ dopant. The second layer includes a p+ dopant when the first layer includes an n+ dopant. The apparatus includes a neutron sensitive material deposited between the coated pillars and above the planar portion of the intrinsic layer. In additional embodiments, an upper portion of each of the pillars includes a same type of dopant as the second layer.

36 MATERIALS SCIENCE↗

NASA NTRS2006

Bias Selective Operation of Sb-Based Two-Color Photodetectors

Multicolor detectors have a strong potential to replace conventional single-color detectors in application dealing with the simultaneous detection of more than one wavelength. This will lead to the reduction of heavy and complex optical components now required for spectral discrimination for multi-wavelengths applications. This multicolor technology is simpler, lighter, compact and cheaper with respect to the single-color ones. In this paper, Sb-based two-color detectors fabrication and characterization are presented. The color separation is achieved by fabricating dual band pn junction on a GaSb substrate. The first band consists of an InGaAsSb pn junction for long wavelength detection, while the second band consists of a GaSb pn junction for shorter wavelength detection. Three metal contacts were deposited to access the individual junctions. Surface morphology of multi-layer thin films and also device characteristics of quasi-dual band photodetector were characterized using standard optical microscope and electro-optic techniques respectively. Dark current measurements illustrated the diode behavior of both lattice-matched detector bands. Spectral response measurements indicated either independent operation of both detectors simultaneously, or selective operation of one detector, by the polarity of the bias voltage, while serially accessing both devices.

Abedin, M. N.↗