Papers by Keyword: Photodetector (PD)

Abstract: This paper reports on fabrication and modeling of 4H- and 6H-SiC metal-semiconductor-metal (MSM) photodetectors (PDs). MSM PDs have been fabricated on 4H-SiC and 6H-SiC epitaxial layers, and their performance analyzed by MEDICI simulation and measurements. The simulations were also used to optimize the sensitivity by varying the width and spacing of the interdigitated electrodes. The fabricated PDs with 2 µm wide metal electrodes and 3 µm spacing between the electrodes exhibited, under UV illumination, a peak current to dark current ratio of 105 and 104 in 4H-SiC and 6H-SiC, respectively. The measured spectral responsivity of 6H-SiC PDs was higher compared to that of 4H-SiC PDs, with a cutoff at 407 nm compared to 384 nm in 4H-SiC PDs. Also the peak responsivity occurred at a shorter wavelength in 6H material. A high rejection ratio between the photocurrent and dark current was found in both cases. These experimental results were in agreement with simulation.

Abstract: An InGaN/GaN-based photodetector with nano-structure on the surface is present. Surface nano-structure was formed by nanoimprint lithography (NIL) and reactive ion etching (RIE) techniques. The NIL technique and nano-structure etching by employing RIE were demonstrated in details. The nano-pattern was designed as regular triangles consisting of columns, whose diameter and period were around 105 and 210 nm, respectively. The height of nano-columns was around 66 nm. The photo-voltage of this type of photodetector had very good wave characteristics with 60° period, and it presented different waveform at different angles and wavelengths of incident light. The periodic characteristics took not only on minimum voltage but also peak voltage. We demonstrated this characteristic by employing Bragg formulation.

Abstract: The optical absorptions are calculated in an InAs/GaSb-based type II and broken-gap quantum well under applied electric field. Two absorption peaks were observed through intraband transitions within the same material layer. The absorption induced by the interlayer transition is rather weak due to the small overlap of electron and hole wavefunctions. The optical absorption can be significantly affected by the applied electric field. Our results suggest that InAs/GaSb-based type II and broken-gap QWs can be employed as two-colour photodetectors, which can be controlled by the applied electric field.

Abstract: This work describes properties of 1-D ZnO nanorods arrays growth using low temperature hydrothermal method on a seeded substrate. The properties of ZnO seed were studied by varying thermal oxidation temperature from 250-450°C. The formation of ZnO nanorods was studied by varying the growth time during hydrothermal process. The optimum oxidation temperature to produce seeded ZnO template was 400°C. The formation of ZnO nanorods was further studied by varying hydrothermal reaction growth time from 1 to 24 hours. The optimum hydrothermal growth time of 4 hours produced blunt tip-like nanorods with length of ~735 nm and top diameter of ~66 nm. I-V characteristics of ZnO nanorods photodetector in dark, ambient light and UV light were also studied. The change in the photoconductivity under UV illumination was found to be 1 order of magnitude higher compared to dark and ambient light. With an incident wavelength of 370 nm and applied bias of 3V, the responsivity of photodetector was 5.0 mA/W, which was higher compared to other reported works. The increase of photosensitivity indicated that the produced ZnO nanorods were suitable for UV photodetector applications.

Abstract: We have presented a technique, based on magnetron sputtering of silicon target in the mixture of argon, silane, and oxygen. Addition of oxygen gas was shown to cause formation of silicon suboxide layers with amorphous silicon nanoclusters without subsequent annealing. The layers exhibit significant photoluminescence at room temperature. Their photoluminescence spectra reveal special features predicted in the preceding well-known theoretical works. Heterostructures, fabricated with such layers, show high photocurrent efficiency in short-wavelength spectral region. Our results demonstrate that the investigated structures are promising for photoelectric and photovoltaic applications.

Abstract: A review is given of what kind technological aspects were used for realizing the defect engineering in semiconductor layers or crystals. The possibilities to change the free carrier capture are presented. The effect of Fermi level pinning at the surface levels allow to avoid the influence of barriers on the photoconductivity as well as to increase a role of recombination in the inter-crystalline region. The isovalent doping or the creation of the clusters allows transforming the defect distribution in the crystal bulk. The detector structure using the high electric field can introduce the recombination in at the contacts therefore allow diminishing a role of carrier capture in the bulk of structure. The cluster generation allows to increase the capture rate in the definite volume by a proton irradiation. The experience of different technologies for Si, GaAs, PbS, CdSe are presented.

Abstract: The thermal expansion of a novel semiconductor material, mercury indium telluride (MIT) grown by vertical Bridgman (VB) method, was measured from room temperature till 573K by two methods, i.e. Macroscopic dilatometric and X-ray measurements. It is found that the macroscopic expansion is quite different from the expansion of the lattice (micro-expansion). The macroscopic expansion is lower than micro-expansion in the temperature range of 303-425.5K and has a minimum of -0.14% linear expansion, while the macro-expansion becomes larger than micro-expansion in the temperature higher than 425.5K. The former may be due to the effects of the existing neutral vacancies. The latter may result from the influence of thermal-activated vacancies on the lattice.

Abstract: In this paper, a promising class of optical filters is introduced, based on Al2O3/PS/Si structure. The filters consist of thin layer of aluminium electrochemically oxidized in different aqueous solution, on porous silicon. The spectral sensitivity can be easily varied by Al2O3 thickness. This result is a consequence of refractive index variation of Al2O3 and PS layers, confirmed by ellipsometry measurements.

Abstract: Metal-semiconductor-metal (MSM) planar photodiodes and photoconductors were fabricated on unintentionally doped homoepitaxial diamond thin films deposited on Ib and IIa-type diamond substrated. The MSM photoconductor on the epilayer grown on the Ib-type substrate exhibits the highest discrimination ratio up to 108 between 210 nm and visible light and a photocurrent gain around 33 at 220 nm. The persistent photoconductivity is rather week for such kind of photoconductor.

Abstract: In this research, nanoscale spatial resolution p-n junction photodetector arrays were developed using ZnO nanorod arrays grown on p-type silicon substrates. In order to optimize the nanorod array quality, an advanced combinatorial spreadsheet approach was used to optimize the Au catalyst thickness. The crystallinity of these as-grown ZnO nanorods’ was compared to that of bulk and thin film ZnO materials.