Z. Gumienny

Fingerprint Structure Imaging Based on an Ultrasound Camera

Abstract This paper describes the design of an ultrasound camera which has a resolution of 0.1mm. The camera allows the observation of the near surface structures of solid objects and is suitable for the finger ridge pattern imaging (i.e., pattern which is reflected in a fingerprint). The device can be used for a biometric identification of individuals (for access verification). It can also be employed for all other sorts of structures which have ultrasound detectable changes in the near surface structure, both natural and artificial (e.g., created for information recording). The paper describes the current version of the camera and the physical phenomena behind its operation. Presented are also perspectives of further development of the device.

Ultrasonic Setup for Fingerprint Patterns Detection and Evaluation

The scope of potential use of identification systems widens, including restricted area or confidential data access, credit card use etc. Only in 1993 banks lost more than three billions dollars due to credit cards forgery and misuse 1.

Si/ZnO nanorods/Ag/AZO structures as promising photovoltaic plasmonic cells

The test structures for photovoltaic (PV) applications based on zinc oxide nanorods (NRs) that were grown using a low-temperature hydrothermal method on p-type silicon substrates (100) covered with Ag nanoparticles (NPs) were studied. The NPs of three different diameters, i.e., 5–10 nm, 20-30 nm, and 50–60 nm, were deposited using a sputtering method. The morphology and crystallinity of the structures were confirmed by scanning electron microscopy and Raman spectroscopy. It was found that the nanorods have a hexagonal wurtzite structure. An analysis of the Raman and photoluminescence spectra permitted the identification of the surface modes at 476 cm−1 and 561 cm−1. The presence of these modes is evidence of nanorods oriented along the wurtzite c-axis. The NRs with Ag NPs were covered with a ZnO:Al (AZO) layer that was grown using the low-temperature atomic layer deposition technique. The AZO layer served as a transparent ohmic contact to the ZnO nanorods. The applicability of the AZO layer for this purpo...

Deep traps and photo-electric properties of p-Si/MgO/n-Zn1−xMgxO heterojunction

In the paper, the photoluminescence (PL) measurements, current–voltage–temperature (I-V-T) measurements, space charge techniques (C-V and deep level transient spectroscopy (DLTS)), and photocurrent spectral characteristics have been applied to investigate defects in p-Si/MgO/ n-Zn1−xMgxO heterojunction (HJ). The HJ structure was grown on p-type Si (111) substrate with resistivity equal to 0.1 Ω cm by the plasma-assisted molecular beam epitaxy technique. A radio-frequency cell was used for the generation of oxygen plasma. PL spectrum let us determine the Mg content ∼10%. Besides the excitonic Zn0.9Mg0.1O line, the PL spectrum also contains green and yellow emission bands indicating the presence of defect states in the investigated structures. I-V measurements reveal the rectifying properties of the HJ and the current thermally activated with a trap with the activation energy equal to 0.42 eV. DLTS studies yield the majority trap of the activation energy 0.42 eV, confirming the result obtained from the I-V ...

Deep traps in n-type GaN epilayers grown by plasma assisted molecular beam epitaxy

In this study, we present the results of investigations on Schottky Au-GaN diodes by means of conventional DLTS and Laplace DLTS methods within the temperature range of 77 K–350 K. Undoped GaN layers were grown using the plasma-assisted molecular beam epitaxy technique on commercial GaN/sapphire templates. The quality of the epilayers was studied by micro-Raman spectroscopy (μ-RS) which proved the hexagonal phase and good crystallinity of GaN epilayers as well as a slight strain. The photoluminescence spectrum confirmed a high crystal quality by intense excitonic emission but it also exhibited a blue emission band of low intensity. DLTS signal spectra revealed the presence of four majority traps: two high-temperature and two low-temperature peaks. Using the Laplace DLTS method and Arrhenius plots, the apparent activation energy and capture cross sections were obtained. For two high-temperature majority traps, they were equal to E1 = 0.65 eV, σ1 = 8.2 × 10−16 cm2 and E2 = 0.58 eV, σ2 = 2.6 × 10−15 cm2 wher...

Laser irradiation effects on the CdTe/ZnTe quantum dot structure studied by Raman and AFM spectroscopy

Micro-Raman spectroscopy has been applied to investigate the impact of laser irradiation on semiconducting CdTe/ZnTe quantum dots (QDs) structures. A reference sample (without dots) was also studied for comparison. Both samples were grown by molecular beam epitaxy technique on the p-type GaAs substrate. The Raman spectra have been recorded for different time of a laser exposure and for various laser powers. The spectra for both samples exhibit peak related to the localized longitudinal (LO) ZnTe phonon of a wavenumber equal to 210 cm−1. For the QD sample, a broad band corresponding to the LO CdTe phonon related to the QD-layer appears at a wavenumber of 160 cm−1. With increasing time of a laser beam exposure and laser power, the spectra get dominated by tellurium—related peaks appearing at wavenumbers around 120 cm−1 and 140 cm−1. Simultaneously, the ZnTe surface undergoes rising damage, with the formation of Te aggregates at the pinhole edge as reveal atomic force microscopy observations. Local temperatu...

Structural and optical characterization of GaN nanowires

Optical properties of GaN nanowires (NWs) grown by plasma-assisted molecular beam epitaxy on Si(111) substrates were studied with the use of micro-Raman spectroscopy and photoluminescence. Two types of NWs, hereafter labeled as A and B, grown with different values of Ga flux were studied. Morphology of the samples was probed by high resolution scanning electron microscopy. It was found that large Ga flux has led to a partial coalescence of nanowires in sample A. Reduction of Ga flux during growth of sample B resulted in an ensemble of separated nanowires. Micro-Raman and photoluminescence spectra were taken under illumination of 325 nm He-Cd laser line. Micro-Raman data reveal hexagonal phase of GaN NWs as well as a slight strain of Si substrate. Photoluminescence data yield that ensembles of separated NWs in sample B are defect free, whereas the spectra for coalesced wires in sample A exhibit both broad yellow luminescence band and defect-related band centered around 3.36 eV. Moreover, it was found that ...

Electrical and photovoltaic properties of CdTe/ZnTe n-i-p junctions grown by molecular beam epitaxy

Preliminary studies have been performed on photoelectrical properties of CdTe/ZnTe n-i-p junctions grown using the molecular beam epitaxy technique. Photovoltaic properties of the cells have been investigated by the measurements of current-voltage (I-V) characteristics under 1-sun illumination. I-V characteristics yield efficiencies of the cells varying from 3.4% to 4.9%. The low efficiency can be due to the presence of electrically active defects. In order to study the origin of defects in CdTe/ZnTe photovoltaic junctions, space charge techniques (C-V and deep level transient spectroscopy (DLTS)) have been applied. From the C-V measurements, a doping profile was calculated confirming charge accumulation in the i-CdTe layer. The results of the DLTS studies revealed the presence of four traps within a temperature range from 77–420 K. Three of them with activation energies equal to 0.22 eV, 0.45 eV, and 0.78 eV have been ascribed to the hole traps present in the i-CdTe material and their possible origin has...

Synthetic aperture acoustic microscope for evaluation of fingertip peripheral skin structure

The setup for reconstruction of 2D quasi periodical structures from the measurements of its ultrasonic diffractive field is presented. Construction of the ultrasonic head is based on the prototype of our ultrasonic sensor for fingerprint pattern recognition. An example of the measured and reconstructed acoustic image of a fingerprint is compared with an optical picture.

Zn3P2: new material for optoelectronic devices

Fundamental optical and electronic parameters of Zn3P2 are presented. Mg-Zn3P2 structures are examined as a solar energy converter and broad-range photodetector. A distinct photodichroism, observed for junctions prepared on oriented single crystal, is applied in light polarization step indicator.