Schottky Barrier Detectors Research Articles

Correlation of Deep Levels With Detector Performance in 4H-SiC Epitaxial Schottky Barrier Alpha Detectors

High resolution Schottky barrier detectors for alpha particles were fabricated using 20 μm thick detector grade n-type 4H-SiC epitaxial layer. The Schottky barrier detectors were characterized through current-voltage (I-V) and capacitance-voltage (C-V) measurements. Deep level transient spectroscopic (DLTS) measurements were carried out to identify and characterize the electrically active defect levels present in the epitaxial layers. The detection properties of the Schottky detectors were characterized in terms of alpha particle peak widths in pulse height spectra obtained using a standard alpha emitting radioisotope source. The differences in the performance of different detectors were correlated on the basis of the barrier properties and the deep level defect type, concentration, and capture cross-section. Varying degree of the presence of deep level defects was found to be the reason behind the leakage current variation and the difference in the ultimate detector performance observed among the detectors. From the DLTS data it was found that at least two defect centers located at E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> -0.6 eV (Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sub> ) and at E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> -1.6 eV (EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6/7</sub> ),both related to carbon vacancies, affected the detector performance the most.

Observation of damage in insulated copper cables by THz imaging

A novel non-destructive inspection method using terahertz waves for the detection of broken wires in copper cables shielded by insulating polymer opaque in the visible and near infrared light region is presented. Terahertz reflection imaging, using a 0.14THz IMPATT oscillator and a Schottky barrier detector, was applied to insulated copper cables that had been artificially damaged. The internal insulated wires embedded in the opaque polyethylene can be clearly visualized using THz radiation. It was shown that a gap in a wire can be detected by a decrease in the intensity of the reflected signal where the size of the gap is greater than the wavelength of the oscillator.

High resolution alpha particle detection using 4H–SiC epitaxial layers: Fabrication, characterization, and noise analysis

In this article we report the fabrication and characterization of large area, room-temperature operable and very high resolution Schottky barrier detectors for alpha particles using 20μm thick n-type 4H–SiC epitaxial layers. Schottky barriers were fabricated by depositing circular nickel contacts of ~11mm2 area on the 4H–SiC epitaxial layers. Room temperature current–voltage measurements revealed very high Schottky barrier height of 1.6eV and extremely low leakage current of 3.5pA at an operating reverse bias of −90V. We also report an energy resolution of 0.29%, which is the best resolution obtained so far for uncollimated 5.48MeV alpha particles in 4H–SiC epitaxial detectors with such a large area. Very low micropipe density (<1cm−2) and low effective doping concentration (2.4×1014cm−3) in the epilayer helped to achieve a high resolution even with the large detector area and a broad source. A diffusion length of ~18.6μm for holes has been determined in these detectors following a calculation based on a drift-diffusion model. A noise analysis in terms of equivalent noise charge revealed that the white series noise due to the detector capacitance has substantial effect on their spectroscopic performance.

Fabrication of High-Resolution Nuclear Detectors Using 4H-SiC n-type Epitaxial Layers

ABSTRACTHigh resolution Schottky barrier detectors for alpha particles have been fabricated on 20 μm n-type 4H-SiC epitaxial layers. Schottky barrier contact structure was accomplished by deposition of 10 nm nickel on the Si face of the epilayers. The detectors were characterized for structural, electrical, and spectroscopic properties. Scanning electron microscopy and Nomarski optical microscopy revealed a micropipe density lower than 1 cm-2. The current-voltage (I-V) characteristics of the device exhibited very low leakage current of the order of 6.5 pA at an operating bias of 90 V. C-V measurements revealed a typical effective doping concentrations of 2.4 × 1014 cm-3 in these epilayers. The detectors were evaluated for alpha particles detection using a 241Am source. An energy resolution of ∼0.98% for 5.48 MeV alpha particles was observed. The separate contribution of charge carrier drift and diffusion to the total charge collection efficiency has been calculated in these detectors following a drift-diffusion model. Detailed electronic noise analysis in terms of equivalent noise charge (ENC) was carried out to study the effect of various noise components that contribute to the total electronic noise in the detection system. Effect of shaping time, presence of source and bias on the ENC has been studied in details.

Schottky barrier detectors on 4H-SiC n-type epitaxial layer for alpha particles

Schottky barrier detectors have been fabricated on 50μm n-type 4H-SiC epitaxial layers grown on 360μm SiC substrates by depositing ∼10nm nickel contact. Current–voltage (I–V) and capacitance–voltage (C–V) measurements were carried out to investigate the Schottky barrier properties. The detectors were evaluated for alpha particle detection using a 241Am alpha source. An energy resolution of ∼2.7% was obtained with a reverse bias of 100V for 5.48MeV alpha particles. The measured charge collection efficiency (CCE) was seen to vary as a function of bias voltage following a minority carrier diffusion model. Using this model, a diffusion length of∼3.5μm for holes was numerically calculated from the CCE vs. bias voltage plot. Rise-time measurements of digitally recorded charge pulses for the 5.48MeV alpha particles showed a presence of two sets of events having different rise-times at a higher bias of 200V. A biparametric correlation scheme was successfully implemented for the first time to visualize the correlated pulse-height distribution of the events with different rise-times. Using the rise-time measurements and the biparametric plots, the observed variation of energy resolution with applied bias was explained.

Particle detectors based on InP Schottky diodes

A study of electrical properties and detection performance of Indium Phosphide detector structures with Schottky contacts prepared on high purity p-type InP was performed. Schottky barrier detectors were prepared by vacuum evaporation of Pd on p-type epitaxial layers grown on Zn-doped p-type substrates. The detection performance of the detectors was characterized by the measurement of pulse-height spectra with alpha particles emitted from 241Am source at room temperature. The influence of the quality of p-type epitaxial layers on the charge-collection efficiency and energy resolution in the full-width half-maximum is discussed.

Influence of the back contact on the electrophysical and functional characteristics of thin-film CdTe Schottky barrier detector structures

To register nuclear radiation, thin-film CdTe Schottky barrier detector structures are developed. The structures are based on large-block p-CdTe films with resistivity ρ = 105 – 107 Ω∙сm. The capacitance-voltage, current-voltage, amplitude, and noise characteristics of the structures are measured, and the mechanisms of charge carrier transfer are identified for different bias voltages. It is established that the functional characteristics of the detector structures are limited by the injection processes arising in the back Mo contact. It is found that the source of electron injection is the MoO3 compound localized between the film and the molybdenum substrate.

Pore size dependence of PtSi/Porous Si Schottky barrier detectors on quantum efficiency response

The paper describes how pore size and geometry of porous silicon can affect the electrical and optical properties of PtSi/Porous Si Schottky barrier detectors. In this study, two techniques used to prepare different porosities on silicon substrate which includes: electrochemical etching process and electroless metal-assisted chemical etching. Surface morphology and geometric properties of PtSi/Porous Si have been characterized using scanning electron microscopy (SEM) and also I–V characteristics of detectors at reverse bias performed at cryogenic temperature 77K; between 1–5μm for IR spectroscopy measurements. It was found that by reducing the overall size of pores from micrometric to nanometric size, the external quantum efficiency increases up to 80% for 1μm radiation and the wavelength of maximum responsivity moves toward the lower IR spectra in 77K. Furthermore, the produced micro metric pores using electrochemical porosification, show more constant responsivity than nanometric one's which obtained from metal-assisted chemical etching.

Effect of asymmetric Schottky barrier on GaN-based metal-semiconductor-metal ultraviolet detector

An asymmetric Schottky barrier metal-semiconductor-metal (MSM) ultraviolet (UV) detector with Ni/GaN/Au structure was designed and the effect of the asymmetric Schottky barrier on the detector response was investigated. This detector had response at 0 V bias and increased responsivity when a positive bias was applied to the Ni/GaN contact; however, the internal gain disappeared when a negative bias was applied to this point. This contrasts with a symmetric Ni/GaN/Ni Schottky barrier MSM UV detector which had no internal gain under positive/negative bias and almost no response at 0 V bias. The improved performance of the asymmetric Schottky barrier detector was because of the lower work function of Au causing reduction of Schottky barrier and hence enhancing a hole-accumulating and trapping process, which resulted in internal gain.

Theoretical investigation of silicide Schottky barrier detector integrated in horizontal metal-insulator-silicon-insulator-metal nanoplasmonic slot waveguide

An ultracompact integrated silicide Schottky barrier detector (SBD) is designed and theoretically investigated to electrically detect the surface plasmon polariton (SPP) propagating along horizontal metal-insulator-silicon-insulator-metal nanoplasmonic slot waveguides at the telecommunication wavelength of 1550 nm. An ultrathin silicide layer inserted between the silicon core and the insulator, which can be fabricated precisely using the well-developed self-aligned silicide process, absorbs the SPP power effectively if a suitable silicide is chosen. Moreover, the Schottky barrier height in the silicide-silicon-silicide configuration can be tuned substantially by the external voltage through the Schottky effect owing to the very narrow silicon core. For a TaSi(2) detector with optimized dimensions, numerical simulation predicts responsivity of ~0.07 A/W, speed of ~60 GHz, dark current of ~66 nA at room temperature, and minimum detectable power of ~-29 dBm. The design also suggests that the device's size can be reduced and the overall performances will be further improved if a silicide with smaller permittivity is used.

Particle detectors based on semiconducting InP epitaxial layers

A study of electrical properties and detection performance of two types of Indium Phosphide detector structures was performed: (i) with p-n-junction and (ii) with Schottky contact prepared on high purity p-type InP. The p-n junction detectors were based on a high purity InP:Pr layers of both n- and p- type conductivity with carrier concentration on the order of 1014 cm−3 grown on Sn doped n-type substrate. Schottky barrier detectors were prepared by vacuum evaporation of Pd on high purity p-type epitaxial layer grown on Mn doped p-type substrate. The detection performance of particle detectors was measured by pulse-height spectra with alpha particles emitted from 241Am source at room temperature.

Zinc Selenide-Based Schottky Barrier Detectors for Ultraviolet-A and Ultraviolet-B Detection

Wide-bandgap semiconductors such as zinc selenide (ZnSe) have become popular for ultraviolet (UV) photodetectors due to their broad UV spectral response. Schottky barrier detectors made of ZnSe in particular have been shown to have both low dark current and high responsivity. This paper presents the results of electrical and optical characterization of UV sensors based on ZnSe/Ni Schottky diodes fabricated using single-crystal ZnSe substrate with integrated UV-A (320–400 nm) and UV-B (280–320 nm) filters. For comparison, characteristics characterization of an unfiltered detector is also included. The measured photoresponse showed good discrimination between the two spectral bands. The measured responsivities of the UV-A and UV-B detectors were 50 mA/W and 10 mA/W, respectively. A detector without a UV filter showed a maximum responsivity of about 110 mA/W at 375 nm wavelength. The speed of the unfiltered detector was found to be about 300 kHz primarily limited by the RC time constant determined largely by the detector area.

Testing metal-dielectric-semiconductor tunnel structures on p-silicon as nuclear particle detectors

Metal-dielectric-semiconductor (MDS) structures with aluminum nitride (AlN) as a tunnel dielectric based on high-ohmic p-type silicon substrates have been studied. The samples were characterized with respect to the charge collection efficiency and energy resolution on probing with 5.4-MeV α particles. In addition, the nature of noises and the state of the AlN-p-Si interface were investigated. It is established that the parameters of these MDS structures as radiation detectors are close to those of widely used Schottky-barrier detectors based on n-Si (Au-n-Si). A decrease in the concentration of deep centers at the AlN-p-Si interface allows the proposed MDS structures to compete successfully with n-Si based detectors, which is due to a higher purity of the initial material.

AlN MSM and Schottky photodetectors

AbstractDeep ultraviolet (DUV) AlN Metal‐Semiconductor‐Metal (MSM) and Schottky barrier photodetectors have been demonstrated by exploiting the epitaxial growth of high quality AlN epilayer on sapphire and n‐SiC substrates, respectively. The fabricated photodetectors exhibited peak responsivity at 200 nm with very sharp cut‐off wavelength at 207 nm along with extremely low dark current, very high breakdown voltages, high responsivity and high DUV to UV/visible rejection ratio. AlN Schottky barrier detectors show high zero bias responsivity and very high thermal energy limited detectivity at zero bias. These outstanding features are direct attributes of the fundamental material properties and high quality of AlN epilayers. These results demonstrated that AlN could be an excellent candidate as an active material for next generation DUV opto‐electronic device applications. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Hybrid AlN–SiC deep ultraviolet Schottky barrier photodetectors

Deep ultraviolet (DUV) Schottky barrier photodetectors have been demonstrated by exploiting the epitaxial growth of high quality AlN epilayer on n-type SiC substrate. The fabricated AlN∕n-SiC hybrid Schottky barrier detectors exhibited a peak responsivity at 200nm with very sharp cutoff wavelength at 210nm, very high reverse breakdown voltages (&amp;gt;200V), very low dark currents (about 10fA at a reverse bias of 50V), and high responsivity and DUV to UV/visible rejection ratio. These outstanding features are direct attributes of the fundamental material properties and high quality of AlN epilayers. The fabricated photodetectors also have a thermal energy limited detectivity at zero bias of about 1.0×1015cmHz1∕2W−1. These results demonstrated that AlN epilayers are an excellent candidate as an active material for DUV optoelectronic device applications.

Fabrication and characteristics of bulk semi-insulating 6H-SiC semiconductor detector for an α radiation at room temperature

The fully depleted SiC Schottky barrier detector was fabricated from a semi-insulating (SI) bulk crystal with a thickness of 388 μm and an orientation of the on axis (0 0 0 1). The bulk SI 6H-SiC detector structure consists of a Ni/Au contact at the Si-face and a Ti/Au contact at the C-face. The fabricated detector dimensions are 10×10 mm with a diameter of 6 mm for the contact dimension. The band gap of the 6H-SiC was determined by using an optical photon absorption spectroscopy in the ranges between 200 and 600 nm. The band gap of 6H-SiC is determined as 3.03 eV. The current density response according to the biased voltage was measured. The Schottky barrier height was determined as 0.86 eV on the basis of the thermo-ionic emission theory. The bulk SI 6H-SiC detector with a multi-layer structure, Au/Ni/6H-SiC/Ti/Au showed a good response for the α radiation in air and at room temperature.

Quantum efficiencies of PtSi∕p-Si composites in the 3–5μm wavelength range

A formula for the quantum efficiency of Schottky barrier metal-semiconductor composite photon detectors is derived. It includes the two factors that completely describe the quantum efficiency of a planar Schottky barrier detector. It has in addition a third factor, that can be larger or smaller than one depending on the ratio of the mean-free path of the photoexcited carriers to the dispersed metal particle sizes. Using this formula, quantum efficiencies, due to photoexcited holes in experimentally prepared PtSi∕p-Si composite films, were calculated in the 3–5μm micron wavelength range using measured absorption and particle size data. The results provide evidence for the contribution of particle size effects to the efficiencies in PtSi∕p-Si composite detectors and are consistent with previous particle size effects in other metal-semiconductor composite materials.

SiC detectors for neutron monitoring

Semiconductor detectors equipped with a converter like 6LiF or 10B can currently be considered a very interesting alternative to conventional neutron detectors, especially because of their compactness and reliability. The materials for the detection of the ions produced in the converter are generally either Si or GaAs. SiC detectors presented in this work are completely new devices which are proved to be very suitable for neutron detection, dosimetry and beam monitoring. Their capability to withstand high radiation doses should largely overcome the performances of Si and GaAs; moreover, because of the lower Z value, gamma-ray discrimination turns out to be more efficient. In this work, the results obtained with a series of large-area epitaxial SiC Schottky barrier detectors will be presented and discussed.

Response of semi-insulating [formula omitted] thick GaAs detector for [formula omitted]-particles, [formula omitted]-rays and X-rays

The 100 μ m thick, transmission, fully depleted GaAs Schottky barrier detector fabricated from LEC bulk GaAs crystals has been tested. The basic structure of the detector consists of a Cr/Au Schottky contact and an Au/Ge/Ni/Au alloyed ohmic contact. Pulse height spectra for α -particles resulting from irradiation with triple source 239 Pu , 241 Am , 244 Cm , with energies 5.155, 5.486, 5.805 MeV were acquired. The energy resolution for these energies was better than 10 keV (1.8%). Using 241 Am 5.486 MeV α -particles a charge collection efficiency (CCE) of about 94% was obtained at 570 V bias potential. The spectra of low-energy γ -rays 59.5 keV and X-rays with average energy 16.2 keV from 241 Am source measured at room temperature are presented. An energy resolution of about 6.1 keV (10.3%) FWHM at 59.5 keV was obtained.

Microstructure, electrical, and optical properties of evaporated PtSi/p-Si(100) Schottky barriers as high quantum efficient infrared detectors

The effects of the microstructure and the electrical and optical properties on the formation at highly efficient infrared PtSi Schottky barrier detectors (SBD) have been studied in detail. Two- to twelve-nanometer-thick PtSi films were grown by evaporation at temperature ranging from 350 to 550 °C. The electron diffraction patterns indicate the existence of both the (11̄0) and (12̄1) orientations when PtSi films formed at 350 °C. However, the diffraction patterns show only the (12̄1) orientation when the PtSi films are formed at 450 °C or above. The electrical barrier height of the Schottky barrier detector that formed at 350 °C was about 20 meV higher than that formed at 450 °C or above. The grain size and the film thickness had a negligible effect on the electrical barrier height. However, the optical performance was strongly dependent on the film thickness and the growth conditions. The 350 °C PtSi film showed increased quantum efficiency as the film thickness decreased. The optimal thickness that provided the highest responsivity was 2 nm. On the other hand, the optimal thickness shifted to 8 nm for PtSi film formed at 450 °C or above. These results indicate that the quantum efficiency of a detector can be improved if the PtSi film has an orientation at (12̄1), a larger grain size, and an optimal film thickness.