Schottky Barrier Detectors Research Articles

Interfacial composition and electrical properties of PtSi/Si 1− xGe x/Si diodes by molecular beam epitaxy (MBE) and pulsed laser deposition (PLD)

By combining pulsed laser deposition (PLD) and molecular beam epitaxy (MBE), it has been demonstrated that PtSi/strained Si 1− x Ge x ( x=0,0.2 and 0.25) Schottky barrier detector (SBD) with extended cutoff wavelengths. Pt was deposited by PLD on the Si 1− x Ge x alloys with a thin Si sacrificial cap layer grown by MBE. By the reaction of deposited Pt film on Si sacrificial cap layer silicide SBDs have been fabricated. Auger electron depth profiling was performed on the films before and after in vacuo annealing to study the redistribution of composition in the reactions. The variation of the barrier height of the junctions with the Ge fraction x was studied, it was found to follow the same change as the bandgap of strained Si 1− x Ge x , and the cutoff wavelength has been extended beyond 10 μm in PtSi/strained Si 1− x Ge x SBDs. In addition, the Schottky barrier height (SBH) of PtSi/Si 1− x Ge x /Si has been found to vary between 0.12 and 0.58 eV in the temperature range 77–293 K. At 293 K, the ideality factor has been found to be 2.00 and 1.32 for PtSi/Si 0.80Ge 0.20 and PtSi/Si 0.75Ge 0.25 diodes, respectively.

Quasi-optical highly sensitive Schottky-barrier detector for a wide-band FIR FEL

A wide-band FIR detector based on the Schottky-barrier diode for the use on a far-infrared FEL facility has been developed. The detector consists of a GaAs chip with diodes of sub-micrometer diameters and a traveling-wave antenna in a 90° corner-cube reflector that provided effective transmission of the FIR power to the diode from the input FIR focusing lens. The antenna has been optimized for a wavelength of 337μm. At this wavelength, the detector has a sensitivity of 200V/W and a noise equivalent power (NEP) of 0.1nW/Hz1/2. These measurements were made by a HCN laser. For a radiation wavelength of 119μm (H2O laser) the sensitivity and NEP values were measured to be 20V/W and 1.0nW/Hz1/2, respectively. The results of measurements from the compact wide-band FIR FEL facility by the detector in a wide wavelength range are presented. The potentialities of the detector are investigated.

The effect of incremental gamma-ray doses and incremental neutron fluences upon the performance of self-biased 10B-coated high-purity epitaxial GaAs thermal neutron detectors

High-purity epitaxial GaAs 10B-coated thermal neutron detectors advantageously operate at room temperature without externally applied voltage. Sample detectors were systematically irradiated at fixed grid locations near the core of a 2 MW research reactor to determine their operational neutron dose threshold. Reactor pool locations were assigned so that fast and thermal neutron fluxes to the devices were similar. Neutron fluences ranged between 10 11 and 10 14 n/cm 2. GaAs detectors were exposed to exponential fluences of base ten. Ten detector designs were irradiated and studied, differentiated between p–i–n diodes and Schottky barrier diodes. The irradiated 10B-coated detectors were tested for neutron detection sensitivity in a thermalized neutron beam. Little damage was observed for detectors irradiated at neutron fluences of 10 12 n/cm 2 and below, but signals noticeably degraded at fluences of 10 13 n/cm 2. Catastrophic damage was apparent for neutron fluences of 10 14 n/cm 2. Comparison studies also included semi-insulating bulk GaAs thermal neutron detectors. It was observed that the SI bulk GaAs Schottky barrier detectors sustained the highest fluences prior to device failure. The main cause of detector failure was determined to result from the 10B(n,α) 7Li reaction product damage.

Neutron irradiation effects on visible-blind Au/GaN Schottky barrier detectors grown on Si(111)

Neutron irradiation effects on the Au/sputtered–GaN Schottky barrier photodetectors grown on Si(111) were investigated. Evidence showed that the optimal fluence (1×1013 n/cm2) of neutron irradiation could not only promote the crystallinity of GaN films, but also effectively repress the occurrence of nitrogen–vacancy-related Et1 traps. We suggested that these two reasons are the main contributing factors to the superior rectifying current–voltage characteristics as well as the enhanced spectral response of Au/sputtered–GaN Schottky detectors.

Film thickness dependence on the electrical and optical properties of PtSi/p-Si(1 0 0) Schottky barrier detector

We report the PtSi film thickness dependence on the electrical barrier height and quantum efficiency of PtSi Schottky barrier detector (SBD). The thickness of the PtSi film was varied from 20 to 120 Å. The electrical barrier height of the SBD is about 0.186±0.002 eV. It was observed that the grain size and the film thickness have negligible effect on the electrical barrier height. However, the quantum efficiency of the SBDs is strongly dependent on the film thickness. When the PtSi thickness is about 80 Å, the quantum efficiency exhibits its peak value exceeding 1%. The positive quantum efficiency dependence on the film thickness is referred to the enhancement of elastic phonon scattering and the absorption dependence on the film thickness. When the film thickness is thicker than 80 Å, the decrease of the quantum efficiency is deduced from the inelastic scattering, like hole/hole scattering, imperfection scattering and impurity scattering during the hot hole transporting to the PtSi/Si interface.

Millimeter-wave radar sensing of airborne chemicals

This paper discusses the development of a millimeter-wave radar chemical sensor for applications in environmental monitoring and arms-control treaty verification. The purpose of this paper is to investigate the use of fingerprint-type molecular rotational signatures in the millimeter-wave spectrum to sense airborne chemicals. The millimeter-wave sensor, operating in the frequency range of 225-315 GHz, can work under all weather conditions and in smoky and dusty environments. The basic configuration of the millimeter-wave sensor is a monostatic swept-frequency radar that consists of a millimeter-wave sweeper, a hot-electron bolometer or Schottky barrier detector, and a corner-cube reflector. The chemical plume to be detected is situated between the transmitter/detector and reflector. Millimeter-wave absorption spectra of chemicals in the plume are determined by measuring the swept-frequency radar return signals with and without the plume in the beam path. The problem of pressure broadening, which hampered open-path spectroscopy in the past, has been mitigated in this paper by designing a fast sweeping source over a broad frequency range. The heart of the system is a backward-wave oscillator (BWO) tube that can be tuned over 220-350 GHz. Using the BWO tube, we built a millimeter-wave radar system and field-tested it at the Department of Energy Nevada Test Site, Frenchman Flat, near Mercury, NV, at a standoff distance of 60 m, The millimeter-wave system detected chemical plumes very well; detection sensitivity for polar molecules such as methylchloride was down to 12 ppm for a 4-m two-way pathlength.

Microstructure effects on quantum efficiency in PtSi/p-Si(100) Schottky barrier detector

The microstructure effects on the performance of the PtSi Schottky barrier detector (SBD) have been investigated in detail. The growth temperatures were ranged from 350 to 550°C. The thickness of the PtSi film measured by high resolution transmission electron microscopy (HRTEM) is around 4 nm. The electron diffraction pattern shows an intermingling of both ( 1 1 ̄ 0 ) and ( 1 2 ̄ 1 ) orientations when the PtSi film is formed at 350°C. However, the diffraction patterns show only ( 1 2 ̄ 1 ) orientation when the PtSi films are formed above 450°C. It was found that the electrical barrier height of the Schottky barrier detector formed at 350°C is about 0.02 eV higher than that formed above 450°C. The microstructure of the PtSi film does not change even though the formation temperature is further increased to 550°C. Nevertheless, the higher the formation temperature, the larger is the grain size. It was also observed that the grain size does not change the electrical barrier height. However, the quantum efficiency of the detector is much higher if the grain size is larger. The results indicate that the quantum efficiency of the detector can be improved if the PtSi film has ( 1 2 ̄ 1 ) orientation and larger grain size.

Random line selected charge accumulation readout structure for random access infrared imager application

A 512×512 monolithic platinum silicide focal plane array with random line selection was proposed. The device was modified from an interline transfer charge couple device configuration by adapting a random line selected charge accumulation structure on a vertical register and four-tap readout structure on a horizontal register to achieve a high fill factor, high charge handling capacity, and high frame rate operation. An on-chip 9-bit decoder was used to select a particular line to transfer charges to their associated vertical charge coupled device (CCD) register. Accompanied with the vertical reset drain circuitry, 1–512 lines can be selected and read out by the vertical CCD registers. The dummy charges on the unselected lines are then transferred to the vertical CCD channel and dumped to the vertical reset drain. In this unique readout structure, a frame rate of upto 240 frames/s can be obtained to select 128×128 of Schottky barrier detectors for 5 MHz clock frequency operation. By changing the selection pattern on a 9-bit decoder, the device can be operated in either interlaced or non-interlaced format, and the charge integration time can be varied which results in variable exposure control. This architecture not only maintains the advantages of CCD structure for its low noise and excellent signal to noise ratio, but also provides readout capability of any portion of the array like MOS structure does.

The effects of growth temperature on the microstructure and electrical barrier height in PtSi/p-Si(100) Schottky barrier detector

The effects of growth temperature on the microstructure and electrical barrier height of the PtSi Schottky barrier detector (SBD) have been investigated. PtSi films, 4 nm in thickness were deposited at various temperatures ranging from 350 to 550°C. The electron diffraction patterns showed that PtSi film formed at 350°C depicts an intermingling of both (1 1 0) and (1 2 1) orientations. However, only (1 2 1) orientation was shown when the PtSi films were formed above 450°C. Moreover, SBD formed at 350°C was found to depict an electrical barrier that is approximately 0.02 eV higher than those formed above 450°C. Although the microstructure and the electrical barrier height of the PtSi film do not change when the formation temperature was further increased from 450 to 550°C. Nevertheless, the higher formation temperature resulted in a larger grain size, indicating that grain size alone does not affect the barrier height of the resultant SBD.

Formation of Continuous Nanometer PtSi Thin Film on Si by Pulsed Laser Deposition (PLD)

ABSTRACTMetal-based silicides on silicon substrates are a widely used material system for infrared detection. PtSi/p-Si infrared Schottky barrier detectors (IRSBD) have become one of the most successful photoemisive infrared detectors. Till now, most of the efforts have been focused on the design of two dimensional PtSi-SBD arrays for the infrared (IR) camera. In this paper, we discussed the formation conditions of PtSi. Qualities are compared for PtSi films prepared at different conditions including different annealing sequences, annealing time, film thickness, and annealing ambient using pulsed laser deposition on various temperature substrates. Film structures and compositions, phase's formation using different processes are analyzed. By studying the kinetics of PtSi formation during various annealing processing, preferable preparing conditions are proposed to form the continuous PtSi ultra-thin film on Si substrate by PLD.

Schottky Barrier Ultraviolet Photodetectors on Epitaxial Lateral Overgrown GaN

Schottky barrier photovoltaic detectors have been fabricated on epitaxial lateral overgrown GaN layers. The devices show a responsivity of 130 mA/W, independent of optical power and diode size. Due to the lower defect concentration, an improvement of one order of magnitude in the visible rejection ratio has been observed, in comparison with Schottky barrier detectors on standard GaN layers on sapphire. The device time response is RC limited, and the low capacitance of these devices results in an increased bandwidth (<30 MHz in devices with a diameter of 200 μm). A lower noise equivalent power is also observed, due to the reduced leakage current. Detectivities of 5 × 109 Hz1/2 mW—1 were obtained in devices with a diameter of 400 μm, working at —3.4 V bias.

Evaluation of 320×240 pixel LEC GaAs Schottky barrier X-ray imaging arrays, hybridized to CMOS readout circuit based on charge integration

Abstract 320×240 pixels GaAs Schottky barrier detector arrays were fabricated, hybridized to silicon readout circuits, and subsequently evaluated. The detector chip was based on semi-insulating LEC GaAs material. The square shaped pixel detector elements were of the Schottky barrier type and had a pitch of 38 μ m. The GaAs wafers were thinned down prior to the fabrication of the ohmic back contact. After dicing, the chips were indium bump, flip-chip bonded to CMOS readout circuits based on charge integration, and finally evaluated. A bias voltage between 50 and 100 V was sufficient to operate the detector. Results on I–V characteristics, noise behaviour and response to X-ray radiation are presented. Images of various objects and slit patterns were acquired by using a standard dental imaging X-ray source. The work done was a part of the XIMAGE project financed by the European Community (Brite-Euram).

High barrier iridium silicide Schottky contacts on Si fabricated by rapid thermal annealing

The silicidation of iridium layers by rapid thermal annealing as a function of temperature and processing time is studied for both vacuum and argon atmosphere. The electrical properties of the resulting IrSi/n-type Si diodes are determined and related to the interface properties. I–V–T spectroscopy allows us to detect interface modifications even in the case where other diagnostics cannot be employed. Rapid thermal annealing (RTA) vacuum annealed diodes show inhomogeneous potential distribution at the metal–semiconductor interface. This is related with the coexistence of different metallurgical phases (Ir, IrSi, and IrSi1.75) at the interface as a consequence of the thermal treatments. The estimated value for the Schottky barrier height of the IrSi1.75 is 0.7 eV. In contrast, RTA argon annealed diodes show more reproducible characteristics. The main effect of the reaction atmosphere is to slow down the reaction rate as well as to inhibit the IrSi1.75 formation. This could be related with the residual oxygen contents of the reaction atmosphere. RTA argon annealing at 500 °C during 5 min is a reliable procedure for homogeneous IrSi infrared Schottky barrier detectors fabrication that can be employed in an industrial environment.

Analysis of uniformity of as prepared and irradiated SI GaAs radiation detectors

SI (semi-insulating) LEC (liquid encapsulated Czochralsky) GaAs (gallium arsenide) Schottky barrier detectors have been irradiated with high energy protons (24 GeV/c, fluence up to 16.45/spl times/10/sup 13/ p/cm/sup 2/). The detectors have been characterised in terms of I/V curves, charge collection efficiency (cce) for incident 5.48 MeV /spl alpha/-, 2 MeV proton and minimum ionizing /spl beta/-particles and of cce maps by microprobe technique IBIC (ion beam induced charge). At the highest fluence a significant degradation of the electron and hole collection efficiencies and a remarkable improvement of the FWHM energy resolution have been measured with /spl alpha/- and proton particles. Furthermore the reduction in the cce is greater than the one measured with /spl beta/-particles and the energy resolution worsens with increasing the applied bias, V/sub a/, above the voltage V/sub d/ necessary to extend the electric field all the way to the ohmic contact. On the contrary, in the unirradiated detectors the charge collection efficiencies with /spl alpha/-, /spl beta/- and proton particles are quite similar and the energy resolution improves with increasing V/sub q/>V/sub d/. IBIC spectra and IBIC space maps obtained by scanning a focused (8 /spl mu/m/sup 2/) 2 MeV proton microbeam on front (Schottky) and back (ohmic) contacts, support the observed electric field dependence of the energy resolution both in unirradiated and most irradiated detectors. The results obtained let us explain the effect of the electric field strength and the plasma on the collection of the charge carriers and the FWHM energy resolution.

Electrical and detection properties of particle detectors based on LEC semi-insulating InP

A preliminary study of electrical properties and detection performance of semi-insulating InP-based particle detectors operated at room temperature is presented. Schottky barrier detectors with the Schottky or P + back contacts exhibit a charge collection efficiency up to about 60% and energy resolution of 7.5% (FWHM) for 5.48 MeV α-particles. The influence of basic material parameters and detector electrodes is discussed with respect to further improvement of SI InP-based particle detectors.

Proton induced bulk damage effects in gallium arsenide detectors

SI GaAs Schottky barrier detectors have been irradiated with high energy protons (24 GeV/c, fluence up to 1.20 × 10 14 p/cm 2 ). The detectors have been characterized in terms of I–V curves and charge collection efficiency for incident α particles ( 241 Am) and by means of PICTS, P-DLTS and TSC spectroscopic techniques. At the highest fluences a significant degradation of the electron and hole collection efficiencies has been observed, more evident in the hole collection, limited by a hole trapping center with an activation energy of 0.56 eV. New electron traps (0.15 eV and 0.20 eV) are observed only in the irradiated detectors. Furthermore, the concentration of the deepest (0.79 eV) electron trap, the well known EL2, increases of one order of magnitude, thus noticeably affecting the electron collection efficiency. For both the charge carriers, the collection efficiency is remarkably affected by the electric field, increasing with it.

New Approaches for Formation of Ultra-Thin PtSi Layers for Infrared Applications

ABSTRACTPtSi is one of the most used silicides in infrared Schottky barrier detectors due to its low Schottky barrier to p-type Si ( Øb ∼ 0.23 eV). Control of the thickness and uniformity of the silicide layer is fundamental for a good infrared detector performance, since the silicide thickness has to be in the range of 3 to 8 nm. Such thin layers are usually made by evaporation of Pt followed by a furnace annealing. We will show different approaches for fabrication of utra-thin PtSi layers. In all of the processes, high-vacuum sputtering is used for Pt deposition and the silicidation is performed in a rapid thermal annealing system. Smooth and uniform Pt Si layers down to 3 nm thick are formed in this way. It will be shown that the controllability of the thickness during sputter deposition is not a critical issue and the deposition process has a large process window. Moreover, when taking an optimal approach, a large process window can also be found for the RTA step. The implementation of these approaches for device fabrication and some electrial results of diodes made with them will also be presented.

Schottky barrier detectors on GaN for visible–blind ultraviolet detection

We report on the fabrication and characterization of vertical geometry transparent Schottky barrier ultraviolet detectors based on n−/n+-GaN structures grown over sapphire substrates. Spectral responsivity measurements were made using illumination through the UV transparent Schottky barrier metal. A responsitivity as high as 0.18 A/W was measured for wavelengths shorter than the absorption edge of GaN. The detector speed was RC limited and the fall time was 118 ns. The 1/f noise is identified to be the main noise contribution. At 300 Hz, we measure the noise equivalent power at less than 4×10−9 W.

Semi-insulating bulk GaAs as a semiconductor thermal-neutron imaging device

Thermal-neutron Schottky barrier detector arrays fabricated from semi-insulating bulk GaAs are presently being tested. The devices use a film of 10B to convert the incident thermal-neutron field into α particles and lithium ions, either of which interact in the detector. Bulk GaAs Schottky barrier detectors are relatively radiation hard to thermal neutrons and γ rays and have shown reasonably good energy resolution for α particles. Additionally, reverse biased radiation detectors fabricated from semi-insulating bulk GaAs have been shown to have truncated electric field distributions, resulting in the formation of a high field active region and a considerably lower field dead region. The device is sensitive only to electron-hole pairs excited in the high field region, thus the truncated field effect is advantageous as an inherent γ-ray discrimination feature for neutron detectors. Preliminary results show no indication of device degradation after over 2400 hr in a thermal-neutron beam from a reactor. Images have been formed of 1, 1.5, and 2 mm holes and crosses from 2 mm thick Cd templates.

Back bias depending polarization sensitivity of PtSi/p-Si Schottky barrier detectors

The optical response of PtSi/p-Si Schottky barrier detectors structured with a lamellar grating was investigated. The quantum efficiency Y for TE and TM polarized light for different samples with grating constants Λ=3 μm, 4 μm, 5 μm, and with a grating amplitude h=1100 nm was measured. The ratio YTM/YTE strongly depends on the back bias of the diode. Theoretical calculations are presented which explain the results taking into account the locally varying Schottky barrier height and optical absorption induced by the grating.