PtSi Schottky-barrier Detectors Research Articles

External quantum efficiency-enhanced PtSi Schottky-barrier detector utilizing plasmonic ZnO:Al nanoparticles and subwavelength gratings

A infrared light trapping structure combining front subwavelength gratings and rear ZnO:Al nanoparticles for a PtSi Schottky-barrier detector over a 3–5 μm waveband is theoretically investigated. By selecting the proper plasmonic material and optimizing the parameters for the proposed structure, the absorption of the PtSi layer is dramatically improved. The theoretical results show that this improvement eventually translates into an equivalent external quantum efficiency (EQE) enhancement of 2.46 times at 3–3.6 μm and 2.38 times at 3.6–5 μm compared to conventional structures. This improvement in the EQE mainly lies in the increase of light path lengths within the PtSi layer by the subwavelength grating diffraction and nanoparticle-scattering effects.

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.

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.

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.

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.

Ultraviolet, visible, and infrared response of PtSi Schottky-barrier detectors operated in the front-illuminated mode

The quantum efficiency of PtSi Schottky-barrier detectors has been measured as a function of wavelength from 0.23 to 7 mu m. For front-illuminated PtSi/p-Si devices operated at low temperatures, quantum efficiencies of 40 to 70% are obtained in the ultraviolet (UV) and visible regions with little loss of the infrared (IR) photoresponse that is obtained for operation in the conventional back-illumination mode. For room-temperature operation of front-illumination PtSi/n-Si devices, the quantum efficiencies are approximately the same in the UV and visible regions, but the IR response decreases abruptly beyond the Si absorption edge. Room-temperature transmission and reflection measurements have been used to determine the values of the real and imaginary parts of the complex dielectric constant for PtSi at wavelengths from 0.2 to 3 mu m. A simple model, used with these values and published values of the dielectric constant for Si, yields calculated quantum efficiencies in the UV and visible regions that agree quite well with the measured efficiencies. The temporal response of front-illuminated PtSi/p-Si detectors in the visible and IR regions is found to be fast enough for operation at video frame rates. >

PtSi Schottky-barrier focal plane arrays for multispectral imaging in ultraviolet, visible, and infrared spectral bands

PtSi Schottky-barrier detectors, which are conventionally used in the back-illumination mode for thermal imaging in the 3-5- mu m infrared (IR) spectral band, are shown to exhibit excellent photoresponse in the near-ultraviolet and visible regions when operated in the front-illumination mode. For devices without antireflection coatings, external quantum efficiency in excess of 60% has been obtained for wavelengths between 400 and 800 nm. The efficiency decreases below 400 nm but is still about 35% at 290 nm. High-quality imaging has been demonstrated in both the visible and 3-5- mu m spectral bands for front-illuminated 160*244-element PtSi focal plane arrays integrated with monolithic CCD readout circuitry.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Display of wide dynamic range infrared images from PtSi Schottky barrier cameras

Twelve-bit digitized images taken with PtSi Schottky barrier detector arrays have been processed on Sun work stations. Two techniques for 8-bit global display are compared: the standard method of histogram equalization and a newly devised technique of histogram projection. The latter assigns equal dynamic range to each occupied level, while the former does so according to the density of the occupied levels. The projection technique generally gives distinctly superior results based on an extensive set of indoor, outdoor, day, and night imagery. For cases in which the two algorithms have complementary advantages, the techniques can be combined in effect by a weighting of their distribution functions, which often gives the desirable features of each. The new projection algorithm also can be used as a powerful and robust local contrast enhancement technique. An alternative method of contrast enhancement, a global algorithm based on modular (sawtooth) displays, affords a comparable degree of enhancement at less computational cost.

A wide spectral band photodetector with PtSi/p-Si Schottky-barrier

The photoresponse of a front-illuminated PtSi Schottky-barrier detector is measured in the wavelength range between 0.4 and 5.2μm. In the wavelength range longer than 1.1μm, the detection mechanism is the internal photoemission. On the other hand, the intrinsic mechanism becomes dominant in the wavelength range shorter than 1.1μm. The measured data are in good agreement with values calculated from these two detection mechanisms. The photoresponse depends on the PtSi thickness in both wavelength ranges. For getting a high responsivity, it is important to make a thin uniform metal film. The visible and the thermal image with a PtSi Schottky-barrier wide spectral band imager are also demonstrated.

160 × 244 Element PtSi Schottky-barrier IR-CCD image sensor

A 160 × 244 element IR-CCD image sensor was developed with PtSi Schottky-barrier detectors (SBD's) for thermal imaging in the 3.0-5.0-µm IR band. This imager has 80 × 40 µm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> pixels, a fill factor of 39 percent, and a chip size of 584 × 464 mil <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . It produces excellent quality thermal imaging with noise-equivalent temperature (NEΔT) of less than 0.1 K for operation at 30 frames/s with standard-TV-interlace f/2.3 optics, and one-point offset-type uniformity corrector. This paper describes the design, construction, and performance of 160 × 244 element IR-CCD imager and the characteristics of the PtSi Schottky-barrier detector elements.

(Invited) “High-Performance Schottky-Barrier IR-CCD Image Sensors”

High-performance PtSi and Pd2Si Schottky-barrier IR-CCD image sensors were developed with 32×63 and 64×128 elements. PtSi Schottky-barrier detectors (SBDs) operated at 80 K have quantum efficiency of several percent in the 3 to 5 µm spectral range and cut-off wavelength of about 6.0 µm. Pd2Si SBDs operated between 120 and 140 K have cut-off wavelength of 3.6 µm and quantum efficiency in the range of 1.0 to 8.0% in the 1.0 to 2.5 µm band. High quality thermal imaging has been demonstrated with a 64×128-element PtSi Schottky-barrier IR-CCD imager in a TV compatible IR camera operated with 60 frames per second. Also SWIR reflective infrared imaging of very good quality was achieved with the Pd2Si Schottky-barrier IR-CCD image sensor.