P. Chakrabarti

ZnO-based interdigitated MSM and MISIM ultraviolet photodetectors

The paper reports the fabrication and characterization of ZnO-based interdigitated metal–semiconductor–metal (MSM) and metal–insulator–semiconductor–insulator–metal (MISIM) ultraviolet photodetectors. The ZnO thin film was grown on a p-type Si 1 0 0 substrate by the sol–gel technique. With applied voltage in the range from −3 to 3 V we estimated the contrast ratio, responsivity, detectivity and quantum efficiency of the photodetectors for an incident optical power of 0.1 mW at 365 nm ultraviolet wavelength. The I–V characteristics were studied and the parameters such as ideality factor, leakage current and barrier height were extracted from the measured data. For Au/Cr/SiO2/ZnO/SiO2/Al (MISIM) structure the product (mχ) of the tunnelling effective electron mass (m) and the mean tunnelling barrier height (χ) was also extracted.

Electronic and optical properties of electrochemically polymerized polycarbazole/aluminum Schottky diodes

We report the fabrication of organic Schottky diodes on indium tin oxide (ITO) coated glass by electrochemically polymerized polycarbazole (PCz) with configuration ITO/PCz/Al. The diode has been characterized in respect of electrical and optical properties. The study involves estimation of optical bandgap of the polymer from UV-visible spectroscopic measurements. The current-voltage (J-V) and capacitance-voltage (C-V) characteristics of the Schottky diode were subsequently used for extracting electronic parameters of the device such as ideality factor, barrier height, reverse saturation current, built-in potential, depletion width, doping concentration, etc. The photoresponse of the Schottky contact was measured by illuminating the device with a laser source operating at 650 nm having an incident optical power density of 10 mW/cm2. The device exhibits a high value of peak detectivity (∼107 cm Hz1/2 W−1) near zero bias voltage and the same attains a value of the order of 109 cm Hz1/2 W−1 at a reverse bias ...

Time-dependent degradation of Pt/ZnO nanoneedle rectifying contact based piezoelectric nanogenerator

A piezoelectric nanogenerator based on the platinum rectifying contact on ZnO nanoneedle arrays (NNA) has been successfully fabricated on silicon substrate by using the thermal evaporation deposition technique. It is demonstrated that the rectifying platinum contact on ZnO NNA can efficiently convert nanoscale mechanical energy into electrical energy by exploiting the piezoelectric and semiconducting properties of ZnO. The effect of key parameters such as scanning speed, force on scanning tip, and tip abrasion on the nanogenerator has been studied along with long-time stability of the piezoelectric nanogenerator. The study reveals that the nanogenerator output degrades with time primarily due to degradation of the rectifying contact with time and abrasion of the tip caused by repeated scanning. The results of the study are expected to provide quantitative ideas about the long-time stability of ZnO NN based nanogenerators.

Effect of thermal treatment on the performance of ZnO based metal-insulator-semiconductor ultraviolet photodetectors

The article reports fabrication, characterization, and testing of the performance of ZnO-based metal-insulator-semiconductor (MIS) Schottky barrier ultraviolet photodetectors under varying thermal treatment. The ZnO thin film was grown on p-type Si ⟨100⟩ substrate by using sol-gel technique. The electrical and optical characteristics of MIS photodetector were studied. The study revealed that the performance of the device improves with increasing postmetal deposition annealing temperature up to 250 °C approximately. For annealing temperature beyond 250 °C the performance of the device degrades drastically. The variation in the electrical and photoresponse properties of MIS photodetector can be attributed to combined effects of interfacial reaction and phase transition during the annealing process.

An improved model of ion-implanted GaAs OPFET

A seminumerical model of an ion-implanted GaAs optical-field-effect-transistor (OPFET) is presented. The objective of the present work is to overcome the limitations of the existing model without changing the basic approach. Analytical expressions obtained using the one-dimensional Poissons equation have been solved numerically to obtain the I-V characteristics of the device in dark and illuminated conditions. It is seen that the saturation drain current of the device changes significantly in the illuminated condition. The existing model of the device has been improved by considering the effects of the photovoltage generated across the metal-semiconductor junction and optical modulation of depletion edge depths in the illuminated condition. Unlike in the previous model, it has been concluded that for a high gate bias resistance the optical radiation controls the saturation drain current by changing the channel conductance rather than its conductivity. >

Effect of ionizing radiation on MOS capacitors

A numerical model of metal-oxide-semiconductor (MOS) capacitor has been developed to investigate the effect of ionizing radiation on the characteristics of the device during exposure and also in the post-irradiated condition. The model takes into account the effect of radiation-induced changes in silicon-dioxide as well as in silicon substrate of MOS structure. It is found that the total high frequency capacitance of the device during exposure to radiation is different from its value in the post-irradiated condition. The results of the study are expected to be useful in predicting the behavior of MOS based devices operating in radiation environment.

Analysis and simulation of a mid-infrared P/sup +/-InAs/sub 0.55/Sb/sub 0.15/P/sub 0.30//n/sup 0/-InAs/sub 0.89/Sb/sub 0.11//N/sup +/-InAs/sub 0.55/Sb/sub 0.15/P/sub 0.30/ double heterojunction photodetector grown by LPE

A photovoltaic detector based on an N/sup +/-InAs/sub 0.55/Sb/sub 0.15/P/sub 0.30//n/sup 0/-InAs/sub 0.89/Sb/sub 0./

Structural and electrical properties of metal contacts on n-type ZnO thin film deposited by vacuum coating technique

d1/sub 1//P/sup +/-InAs/sub 0.55/Sb/sub 0.15/P/sub 0.30/ double heterostructure (DH) suitable for operation in the mid-infrared (MIR) spectral region (2 to 5 /spl mu/m) at room temperature has been studied. A physics based closed form model of the device has been developed to investigate the relative importance of the different mechanisms which determine dark current and photoresponse. The results obtained on the basis of the model have been compared and contrasted with those obtained from experimental measurements on DH detectors fabricated previously in our laboratory using liquid phase epitaxy (LPE). The model helps to explain the various physical mechanisms that shape the characteristics of the device under room temperature operation. It can also be used to optimize the performance of the photodetector in respect of dark current, responsivity and detectivity. A comparison of theoretical predictions and experimental results revealed that Shockley-Read-Hall (SRH) recombination is more important than Auger recombination in determining the room temperature detector performance when the concentration of nonradiative recombination centers in our material exceeds 10/sup 17/ cm/sup -3/. Furthermore, compositional grading in the cladding regions of the double heterostructure has been found to be responsible for the reduction of the detectivity of the device in the shorter wavelength region.

Electronic Properties and Junction Behavior of Polyanthranilic Acid/Metal Contacts

The authors report on fabrication and characterization of Al and Pt metal contacts on ZnO thin films grown on ITO coated glass substrates using thermal evaporation technique. The structural and surface properties of ZnO thin film were studied by using x-ray diffraction and atomic force microscopy techniques. Atomic force micrographs revealed that ZnO microparticles have perfect pyramidal shape with small surface roughness (average rms value of 3nm). The current voltage characteristics of Pt∕ZnO and Al∕ZnO contacts were studied by scanning tunneling microscopy. The Pt contact on ZnO thin films behaves as a rectifying contact with a barrier height of 0.72eV, while Al contact on ZnO thin film turns out to be Ohmic in nature. The band gap of ZnO thin film was estimated to be 3.10eV from absorption spectroscopic measurements.

Fabrication and characterization of thin film ZnO Schottky contacts based UV photodetectors: A comparative study

Polyanthranilic acid (PANA), a self-doped processible conducting polymer, was synthesized and used for the first time for fabrication of contacts with configurations of (Al, Ti, Sn metal)/PANA/indium tin oxide-coated glass. The current-voltage (I-V) characteristics were measured by using microprobe arrangements, and the diode performance parameters were extracted. The I-V characteristics of the aforementioned configuration exhibited a rectifying contact for the case of Al and Ti metal contacts but an ohmic contact for the case of Sn metal contact. The electroactivity of PANA was carried out in acidic solution, and film morphology was studied by using atomic force microscope. UV-Vis spectroscopic technique was used to obtain the optical bandgap of the polymer.