Algirdas Suziedelis

Sensitive Planar Semiconductor Detector From Microwave to IR Applications

In this paper, we propose a novel concept for a semiconductor planar detector. At room temperature, the diode exhibits markedly high responsivity and strong spectral dependence of it: the responsivity value around 2000 V/W is inherent in K ¿ microwave frequency range, and while going up to frequency range D, it decreases by about two orders. Rectification of microwave currents and intervalley electromotive force are discussed to be mainly responsible for high responsivity and its rapid decrease within microwave range. Nevertheless, experiments at higher radiation frequencies performed under the action of pulsed CO2 laser radiation reveal the planar diode as a fast IR detector and a promising candidate for terahertz radiation sensing.

Fast infrared detectors based on nonuniform semiconductors

We review novel group of fast infrared detectors based on hot carrier effects in nonuniform Ge, Si, GaAs, AlGaAs and Ti/n-Si Schottky structures. It is demonstrated that the devices can be used to detect infrared pulses of nanosecond duration at room temperature. Physcial mechanism responsible for the photovoltage signal formation both in p-n and l-h junction of moderately and degenerately doepd semiconductors are analyzed and discussed. The influence of aluminum arsenide mole fractin on th emagnitude of the photoresponse to infrared radiation in AlGaAs/GaAs p-n junction is studied. Operational principle of the Schottky barrier detector at various radaition frequencies is considered. It is shown that photoresponse of the Schottky barrier detector superlinearly depends on infrared radiation intensity.

Electric properties of Y-Ba-Cu-O micro-diodes based on asymmetrically narrowed mesas

We present our studies of electric properties of micro-diodes based on asymmetrically narrowed, partially oxygen-depleted, semiconducting YBa2Cu3O7−x thin-film mesas. A level of asymmetry of nonlinear current-voltage characteristics of our diodes increases with the decrease of the residual oxygen content in their neck region and with increasing the operating temperature. The largest asymmetry is observed for diodes with x ∼ 0.5 and at T = 300 K. An asymmetric distribution of the electric potential for different bias polarities initiate an asymmetric, non-uniform distribution of intrinsic electric field due to heating of carriers in the diode. The experimental results and possible diodes technology are discussed.

Photothermovoltaic effects induced by CO2 laser illumination of PbTe-metal junctions

Our study is concerned with the photo-thermovoltaic effects caused by the absorption of CO2 laser light in narrow gap AIVBVI semiconductors. We report on results of experimental study of photoresponse induced in n-type and p- type lead telluride with Ni contacts. We show that in the case of ohmic contacts (n-PbTe-Ni and p-PbTe-Ni at 300K) the detected signal originated from thermoemf due to created crystal lattice temperature gradient. In the case of p- PbTe-Ni at 80K we have Schottky contacts and the photoresponse consists at least of two components: fast and great in value photoemf- due to carrier generation resulting from two-photon absorption, and slow as well as of lower magnitude thermoemf.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Temperature dependence of the detected voltage of planar microwave diode that operation is based on carrier heating phenomena in strong electric field

Microwave (MW) detectors operating on the basis of charge carrier heating phenomena in semiconductor structures attracts attention of researchers due to the possibility to use such detectors in a wide frequency range. The voltage detected in the devices consists of hot carrier electromotive force arising over the contacts of the structure having n-n+ (or p-p+) junction. Planar design of the microwave diode enabled us to measure the power of electromagnetic radiation from microwaves up to infrared region [1]. The measurements were performed at room temperature, while, the decrease of crystal lattice temperature increases voltage sensitivity of the MW [2]. This increase is caused by an electron mobility and energy relaxation time increase in a high resistivity semiconductor. The sensitivity increase is also influenced by charge carrier density decrease due to their freeze-out at low temperatures. However in a number of applications flat dependence of voltage sensitivity on temperature is preferred. As it is well known, the electron mobility and energy relaxation time depend slightly on temperature in low resistivity semiconductors [3]. Moreover, carrier density in degenerated semiconductors does not depend on temperature. However, carrier heating in degenerated semiconductors encounters phonon assisted difficulties. We have recently demonstrated the ability to detect microwave radiation with planar microwave diode on the base of n-n+ junction with low resistivity n-GaAs at room temperature [4].

Influence of free carrier heating on IR light detection in narrow-gap semiconductors

Our study is concerned with peculiarities of intense CO2 laser light detection in narrow-gap semiconductor p-n junctions. Samples of InSb, PbTe and HgCdTe were udner investigation. We present experimental evidence of free carrier heating phenomenon in the semiconductors and its influence on photovoltaic signal. We show, that in particular cases, depending on laser light intensity and applied bias, the hot carrier photosignal of opposite polarity may predominate over the ordinary photovoltaic one.

Microwave-terahertz detection by asymmetrically-necked modulation-doped GaAs/AlGaAs structures

Asymmetrically-necked GaAs/Al0.25Ga0.75As modulation-doped structures are examined as possible active parts of the detector for operation within 10 GHz -3 THz frequency range. The estimations of the device parameters are performed for real structure planned to be used in the experiments. Calculations show that i) Sensitivity of the diodes based on modulation doped structures at liquid nitrogen temperature is significantly higher than at room temperature; ii) this trend remains over the microwave frequency range of operation; iii) narrowing of the necked- size of the device with 300 nm size of the necked-part, the sensitivity could reach 4000 V/W for microwaves and 100 v/W at 1 THz at room temperature with respect to absorbed power. At liquid nitrogen temperature the frequency dependence of voltage sensitivity at the same conditions becomes more pronounced for microwaves- it is 30 000 V/W while in terahertz frequency range the voltage sensitivity drops to the value of 240 V/W.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

CO2 laser radiation detection in compensated germanium

We report the results of experimental study of IR radiation detection in a bulk of compensated germanium. Au or Ni with deep levels in the forbidden energy ap was used as compensating impurities. In spite of great difference in their activation energies the change of electrical resistance of the samples under CO2 laser illumination indicated the similar rise of carrier density in the valence band which can not be explained only by means of direct hole activation character of the electrical conductivity of compensated semiconductors. Evaluation of spatial quantity of in-homogenates in compensated semiconductors confirmed the importance of energetic bands bending due to the existence of ionized impurities complexes for IR detection.

Wide frequency band radiation detector

An original planar n-GaAs diode with n-n+ junction has been constructed to detect radiation in the range from millimeter wavelength. The operational principle of this detector is based on free carrier heating in semiconductor by incident power. The analytical formulae for the voltage arising in the planar diode under microwave and laser radiation obtained by solving phenomenological carrier transport and Poisson equations shows no frequency dependence of the detected voltage up to 1 millimeter wavelength. The frequency dependence of detected voltage in high frequency range results from the frequency dependence of the momentum relaxation time of hot carriers. Experimental results of microwave and laser radiation measurements have shown a good agrement with theoretical suggestions.