Jonas Gradauskas

Giga- and terahertz frequency band detector based on an asymmetrically necked n-n+-GaAs planar structure

We describe the concept of an asymmetrically shaped n-n+-planar GaAs diode whose operation is based on nonuniform free charge carrier heating effects. The detector was fabricated on thin elastic polyimide film and has been shown to have an operational bandwidth for detection ranging from 30 GHz up to 2.5 THz at room temperature. The voltage sensitivity of the detector is nearly independent of the frequency from 30 GHz up to 0.7 THz and is close to 0.3 V/W. In the upper section of the frequency range, 0.7–2.5 THz, the sensitivity is limited by the electron momentum relaxation time. The induced signal responds linearly to the incident power over the frequency range studied. It is shown that the performance of the detector can be explained well by a phenomenological theory.

Enhanced exciton photoluminescence in the selectively Si-doped GaAs/AlxGa1−xAs heterostructures

Experimental results examining the photoluminescence spectra of selectively Si-doped GaAs/AlxGa1−xAs heterostructures is presented. Possible mechanisms of carrier recombination are discussed with a special emphasis on the peculiarities of excitonic photoluminescence. Strong intensity lines in photoluminescence spectra are associated with the formation and enhancement of free exciton and exciton-polariton emission in the flat band region of an active i-GaAs layer. The excitonic PL intensity is sensitive to the excitation intensity indicating high nonlinear behavior of spectral-integrated photoluminescence intensity and exciton line narrowing. These observed phenomena may be related to the collective interaction of excitons and the interaction of excitons with emitted electromagnetic waves. The gain of the amplification of the excitonic photoluminescence intensity in the heterostructure was found to be more than 1000 times larger than the intensity of i-GaAs active layer. The quality factor of the exciton l...

Microwave sensor based on modulation-doped GaAs/AlGaAs structure

We propose a microwave diode based on a modulation-doped GaAs/Al0.25Ga0.75As structure. The principle of the diode operation relies on a non-uniform heating of the two-dimensional electron gas in microwave electric fields arising due to the asymmetric shape of the device. The voltage sensitivity of the diode at room temperature is close to 0.3 V W−1 at 10 GHz, which is comparable to the value obtained using similarly shaped and sized diodes based on bulk n-GaAs. At liquid nitrogen temperature, the voltage sensitivity strongly increases reaching a value of 20 V W−1 due to the high mobility of the two-dimensional electron gas. The detected signal depends linearly on power over 20 dB, until hot-electron real-space-transfer effects begin to predominate. We discuss noise temperature measurements at 10 GHz, consider the frequency dependence of the voltage sensitivity in the microwave range and compare the performance data of the proposed device and the asymmetrically shaped bulk GaAs diode within the 10 GHz–2.5 THz frequency range.

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.

Microwave detectors based on porous silicon

Two types of structures comprising porous silicon (por-Si) layers between metal electrodes were prepared, which possessed nonlinear (A type) and linear (B type) current-voltage characteristics. The exposure to microwave radiation leads to the appearance of an emf between electrodes. The B-type structures exhibit high voltage responsivity and can be used as microwave radiation sensors.

Photoelectrical properties of nonuniform semiconductor under infrared laser radiation

Photoelectrical properties of nonuniform semiconductor under IR laser radiation has been investigated theoretically and experimentally. It is shown that photoemission of hot carriers across the potential barrier and the crystal lattice heating are dominant mechanisms of the photovoltage formation in p-n and l-h junction when laser photon energy less than the semiconductor energy gap. Influence of aluminum arsenide model fraction in GaAs/AlxGa1-xAs p-n heterojunction on CO2 laser radiation detection has been studied. It has been established that the photoresponse originating from the free carrier heating depends on the energy band discontinuities in heterojunction. GaAs/AlxGaz-xAs heterojunction with x <EQ 0.2 is found to be more suitable for IR detection compared to GaAs homojunction. In metal- semiconductor Schottky contact photoresponse demonstrates strongly nonlinear dependence on excitation intensity when photon energy is less than Schottky barrier height. We suppose that in this case the photosignal is caused by the multiphoton and multi step electron photoemission across the Schottky barrier.

Photothermal effect in narrow band gap PbTe semiconductor

In this paper we report the observation of photothermal effect in PbTe p-n junction. The effect is expressed in photosignal generation due to illumination by 100 ns pulse CO2 laser with photon energy less than PbTe forbidden gap.

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.

Hot carrier photocapacitive effect

Semiconductor p-n and metal-insulator-semiconductor structures containing a capacitive element were investigated under pulsed ir laser irradiation. It is shown that the carrier heating in the structures is responsible for the rise of the photosignal. A direct correlation between the photosignal and the capacitance of the structures is confirmed. Possible applications of the effect are discussed.