Phase separation and microwave response of epitaxial and polycrystalline manganite films

The resistance, magnetoresistance, and resistance response under microwave irradiation (f=10 and 35GHz) were measured for epitaxial and polycrystalline La 0.67 Ca 0.33 MnO 3 and La 0.67 Sr 0.33 MnO 3 thin films in the temperature range 78÷300K. The microwave induced resistance increase observed for the epitaxial films in a narrow temperature range below the ferromagnetic to paramagnetic transition temperature T c certifies coexistence of low resistance (ferromagnetic) and high resistance (paramagnetic) regions in the manganites. Resistance of polycrystalline films decreased under microwave irradiation in a wide temperature range below T c . The effect was explained in terms of microwave assisted hopping of carriers in high resistance regions formed at grain boundaries of the polycrystalline films

Studies of response of metal-porous silicon structures to microwave radiation

Structures containing layers of porous silicon with two metal contacts are investigated. Porous silicon is manufactured by anodizing p-type crystalline silicon plates of resistivity of 0.4 Ω cm. Contacts for the samples are made by additional boron doping of the surface and by thermal evaporation of aluminium. Resistance and current-voltage characteristics are investigated. Response of the porous silicon layer containing structures under action of pulsed microwave radiation was investigated for the first time. The origin of the response is discussed

Indirect Measurement of Electron Energy Relaxation Time at Room Temperature in Two-Dimensional Heterostructured Semiconductors

Hot carriers are a critical issue in modern photovoltaics and miniaturized electronics. We present a study of hot electron energy relaxation in different two-dimensional electron gas (2DEG) structures and compare the measured values with regard to the dimensionality of the semiconductor formations. Asymmetrically necked structures containing different types of AlGaAs/GaAs single quantum wells, GaAs/InGaAs layers, or bulk highly and lowly doped GaAs formations were investigated. The research was performed in the dark and under white light illumination at room temperature. Electron energy relaxation time was estimated using two models of I-V characteristics analysis applied to a structure with n-n+ junction and a model of voltage sensitivity dependence on microwave frequency. The best results were obtained using the latter model, showing that the electron energy relaxation time in a single quantum well structure (2DEG structure) is twice as long as that in the bulk semiconductor

Dynamical study of heat transport properties of porous silicon

A new fast technique to determine thermal conductivity of porous silicon is proposed. Transient thermoelectric voltage is measured after a pulsed laser irradiation, and analysis of the voltage decay time constant and porosity of the structure gives the value of the thermal conductivity. For n-type Si of 70 % porosity we show the value of 35 W·m–1·K–1. The method can be easily applied for any other porous or otherwise structured low-dimensional media

Charge carrier heating effect in porous silicon structures investigated by microwaves

Diode-like samples, containing porous silicon structures, were investigated by microwave radiation pulses. The resistance of the samples and electromotive force arising over the samples placed in a section of waveguide was measured. Reduction of resistance of the samples was observed with increase in microwave power. More complicated shape of the electromotive force dependence on pulse power was found. It is shown that both effects could be explained by models based on a concept of carrier heating by microwave radiation

Peculiarities of high power infrared detection on narrow-gap semiconductor p-n junctions

We report on experimental results of photosignal investigation in HgCdTe, InSb and PbTe semiconductor p-n junctions under the action of an intense pulsed CO2 laser. The influence of laser power, external bias voltage as well as the diode temperature on the photosignal formation has been studied. We show that under certain conditions both classical photovoltaic and hot carrier phenomena may act simultaneously within a junction thus strongly impacting on responsivity and speed of operation of the device. The drawn conclusions may be of great importance for the development of high power optoelectronic devices

Hot electron effect in degenerate semiconductor tunnel junction

We report on the results of experimental study of free carrier heating in degenerate GaAs tunnel p-n diodes when the carriers are excited by pulsed microwave radiation. Free carrier heating is responsible for the electromotive force in the diode. The magnitude of the electromotive force linearly depends on pulsed microwave power and increases with the decrease in semiconductor lattice temperature. It is almost independent of the pulsed microwave frequency and of p-n junction plane orientation in respect to electric field direction. In the tunnelling regime the dark current in the diode is reduced, however, at high enough forward bias the diffusive current is stimulated due to hot carrier phenomenon

Peculiarities of excitonic photoluminescence in Si δ-Doped GaAs structures

We present investigation of photoluminescence properties of Si δ-doped GaAs structures at different temperatures and various laser excitation intensities. Strong excitonic emission was observed in the δ-doped structures. The photoluminescence in the infrared region, below excitonic emission, originates from a non-phonon free electron-acceptor e-A transitions and longitudinal optical phonon sidebands of e-A transitions. Possible mechanisms for recombination of photocarriers are discussed, with a particular focus on an enhanced excitonic photoluminescence emission in comparison with that from intrinsic GaAs layers of the same structures