Temperature Dependence Of Photocurrent Research Articles

Photovoltaic Properties of MnGaInS4 Single Crystals

The spectral distribution of photoconductivity and the temperature dependence of photocurrent in MnGaInS4 single crystals have been investigated. Photoconductivity spectra demonstrate both intrinsic and impurity conductivity. In the case of manganese deficiency in crystals, an acceptor-type defect is seen in the wavelength range of 0.64–0.76 μm. The temperature dependence of the MnGaInS4 single crystal bandgap is due to exciton–phonon interaction. In the temperature interval studied, photocurrent rises because of thermal depletion of trapping levels. The activation energy of trapping levels has been calculated.

Boosted photocurrent via cooling ferroelectric BaTiO3 materials for self-powered 405 nm light detection

Research of photovoltaic effect has been increased based on ferroelectric materials, generating a series of important discoveries. However, the conventional ferroelectric ceramics usually have low photocurrent values. How to increase the photocurrent of ceramics becomes an important issue to push forward the practical application of these devices. Here, we report the intrinsic properties about the temperature dependence of photocurrent and its relationship with the ferroelectric polarization. The photocurrent of BaTiO3 ceramics strongly depends on the temperature, which can achieve an enhancement of 121.9～179.6% at low temperature (80–240 K) as compared with that at room temperature. The enhancement of photocurrent is associated with ferro-pyro-phototronic effect, evidencing by the enhanced ferroelectric polarization and the activation of shallow trap levels at low temperature, which can be used for detecting 405 nm light under low temperature. This research provides a potential approach to boost the photocurrent of ferroelectric ceramics and enable the development of a wide range of optoelectronic devices.

Analysis of Photovoltaic Properties of a Perovskite Solar Cell: Impact of Recombination, Space Charge, Exciton, and Disorder

We present the analysis of photovoltaic properties in perovskite solar cells to explore the impact of excitonic features, disorder, recombination, and space charge effects using temperature and photo-intensity dependence. Photo-intensity dependence reveals an enhancement of classical Einstein relation due to the presence of traps and formation of space charge effects resulting in reduced conductivity. Exciton versus free charge density upon photo-excitation is analyzed from temperature dependence of photocurrent. Temperature dependence of VOC is excellently explained by considering a combined energetic disorder in a solar cell, and a moderately high value of variance ~125 meV is obtained.

THE INFLUENCE OF GROWTH CONDITIONS AND DONOR DOPING ON CONDUCTIVITY MODE AND DEEP TRAPS SPECTRA IN TLBR SINGLE CRYSTALS

Studies of electrical characteristics, deep traps spectra, microcathodoluminescence (MCL) spectra of undoped and donor (Pb, Ca) doped TlBr crystals as influenced by growth conditions (Br pressure, Ar pressure, growth in air) are presented. It is shown that, for the 85−320 K temperature range, the crystal conductivity was determined not by ionic conductance but by the density of electrons and holes supplied by the ionization of deep centers. Centers with activation energies of 1−1.2 eV that pin the Fermi level in donor doped crystals are shown to play a prominent role in the recombination of nonequilibrium charge carriers. In undoped crystals the Fermi level is pinned near Ev+0.8 eV and these centers are also active in the recombination of charge carriers and are responsible for the MCL band peak near 1.85 eV. The temperature dependence of photocurrent in undoped crystals is strongly influenced by electron trapping on relatively shallow centers located 0.1−0.2 eV below the conduction band edge. Deep traps spectra revealed the presence of centers with activation energies 0.36, 0.45, 0.6 eV whose concentration increases with donor doping. Doping with Pb or Ca increases the dark resistivity of the crystals by about an order of magnitude, but Pb doping enhances the density of deep traps, which is not favorable for use of this material in radiation detectors.

Effects of Exciton-polariton on Mach-zehnder Interference Devices

A new optoelectronic device based on excitonpolariton was studied. In particular a Mach-Zehnder interference device fabricated by using a GaAs quantum well was studied. We simulated the output characteristics of Mach-Zehnder interference device by using a Finite Difference Time Domain (FDTD) method. Then we compared them with the experimental results measured in a low-temperature. After that we obtained the numerical values of electro-optic effect coefficients. Those were as large as 105×10^(-11) m/V for 4.5 K, while 74×10^(-11) m/V for 77 K. Therefore this estimation is considerably large, showing 57 (4 K) and 41 (77 K) times larger than conventional KDP crystal. This effect is probably caused by the excitonpolariton effect. Furthermore, we performed a photocurrent experiment to understand the transmitted light phase change characteristics, causing such large electro-optics effect at a comparatively higher temperature. Temperature dependence of photocurrent showed that the absorption edge and exciton peak remained constant up to 77 K, and then shifted to lower energy as the temperature increased. This probably explains how the large electro-optic effect can be obtained at a comparatively high temperature, i.e., 77 K.

Investigation of the photoelectric characteristics of photodiode structures with silicon-based potential barriers

Based on silicon with a base region thickness of 300 μm, phototransforming Au–nSi–Au structures with potential barriers are prepared. The diode structures obtained possess high photosensitivity in the spectral region 0.9–1.1 μm at low illumination intensities of 10 lux (up to 5 A/W). Based on investigations of the photoelectric characteristics, it has been established that the Au–nSi–Au structures in the range of temperatures from room temperature to 40 o C at low working voltages (0.1–0.2 V) are distinguished by the weak temperature dependence of photocurrents. In principle, in the spectral range 0.7–1.1 μm the Au–nSi–Au structures obtained can easily replace both gallium arsenide and classical silicon photodiodes with one rectifying junction in optoelectronic devices.

Photoconductivity in LiNbO3 crystals codoped with MgO and Cr2O3

The photoconductivity of LiNbO3 crystals codoped with Cr2O3 and different concentrations of MgO from 0 up to 6 mol % is reported. The spectral excitation of photocurrent presents an intense band corresponding to the Cr3+ induced blue absorption edge, but illuminating at the (4)A(2) -> T-4(1) ionic transition band a weak photocurrent is also excited. The photoconductivity is interpreted in terms of Cr3+ ionization and the formation of Nb-Nb(4+) small polarons as charge carriers. Photoconductivity below about 140 K is suppressed. The analysis of the photocurrent temperature dependence results in a 0.14 +/- 0.02 eV binding energy of the polaron at low temperature. Photoconductivity induced by excitation in the intraionic Cr3+ can be explained by a tunnelling process between the excited Cr3+ and the polaron state at the next-nearest-neighbour Nb-Nb(5+).

Temperature Dependence of Photocurrent and Band Gap of Cl-Doped Semi-Insulating CdTe with Evaporated Au Electrodes

Photocurrent was measured as a function of wavelength for Cl-doped semi-insulating CdTe specimens with evaporated Au electrodes. It is found that the photocurrent decreased with decreasing temperature. This behavior of the photocurrent is different from that usually observed in other semiconductor specimens. Employing the theory, which was proposed for the amorphous semiconductor, we attempted to explain this phenomenon. From the photocurrent spectral peak at various temperatures, the band gap of CdTe was deduced and an empirical equation for the temperature dependence of the band gap EG(T) was obtained as EG(T)=EG(0)-αT2/(T+β), α=5.21×10-4 eV/K, β=37.5 K.

Dark and photoelectric conversion properties of p-MgPc/n-Si (Organic/Inorganic) heterojunction cells.

Heterojunction cells of p-MgPc/n-Si have been fabricated by thermal evaporation of MgPc thin films onto Si〈100〉 single crystal wafers. The devices exhibit strong photovoltaic characteristics with an open–circuit voltage of 0.35 V, a short–circuit current of 3.57 mA and a power conversion efficiency of 1.05%. These parameters have been estimated at room temperature and under a monochromatic illumination of 633 nm with an input power density of 50 mW/cm 2. The activation energy of the charge carriers of 0.32 eV and the cell series resistance of 2 kΩ have been evaluated from the measurements of the dark I– V characteristics. A free–carrier concentration of 2.2×10 16 cm −3 and a barrier width of 75 nm have been estimated from C– V measurements. The temperature dependence of photocurrent, at constant illumination, has been also investigated.

Molecular orientation dependent photoconductivity of liquid crystalline oligosilanes

Abstract Polysilanes are known to be promising hole transport materials among conducting polymers. Their structure can be better controlled by using single dispersed oligomers. Recently an oligosilane (Me(SiMe 2 ) 10 Me) is found to show a mesophase (S B ). In the mesophase, we have observed unusual negative temperature dependence of photocurrent. This can be explained by temperature dependent molecular orientation, which has been confirmed by polarized UV absorption spectroscopy.

Photoconductivity of C 60/C 70 films

We report results on the steady-state photoconductivity of solid C 60/C 70 films including a comparison between the optical absorption and the photocondutivity action spectra, and the photocurrent temperature dependence at different wavelengths. We observed photoconductivity in the visible range of the spectrum, the temperature dependence of which indicated two distinct transport regions. The mechanisms involved are discussed and compared with the behaviour observed in hydrogenised amorphous silicon.

Vaculjm Vapor Deposition of C60 Thin Films and Their Lateral Photoconductivity

Abstract Thin films of C60 are fabricated by vacuum vapor deposition and their lateral photoconductivity is measured. We found unusual temperature dependence of photocurrents, the cause of which is so far unknown. From the comparison of photocurrent and absorption spectra it is shown that photocarrier generation efficiency is higher around absorption edge (600 nm). Photocurrents are found to increase in proportion to the square root of light intensity.

Temperature Dependence of Photocurrent in Undoped Semi-Insulating Gallium Arsenide

The temperature dependence of extrinsic and intrinsic photocurrent, in undoped semi-insulating GaAs containing EL2, in the range 20 K to 200 K is studied. The photocurrent increases ecponentially as the temperature is decreased down to 50 K and then decreases slightly for lower temperatures. It is argued that the exponential increase in photocurrent is due to the thermal activation energy of hole capture cross-section of the lifetime controlling centre

Influence of in on some electrical, photoelectrical and optical properties of a-CdS

Amorphous CdS films have been modified by coevaporation of CdS and In. An increase of the dark conductivity by 1–2 orders is obtained. A new maximum in the photocurrent temperature dependence is observed. For In-doped films the photosensitivity in the extrinsic absorption region decreases and the refractive index increases from 2.1 to 2.3. It is suggested that In-doping decreases the disorder in the layers.

Temperature dependence of the stationary photocurrent in doped sillenite type crystals

The temperature dependence of the photocurrent in doped sillenite-type crystals is investigated in the temperature range 80–300°K. In the region of low temperatures thermally activated photocurrent is observed, while at high temperatures quenching is observed. In a number of specimens the temperature quenching section is absent. The results are explained within the framework of a multilevel recombination model involving slow and fast recombination centers as well as capture levels.

Interference oscillations in the temperature dependence of photocurrent and transmission of GaSe, GaTe, and GaSexTe1–x single crystals

Interference oscillations in the temperature dependence of photocurrent and transmission of GaSe, GaTe, and GaSexTe1–x single crystals

Thermal Quenching and Thermally-Assisted Optical Quenching Effects of Photocurrents in Evaporated Thin Films of β-Copperphthalocyanine

The temperature dependence of photocurrents under steady light excitation was investigated in evaporated thin films of β-copperphthalocyanine in the near ultraviolet, visible and near infrared regions under an ultra-high vacuum. Thermal photocurrent-quenching has been observed in every spectral region, and thermally-assisted optical quenching has been newly observed in the near ultraviolet and visible regions. The mechanisms are explained by the scheme that excitons produced by light quanta cannot be dissociated into free carriers in the definite absence of adsorbed gases and that thermal desorption and thermally-assisted photodesorption of these gases cause the thermal and thermally-assisted optical quenchings to occur, respectively. These quenching effects are characteristic of extremely thin films.

Thermal Quenching Effect of Transient Photocurrents in Evaporated Thin Films of β-Copperphthalocyanine under an Ultra-High Vacuum

The temperature dependence of photocurrents was investigated in evaporated thin films of β-copperphthalocyanine in the near ultraviolet and visible regions under an ultra-high vacuum. Thermal quenching of the photocurrent was observed to begin at about 120°C and the photocurrent was completely quenched at about 150°C. The photocurrent re-appeared as the temperature was decreased. The quenching mechanism is discussed in terms of the extrinsic dissociation of excitons, which generates free electrons and holes. Thermal desorption of the adsorbed gases, which is a key factor in carrier formation, causes thermal quenching. The thermal quenching was found to be a characteristic of thin films.

Temperature Dependence of Photocurrent in Polyethylene

Temperature Dependence of Photocurrent in Polyethylene

Si-photodiodes as dosimeters for fast neutrons

The dosimeter properties of Si-photodiodes, e.g. dose sensitivity, detection limit (1 rad), temperature dependence of photocurrent at different doses, have been investigated. The evaluation equipment is described and further improvements shall be discussed.