Effects of a dead layer localized at the interface in a photodiode are studied theoretically. The model proposed here is developed for a Schottky junction but can be adapted to any other structure. A sharp decrease of the quantum efficiency in the short wavelength range is predicted, as generally observed experimentally. The various features encountered for the spectral responses are explained by the influence of the diffusion length L and of the dead layer thickness d. It is shown, moreover, that measuring the diffusion length from the photovoltaic short circuit spectra gives, in fact, the sum of L and d but determination of the maximum in the spectral response allows to separate the two.
Thin films of the organic complex PVK:TNF were studied for various rates of TNF (0 to 50%) by means of photoinduced current transient spectroscopy (PICYS) and photoconductivity measurements. PICTS reveals the presence of a continuous trap distribution. Both the two models of the transport phenomenon by hopping (microscopic behavior) or by multiple trapping (more efficient for a quantitative explanation) explain the shape of the decay of photoconductivity and the observed results. Contrarily to amorphous semiconductors, the trap distribution is not here exponential. In a first approximation, the distribution is fairly uniform until 0.6-0.65 eV, followed by a sharp decrease until about 0.85 eV where the density of states practically vanishes. The microscopic model of hopping allow an interpretation of the distribution and gives a plausible explanation of the observed results.
Photoelectronic processes in CdIn2Te4 are investigated by means of photoconductivity studies and by the thermal spectroscopy: the photoinduced current transient spectroscopy. The so-called four-gate method shows that we are in presence of a continuous or quasi-continuous distribution of levels in the energy bandgap. This occurs in the whole range of energy prospected: 0.1 to 0.7 eV. The analysis of the decay of the photocurrent transients at various temperatures allows to calculate the density of states and leads to the conclusion that the trap distribution inside the gap is formed by two parts: a continuous exponential trap distribution under the conduction band, until 0.35 eV, and a Gaussian distribution from 0.35 to 0.7 eV with a maximum at 0.55 eV, near the middle of the gap.
Semi-insulating CdTe:V has been revealed very interesting for photorefractive applications in the near IR region, at room temperature. Addition of Zn, in amounts of some percents, improve highly the photorefractive properties of this material and its mechanical quality. We have studied Cd1-xZnxTe:V for x = 0.01, 0.04, 0.07 and 0.10 in comparison with CdTe:V, i.e. for x = 0. Photorefractive CdZnTe:V crystals are investigated by thermal and optical spectroscopies, by spectral response of steady-state photoconductivity at various temperatures, mainly in the near infrared region. The deep levels have been characterized. The role of zinc and those of the two charge levels of vanadium, V2+and V3+, in the photorefractivity properties have been determined.
Photorefractive CdTe:V crystals are investigated in comparison with undoped CdTe and with As and Cl codoped samples by spectral response of steady-state photoconductivity at various temperatures, mainly in the near infrared region. The deep levels have been characterized. The two charge levels of vanadium, V2+ and V3+, have been identified and their roles in the photorefractivity properties determined.
Reliable and reproducible results on Bi12GeO20 (BGO) crystals depend on the thermal and optical history of the samples. It is then necessary to find well defined state of the material for which the experimental observations are reproducible. The de-excited state is reached either by an annealing at 450 - 500 K, or by illumination with photons of energies less than 2.2 eV. The corresponding photoconductivity is called the background photoconductivity. The excited state is obtained when the crystal is illuminated with photons of energies higher than 2.4 eV until reaching an optical and electrical steady state. The corresponding photoconductivity is the photoinduced photoconductivity. Comparison between these two states show that for energies higher than 2.4 eV the background and the photoinduced photoconductivity are the same, but for energies lower than 2.2 eV they are very different and the ratio of their magnitudes can reach a factor 1000. This study allows to define the conditions of writing, reading and erasing information on the BGO crystals. These effects are explained in terms of charge transfers between deep and trap levels, induced by the appropriate illuminations.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.