Calculation Of Quantum Efficiency Research Articles

Calculation of the structural dependence of infrared absorption in p-type strained layer SiGe/Si quantum wells

A study of infrared absorption due to intersubband transitions in p-type Si1−xGex/Si quantum wells has been performed. The influence of the hole envelope wave-function and the subband structure on the absorption characteristics is evaluated. In the calculation, the subbands in a SiGe strained layer are computed by using a bond orbital model, which combines the k⋅p and the tight-binding methods, with a strain Hamiltonian. Both of the Poisson and the Schrödinger equations are solved self-consistently to take into account a band-bending effect. The calculated quantum efficiency in a 40 Å Si0.75Ge0.25/Si quantum well detector is compared favorably with an experimental result. The structural dependence of infrared absorption on quantum well width, doping and Ge content in a wavelength range of 3–15 μm is investigated. By varying a well width, our study reveals that a maximum absorption coefficient is obtained when the energy level of the excited-state subband is near the top of a quantum well.

Self-calibration of a thinned, backside illuminated charge coupled devices in the soft x-ray region

A semiempirical method of calibrating a thinned, backside illuminated charge coupled device (CCD) chip in the soft x-ray region is presented. It is based on determining the thickness of the dead layer self-consistently using the continuum emission from laser produced plasmas. The CCD camera system was coupled to a transmission grating spectrometer and recorded the spectrally resolved continuum emission from laser irradiated tungsten targets. The thickness of the dead layer was then determined by comparing the experimental spectra with the calculated quantum efficiency for a thinned CCD using a simplified model. In this way the CCD chip was semiempirically calibrated. The accuracy of the calibration in the soft x-ray range was assessed by comparing the CCD recorded spectra with those recorded by a spectrometer using the absolutely calibrated Kodak 101 photographic plates and a similar transmission grating. Based on this calibration, the CCD sensitivity is deduced to be about two orders of magnitude higher than that of the Kodak plates in this wavelength range.

Low-energy electron transport in alkali halides

A model of electron transport in alkali halides, below 10 eV, is described. It is based on theoretically calculated microscopic cross sections of electron interactions with lattice phonons. Both acoustic and optical scatterings are taken into account, the former being also treated as a quasielastic process that randomizes the electron motion. Monte Carlo calculations based on the model simulate the UV-induced photoelectron emission from CsI. The calculated quantum efficiency and energy spectra are in good agreement with experimental data, in the photon energy range of 6.3–8.6 eV. The probability for an electron to escape from CsI, NaCl, and KCl is provided as a function of its energy and creation depth. A comparison is made between our approach and other phenomenological models.

Ultraviolet, visible, and infrared response of PtSi Schottky-barrier detectors operated in the front-illuminated mode

The quantum efficiency of PtSi Schottky-barrier detectors has been measured as a function of wavelength from 0.23 to 7 mu m. For front-illuminated PtSi/p-Si devices operated at low temperatures, quantum efficiencies of 40 to 70% are obtained in the ultraviolet (UV) and visible regions with little loss of the infrared (IR) photoresponse that is obtained for operation in the conventional back-illumination mode. For room-temperature operation of front-illumination PtSi/n-Si devices, the quantum efficiencies are approximately the same in the UV and visible regions, but the IR response decreases abruptly beyond the Si absorption edge. Room-temperature transmission and reflection measurements have been used to determine the values of the real and imaginary parts of the complex dielectric constant for PtSi at wavelengths from 0.2 to 3 mu m. A simple model, used with these values and published values of the dielectric constant for Si, yields calculated quantum efficiencies in the UV and visible regions that agree quite well with the measured efficiencies. The temporal response of front-illuminated PtSi/p-Si detectors in the visible and IR regions is found to be fast enough for operation at video frame rates. >

Deep-UV lithographic response and quantum efficiency calculations of poly((trimethylsilyl)methyl Methacrylate-(chloromethyl)styrene) copolymers

Deep-UV lithographic response and quantum efficiency calculations of poly((trimethylsilyl)methyl Methacrylate-(chloromethyl)styrene) copolymers

Photodesorption from CdS(0001) exposed to NO and CO

Photodesorption from the (0001) surface of CdS has been studied with low-energy photons of wavelength 200–850 nm. The clean, unannealed surface was exposed to high doses (∼108 L) of CO and NO at room temperature. CO and CO2 were observed to desorb from the surface exposed to CO while NO was the only desorbing specie from the NO/CdS system. The measured photodesorption threshold energy for all species is ∼1.77 eV, which is much less than the CdS energy gap and is approximately the energy of surface states within the band gap of CdS. A second threshold is observed at the direct gap of CdS. The desorption signal is found to be proportional to the incident photon flux, with the calculated quantum efficiency (yield) of ∼10−5 molecules/photon at λ=300 nm. The desorption mechanism for this system agrees with past work on silicon where photohole creation in both the surface states and bulk valence bands was prominent.

A new infrared avalanche photodiode for long distance fiber optic communication

Theoretical studies are presented for the response characteristics and quantum efficiency of a new infrared avalanche photodiode (APD) for the 3–4 μm wavelength range. The device structure is a photo-DOVATT (see below) made of InAs xSb 1−x InAs , InAs xSb 1−x being lattice matched to InAs. We expect it to be used in long distance fiber-optic communication. The calculated gain-bandwidth product is around 20 GHz and the calculated quantum efficiency is 75% near 3 μm wavelength.

Reaction of singlet oxygen with styrene-butadiene copolymer: 1. 9-Methylanthracene photo-sensitized oxidation of styrene-butadiene copolymer

9-Methylanthracene (9MA) photo-sensitizes the oxidation of styrene-butadiene copolymer (SBR). This effect was explained as being associated mainly with the ability of 9MA to form singlet oxygen. The calculated quantum efficiency of singlet oxygen formation resulting from the quenching by oxygen of electronic excited states of 9MA is high ( γ Δ M = 0·74 ± 0·04). This indicates that 9MA should be a rather efficient photo-sensitizer in photo-oxidation processes.

Photoacoustic spectra of transparent solids doped with localised absorbing centres

A theoretical method for obtaining the band shapes of photoacoustic (PA) spectra in solids containing absorbing centres is reported. This theory combines some standard approaches used in PA spectroscopy and the Huang-Rhys model for electron-lattice coupling, and provides a PA method for quantum efficiency calculations. An application to real systems such as Al2O3:Cr, ZnS:Mn is made. The theoretical predictions show a fairly good agreement with the published experimental results. Further improvements of the models proposed are discussed in the concluding section.

ChemInform Abstract: PROCESS FOR HIGH PHOTOCURRENT IN IBC SOLAR CELLS

AbstractDie IBC‐Sonnenzellen (interdigitated back contact solar cells) eignen sich besonders für hohe Intensitäten, haben keine Abschattung durch das Kollektionsgitter und niedrigere Kontakt‐ und Elektrodenwiderstände.

Process for High Photocurrent in IBC Solar Cells

An interdigitated back contact solar cell fabrication process that yields cells with current‐collection efficiencies in excess of 90% in n‐type silicon is presented. This process maintains high bulk minority‐carrier lifetime through the use of diffusion gettering steps and relatively low processing temperatures. Low front and back surface recombination velocities are achieved by growing thermal oxides on these surfaces followed by a forming gas anneal. Bulk lifetimes on the order of 350μsec and front surface recombination velocities of less than 30 cm/sec are determined by comparing measured quantum efficiency data to calculated quantum efficiency using an analytical code which solves the transport equations in one dimension. These lifetimes are compared to values of 290‐190 μsec measured for cells with and without a front surface n+ layer, respectively. These were measured with a laser scanning technique using the 514 nm wavelength and are considered a lower limit to the lifetimes.

Calculation of photoemission characteristics of cubic K3Sb

A three-step model of photoelectron emission is used to calculate the quantum efficiency and the energy distribution functions of emitted electrons with allowance for the scattering of the excited electrons leading to the production of electron-hole pairs. The calculated quantum efficiency is compared with experimental data in the visible part of the spectrum. The correlation between the structure of the photoemission characteristics and the density of the electron states is discussed.