Volume 89, Issue 10, 15 May 2001
Index of content:
- DEVICE PHYSICS (PACS 85)
89(2001); http://dx.doi.org/10.1063/1.1346651View Description Hide Description
A self-assembled Ge/Si quantum dot interlevel infrared photodetector operating at room temperature and at normal incidence is demonstrated. The spectral response exhibits two peaks in the 58–82 and 132–147 meV energy regions with full width at half maximum linewidths as narrow as 25 meV. The two photocurrent maxima are ascribed to transitions from the hole ground state to the excited states in the dots. The peak detectivity and responsive quantum efficiency are and 0.1% for the transition from the ground state to the first excited state and and 0.08% for the transition from the ground state to the second excited state. At large dc bias, a redshift in the transition energies is observed. We argue that the resonance shifts are due to suppression of the depolarization field effect, representing the experimental manifestation of dynamic screening associated with collective electron–electron interaction in the dots.
89(2001); http://dx.doi.org/10.1063/1.1338984View Description Hide Description
layer/four-period amorphous-superlattices (ASSOSLs) with amorphous-Si layers having 12 thicknesses in a range of 1.0–3.2 nm were deposited on substrates using the two-target alternation magnetron sputtering technique. Electroluminescence(EL) from semitransparent Au film/ diodes and from a control diode without any amorphous-Si layer in the ASSOSL has been observed when the applied forward bias exceeded about 5 V; under reverse biases, however, no EL was observed. Every EL spectrum of the diodes along with the control one could be decomposed into two Gaussian bands with peak energies of 1.82 and 2.22 eV, and full widths at half maximums of 0.40 and 0.65 eV, respectively; and their intensities and the current swung synchronously with increasing Si layer thickness with a period length being consistent with half a De Broglie wavelength of the carriers. The experimental results indicated that the EL originates mainly from the radiative recombination of electron-hole pairs via two types of luminescence centers with luminescence energies of 1.82 and 2.22 eV in the layers, rather than within the nanometer Si quantum wells in the ASSOSLs.
Reconstruction of the charge collection probability in a solar cell from internal quantum efficiency measurements89(2001); http://dx.doi.org/10.1063/1.1363677View Description Hide Description
A method is proposed to analyze the internal quantum efficiencyspectra that are commonly obtained on solar cells by measuring their current response in monochromatic light as a function of wavelength. The efficiency values η are regarded as a function of the reciprocal of the light absorption coefficient. The integral relation between and the charge collection probability distribution in the cell with a simple change of variables, can be put in the form of a convolution. A transformed version of this convolution is approximately inverted to yield an explicit expression of in terms of and its derivatives. The method is preliminarily tested on simulated data and is used to analyze published measurements obtained on a Si solar cell and a proton-irradiated InP solar cell.