Steady-state photoluminescent excitation characterization of semiconductor carrier recombination.

Photoluminescence excitation spectroscopy is a contactless characterization technique that can provide valuable information about the surface and bulk recombination parameters of a semiconductor device, distinct from other sorts of photoluminescent measurements. For this technique, a temperature-tuned light emitting diode (LED) has several advantages over other light sources. The large radiation density offered by LEDs from near-infrared to ultraviolet region at a low cost enables efficient and fast photoluminescence measurements. A simple and inexpensive LED-based setup facilitates measurement of surface recombination velocity and bulk Shockley-Read-Hall lifetime, which are key parameters to assess device performance. Under the right conditions, this technique can also provide a contactless way to measure the external quantum efficiency of a solar cell.

High signal-to-noise Fourier transform spectroscopy with light emitting diode sources.

A temperature tuned light emitting diode (LED) has several advantages over conventional sources for Fourier transform spectroscopy. The large radiation density of LEDs, concentrated in a small spectral region, is ideal for high resolution Fourier transform spectroscopy where a high signal-to-noise (S/N) ratio is desired. A simple, inexpensive LED source leads to a superior performance at high resolutions exceeding that of a tungsten halogen lamp, in the visible region of spectrum.

Spectroscopic signatures of novel oxygen-defect complexes in stoichiometrically controlled CdSe.

Growth of single crystals of CdSe with oxygen, introduced by stoichiometric control to suppress the formation of native Se and Cd vacancies, generates oxygen centers replacing Cd (O Cd) rather than Se (O Se) as expected. This antisite substitution is unambiguously singled out by the host isotope fine structure of the nearest neighbor (NN) Se atoms in the localized vibrational modes (LVMs) of O Cd. When the stoichiometry control favors the formation of Cd vacancies, three infrared signatures gamma1, gamma2 and gamma3 appear ascribable to the LVMs of O Se in association with a Cd vacancy in the NN position as (O Se-V Cd) centers. Polarization measurements establish the monoclinic Cs symmetry for these centers. As a function of temperature, they display a remarkable two-step symmetry transformation, Cs-->C3v-->Td, due to the dynamic switching of the O Se-V Cd dangling bond.