Showing papers by "Oscar E. Martínez published in 2007"

Photon counting statistics using a digital oscilloscope

Abstract: We present a photon counting experiment designed for an undergraduate physics laboratory. The statistics of the number of photons of a pseudo-thermal light source is studied in two limiting cases: much longer and much shorter than the coherence time, giving Poisson and Bose-Einstein distributions, respectively. The experiment can be done in a reasonable time using a digital oscilloscope without the need of counting boards. The use of the oscilloscope has the advantage of allowing the storage of the data for further processing. The stochastic nature of the detection phenomena adds additional value because students are forced to do data processing and analysis.

Stress distribution mapping of GaAs on Si conformal layers

Abstract: Cathodoluminescence and micro-Raman studies of GaAs on Si layers grown by the conformal method show a characteristic quasiperiodic modulation of the stress distribution perpendicular to the growth direction. Using the capability of the spectral imaging in the cathodoluminescence technique, the stress distribution has been directly mapped. The Raman data give accurate information of the stress level variations in the upper part of the samples, which compare well with the luminescence data. The origin of the quasiperiodic stress variations are discussed in terms of the growth geometry, taking account of the presence of a compliant thin SiO2 layer in between the Si substrate and the ⟨110⟩ growing GaAs layer.