Parallel Detection of Cathodoluminescence.

Available from UMI in association with The British Library. A GEC P8600 Charge-coupled device has been used in the design and fabrication of a parallel detection system or optical multichannel analyser for the analysis of Cathodoluminescence Spectra. The P8600, whilst designed for video applications, is used as a linear array by merging entire rows of pixels together on the on-board output amplifier. A dual slope integration method of correlated double sampling has been used for noise reduction. An analysis of the performance of this system is given and the achieved noise level of 22 electrons is found to be in good agreement with that theoretically possible. A complete description of the circuits is given together with details of its use with a "Link 860" computer/analyser and a "Philips 400" electron microscope. To demonstrate the system, a study of the cathodoluminescent properties of Cadmium Telluride grown by molecular beam epitaxy has been made. In particular the effect of dislocations, stacking faults and twins on luminescence has been studied. Dislocations are seen to cause a quenching of excitonic emission with no corresponding increase in any other emission. The effect of stacking faults was seen to vary between different samples with an enhancement of long wavelength emission seen in poor quality samples. This supports the premise that the faults are nucleated by surface impurities which are also responsible for the enhanced emission. Some twin defects have been found to cause enhanced excitonic emission. This is compatible with the existence of natural quantum wells at twin faults proposed by other workers. The speed with which the parallel detection system can acquire spectra makes it a valuable tool in the study of beam sensitive materials. To demonstrate this, measurements were made of the decay rates of the weak cathodoluminescence from the organic crystal Coronene. These rates were seen to have time constants less than two minutes and such measurements would not have been amenable by conventional methods.