STRUCTURAL AND OPTICAL PROPERTIES IN POROUS NANOSTRUCTURED SEMICONDUCTORS

Non-radiative processes in porous silicon (PS) have been examined using a variety of techniques to examine the effects on photoluminescence (PL) in order to determine the nature of the PL process and the ability to modulate this for eventual incorporation of the material within devices. Voltage quenching of PL from p-type PS with a nanoporous structure has been studied using samples with different types of solid contacts and the effect of these on quenching examined. Voltage quenching has allowed us to distinguish quenching mechanisms with two distinct induced non-radiative processes. X-ray photoelectron spectroscopy (XPS) has been used to examine chemical evolution on the surface of free-standing PS during the application of an external bias. XPS has also been used to study the valence band of porous silicon during the application of an electric field, in order to study the depletion of carriers from the nanocrystallites. It is believed that this is an important factor in the voltage quenching effect. Further more a model is proposed for the device band structure to explain the invariance of the energy-selective quenching to bias polarity. This work has been extended to cover optical quenching of PL using dual laser excitation with a small bias applied across the sample and these results back up the proposed model. Si and O K-edge extended X-ray absorption fine structure (EXAFS) and Fourier transform infared spectrometry (FTIR) have been used to correlate changes in 1st shell Si-Si co-ordination numbers and peak PL output to size changes in PS nanocrystallites. Ge K-edge EXAFS has been used to characterise porous SixGei-x and, in conjunction with time-resolved luminescence, to assess this materials suitability for devices relative to PS. Time-resolved luminescence has been used to assess the spectral output of PS. The results indicate that quantum confinement is a strong factor in causing the blue-shifted PL emission of PS. In addition, detailed results of the temperature dependence of the PL have been obtained and mechanisms proposed to explain the blue shift of the PL peak as the temperature of the PS is reduced. The study of non-radiative processes in PS has allowed us to move a step closer to potential device applications using this material.

Name dc:type.qualificationname

PhD

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

De Montfort University

Year dc:date.issued

1998

Author dc:creator

• PARKINSON, MARK

Licence

• https://dora.dmu.ac.uk/bitstreams/9c8d34c3-d7ae-4d3c-8d5a-3a19089b436b/download