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Title: Study of piezoelectricity on III/V semiconductors from atomistic simulations to computer modelling
Author: Tse, Geoffrey
ISNI:       0000 0004 2729 7414
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2012
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High quality and accurate computational data was obtained through first principle quantum mechanical calculations originated from density functional theory without the inclusion of empirical data (ab initio). The support of the computing facility NGS allows us to carry out our research involving large scale atomistic simulations. The data we recently obtained clearly shows piezoelectricity in GaAs and InAs are proved to be non linear in relation to a general strain.The high order fitting equation obtained through the parameterization procedure allowed us to directly evaluate higher order piezoelectric coefficients. By comparing with other linear and non linear models and also experimental data, we reached the conclusion that the validity of our model is correct in the limitation of small shear strain, particularly in case of (111) grown semiconductors. Such limitation however is not restricted under pseudomorphic growth in (001) direction where typically shear strain is small.We further validate our model through elasticity theory to demonstrate the sign of the polarization is found to be opposite to bulk values for an InAs semiconductor layer grown in the (001) direction of growth and subject to 6-7% of lattice mismatch. This is additionally supported with experimental evidence (optical absorption spectra).Furthermore our model provides a direct way in evaluating the polarization for any crystal structure described on the atomic level. This is mainly beneficial to researchers who use molecular dynamics and empirical methods for predicting bandstructure.The fundamental performance for semiconductor devices can be improved through the use of the small polarization created from strain and is likely to bring advantages in future photovoltaics devices.
Supervisor: Migliorato, Max Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: density functional theory; piezoelectric; parameterisation; gallium arsenide; indium arsenide; polarization and dielectric properties ; Born effective charges ; Kleinman parameter ; polarity