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Title: Modification of band discontinuities using ionic dipole intralayers
Author: Pan, M.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1999
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The band discontinuities or band offsets in semiconductor heterojunctions are crucial parameters that affect the transport and optical properties of the heterojunction devices. The ability to control and modify the band offsets to desired values would enable the performance of solid devices to be significantly improved. The effect of a one monolayer intralayer of an ionic material (ZnSe) has been investigated for band offset engineering at Ge-Si junctions. Soft x-ray photoelectron spectroscopy (SXPS) was performed to probe the Ge(111)/Si and Ge(111)/ZnSe/Si interface formation. The evolution of the valence band edges and the movements of core levels were monitored as the interfaces were formed under ultra-high vacuum conditions. It was found that the ZnSe intralayer dramatically modified the valence band offset of the Ge(111)/Si heterojunction. The valence band offset was increased by ˜0.57 eV due to the presence of the ZnSe intralayer, as compared to a negligible valence band offset for the intralayer-free junction. The effect of band bending on the interpretation of the valence band offset was found to be negligible for the interfaces studied. The dipole effect was bound to be destroyed at higher coverages (>10 Å of Si) due to the out-diffusion of Se. X-ray photoemission was used to examine the effect of placing a ZnSe intralayer at the Si(111)/Si homojunction. An effective change of ˜0.2 eV in band profile was measured. The initial growth of ZnSe layer on Si(111) substrate was investigated with STM/STS technique. STM images indicated the growth of ZnSe islands on the substrate and STS measurements illustrated the effect of the ZnSe clusters on the electrical properties of the substrate. The ZnSe intralayer-induced modifications of the valence band offsets for these interfaces are interpreted in terms of the charge transfer at the interfaces. It is believed that the orientation and structural geometry of the ZnSe molecule at the interface are of vital importance in determining the magnitude and direction of the dipole moment and hence the band offset. Strain and stability of chemical bonds are also addressed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available