Title: Electron spin resonance study of near interfacial point defects in semiconductor (GaAs, Si)/insulator heterostructures
Other Titles: Elektron spin resonantie studie van puntdefecten aan halfgeleider(GaAs, Si)/isolator-heterostructuren
Authors: Nguyen, Xuan Sang; S0210353
Issue Date: 20-Dec-2013
Abstract: It goes without saying that point defects play a crucial role in semiconductors, either benificial or detrimental. Introduced as dopants, they ‘define’ one of the most typical electrical characteristics of semiconductors. But often, point defects −mostly intrinsic ones−may play a most detrimental role such as encountered at semiconductor/insulator interfaces where they may be at the origin of an untolerable amount of interface traps and/or recombination centers. As stated, it points to inadequate interface passivation. This makes the study of point defects an indispensible part of bulk semiconductor andsemiconductor/interface science. The current work fits within the latter prospect, where in a fundamental approach, the conventional electron spin resonance (ESR) technique is applied to attempt atomic identification of crucial device-impacting point defects. By means of multi-frequency ESR study, thiswork is concerned with point defects in ZnS:Mn nanowires, IIIV semiconductor GaAs/oxide entities, and (100)Si/oxide structures with oxides of low dielectric constant . In the first part, multi-frequency ESR and electron spectroscopy techniques were combined to study the symmetry and electronic structures of Mn2+ dopants in solvothermally synthesized c-ZnS nanowires (average diameter 5 nm and 10 nm) with mixed hexagonal and cubic stacking structures. Three different symmetry sites for incorporation of Mn2+ in ZnS have been identified, i.e., substitutional, interstitial/surface sites, and Mn clusters at the surface. Quantum confinement effects are observed, the data indicating a drastically higher efficiency of Mn2+ substitution in large diameter nanowires. The major part of this work has focused on the study of inherently generated interface defects during thermal oxidation of GaAs aiming to assess the atomic-structural identity. The study has been carried out on (100)GaAs/native oxide structures thermally grown in the range Tox = 350-615 oC on both powders and slices of semi-insulating (100)GaAs. Generally, four types of ESR signals (defects) are observed.The first major one is undubiously identified as the As antisite defect which upon oxidation is seen, from Tox = 350 oC onward to be generated in densities increasing with Tox reaching alarmingly high levels ( 10 13 cm−2). This compellingly reveals substantial generation of interfacial 75As+Ga antisites inregistry with the GaAs substrate layer, thus providing solid independent evidence of substantial interfacial As enrichment, appearing as endemic to oxidation of GaAs, and at the same time providing an answerof how a major part of excess As gets interfacially incorporated. Given the known electrical deep double donor attribute of As+Ga, direct identification is thus established of a major system of detrimental interface traps, well fit to cause Fermi level pinning. As to technological relevance, it indicates thatoxidation of the GaAs substrate should be efficiently avoided, or if occurred, the impact of it should be strictly removed when aiming realization of device-grade semiconductor/insulator interfaces.A second spectrum, observed in oxidized c-GaAs slices after additional VUV irradiation, is composed of a quartet, centered at gc 2.268 for the applied field direction in the (100)GaAs sample plane, and shows distinct anisotropic behavior; this newly observed spectrum is suggested to concern a VGa in GaAs. Two more isotropic signals are observed at g 2.06 and 1.937. However, in absence of any attendant resolved hyperfine structure, no atomic model can be proposed. Finally, also observed is the spectrum from substitutional Fe3+ ions introduced as compensation dopants (deep acceptors) in the semi-insulating parent GaAs substrate, of which the inferred crystal field data are found to comply will with previous results. The next part of the work deals with the study of CZ-(100)Si/insulator structures with organosilicate films of lowdielectric constant grown at 300 oC. This deals with the observation ofthe NL8 ESR spectrum of C2v symmetry defect −a thermal double donor, which is found to be introduced in the c-Si substrate during a short UV-assisted thermal curing treatment at 430 oC. A remarkable non-uniform (in depth) generation profile is observed which is concluded asbeing associated with interface stress. Theresults provide a different and affirmative illustration of the influence of in situ strain during the formation of thermal donors during thermal treatment. The result points to the presence of substantial interface stress.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Semiconductor Physics Section

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