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Oxygen vacancies effects in a‐IGZO: Formation mechanisms, hysteresis, and negative bias stress effects
Author(s) -
de Jamblinne de Meux Albert,
Bhoolokam Ajay,
Pourtois Geoffrey,
Genoe Jan,
Heremans Paul
Publication year - 2017
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.201600889
Subject(s) - hysteresis , materials science , amorphous solid , oxygen , condensed matter physics , indium , semiconductor , active matrix , oxide , stress (linguistics) , chemical physics , thin film transistor , chemistry , nanotechnology , optoelectronics , crystallography , metallurgy , physics , linguistics , philosophy , organic chemistry , layer (electronics)
The amorphous oxide semiconductor Indium‐Gallium‐Zinc‐Oxide (a‐IGZO) has gained a large technological relevance as a semiconductor for thin‐film transistors in active‐matrix displays. Yet, major questions remain unanswered regarding the atomic origin of threshold voltage control, doping level, hysteresis, negative bias stress (NBS), and negative bias illumination stress (NBIS). We undertake a systematic study of the effects of oxygen vacancies on the properties of a‐IGZO by relating experimental observations to microscopic insights gained from first‐principle simulations. It is found that the amorphous nature of the semiconductor allows unusually large atomic relaxations. In some cases, oxygen vacancies are found to behave as perfect shallow donors without the formation of structural defects. Once structural defects are formed, their transition states can vary upon charge and discharge cycles. We associate this phenomenon to a possible presence of hysteresis in the transfer curve of the devices. Under NBS, the creation of oxygen vacancies becomes energetically very stable, hence thermodynamically very likely. This generation process is correlated with the occurrence of the negative bias stress instabilities observed in a‐IGZO transistors. While oxygen vacancies can therefore be related to NBS and hysteresis, it appears unlikely from our results that they are direct causes of NBIS, contrary to common belief.