Abstract
In this paper, we investigate the embryonic stage of oxidation of an epi Ge(001)-2 × 1 by atomic oxygen and molecular O2 via synchrotron radiation photoemission. The topmost buckled surface with the up- and down-dimer atoms, and the first subsurface layer behaves distinctly from the bulk by exhibiting surface core-level shifts in the Ge 3d core-level spectrum. The O2 molecules become dissociated upon reaching the epi Ge(001)-2 × 1 surface. One of the O atoms removes the up-dimer atom and the other bonds with the underneath Ge atom in the subsurface layer. Atomic oxygen preferentially adsorbed on the epi Ge(001)-2 ×1 in between the up-dimer atoms and the underneath subsurface atoms, without affecting the down-dimer atoms. The electronic environment of the O-affiliated Ge up-dimer atoms becomes similar to that of the down-dimer atoms. They both exhibit an enrichment in charge, where the subsurface of the Ge layer is maintained in a charge-deficient state. The dipole moment that was originally generated in the buckled reconstruction no longer exists, thereby resulting in a decrease in the ionization potential. The down-dimer Ge atoms and the back-bonded subsurface atoms remain inert to atomic O and molecular O2, which might account for the low reliability in the Ge-related metal-oxide-semiconductor (MOS) devices.
Highlights
Due to their high carrier mobilities, both the Ge and III-V compound semiconductors are channel materials that might replace silicon in p- and n-type metal-oxide-semiconductor field-effect transistors (MOSFETs) [1,2,3,4,5,6,7,8,9,10]
For the III-V metal-oxide-semiconductor (MOS), the established reports clearly show that a high-quality oxide/(In)GaAs interface leads to high-performance (In)GaAs MOSFETs in the drain currents and transconductances [9,10,11,12,13]
The present experimental results provide direct evidence that the unpassivated down-dimer atoms might account for the reliability issue that is related to Ge MOS devices [39,40]
Summary
Due to their high carrier mobilities, both the Ge and III-V compound semiconductors are channel materials that might replace silicon in p- and n-type metal-oxide-semiconductor field-effect transistors (MOSFETs) [1,2,3,4,5,6,7,8,9,10]. Years of researches on (In)GaAs(001) have concluded that chemical processes to the hetero-element surfaces would destroy the long-range order; the removal of the native oxides is out of the question for attaining a high-quality high-κ/III-V interface. The rethproorutegdh fcohuemr Gicealclyhawregtetesdtattresatwmeernetsco[2m6]m, dounrliyngobacsiedrvparobclesbsyesn[e2u7,t2r8a]l, boeraumpoonxsidudatdieonne[x2p5o],stuhrreough chemtiocaalllyarwgeetatmedoutrnetaotfmaetonmtsic[2o6x]y,gdeunroinngaa2ci×d1prreoccoenssstreusc[t2ed7,2su8]r,faocreu[2p9o].nItsuisdoddednteoxspeeostuharet tthoesaelarge amoutnhticokf aGteomoxiicdoexsyrgeespnoonndad2if×fer1enretlcyonwsittrhuchteeadt,swuritfhacoen[e29s]h.oIwt iisnogdadntionscereeatshea[t3t0h]easnedthtihcek oGteheorxides resposnhdowdiiffngereantdlyecwreiathsehe[2a7t,] winiththoenessthreonwgtihngoafnGinecOr2eawseit[h30i]nacnredastihnegotahnenreashlinogwintegmapedreactrueraess.e [27] itnhitchkeNoGsxetyevrgeeoenrxntghi-dtceholeenosfitsafl,cmGttheededOoiG2nevews-eGnisttoehigt daihntiiemcolrnpeeraosusfsilnaatygoteharfi.uncklnAlyenGaoueltinhnoedxgriedtrmeesmtefatiplhnmoedrdda,thtouaeenrseonisxno.ytNgvhaeeecnvlup-eocroutphsnrettoalocecesftsuses,ldltyuhGseuienni-gndGvesereussdtptaiienmgrdsaeottrnihosiecnlaoyfear Another method, an in vacuo process using supersonic molecular oxygen beams, only produces the 1+ and 2+ oxidation states in the sub-monolayer thickness [31]. The established records fall short of experimental investigations on the interfacial electronic structure of Ge(001) with atomic O and molecular O2, especially at the embryonic stage of adsorption. The present experimental results provide direct evidence that the unpassivated down-dimer atoms might account for the reliability issue that is related to Ge MOS devices [39,40]
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