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Chemistry group Electrochemistry group EPS group Irregularity group

 

Physics/chemistry of III-V surfaces

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People involved :

Daniel Paget

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External collaborators:

V. L. Berkovits (Saint Petersbourg, Russia)
O. E. Tereshchenko (Novosibirsk, Russia)
P. Chiaradia (Rome, Italy)

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Methodology

Using optical techniques such as anisotropic reflectivity spectroscopy (ARS), Auger spectroscopy, photoemission spectroscopy and X-ray diffraction, simple me asurements of surface optical transitions are possible. These measures are sensi tive to the surface reconstruction and also to chemical interactions between the surface and atoms deposited onto the surface. These methods have been applied t o a diverse range of systems:

Preparation of reconstructed III-V semi-conductor surfaces

In collaboration with the University of Novosibirsk, we have elaborated an ox ygen-free surface treatment based on a mixture of hydrochloric acid and isopropa nol which, when combined with a post-anneal in UHV, yields high quality GaAs, In As and Inp surface reconstructions. It was shown that cesium could be desorbed o nto a GaAs(001) surface in order to obtain Gallium rich surfaces at temperatures much lower than previously possible, and thus with a much lower density of surf ace defaults.

Passivation of GaAs(001) surfaces

We have previously identified the mechanisms for Sulfur passivation of GaAs(0 01) surfaces. The focus today is directed toward soft (wet chemical) nitridation techniques for the chemical and electronic passivation of GaAs. This technique can yield GaAs surfaces that are stable for many months in ambient conditions. T his can be particularly important for applications in which the surface state st rongly affects the electrical properties of a semiconductor device. An example o f current interest is tunneling between a semiconducting tip and a metallic surf ace where chemical changes in the tip surface result in large tunneling current fluctuations (see our project on spin ploarized tunneling).

Interaction of the clean GaAs surface with electronegative (oxygen) and e lectropositive (alcalines) elements

In the case of InAs at 140 K, ARS permitted us to observe for the first time the effect of surface stochiometry on oxygen adsorption: on a In rich surface, o xygen is chemisorbed whereas for As rich surfaces oxygen is physisorbed.

We have also studied in detail the adsorption and properties of alcaline met als onto GaAs(001) as a function of temperature. Because diffusion of the metal over the surface below 90 K is limited, a disordered 2D percolative metal layer is formed. ARS and photoreflectance spectroscopy allows both the structure and m etallicity of the alkaline layer to be determined. The figure below shows the re sults for the case of sodium: we note that there are zones of co-existence in th e phase diagram between insulating and metallic regions (purple) as well as phas es which depend on the surface preparation (green). Metallicity and disorder are found to be related since the critical temperature for the metal/insulator and the order/disorder transitions are identical.

Selected publications:

• "Soft nitridation of GaAs(100) by hydrazine sulfide solutions: Effect on surface recombination and surface barrier", V.L. Berkovits, D. Paget, A.N. Karpenko, V.P. Ulin, and O.E. Tereshchenko Appl. Phys. Lett. (2007)
• "Insulator - metal phase transitions of alkali atoms on GaAs (001)", P. Chiaradia, D. Paget, O.E. Tereshchenko, J. E. Bonnet, A.Taleb-Ibrahimi, R. Belkhou, and F.Wiame, Surface Science 600, 287, (2006)
• "Optical anisotropy induced by cesium adsorption on the As-rich c(2x8) reconstruction of GaAs(001)", C. Hogan, D. Paget, O. E. Tereshchenko, L. Reining, and G. Onida, Phys. Rev. B 69, 125332, (2004)
• "Surface and bulk origin of the optical anisotropy of As-rich (001) GaAs and (001) Ga_1-x In_x As", D. Paget, C. Hogan, V. L. Berkovits, and O. E. Tereshchenko, Phys. Rev. B 67, 245313, (2003)
• "Effect of surface reconstruction on the low temperature oxidation of InAs(100) : optical investigation", V.L. Berkovits, N. Witkowski, Y. Borensztein, and D. Paget, Phys. Rev. B 63, R121314, (2001)
• "Metallicity and disorder at the alkali-metal/GaAs(001) interface", O.E. Tereshchenko, D.V. Daïneka, and D. Paget, Phys. Rev. B 64, 085310, (2001)
• "X-ray diffraction analysis of the gallium-rich surface of GaAs(001)", D. Paget, Y. Garreau, M. Sauvage, P. Chiaradia, R. Pinchaux, and W.G. Schmidt, Phys. Rev. B 64, 161305(R), (2001)