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Browsing by Author "Epp, June Miriam"

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    The effects of ion bombardment on the chemical reactivity of GaAs(100)
    Epp, June Miriam (Virginia Polytechnic Institute and State University, 1989)
    The effects of ion bombardment on the chemical reactivity of GaAs(100) were investigated by X-ray photoelectron spectroscopy. The enhancement in reactivity was shown to be related to the energy and mass of the bombarding ion. The oxidation results were compared to chemically cleaned (1:1 HCI(conc)/H₂O) and IHT (simultaneous ion/heat treatment) prepared GaAs(100). Before ion bombardment, GaAs(100) was chemically cleaned with 1:1 HCI(conc)/H₂O to remove surface oxides. Chemically cleaned GaAs was bombarded with 0.5-3 KeV Ar⁺ ions (fluences = 10¹⁶-10¹⁷ ions/cm²) and with 3 KeV Xe⁺, Ar⁺, ²⁰Ne⁺, and ³He⁺ ions (fluence =10¹⁷ ions/cm²) to investigate the effect of ion bombardment energy and mass on chemical reactivity. Ion bombardment results in the preferential sputtering of As and the amount of As depletion is dependent upon ion bombardment energy and mass. Following chemical cleaning and ion bombardment, GaAs was exposed to 10⁷-10¹³ L O2, 10⁹-10¹³ L H₂O,10⁶-10⁸ L NO, and 10⁷-10¹¹ L N₂O (1 Langmuir (L) = 1.3x10⁻⁴ Pa•sec). Chemically cleaned GaAs produced equivalent amounts of Ga₂O₃ and As₂O₃ upon O₂ exposure. Oxygen exposure of ion bombarded GaAs resulted in the formation of Ga₂O₃, As₂O₃, and As₂O₅. Nitric oxide exposure produced Ga₂O₃ and As₂O₃, and N₂O exposure produced only Ga₂O₃. Gallium oxide was preferentially formed for ion bombarded material and the relative amount of Ga₂O₃ increased with increasing ion energy. 3 KeV Xe⁺ ion-bombarded GaAs exhibited the greatest reactivity to O₂ and NO. Exposure of ion bombarded GaAs to NO produced the greatest amounts of Ga₂O₃. Ion bombarded GaAs was the least reactive to N₂O. Exposure of ion bombarded GaAs to H₂O resulted in the formation of GaOOH and Ga(OH)₃, with Ga(OH)₃ formation occurring only on 2 KeV Ar⁺ and 3 KeV Ar⁺ and Xe⁺ ion-bombarded material at exposures above 10¹⁰ L. It was shown that defects were responsible for the increased reactivity and that preferential formation of Ga₂O₃ on ion bombarded material was not determined by the Ga/As surface ratio. Exposing IHT prepared GaAs to O₂ produced equivalent amounts of Ga₂O₃ and As₂O₃ when the Ga/As ratio was 1.23±0.07. The damage caused by ion bombardment was investigated by optical reflectivity in the visible and near-ultraviolet region (1.6-5.6 eV), Raman spectroscopy, and capacitance-voltage measurements. Ion bombardment forms a damaged layer that is amorphous. The depth of damage is proportional to the energy of the bombarding ion and inversely proportional to the mass of the bombarding ion. The shallow damage depth for 3 KeV Xe⁺ ion-bombarded GaAs offers some explanation for increased chemical reactivity. The increased reactivity of ion bombarded GaAs with O₂ and NO is attributed to surface defects (broken surface bonds). It is suggested that these broken bonds are in the form of singly occupied dangling bonds. A model for the surface and possible reaction pathways for O₂ and NO reactions are discussed.
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    Raman-scattering and optical studies of argon-etched GaAs surfaces
    Feng, G. F.; Zallen, Richard H.; Epp, June Miriam; Dillard, John G. (American Physical Society, 1991-04)
    We have studied the structual damage in low-energy argon-ion-bombarded (ion-etched) GaAs using Raman scattering and ultraviolet reflectivity. When combined with post-bombardment sequential chemical etching, the Raman results reveal a graded depth profile of the damage layer, with a nearly linear damage dropoff with depth. The total damage-layer thickness is about 600 angstrom for high-fluence bombardment with 3.89-keV Ar+ ions. The spectral effects produced by argon etching are very different from those produced by high-energy ion implantation. The longitudinal-optic Raman line seen for argon-etched GaAs is not shifted and broadened as in ion-implanted GaAs. More striking are the results of the reflectivity measurements. For argon-etched GaAs, the electronic interband peaks are both broadened and strongly red shifted relative to the crystal peaks; for ion-implanted GaAs, only the broadening occurs. Distinct nanocrystals, which account for the effects seen in ion-implanted GaAs, are evidently absent in argon-etched GaAs. Instead, the damage layer caused by argon etching appears to be characterized by a very high density of point defects, which previous work suggests may be arsenic vacancies.