Reaction ofI2with the (001) surfaces of GaAs, InAs, and InSb. I. Chemical interaction with the substrate

Abstract

InAs͑001͒-c͑8ϫ2͒, InSb͑001͒-c͑8ϫ2͒, and several reconstructions of GaAs͑001͒ are exposed at room temperature to iodine molecules ͑I 2 ͒. Low-energy electron diffraction ͑LEED͒ and synchrotron soft x-ray photoelectron spectroscopy ͑SXPS͒ are employed to study the surfaces as a function of I 2 dose and sample anneal. In the exposure range studied, GaAs and InAs become saturated with I 2 , resulting in removal of the clean surface reconstruction and the formation of a very strong 1ϫ1 LEED pattern. Iodine bonds primarily to the dominant elemental species present on the clean surface, whether it is a group-III or-V element. The InSb͑001͒-c͑8ϫ2͒ reconstruction is also removed by I 2 adsorption, and a strong 1ϫ1 LEED pattern is formed. SXPS data, in conjunction with scanning tunneling microscopy images, however, reveal that InSb͑001͒-c͑8 ϫ2͒ does not saturate at room temperature, but is instead etched with a preferential loss of In. Heating the iodine-covered group-III-rich InAs͑001͒-c͑8ϫ2͒ and InSb͑001͒-c͑8ϫ2͒ surfaces causes removal of the iodine overlayer and transformation to a group-V-rich reconstruction. When the iodine-covered As-rich GaAs͑001͒-c͑2ϫ8͒ surface is heated to remove iodine, however, the c͑2ϫ8͒ reconstruction is simply regenerated. ͓S0163-1829͑96͒12427-9͔

Fundamental Studies of Halogen Reactions With Iii-v Semiconductor Surfaces

“…Examples of the morphologies that result from etching GaAs with Br 2 under various conditions are shown in Figure 2. Varekamp et al (93) observed similar etchinduced morphologies, i.e. rectangular etch pits and jagged step edges, in the room-temperature reaction of InSb(001) with I 2 .…”

“…At other times, however, Cl 2 adsorption leads to the complete removal of the low-energy electron diffraction (LEED) pattern, thereby indicating that the surface has become disordered. This has been seen for Cl 2 (93) describe in detail the coverage dependence of the LEED pattern for I 2 adsorption on GaAs(001)-4 × 6, which is representative of I 2 adsorption on several other surfaces. Small I 2 exposures simply increase the background intensity without changing the 4 × 6 pattern, suggesting that the iodine initially adsorbs randomly on the surface.…”

“…Heating iodinated Ga-rich GaAs(001)-4 × 1 and GaAs(001)-4 × 6, and As-rich GaAs(001)-c(2 × 8) surfaces results, in all cases, in a c(2 × 8) reconstructed surface (93). Also, In-rich InAs(001)-c(8 × 2) is transformed into As-rich InAs-c(2 × 8) by I 2 exposure and annealing (93).…”

“…The only other atomic scale STM study, to date, of halogen adsorption on a III-V semiconductor is by Varekamp et al (93,94), who investigated I 2 adsorption on InSb(001)-c(8 × 2). In those studies, the STM images of an I 2 -saturated surface were found to exhibit an ordered square lattice of spots separated by 4.6Å in both the [110] and [110] directions, which agrees with the size of the InSb(001) surface unit cell.…”

“…Varekamp et al (93) determined, using SXPS, that I 2 dissociatively chemisorbs, and by comparing results from various MBE-grown surfaces, they showed that iodine bonds to whichever atoms are exposed at the surface. Reaction at room temperature or below often halts as soon as approximately 1 ML of iodine is adsorbed, as is the case for certain GaAs(001), InAs(001), and InSb(001) reconstructions (88,91,93). Yet, when exposed to excess I 2 , other surfaces etch, including As-terminated GaAs(111) (145), stoichiometric GaAs(110) (109), and In-rich InSb(001)-c(8 × 2) (93).…”