Surface morphology of ex situ sulfur-passivated (1×1) and (2×1) InP(100) surfaces

Abstract

Ex-situ aqueous ͑NH 4 ) 2 S treated sulfur-passivated InP substrates have been studied using ultrahigh vacuum scanning tunnelling microscopy ͑STM͒ and low-energy electron diffraction ͑LEED͒. The morphology of the passivated surface was imaged after a mild sample annealing. The STM images of a surface exhibiting a good 1ϫ1 LEED pattern show that the top layer of the sulfur-passivated surface is poorly ordered. A surface bilayer atomic step has been observed to be common on sulfur-passivated surfaces. The magnitude of the surface roughness for the passivated surfaces lies between 10 Å and 25 Å; this is much smaller than the roughness of InP͑100͒ substrates prepared using previously published methods. After annealing the sample at ϳ420°C, a ͑2ϫ1͒ LEED pattern with split half-integer spots has been observed. The associated STM images show that these split half-integer diffraction beams correspond to regularly spaced domains with a width of ϳ20-30 Å in the ͓011͔ direction. The surface roughness increases with annealing temperature; the surface corresponding to the best 2ϫ1 LEED symmetry ͑annealing at ϳ420°C͒ has a roughness double that of the 1ϫ1 phase.

Towards Passivation of Ge(100) Surfaces by Sulfur Adsorption from a (NH4)2S Solution: A Combined NEXAFS, STM and LEED Study

“…In this case, the diffraction pattern will not reflect the presence of the disordered top atomic layer that is observed in the STM images since the contribution of the surface adsorbates is insufficient to influence the electron diffraction pattern. Similar findings have also been reported in literature for (NH 4 ) 2 S treated InP substrates 31 as well as for in situ prepared S/Ge substrates. 32 Our results clearly indicate the strength and need of using complementary surface analysis techniques such as STM and LEED to provide detailed information about complex surface atomic structures.…”

Adsorption and Decomposition of H2S on InP(100)

“…Similar to that observed from a sample treated by a wet passivation process, a 1 × 1 LEED pattern is observed after the surface is heated to 500 K. ,,, However, in contrast with the result obtained from a previous study of wet passivation, a change of LEED pattern from (1 × 1) to (2 × 1) is not observed when the surface is further annealed to 540 K . On the basis of a recent STM study, it was found that the top layer of the S-passivated surface lacks a long-range order, and the (1 × 1) LEED pattern was postulated to originate from the underlayer substrate . However, if the (1 × 1) surface order is imposed, the bridge site is proposed to provide the most favorable energy for the S absorption, as proposed in the case of GaAs−S. , In the previous XPD studies, the S atoms on the InP(100) by wet passivation were also proposed to bridge-bond to two In atoms of the first layer, which have two dangling bonds in opposite directions. ,, …”

Interfacial electronic structure of a hybrid organic-inorganic optical upconverter device: The role of interface states

“…The presence of surface states arising from atomic steps has also been confirmed by scanning tunneling microscopy on the S-passivated InP͑100͒ surface. 50 Even after S-passivation the surface state density still remains high at ϳ10 12 cm −2 / eV. 51 More compelling is the high density of surface states at 1.2-1.3 eV above the VBM reported for a variety of different chemically treated InP surfaces.…”