Surface morphologies associated with thermal desorption: Scanning tunneling microscopy studies of Br–GaAs(110)

Abstract

Scanning tunneling microscopy was used to characterize the developing surface morphology found during typical temperature programmed desorption experiments for halogen-GaAs. Surfaces exposed to Br 2 at 300 K were heated to temperatures between 450 and 675 K, followed by scanning at room temperature. This made it possible to relate the temperature-dependent gas phase etch product distribution to the surface structure and thereby examine atomic-level surface processes associated with the evolution of volatile products. We associate the desorption of GaBr 3 around 500 K with the initiation of single-layer-deep terrace pits. Desorption of GaBr and As 2 above 600 K accounts for the lateral enlargement of the pits.

Etching of GaAs(100) Surfaces by Halogen Molecules: Density Functional Calculations on the Different Mechanisms

“…The As 2 desorption requires a relatively high temperature (>600 K) as found for Br 2 etching. 9 For Cl 2 etching the consideration of barriers for chemisorption shows 1 that As 2 desorption also is the most probable path for arsenic removal and the bottleneck of Cl 2 etching, which is in agreement with experiment. 11 For the iodine case the recombinative I 2 desorption from the outside Ga atoms (Figure 7: 52 kcal/mol) has to be considered.…”

“…19 The desorption probability of GaX is much higher (39-44 kcal/mol). GaCl and GaBr desorb above 600 K. 9,11,[18][19][20] For GaX 3 the desorption energies and the barrier heights are low and decrease from F to I. The relatively high energy for the removal of GaF 3 is consistent with the found layer built from this molecule.…”

Layer-by-layer etching of GaAs (110) with halogenation and pulsed-laser irradiation

“…1͑a͒ represents the surface after condensing ϳ0.25 ML of Br at 400 K. The surface is decorated with bright features that form two-dimensional islands and chains elongated along ͓001͔, i.e., perpendicular to the substrate atomic row direction ͓110͔. As discussed previously, 13,14 Br 2 chemisorbs dissociatively on GaAs ͑110͒ and these features reflect Br bonded to As. Associated with them are Br-Ga features, but they are obscured by the brightness of Br-As.…”

“…The decoration of pit boundaries by Br reflects the fact that such sites have lower coordination numbers and are favorable adsorption sites. 13,14 Comparison with thermal etching 13,14 indicates that pulsed-laser-induced etching produced a much higher density of smaller and less regular etch pits.…”

“…3,9 In thermal etching, similar reaction pathways were observed for Cl-GaAs and Br-GaAs. 14 Terrace pit creation is a costly process in view of bond breaking and it involves formation/ desorption of GaBr 3 , while GaBr desorption is primarily involved in pit enlargement at low local Br concentration. The irradiation etch yield deduced from Figs.…”