Reactivity of heteropolyanions toward GaAs compound

Abstract

We studied the reactivity of GaAs in contact with acidic solutions of, respectively, four heteropolyanions (HPAs): SiW12O404−, SiMo12O404−, PW12O403−, and P2W18O626−. The results obtained by both x-ray photoelectron spectroscopy and etching rate and absorbance measurements showed that GaAs dipped into such solutions undergoes an oxidation/dissolution process while the HPAs are reduced. Indeed, after each immersion of GaAs into an heteropolyanionic solution, a deposit, which consists of As0 atoms with either partially reduced HPA or WO3 is observed. This study has given us the opportunity to determine the reactions which occur at the GaAs/“HPA solution” interface and to point out the importance of the semiconductor energy-band position with respect to the first redox potential of the HPA. Knowledge of the semiconductor/HPA energetic diagram allows one to predict the behavior of HPA species toward semiconductors.

Use of XPS to follow the evolution of a solution/solid interface: SiMo12O404− acidic solution/GaAs interface

“…8 This chemical shift is in good agreement with the value obtained for a sample immersed for 1 h in 5 ð 10 3 M SiMo 12 solution. 2 Moreover, the ratio between the contributions of As in GaAs and As 0 is very similar in the case of both samples immersed for 1 h in 5 ð 10 3 M SiMo 12 solution and for 72 h in 5 ð 10 4 M SiMo 12 solution, which correspond to 220 and 1660 nm of dissolved GaAs, respectively. After these two treatments, the substrate is still detected by XPS analysis.…”

“…Based on the Mo 3p 3/2 level, we previously established that partially reduced HPAs are present in the film. 2 In the Mo 3d peak shown here in Fig. 3, Mo(VI) and Mo(V) can be detected.…”

“…4 -6 After contact with SiMo 12 solution, the GaAs surface is covered with a deposit consisting of elemental arsenic and partially reduced HPA. 2 At the GaAs/solution interface, the SiMo 12 is therefore reduced while the semiconductor is oxidized. Both SiMo 12 and other HPAs can therefore be regarded as a new class of semiconductor etching agent.…”

“…We recently presented an example 2 focusing on the behaviour of a III-V semiconductor compound, GaAs, in the presence of a Keggin-type heteropolyanion (HPA), 3˛-SiMo 12 O 40 4 species, denoted SiMo 12 . In acidic aqueous solution, these species can undergo multiple two-electron reduction of the metallic atoms (Mo) without decomposition.…”