Electrodeposition of Crystalline GaAs on Liquid Gallium Electrodes in Aqueous Electrolytes

• Published in: Journal of the American Chemical Society Vol. 135; no. 1; pp. 330 - 339
• Main Authors: Fahrenkrug, Eli, Gu, Junsi, Maldonado, Stephen
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 09-01-2013
• Subjects: Arsenicals - chemistry; Crystallization; Electrodes; Electrolytes - chemistry; Electroplating; Gallium - chemistry; Water - chemistry
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja309476x

Crystalline GaAs (c-GaAs) has been prepared directly through electroreduction of As2O3 dissolved in an alkaline aqueous solution at a liquid gallium (Ga(l)) electrode at modest temperatures (T ≥ 80 °C). Ga(l) pool electrodes yielded consistent electrochemical behavior, affording repetitive measurements that illustrated the interdependences of applied potential, concentration of dissolved As2O3, and electrodeposition temperature on the quality of the resultant c-GaAs(s). Raman spectra indicated the composition of the resultant film was strongly dependent on both the electrodeposition temperature and dissolved concentration of As2O3 but not to the applied bias. For electrodepositions performed either at room temperature or with high (≥0.01 M) concentrations of dissolved As2O3, Raman spectra of the electrodeposited films were consistent with amorphous As(s). X-ray diffractograms of As(s) films collected after thermal annealing indicated metallurgical alloying occurred only at temperatures in excess of 200 °C. Optical images and Raman spectra separately showed the composition of the as-electrodeposited film in dilute (≤0.001 M) solutions of dissolved As2O3(aq) was pure c-GaAs(s) at much lower temperatures than 200 °C. Diffractograms and transmission electron microscopy performed on as-prepared films confirmed the identity of c-GaAs(s). The collective results thus provide the first clear demonstration of an electrochemical liquid–liquid–solid (ec-LLS) process involving a liquid metal that serves simultaneously as an electrode, a solvent/medium for crystal growth, and a coreactant for the synthesis of a polycrystalline semiconductor. The presented data serve as impetus for the further development of the ec-LLS process as a controllable, simple, and direct route for technologically important optoelectronic materials such as c-GaAs(s).