Benchtop Electrochemical Growth and Controlled Alloying of Polycrystalline In x Ga1-x As Thin Films.

Compared to Si, GaAs offers unique material advantages such as high carrier mobility and energy conversion efficiency, making GaAs a leading competitor to replace Si on several technological fronts related to optoelectronics and solar energy conversion. Alloying the GaAs lattice with elemental In allows the direct bandgap of the resulting ternary alloy to be tuned across the near-infrared (NIR) region of the electromagnetic spectrum from ∼0.9 to 3.5 µm. However, methods of fabricating high-quality crystalline GaAs are currently limited by their high cost and low throughput relative to Si growth methods, suggesting the need for alternative low-cost routes to GaAs growth and alloying. This research documents the first instance in the literature of the electrodeposition and controlled alloying of polycrystalline In x Ga1-x As films at ambient pressure and near-room temperature using the electrochemical liquid-liquid-solid (ec-LLS) process. X-ray diffraction and Raman spectroscopy support the polycrystalline growth of (111)-oriented In x Ga1-x As films. Consistent redshifts of the GaAs-like TO peaks were observed in the Raman data as the In composition of the liquid metal electrode was increased. Optical bandgaps, determined via diffuse reflectance measurements, displayed a consistent decrease with the increase in the In composition of In x Ga1-x As films. While Raman, diffuse reflectance, and energy-dispersive X-ray spectroscopy data support controlled alloying efforts, all techniques suggest an overall decrease of the In/Ga ratios present in deposited films relative to those of the liquid metal electrodes. These results lend support for the continued development of ec-LLS as a viable method of achieving crystalline growth and alloying of binary and ternary semiconductor material systems using a benchtop setup under ambient pressure and near-room temperature.