Surface Modification for III-V Selective Area Molecular Beam Epitaxy of Non-Selective Mask Materials

Abstract

Selective-area embedded regrowth of III-V semiconductors by molecular beam epitaxy enables the seamless integration of metals and dielectrics into crystalline material for novel design of optoelectronic devices. However, traditional masks like $Si{O}_2$ and $S{i}_3{N}_4$ limit the design of high-contrast photonics in the infrared due to their high extinction coefficients at technologically relevant wavelengths. Consequently, there is a need to explore alternative mask materials to expand the selective area molecular beam epitaxy capabilities beyond those traditionally used. This study evaluates the deposition selectivity of the alternative materials $A{l}_2{O}_3$, $Ti{O}_2$, and $Hf{O}_2$, films with preferable spectral responses but higher surface reactivity. It was found that $A{l}_2{O}_3$ exhibits promising selective growth characteristics within typical GaAs growth temperatures, $Hf{O}_2$ demonstrated a high non-selectivity dominated by Ga adsorption on the mask at temperatures up to 650 ${}^{\circ }$C, and $Ti{O}_2$ proved reactive during deposition. To achieve selective growth of highly non-selective and even reactive mask materials, a surface modification technique was employed to improve the selective growth characteristics of any given film. Selective growth of $S{i}_3{N}_4$ and $Ti{O}_2$ films was achieved with the application of a thin $Si{O}_2$ capping layer utilizing growth conditions typical of the GaAs/$Si{O}_2$ system. The relationship between the thickness of $Si{O}_2$ caps and growth selectivity was examined, revealing that sub-1 nm capping layers can significantly influence the mask surface chemistry, indicating that by depositing a thin layer of $Si{O}_2$, $Si{O}_2$-like selectivity for any mask material can be realized without degrading its optical response.