Selective molecular beam epitaxy of GaAs and related compounds by shadow mask technique

Abstract

The selective growth of GaAs epitaxial layers on two kinds of substrates, i.e., GaAs and Si, by molecular beam epitaxy (MBE) was studied. The sandwich layers of Al0.58Ga0.42As / GaAs (in case of GaAs substrate) and SiO2 /Si3 N4 (in case of Si substrate) were used in fabricating shadow masks by selective chemical etching. Shadow masks with line pattern of 5 {u1D707}m width were prepared in most of the experiments. The selective GaAs molecular beam epitaxial layers were grown through the shadow masks under appropriate conditions. These selective GaAs epitaxial layers were evaluated by photoluminescence (PL) measurements at 10 K using a 50mW argon laser as the excitation source. The samples having multiquantum well (MQW) structures were analyzed in the experiments. The PL spectrum characteristics reflect the quantum well structure as well as the crystal quality of shadow masked epitaxial layers. The strong and sharp PL peak at 818 nm was clearly detected from a stripped-off sample having 60 monolayer well width. The PL peak of the stripped-off sample having full width at half maximum (FWHM) of 14 nm was > 2.5 times stronger than that obtained from conventional MQW grown on a plain surface (100) GaAs sample. The selective epitaxy of GaAs on silicon substrates has been grown through the shadow masks. It was found that the growth temperature should not exceed 450℃ to avoid the nitride mask bending. The number of point defects on selective surface was observed by a scanning electron microscope (SEM). Fewer defects on a smaller opening area could be applied for future microelectronic device fabrication by selective growth through the shadow mask technique.