Semiconductor Materials - 08

Abstract

Group-IV chalcogenide materials such as tin sulfide (SnS_x) and germanium sulfide (GeS_x) have attracted significant attention due to their wide range of potential applications, including next-generation transistors, solar cells, and anode materials for lithium-ion batteries. Various growth techniques have been reported, such as vapor-phase deposition [1] and reactive sputtering [2]. In this study, we investigated molecular beam deposition (MBD), which enables deposition under high vacuum conditions with high cleanliness and excellent controllability of film thickness.

In the experiments, Si(100) substrates with a 100-nm thermal oxide layer were cleaned and then introduced into an MBD chamber (base pressure: ~10-6 Pa). During deposition, substrates were heated at temperatures ranging from room temperature (RT) to 500 °C, while Sn and S were co-supplied to form SnS_x films [Fig. 1]. Here, while a solid K-cell was used as the Sn source, since elemental sulfur typically exists in a stable 8-membered ring structure with low reactivity, we employed a cracking cell equipped with an Ar plasma source to enhance the reactivity of sulfur [3], thereby promoting the formation of SnS_x.

The XRD results of the deposited films are shown in Fig. 2. A diffraction peak corresponding to SnS(400) was observed in samples deposited at 200–300 °C, indicating crystallization of SnS. In contrast, the peak disappeared in samples deposited above 350 °C. Thickness measurements confirmed that the SnS layer vanished at these higher substrate temperatures [Fig. 3], suggesting that the disappearance was due to re-evaporation of SnS. Furthermore, compositional analysis revealed that the deposited films maintained the stoichiometric ratio of SnS [Fig. 3].