Digermane Deposition on Si(100) and Ge(100): from Adsorption Mechanism to Epitaxial Growth

Abstract

Controlled fabrication of nanometer-scale devices such as quantum dots and nanowires requires an understanding of the initial chemisorption mechanisms involved in epitaxial growth. Vapor phase epitaxy can provide controlled deposition when using precursors that are not reactive with the H-terminated surfaces at ambient temperatures. For instance, digermane (Ge2H6) has potential as such a precursor for Ge ALE on Si(100) surfaces at moderate temperatures; yet, its adsorption configuration and subsequent decomposition pathways are not well understood. In situ Fourier transform infrared spectroscopy and first principles calculations reveal that Ge2H6 chemisorbs through a β-hydride elimination mechanism, forming Ge2H5 and H on both Si(100)-(2 × 1) and Ge(100)-(2 × 1) surfaces, instead of the previously proposed Ge–Ge bond breaking mechanism, and subsequently decomposes into an ad-dimer. The resulting coverage of Ge after a saturation exposure is estimated to be about 0.3 monolayers. Interestingly, the decomposition of adsorbed Ge2H5 on Si(100) is faster than Si2H5 on Ge(100) at 173 K. The desorption temperature of hydrogen on Si(100) is shown to depend on the Ge coverage, falling from 698 K for ∼1/4 ML Ge on Si(100) to 573 K for a nearly full Ge coverage, consistent with H desorption on Ge(100). Furthermore, hydrogen is observed to migrate from Ge to Si, prior to desorption. This property opens the door for selective growth of Ge on patterned H-terminated Si surfaces.

Toward Selective Ultra-High-Vacuum Atomic Layer Deposition of Metal Oxides on Si(100)

“…The gas deposition system used in this article is the same as was used in our earlier work on digermane . This system is equipped with in situ FT-IR in order to monitor the gas reactions with the sample surface with a base pressure of 2 × 10 –10 Torr.…”

“…The experiments reported in this work are performed using 3.8 cm × 1.5 cm × 500 μm Si(100) samples. The Si(100) samples are cleaned and chemically reoxidized in the same manner as described in our previous work on digermane . The chemically oxidized Si(100) sample is then inserted into the UHV chamber, described below, and annealed to 773 K for 6 h in order to thoroughly degas the sample holder.…”

“…The Si(100) samples are cleaned and chemically reoxidized in the same manner as described in our previous work on digermane. 4 The chemically oxidized Si(100) sample is then inserted into the UHV chamber, described below, and annealed to 773 K for 6 h in order to thoroughly degas the sample holder. After cooling the whole chamber including the sample holder to room temperature, the sample is briefly (<10 s) heated to approximately 1300 K in order to remove the protective oxide layer and subsequently cooled to either 373 or 423 K for the infrared absorption measurements described below.…”

“…The gas deposition system used in this article is the same as was used in our earlier work on digermane. 4 This system is equipped with in situ FT-IR in order to monitor the gas reactions with the sample surface with a base pressure of 2 × 10 −10 Torr. The flow of gas is controlled via a leak valve volume (LVV) which is filled to a desired pressure of the gas and exposed to the sample through a pair of capillaries aimed at the surface.…”

Ultrathin films of Ge on the Si(100)2 × 1 surface

“…Several methods of Ge growth on Si have been utilized. Among them, the most popular are the chemical vapor deposition using digermane (Ge 2 H 6 ) or simply germane GeH 4 as Ge precursor, the molecular beam epitaxy and the physical vapor deposition …”