Understanding Thermal Evolution and Monolayer Doping of Sulfur-Passivated GaAs(100)

Abstract

Monolayer doping (MLD) is an attractive method to precisely tailor dopant profiles for nanoelectronic semiconductor devices. The approach has been demonstrated for a number of different dopant/substrate combinations, but the mechanistic understanding of reactions of dopantcontaining monolayers, intermediate structures, and the role of capping layers has suffered from lack of in situ characterization. Here, we investigate the thermal evolution of sulfurpassivated GaAs(100) without any additional capping layers in the context of MLD, using a combination of in situ X-ray photoemission spectroscopy (XPS), low-energy ion scattering (LEIS), and infrared (IR) absorption spectroscopy. In the case of (NH 4 ) 2 S-passivated GaAs(100), the intermediate structure that precedes subsurface diffusion is characterized by a (2 × 1) reconstruction that has previously been ascribed to several different dimer moieties. These dimer structures are currently unresolved yet could influence subsequent doping processes. By use of LEIS, temperature-dependent measurements provide unambiguous information on the chemical origin of the intermediate (2 × 1) reconstruction, originating from the dimerization of S atoms. Annealing beyond 813 K results in a loss of the surface S signal and is accompanied by free-carrier absorption in IR spectra, consistent with doping. The magnitude of this absorption and the carrier densities extracted from these data indicate that peak doping levels exceeding 10 20 cm −3 can be achieved and that the free carrier concentration within a shallow profile can be tuned by adjusting the annealing time.

Monolayer Doping of Germanium with Arsenic: A New Chemical Route to Achieve Optimal Dopant Activation

“…The dopant atoms are transported into the target structure via diffusion during an annealing step, which causes the adsorbed molecule to decompose, releasing the dopant. While MLD has been well studied and used to dope Si, − silicon–germanium alloys, and III–V’s, , it has been less studied for Ge doping. − …”

“…The dopant atoms are transported into the target structure via diffusion during an annealing step, which causes the adsorbed molecule to decompose, releasing the dopant. While MLD has been well studied and used to dope Si, 16−23 silicon− germanium alloys, 24 and III−V's, 25,26 it has been less studied for Ge doping. 27−29 Finding new methods to nondestructively dope Ge to the required dopant concentration is imperative given the use of Ge not only as the channel material in FETs but also in other devices, which requires doping concentrations typically on the order of 1 × 10 19 atoms/cm 3 .…”

Towards Fabrication of Atomic Dopant Wires via Monolayer Doping Patterned by Resist-Free Lithography

“…into silicon. Introducing dopants via MLD into other semiconductors such as Ge, [22,23] GaAs, [24] and InAs [25] has also been explored. However, most of the researches in this field focus on the synthesis of precursors and wafer scale doping.…”