Monolayer doping of silicon-germanium alloys: A balancing act between phosphorus incorporation and strain relaxation

Abstract

This paper presents the application of monolayer doping (MLD) to silicon-germanium (SiGe). This study was carried out for phosphorus dopants on wafers of epitaxially grown thin films of strained SiGe on silicon with varying concentrations of Ge (18%, 30%, and 60%). The challenge presented here is achieving dopant incorporation while minimizing strain relaxation. The impact of high temperature annealing on the formation of defects due to strain relaxation of these layers was qualitatively monitored by cross-sectional transmission electron microscopy and atomic force microscopy prior to choosing an anneal temperature for the MLD drive-in. Though the bulk SiGe wafers provided are stated to have 18%, 30%, and 60% Ge in the epitaxial SiGe layers, it does not necessarily mean that the surface stoichiometry is the same, and this may impact the reaction conditions. X-ray photoelectron spectroscopy (XPS) and angle-resolved XPS were carried out to compare the bulk and surface stoichiometry of SiGe to allow tailoring of the reaction conditions for chemical functionalization. Finally, dopant profiling was carried out by secondary ion mass spectrometry to determine the impurity concentrations achieved by MLD. It is evident from the results that phosphorus incorporation decreases for increasing mole fraction of Ge, when the rapid thermal annealing temperature is a fixed amount below the melting temperature of each alloy.

Vertical van der Waals Heterostructure of Single Layer InSe and SiGe

“…The experimentally realized SiGe alloy was reported as an appropriate material for solar cell applications . Recent studies have shown that Ge atoms can be incorporated into Si-based nanostructures with negligibly small induced strains. , The exchange of Si and Ge atoms in Si-based or Ge-based nanostructures may allow the possible experimental realization of the 2D form of SiGe. In addition, the single layer form of SiGe was theoretically predicted to exhibit a dynamically stable buckled structure as a free-standing layer which can be formed upon the incorporation of Si atoms into the germanene layer .…”

Carbon-Free Solution-Based Doping for Silicon

“…Figure 3 a shows the SRP results obtained on four different samples doped with PA and processed at the annealing temperature of 1050 °C for 20 s, after the MD deposition. The dose of carriers obtained by integrating the reported profiles is as high as 3 × 10 15 #/cm 2 , indicating an outstanding yield compared to both traditional and MD methods [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ]. The peak of the charge carriers is 1 × 10 20 #/cm 3 .…”

“…Recently, an alternative method of doping has been proposed based on the use of liquid solutions, the Molecular Doping (MD) [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ]. The dopant precursor is in liquid form, and the semiconductor (e.g., silicon, germanium, or gallium arsenide) is immersed in the solution.…”

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 .…”