New Method for Precision Doping in 2D Semiconductors Enables Next-Gen CMOS Integration

Researchers have achieved a breakthrough in doping two-dimensional (2D) semiconductors, paving the way for monolithic integration of p-type and n-type semiconductor channels on a single chip. This development holds promise for advancing complementary CMOS technology, allowing further transistor scaling and efficient interlayer connections.

The study focuses on 2H-MoTe2, a van der Waals material, and employs a precise substitutional doping technique. Unlike conventional methods such as ion implantation—which do not work well with 2D materials—this approach allows the targeted introduction of niobium (Nb) for p-type doping and rhenium (Re) for n-type doping, using a magnetron co-sputtering method followed by chemical vapor deposition (CVD). By precisely adjusting the concentration of these dopants, researchers produced wafer-scale films with consistent carrier properties, even enabling spatial control of the doped regions. This advance allows for the patterning of p-type and n-type channels on the same wafer in a single growth process, which is essential for CMOS device fabrication.

Using this novel technique, the team created a large-scale 2D CMOS inverter array that achieved impressive performance metrics. For instance, a typical inverter from this array demonstrated a voltage gain of 38.2 and low static power consumption, key parameters for efficient CMOS operation. The new doping method also exhibits high uniformity and reliability, essential for scaling up 2D materials in commercial semiconductor applications.

This innovation in 2D semiconductor doping introduces a promising pathway for integrating materials like 2H-MoTe2 into very-large-scale integration (VLSI) technology, further driving forward Moore's Law and the miniaturization of semiconductor devices.

Figure 1 from paper, Pan, Y., Jian, T., Gu, P. et al. Precise p-type and n-type doping of two-dimensional semiconductors for monolithic integrated circuits. Nat Commun 15, 9631 (2024). https://doi.org/10.1038/s41467-024-54050-2

Experimental

In the study, co-sputtering and CVD is used to create large-scale, precisely doped 2D 2H-MoTe2 films by transforming a molybdenum film doped with niobium or rhenium into 2H-MoTe2 through a process called tellurization. Here’s a breakdown of how this process works:

Preparation of the Mo Film: Initially, thin Mo films are deposited on a silicon/silicon dioxide (Si/SiO2) substrate using magnetron co-sputtering. During this step, controlled amounts of Nb (for p-type doping) or Re (for n-type doping) are co-sputtered with the Mo film, resulting in a doped Mo layer.

Tellurization Process in the CVD Reactor: The Mo film, now doped with Nb or Re, is placed in a CVD furnace along with solid tellurium (Te) lumps. Under a controlled flow of carrier gases (argon and hydrogen), the CVD chamber is heated to high temperatures (around 650°C). The Te vapor reacts with the Mo, leading to the formation of 1T'-MoTe2.

Phase Transformation to 2H-MoTe2: At the elevated temperatures within the CVD system, the 1T'-MoTe2 structure undergoes a phase transformation into the more stable 2H phase, producing the final doped 2H-MoTe2 film. This phase is crucial because 2H-MoTe2 has semiconducting properties suitable for integrated circuits.

Doping Incorporation: During the CVD tellurization, Nb and Re atoms from the initial Mo film become substitutionally incorporated into the MoTe2 lattice. This incorporation determines the semiconductor type (p-type or n-type) and carrier concentration of the resulting 2H-MoTe2 film.

Large-Scale Uniformity: By controlling the initial dopant concentration and maintaining consistent conditions in the CVD process, the researchers achieved uniform doping across large-scale wafers, crucial for creating reliable semiconductor devices.

Source: Precise p-type and n-type doping of two-dimensional semiconductors for monolithic integrated circuits | Nature Communications