An official website of the United States government
GaAs(111)B are commercially available substrates widely used for the growth of van der Waals chalcogenide films. Wafer-scale, high-quality crystalline films can be deposited on GaAs(111)B substrates using molecular beam epitaxy. However, two obstacles persist in the use of GaAs(111)B: first, the surface dangling bonds make it challenging for the growth of van der Waals materials; second, the As-terminated surface is prone to aging in air. This study investigated a thermal treatment method for deoxidizing GaAs(111)B substrates while simultaneously passivating the surface dangling bonds with Se. By optimizing the treatment parameters, we obtained a flat and completely deoxidized platform for subsequent film growth, with highly reproducible operations. Furthermore, through first-principle calculations, we find that the most energetically favorable surface of GaAs(111)B after Se passivation consists of 25% As atoms and 75% Se atoms. Finally, we discovered that the common storage method using food-grade vacuum packaging cannot completely prevent substrate aging, and even after thermal treatment, aging still affects subsequent growth. Therefore, we recommend using N2-purged containers for better preservation.
more »
« less
New value of old knowledge: sulphur-based GaAs surface passivation and potential GaAs application in molecular electronics and spintronics
Abstract GaAs is well known for its extremely high electron mobility and direct band gap. Owing to the technological advances in silicon-based technology, GaAs has been limited to niche areas. This paper discusses the application of GaAs in molecular electronics and spintronics as a potential field for considering this amazing but challenging material. GaAs is challenging because its surface is characterized by a high density of surface states, which precludes the utilization of this semiconducting material in mainstream devices. Sulfur(S)-based passivation has been found to be significantly useful for reducing the effect of dangling bonds and was researched thoroughly. GaAs applications in molecular spintronics and electronics can benefit significantly from prior knowledge of GaAs and S interactions because S is a popular functional group for bonding molecular device elements with different semiconductors and metals. In this article, the problem associated with the GaAs surface is discussed in a tutorial form. A wide variety of surface passivation methods has been briefly introduced. We attempted to highlight the significant differences in the S-GaAs interactions for different S passivation methods. We also elaborate on the mechanisms and atomic-scale understanding of the variation in surface chemistry and reconstruction due to various S passivation methods. It is envisioned that GaAs and thiol-terminated molecule-based novel devices can exhibit innovative device characteristics and bring the added advantage of S-based passivation.
more »
« less
- Award ID(s):
- 1914751
- PAR ID:
- 10409901
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Materials Research Express
- Volume:
- 10
- Issue:
- 4
- ISSN:
- 2053-1591
- Page Range / eLocation ID:
- Article No. 042003
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Arsenic’s high vapor pressure leads to thermal instability during hightemperature processing of GaAs, contributing to the performance degradation of subsequently fabricated devices. The resulting surface damage also obfuscates the exact quantitative characterization of the diffusion process, a critical step in device manufacturing. In this experiment, an encapsulant-and-sacrificial-layer procedure is employed to reduce arsenic sublimation and preserve a smooth surface. A capped GaAs/InGaAs/GaAs quantum well structure is subjected to rapid thermal annealing, and AFM, SEM, and EDS are used to compare the surface qualities of the postannealed encapsulated GaAs against the reference GaAs. For the encapsulated substrate, a smooth surface with an average root-mean-squared value of 6.5 Å is achieved after high-temperature processing. SIMS analysis is used to obtain the diffused indium atomic concentration profiles for a smooth and roughened GaAs surface and their corresponding diffusion parameters. The analysis demonstrates how precise diffusion parameter extraction requires preserving an atomically-smooth surface in semiconductor diffusion characterization.more » « less
-
Crystalline zinc blende GaAs has been grown on a trigonal c-plane sapphire substrate by molecular beam epitaxy. The initial stage of GaAs thin film growth has been investigated extensively in this paper. When grown on c-plane sapphire, it takes (111) crystal orientation with twinning as a major problem. Direct growth of GaAs on sapphire results in three-dimensional GaAs islands, almost 50% twin volume, and a weak in-plane correlation with the substrate. Introducing a thin AlAs nucleation layer results in complete wetting of the substrate, better in-plane correlation with the substrate, and reduced twinning to 16%. Further, we investigated the effect of growth temperature, pregrowth sapphire substrate surface treatment, and in-situ annealing on the quality of the GaAs epilayer. We have been able to reduce the twin volume below 2% and an X-ray diffraction rocking curve line width to 223 arcsec. A good quality GaAs on sapphire can result in the implementation of microwave photonic functionality on a photonic chip.more » « less
-
Abstract While the discovery of two-dimensional (2D) magnets opens the door for fundamental physics and next-generation spintronics, it is technically challenging to achieve the room-temperature ferromagnetic (FM) order in a way compatible with potential device applications. Here, we report the growth and properties of single- and few-layer CrTe 2 , a van der Waals (vdW) material, on bilayer graphene by molecular beam epitaxy (MBE). Intrinsic ferromagnetism with a Curie temperature ( T C ) up to 300 K, an atomic magnetic moment of ~0.21 $${\mu }_{{\rm{B}}}$$ μ B /Cr and perpendicular magnetic anisotropy (PMA) constant ( K u ) of 4.89 × 10 5 erg/cm 3 at room temperature in these few-monolayer films have been unambiguously evidenced by superconducting quantum interference device and X-ray magnetic circular dichroism. This intrinsic ferromagnetism has also been identified by the splitting of majority and minority band dispersions with ~0.2 eV at Г point using angle-resolved photoemission spectroscopy. The FM order is preserved with the film thickness down to a monolayer ( T C ~ 200 K), benefiting from the strong PMA and weak interlayer coupling. The successful MBE growth of 2D FM CrTe 2 films with room-temperature ferromagnetism opens a new avenue for developing large-scale 2D magnet-based spintronics devices.more » « less
-
We report on the growth of high-quality GaAs semiconductor materials on an AlAs/sapphire substrate by molecular beam epitaxy. The growth of GaAs on sapphire centers on a new single-step growth technique that produces higher-quality material than a previously reported multi-step growth method. Omega-2theta scans confirmed the GaAs (111) orientation. Samples grown at 700 °C displayed the highest crystal quality with minimal defects and strain, evidenced by narrow FWHM values of the rocking curve. By varying the As/Ga flux ratio and the growth temperature, we significantly improved the quality of the GaAs layer on sapphire, as compared to that obtained in multi-step studies. Photoluminescence measurements at room temperature and 77 K further support these findings. This study underscores the critical role of the As/Ga flux ratio and growth temperature in optimizing GaAs epitaxial growth on sapphire.more » « less
