Publication Date

8-2025

Date of Final Oral Examination (Defense)

5-29-2025

Type of Culminating Activity

Dissertation

Degree Title

Doctor of Philosophy in Materials Science and Engineering

Department

Materials Science and Engineering

Supervisory Committee Chair

Paul J. Simmonds, Ph.D.

Supervisory Committee Member

David Estrada, Ph.D.

Supervisory Committee Member

Paul Davis, Ph.D.

Supervisory Committee Member

Brelon J. May, Ph.D.

Abstract

Lattice constants of the III-V semiconductors range from 5.45 Å (GaP) to 6.48 Å (InSb). III-V semiconductors are grown on commercially available substrates made from binary III-V materials (e.g., GaAs, InP, and GaSb), or group IV materials (e.g., Si or Ge). These substrates offer very high quality, but only offer access to a small number of specific lattice constants. Given this constraint, it is desirable to develop growth methods that would allow the grower to modulate from the substrate lattice constant into the lattice constant of the material structure under investigation.

Device structures made from III-V semiconductors lattice-mismatched to these binary substrates can be challenging to grow due to the deleterious effects of strain relaxation on their electronic and optical properties. One way to overcome this limitation is to use metamorphic buffers to gradually adjust the lattice constant from that of the substrate to that of the desired III-V compound. Metamorphic buffers are frequently much thicker than the device structure grown on top, adding time and expense to the overall growth.

An alternative way to accommodate lattice mismatch involves the creation of interfacial misfit (IMF) arrays. These 2D networks of 90º misfit dislocations lie in the plane of the substrate/III-V interface and efficiently relieve the strain. Careful control of this process can limit the density of undesirable 60º threading dislocations extending away from the interface, helping protect the quality of layers grown above. To date, the IMF process has been studied in only a few binary “virtual substrate” systems, notably GaSb on GaAs, and GaSb on Si, which crucially both still only offer access to relaxed semiconductor layers with a fixed lattice constant of ~6.1 Å.

Motivated by producing virtual III-V substrates with any lattice constant, we have expanded the IMF approach to also enable growth of ternary compounds. Molecular beam epitaxy (MBE) is the tool chosen for this work where a large emphasis is placed on the identification of ideal tool parameters for optimal material quality. Due to the benefits of Si substrates (availability, cost, scalability, and ease of integration with Si electronics) we chose as a starting point the GaSb-on-Si IMF system. For lattice constants > 6.1 Å we have explored IMF-based MBE growth of ternary Al1-xInxSb and Ga1-xInxSb compounds directly on Si substrates. Similarly, for lattice constants < 6.1 Å we have explored IMF based AlSb1-xAsx and GaSb1-xAsx grown on Si. By varying their composition, we have grown ternary buffers with lattice constants ranging from 5.85 Å – 6.3 Å.

The overall goal of this dissertation is to produce a variety of virtual substrates, having lattice constants between the aforementioned range mentioned above. We first optimize a GaSb-on-Si virtual substrate by minimizing the threading dislocation density (TDD) via MBE growth parameter optimization. A device was then fabricated on this GaSb virtual substrate to partially determine the effect of the non-native wafer. Note that a number of materials and device characterization techniques, including: X-ray diffraction (XRD), atomic force microscopy (AFM), electron channeling contrast imaging (ECCI), temperature dependent photoluminescence (PL), and IV curves, were performed to gauge both material and device quality. Virtual substrates lattice matched to InP and 6.3 Å were then made to verify that we change what lattice constant the virtual substrate would relax to.

DOI

10.18122/td.2408.boisestate

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