Collaborative Research: Atomic Displacement Engineering of Post-epitaxial Thin-films (ADEPT)

University Of Pennsylvania, Philadelphia PA

Investigators

Abstract

Nontechnical Description: The advent of modern epitaxial semiconductor technologies has resulted in a paradigm shift in optoelectronic and electronic device fabrication. Specifically, the control of semiconductor layer thickness to within a single atomic layer and the creation of multiple, abrupt interfaces between two different semiconductor materials have led to the realization of a host of structures that are key elements in modern lasers, detectors and transistors. However, to date, precise control of chemical composition in heteroepitaxial semiconductor assemblies has been limited to the growth direction - the next leap in the evolution of semiconductor structures will be to realize precise control of composition in all three dimensions, opening routes to optoelectronic building blocks for new technologies, such as quantum computing and cryptography. This project seeks to achieve this goal by using mechanical forces induced by nano-indentation to laterally control chemical composition in semiconductor heterostructures created with existing epitaxial technology. The project integrates experimental measurements of chemical composition and structure at the nanoscale with multiscale computer modeling of atomic diffusion. Using computer models that have been partially informed by specifically tailored experiments, the team explores a broad parameter space and identifies the necessary operating conditions needed to efficiency and robustly drive atomic diffusion. If successful, the outcome of this project could pave the roadmap for creating a new class of semiconductor structures with broad potential applications. The project serves as a multidisciplinary home for training graduate and undergraduate students at both participating institutions. Undergraduate research opportunities for underrepresented groups is a special emphasis whereby students identified at the University of New Mexico are recruited into summer research opportunities at the University of Pennsylvania. Technical Description: In this project, the research team investigates a new strategy for laterally defining nanoscale compositional patterns in epitaxially-grown III-V semiconductor systems. This multistep strategy is referred to as Atomic-Displacement Engineering of Post-epitaxial Thin-films, or ADEPT, which, coupled with traditional heteroepitaxial methods, may provide a practical pathway for creating three-dimensional quantum barrier configurations with a high degree of controllability. The ADEPT approach employs spatially patterned stress fields and thermal annealing to drive diffusion in a compound semiconductor alloy film comprised of two mobile atomic species with different sizes and diffusional responses to elastic stress. The stress fields are applied by pressing a reusable, pre-patterned array of nanopillars against the semiconductor substrate. Notably, the "press-and-print" ADEPT strategy does not rely on nucleation and growth of sub-phases that are difficult to control and is applicable to any material system in which two mobile atomic species of different sizes are present. The team has recently demonstrated the ADEPT approach in SiGe and here investigates its broader application to III-V heteroepitaxial systems, namely InGaAs and GaAsSb, both supported on InP. In contrast to SiGe, atomic diffusivities in these materials is not fully characterized, particularly as a function of temperature and elastic stress, preventing predictive modeling and the ability to fully explore the ADEPT process. The research activity seeks to overcome the obstacles posed by a large process parameter space and limited experimental throughput with a two-step, computer-aided experimental design approach. In the first stage, data-assisted models are developed using a sequence of relatively "simple" experiments specifically designed to generate information for parameterizing models for interdiffusion in III-V materials. In the second stage, the parameterized models are used to explore the multidimensional parameter space and identify suitable conditions for performing experimental demonstrations of the ADEPT process. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.