Heterogeneous Integration of III-V and II-IV Semiconductor Sheets onto Silicon Substrate through Electric-Field Assisted Assembly for Device Applications

Open Access
Author:
Levin, Scott M
Graduate Program:
Materials Science and Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
February 02, 2015
Committee Members:
  • Theresa Stellwag Mayer, Dissertation Advisor
  • Theresa Stellwag Mayer, Committee Chair
  • Suzanne E Mohney, Committee Member
  • Roman Engel Herbert, Committee Member
  • Suman Datta, Committee Member
  • Timothy John Eden, Special Member
Keywords:
  • III-V semiconductors
  • electric-field assisted assembly
  • heterogeneous integration
  • FinFET
  • GeSe
Abstract:
Market forces are creating a strong need to make value-added enhancements to silicon (Si) complementary metal-oxide semiconductor (CMOS) integrated circuit (IC) technology. One approach to achieve this goal is through continued scaling following Moore’s law. With the future of device scaling being relatively uncertain in the next 10-20 years, it is important to find new ways to add value to CMOS. Theoretical projections show that monolithic three-dimensional (3D) integration of compound semiconductor (CS) devices can enhance the performance and functionality of future CMOS-based IC’s. This becomes increasingly important with continued scaling. With each new technology node the interconnect pitch is reduced, increasing the RC delay. The net result is an increase in response time between circuit components, resulting in a greater need for 3D integration to minimize the length of the contact lines between CMOS and other non-digital functionalities. To achieve this complex goal, a flexible heterogeneous integration strategy is required that can incorporate a diverse selection of materials all onto a single substrate. Electric-field assisted assembly is a promising technique that allows for fast, low temperature and versatile integration of a large variety of materials onto alternative substrates. In this technique, particles can be assembled from solution at high yields, achieving sub-micron alignment registration to predefined features on the substrate. The approach is not limited by mismatch in coefficient of thermal expansion (CTE) and lattice constant, offering the flexibility to apply materials at the device layer, or any subsequent layer in the CMOS backend. In this thesis research, electric-field assisted assembly of micron-sized compound semiconductor (CS) sheets is studied through a combination of experiment and finite element method (FEM) modeling. This work presents a clear picture of charge distribution within an assembled particle on the substrate, and uses the model to accurately predict the preferred assembly position. The assembly position is confirmed experimentally, demonstrating reproducible sub-micron alignment accuracy with respect to patterned features on a substrate. Through a combination of electric-field assisted assembly and top down fabrication, a novel heterogeneous integration strategy is demonstrated. As a proof of concept, this technique is used to create In0.53Ga0.47As fin geometry p+-i-n+ junctions directly on Si substrates. The as-etched fin devices are not rectifying, but with annealing at 350ºC in N2 for 20 minutes, the electrical properties are restored. This process is further developed to implement fin tunnel field-effect transistors (TFETs) and metal-oxide semiconductor field-effect transistors (MOSFETs) integrated on Si. While dry etch-induced damage degrades the TFET device performance, fin MOSFETs show considerably better device performance due to their majority carrier device operation. Fin MOSFETs have a subthreshold slope of 280mV/decade and an on/off ratio of ~103 at 100mV. Through technology aided computer design (TCAD) simulations, it is shown that MOSFET performance can be improved by implementing an optimized doping design. To further emphasize the versatility of this heterogeneous integration strategy, solution-synthesized germanium selenide (GeSe) particles are assembled onto Si substrates. GeSe offers promise for phase change memory applications and non-toxic solar cells, due to its bandgap in the visible spectrum and use of earth-abundant non-toxic elements. GeSe nanobelts are measured both with 2-pt and 4-pt single particle measurements, and a resistivity of 360 Ω-cm is determined. This integration strategy is a reproducible technique for single particle measurements of solution-synthesized materials, something significantly lacking in the field. With such a technique, solution-synthesized particles can be evaluated for their use in future device applications.