Gallium nitride selective area growth and heteroepitaxy via PAMBE for power device applications
Kelly, Frank Putnam
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https://hdl.handle.net/2142/127397
Description
Title
Gallium nitride selective area growth and heteroepitaxy via PAMBE for power device applications
Author(s)
Kelly, Frank Putnam
Issue Date
2024-12-05
Director of Research (if dissertation) or Advisor (if thesis)
Kim, Kyekyoon
Doctoral Committee Chair(s)
Kim, Kyekyoon
Committee Member(s)
Bayram, Can
Dallesasse, John
Lee, Minjoo L
Zuo, Jian-Min
Department of Study
Electrical & Computer Eng
Discipline
Electrical & Computer Engr
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Gallium nitride
PAMBE
materials growth
semiconductor processing
power electronics
heteroepitaxy
characterization
Abstract
Using a custom PAMBE system, growth of GaN is explored on different substrates for vertical power device applications. Undoped and doped films are grown in different conditions and characterized via SEM, XRD, and TEM. Devices are fabricated to test novel methods and structures via I-V and C-V analysis.
SAG as a method of selective area processing is developed from a method for producing thin contact layers into SNS-SAG, a technique suitable for power device geometries. Comparisons to conventional methods are made, showing an improvement of four orders of magnitude in leakage current over an ICP-RIE produced device. Thermal stress was optimized via adjustment of the mask PECVD deposition conditions and addition of a backside layer. Improvement was verified via Raman spectroscopy mapping. Novel edge termination schemes are explored via theoretical analysis and growth simulation. Application to preliminary devices is presented and routes towards improvement are outlined.
Nitridation of (-201)-oriented β-Ga2O3 was investigated for the purpose of enabling GaN heteroepitaxy. Conversion of Ga2O3 to GaN was confirmed via XRD and RHEED, and layers were characterized via TEM, XRR, and AFM. Optimization allowed for growth of high quality UID GaN films as quantified by XRD rocking curves, and a model for misfit strain relief is discussed. Defect analysis is carried out via advanced x-ray and TEM methods to determine mechanisms of defect structure formation, as well as validate proposed models. Undoped films are analyzed to verify the impact of defects on leakage conduction. p-n diodes are grown and fabricated with record rectification for the p-GaN/n-Ga2O3 system demonstrated. Reverse bias carrier transport is investigated to determine leakage mechanisms.
Future work is proposed, involving improvement of SNS-SAG films to allow for full application of high-efficiency edge termination schemes. The use of growth simulation will be used to investigate new geometries such as side-by-side SAG, enabling more complex devices such as vertical transistors. Advanced buffer layer schemes for GaN-on-Ga2O3 films are proposed to improve p-n diode performance. The extension of developed nitridation methods to selective area growth on Ga2O3 is discussed with preliminary work presented.
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