Date of Graduation

12-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Microelectronics-Photonics (PhD)

Degree Level

Graduate

Department

Microelectronics-Photonics

Advisor/Mentor

Salamo, Gregory J.

Committee Member

Ware, Morgan E.

Second Committee Member

Yu, Shui-Qing "Fisher"

Third Committee Member

Bellaiche, Laurent

Fourth Committee Member

Wise, Rick L.

Keywords

Gallium nitride; Molecular beam epitaxy; MQW; quantum well; RHEED; semiconductor; adsorption; desorption

Abstract

Fully realizing the potential of InGaN semiconductors requires high quality materials with arbitrary In-content. To this date the growth of In-rich InGaN films is still challenging since it suffers from the low growth temperatures and many detrimental alloying problems. InN/GaN multiple quantum wells (MQWs) and super lattices (SLs) are expected to be promising alternatives to random InGaN alloys since in principle they can achieve the equivalent band gap of InGaN random alloys with arbitrarily high In-content and at the same time bypass many growth difficulties.

This dissertation focuses on studying the growth mechanisms, structural properties and energy structures of InN/GaN MQWs. Molecular beam epitaxy (MBE) growth of InN/GaN MQWs were carried out at 550 ○C and 680 ○C, which are close to the low and high ends of the allowed growth temperature window. Reflection high energy electron diffraction (RHEED) was demonstrated to be a valuable tool for understanding the MQW growth. By associating the RHEED intensity transient features with surface atomic processes such as the adsorption/desorption of metal species, the growth process was successfully monitored in situ. Also, at the high growth temperature, RHEED was successfully used to study the adsorption/desorption kinetics of indium surface coverage to gain knowledge of how to control InN deposition. The MQW growth at 680 ○C show that indium surface coverage over 2 MLs before GaN capping is a key factor for consistent quantum well formation. The consistent PL emissions at ~375 nm were attributed to the insertion of 1-ML thick QWs. At 550 ○C, both PL emission and QW thickness showed a self-regulating behavior. The redshift of PL emissions with the InN deposition saturated at ~423 nm while the QW apparent thickness were no more than 2 MLs. The residual indium accumulation identified by RHEED suggests that QWs are generally InGaN layers instead of coherent InN layers, which is supported by k.p calculations. Finally, a growth mechanism was proposed to explain the preservation, structural and optical properties of the quantum wells.

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