Magnetron Sputtering of III-N Thin Films
Restricted (Penn State Only)
- Author:
- Nordlander, Josh
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 02, 2024
- Committee Members:
- John Mauro, Program Head/Chair
Rongming Chu, Outside Unit & Field Member
Jon-Paul Maria, Chair & Dissertation Advisor
Joan Redwing, Major Field Member
Stephanie Law, Major Field Member - Keywords:
- GaN
III-N
sputter deposition - Abstract:
- Since bulk substrates of III-V semiconductors were first introduced in the 1950s, the favorable electronic and optical properties of this family of semiconductors have been explored and exploited for many applications. Gallium nitride is an important III-N semiconductor material, currently used in many commercial applications, especially for high power and high efficiency devices such as light-emitting diodes. While GaN technology has been commercialized, current growth technology suffers from drawbacks of high growth temperature or poor scalability, limiting potential future applications. As commercialization of III-N based devices continues to increase, any alternative growth methods with a large scalability are highly favored. A plethora of available growth techniques allows the proper growth technology to be employed for each application to better suit the benefits and drawbacks of each method. For example, the high temperatures associated with metal-organic chemical vapor deposition can limit the scalability of devices grown on low cost Si substrates due to a large mismatch in thermal expansion coefficients. While the growth temperature for molecular beam epitaxy is lowered, the equipment is costly and can be challenging to upkeep due to the stringent ultra-high vacuum requirements. Meanwhile, sputter deposition is a highly scalable growth technique that may offer some benefits to these techniques for certain application, though it comes with its own drawbacks. Starting in the 2010s there were reports of high-quality sputtered GaN. Other groups have reported sputtered GaN that is highly defective and does not live up to the promises of such work. In order to understand the benefits and drawbacks of each growth technique, each deposition process must first be well-characterized so that the practical limitations are understood. This work provides an understanding of the important processing parameters for the sputter deposition of III-N thin films, their interplay, and how they affect the structural properties and surface morphology of deposited films. An introduction to III-N growth in bulk and epitaxial thin film form is reviewed followed by the description of a high electron mobility transistor. The main body of work describes the important processing knobs for generating step flow growth GaN on native templates at remarkably low temperatures, albeit with a narrow processing space. In order to glean a better understanding of the interplay of processing parameters, InN is deposited on sapphire substrates. Finally, this understanding is used to deposit high-quality GaN films on sapphire substrates which are then doped highly n-type for integration with ferroelectric heterostructures. Finally, all of these findings are summarized and future and ongoing work is suggested for applications where sputter deposition has clear advantages over other growth technologies. While these findings are applied to III-N deposition, the work and general trends may apply to other wide-bandgap or ultra-wide-bandgap material systems.