Apr 14 (Thu) @ 1:00pm: "Investigation of p-type GaN / AlGaN Superlattices," Athith Krishna, ECE PhD Defense

Date and Time
Elings Hall 1605


Post the commercialization and widespread use in light emitting diodes (LEDs), heterostructures of III-nitride semiconductors (GaN, AlN, InN, and BN) with their alloys, have shown immense promise in applications not limited to optoelectronics, but ranging from high power and high frequency electronics to plasmonics, and quantum computing. While the properties of electrons and the two-dimensional electron gas (2DEG) have drawn a great deal of attention to this materials system, corresponding advances in p-type III-nitrides are required to explore the complete benefits this semiconductor family can potentially provide. Like in most other wide-bandgap materials, the poor performance of p-type material in III-nitrides has led to only a few studies reported on p-channel III-nitride electronic devices. The use of p-type superlattices (SL) is valuable for III-nitride semiconductor-based LEDs and p-channel Field effect transistors (pFETs) because the polarization effects create a periodic oscillation of the energy bands, enhancing the ionization of the deep acceptors. Thus, the use of Mg-doped GaN/AlGaN SL is a pathway to get high hole concentration and mobility simultaneously, and pFETs engineered around a GaN/AlGaN SL have demonstrated record electrical performance. 

The present study will systematically explore the electrical properties of epitaxially grown p-type Ga-polar and N-polar, modulation doped and uniformly doped GaN/AlGaN, and GaN/AlN/AlGaN superlattices (grown using the MOCVD growth technique). Following this, the discovery of a novel acceptor trap, proposed at 0.8 eV above the valence band of GaN, will be presented with simulations and experiments. The implications of this trap level, and its impact as the source of holes in dopant-deficient systems will be elucidated. This study will also explain in detail how charge balance is achieved in recent p-channel III-nitride electronic and optoelectronic devices. A systematic methodology will also be presented to predict and explain the mobility and high sheet concentration of holes in p-type III-nitride systems, and p-type III-nitride material with sheet resistance as low as 2 kΩ/sq will be shown. This work concludes with the development of highly doped p++ GaN regrowth using MOCVD for use in p-channel III-nitride FinFETs with record normally-off performance. 


Athith Krishna is a Ph.D. candidate in the Department of Electrical & Computer Engineering at the University of California, Santa Barbara. His research focuses on performance improvement of p-type III-nitride semiconductors for electronics, under the supervision of Prof. Umesh Mishra. He obtained his Bachelor’s degree from Cornell University, Ithaca, NY in 2017, and Master’s degree from UC Santa Barbara in 2019. His research attempts to understand the physics, and the epitaxial material growth of III-nitrides for applications in electronic devices, in a systematic way. 

Hosted by: Professor Umesh Mishra

Submitted by: Athith Krishna <athith@ucsb.edu>