Gallium nitride super-heterojunction device design and single event effect response
Restricted (Penn State Only)
- Author:
- Song, Jianan
- Graduate Program:
- Electrical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- January 28, 2025
- Committee Members:
- Madhavan Swaminathan, Program Head/Chair
Michael Lanagan, Outside Unit & Field Member
Tom Jackson, Major Field Member
Rongming Chu, Chair & Dissertation Advisor
Mehdi Kiani, Major Field Member
Suzanne Mohney, Major Field Member - Keywords:
- GaN
Superjunction
Radiation
TCAD
Single event effect
Dielectric - Abstract:
- GaN emerged as a promising semiconductor material for a wide range of high-power, high-frequency applications due to its excellent properties: wide band gap of 3.4 eV, high critical field of 3.3 MV/cm, and a high electron mobility of around 2000 cm2/V∙s. The commercial GaN device usually implements the AlGaN/GaN heterojunction design, featuring high mobility two-dimensional electron gas (2DEG). Currently, most GaN HEMT as a lateral power device has a limited voltage rating of 650V. It also suffers from the current recovery loss due to surface trapping. Super-junction is the design to solve these problems with improved electric field profile management. The development of GaN super-junction devices requires exploring and understanding the design factors: (i) significant leakage current at mA/mm range was observed on GaN super-junction diodes. This leakage current was found to be hole conduction current through p+-GaN. The notch etch process effectively reduces the leakage and improves device breakdown voltage. The hydrogen passivation process as a less destructive alternative was studied as well. (ii) Implementing super-junction to a GaN transistor also requires the application of a gate dielectric for a reduced gate leakage, favorable normally-off operation and forward bias insulation. The aluminum oxynitride (AlOxNy) - GaN MOS structures showed good interface quality, particularly for non-polar GaN, indicating its potential to be sidewall contact oxide in GaN super-junction devices. GaN devices are also finding applications in space, where the device's reliability can be severely affected by space radiation. The heavy ions in space can cause single event effects, which disrupt the device performance and cause device destruction. It is of critical importance to characterize device degradation and investigate the mechanism of single event effects in GaN devices. TCAD simulation showed the single event effect is caused by raised bulk potential inducing electron injection, which addresses the importance of maintaining low bulk potential. It also revealed the advantage of super-junction as a radiation-resistive design. Radiation tests of GaN devices showed the permanent leakage current increase, the leakage current is temperature and field dependent. A hypothesis is proposed that leakage current follows the Poole-Frenkel emission and thermionic emission model depending on temperature.