Researchers Probe Radiation Resistance Of GaN LEDs
GaN based devices are attractive for harsh environment electronics because of the high chemical and mechanical stability of GaN. However their breakdown mechanisms under radiation are not well understood, This is because devices consist of many different types of semiconductors, such as p-type and n-type layers in LEDs, and each layer has a different hardness to radiation.
Now researchers at the Electronics-Inspired Interdisciplinary Research Institute (EIIRIS) and Department of Electrical and Electronic Information Engineering at Toyohashi University of Technology, and the Japan Atomic Energy Agency (JAEA) have described the physical mechanism of an observed increase in the resistance of p-type GaN irradiated with 380 keV protons compared with n-type GaN.
The GaN-based LED structure shown above was irradiated with protons and the resulting electrical properties measured. Notably, the electrodes to measure the resistance of the p-type and n-type layers were produced independently using the clean room facilities at EIIRIS and the ion implanter in JAEA.
The two terminal resistance of the n-type GaN did not vary from its initial value after 1x1014 cm-2 proton irradiation, and remained of the same order after 1x1015 cm-2 protons. However, a clear increase of the resistance was found in the p-type GaN after 1x1014 cm-2 irradiation. The resistance increased further by six orders of magnitude after 1x1015 cm-2.
According to the researchers, the observed increase of the resistance in p-type GaN is due to the lower initial carrier density than in n-type GaN due to a lack of efficient p-type doping technology for GaN, which is a key for the realisation of novel devices operable in harsh environments.
'Study of Proton Irradiation Effects on p- and n-Type GaN Based-on Two-Terminal Resistance Dependence on 380 keV Proton Fluence' by Hiroshi Okada et al, appeared in IEICE Transactions on Electronics E97-C, 409 (2014). (DOI): 10.1587/transele.E97.C.409