p-Type GaN

Abstract

Ever since research into the GaN system began in the 1960s, the biggest unsolved problem has been the production of p-type GaN. For a long time it was impossible to obtain p-type GaN films. Unavailability of p-type GaN films has prevented III-V nitrides from yielding visible light emitting devices, such as blue LEDs and LDs. In 1989, Amano et al. succeeded in obtaining p-type GaN films using Mg doping, MOCVD, and post low-energy electron-beam irradiation (LEEBI) treatment [190, 191, 192] . After growth, LEEBI treatment was performed for Mg-doped GaN films to obtain a low-resistivity p-type GaN film. The hole concentration and lowest resistivity were 10¹⁷ cm^-3 and 12 Ωcm, respectively [192]. These values were still insufficient for fabricating blue LDs and high-power blue LEDs. On the other hand, Amano et al. first discovered the LEEBI treatment as a method for obtaining p-type GaN. However, in 1983 Saparin et al. [193] had already investigated the LEEBI treatment effects on Zn-doped GaN in detail. The effect of the LEEBI treatment was argued to be Mg-displacement due to energy transfer from the electron beam: in the case of as-grown Mg-doped GaN, the Mg atoms occupy sites different from Ga sites where they are acceptors. Under the LEEBI treatment, the Mg atoms move to exactly occupy Ga sites.