Paper TF-TuE3
Improvement of Thermal Stability of p-ZnO:(Al,N) Thin Films by Oxidizing Amorphous Zn3N2:Al Thin Films
Tuesday, December 9, 2014, 6:20 pm, Room Makai
ZnO has attracted much more attention as a potential cadidate for more efficient UV-lasers due to its wide band gap of 3.374 eV and a large exciton binding energy of 60 meV. However, the problem associated with the preparation of stable p-type ZnO with high hole density hinders the ZnO-based device application as UV-emitters. Although substantial studies have been focused on this challenging issue, there are, so far, no efficient and practical doping methods to prepare stable p-ZnO with high hole density. The n-type conduction with high electron density (1021 cm-3) have been achieved by doping ZnO with group-III elements (Al, and Ga). On the other hand, although extensive studies have been focused on the p-type doping issue of ZnO, the ZnO-based optoelectronic devices fabricated from p/n junction still suffer from p-type ZnO problem. P-type conduction has been reportedly realized with chemical doping. However, the low hole density and instability in electronic behavior become the bottleneck to improve the ZnO-based device performance. For improving the thermal stability of p-ZnO, we introduce Al to capture the N by forming Al-N chemical bonds. The bond dissociation energy, △Hf298, of Al-N is 297kJ•mol-1, is much larger than the Zn-N（△Hf298 = 160 kJ•mol-1). Theoretical calculations suggested the possible approach to the p-type doping in ZnO with III-V Ga-N co-doping or cluster-doping, which can increase the solubility and stability of N in ZnO. Here, we use Al to stabilize the N-doping, because the corresponding bonds with N and O are stronger for Al than for Ga. For stabilizing N in p-type ZnO, the key issue is to reduce the compensation of single Al doping due to the formation of only Al-O bands. Another crucial point is to make sure the Al captures more than one N-atoms to form AlN2, AlN3, and AlN4 in ZnO. To realize that, we prepared Zn3N2:Al and convert it to ZnO by an oxidization procedure. For Zn3N2:Al, p-ZnO appears around 600 oC and do not convert back to n-type with further increase of annealing temperature. However, for Zn3N2, we did not obtain p-type ZnO. A reasonable explanation is that the Al will stabilize the N during the reaction to form ZnO from Zn3N2. Comparing with previous reports, the thermal stability is improved. However, the hole density is still low and needs further improvements. More details about the structural, optical, and electronic properties of the samples will be given in the presentation.
We will optimize the concentration of Al dopant in Zn3N2:Al. The dependence of the hole density in ZnO, oxidized from Zn3N2:Al, on the Al concentration in Zn3N2:Al will be studied.