Impurity level properties in transition metal doped α-Ga2O3 for optoelectronic applications

Abstract

Doping engineering is necessary in the preparation of high-performance devices based on ultra-wide bandgap semiconductors. However, we do not yet understand the impurity level properties and their effects on performance modulation of transition metal doped α-Ga2O3. Here, using first-principles calculations with a hybrid functional, we find that IB and IIB transition metal dopants exhibit relatively lower formation energies with a theoretically high hole concentration compared with Mg dopant. However, the induced acceptor levels are so deep that the impurity levels are transformed into AX centers. Although such AX centers hinder the formation of p-type conductivity, they can increase the optical absorption, ranging from deep ultraviolet to infrared regions. For electron-rich doped α-Ga2O3, the donor levels go from deep to shallow, then turn into deep levels again and finally to relatively shallow again as the transition metal dopant goes from group IIIB to VIIIB of the periodic table. Because ionic bonds are formed between O and a dopant (IVB to VB) with a raised d-orbital, covalent characteristics are observed for the O dopant (VIB to VIIIB) bonds with evident d-orbital splitting. These results add new insights into the impurity levels of α-Ga2O3, but also reveal potential applications of transition metal dopants in α-Ga2O3.