Review for Novel 2DEG Based on Diverse Oxide Substrates

The two-dimensional electron gas (2DEG) residing at complex oxide interfaces has been drawing considerable interests due to its abundant physical characteristics. Moreover, it exhibits a response towards diverse external stimuli and a correlation among different freedoms, like spin, lattice, orbital charge, etc. The most studied objects are SrTiO3 (STO) and KTaO3 (KTO)-based heterointerfaces (HIs), which fully utilize their d-orbital characteristics. On the other hand, other oxides may also have enough potential to host 2DEG. Here, an investigation has been done for those oxide-based 2DEGs. Five series of oxides are investigated, including stannate oxide, niobate oxide, scandate oxide, germanate oxide and some simple oxides. Most existing works of such novel oxide substrates rely on theoretical prediction severely, while experimentally achieving them still needs much effort. On the other hand, some so-called substrates need to be grown on other solid substrates first. However, proper surface treatment would be a useful way to overcome the difficulties and develop the potential of such novel oxide substrates. These probable series of oxide-conducting HIs will not only be a great breakthrough for the d-orbital-based oxide 2DEG systems but may also hold diverse novel physical phenomena, thus pointing out the route for further development of research and fabrication on oxide electronic devices. Hence, we believe a review of the existing works will be meaningful for stepping across the threshold toward the new era of all-oxide electronics.