Tailoring the Band Alignment of GaxZn1-xO/InGaZnO Heterojunction for Modulation-Doped Transistor Applications

In this work, the band alignments of G(x)Z(1-x)O(y)/a-IGZO heterojunctions with different Ga contents (x) are investigated by X-ray photoelectron spectroscopy (XPS). It is found that for increasing Ga content, the valence-band offset is monotonically reduced, whereas the conduction-band offset is continuously increased. Moreover, the band alignment changes from type I to II. The variation of band alignment is mainly attributed to the band bending at the interface of the heterojunction, which can be traced back to oxygen vacancies for higher Ga content, rather than enlarged bandgap. As a result, G(0.47)Z(0.53)O(1.14)/a-IGZO heterojunction exhibites a more ideal band alignment structure, which can favor the formation of two-dimensional electron gas. In summary, it is found that the band alignment of G(x)Z(1-x)O(y)/a-IGZO heterojunction can be effectively tailored by its Ga content, thus providing a method to achieve high-performance a-IGZO-based modulation-doped transistors.