Vibrational modes of dopant defects in gallium oxide reveal hydrogen’s role

The high electric field strength and breakdown voltage of gallium oxide has led to its emergence as an ultrawide bandgap semiconductor for applications like high power electronics and transparent conducting oxides. However, the unintentional ingress of hydrogen impurities can impair its performance by creating variability and instability in the conductivity. Understanding the role of hydrogen in gallium oxide poses an important challenge for engineering device fabrication processes.

New research in Applied Physics Letters determines the vibrational modes of hydrogen impurities in gallium oxide to determine which hydrogen interactions have the greatest impact on the device conductivity. Researchers annealed intrinsic wafers in atomic hydrogen or deuterium under controlled conditions to introduce the hydrogen defects. They then used Fourier transform infrared spectroscopy to locate and quantify the resulting hydrogen-oxygen and deuterium-oxygen interactions.

The polarization-dependent vibrational modes from hydrogen and deuterium centers were determined from narrow peaks in the infrared spectra. Density functional theory helped determine the nature of the observed vibrational modes. The authors found that the dominant hydrogen-induced defect consisted of two hydrogen atoms trapped at a gallium vacancy site, which can act as either a source or a sink for hydrogen. They found the peak for this defect site at 3,437 inverse centimeters.

This work sheds new light on the underlying physics of hydrogen defects in the important ultrawide bandgap semiconductor material. This understanding enables better knowledge of the processing strategies to be used to fabricate devices, which could allow the more ubiquitous use of gallium oxide-based devices.

Source: “Structure and vibrational properties of the dominant O-H center in β-Ga₂O₃,” by Philip Weiser, Michael Stavola, W. Beall Fowler, Ying Qin, and Stephen Pearton, Applied Physics Letters (2018). The article can be accessed at https://doi.org/10.1063/1.5029921 .