Hydrogen: a relevant shallow donor in zinc oxide

Area of Science:

• Solid State Physics
• Materials Science
• Semiconductor Physics

Background:

• Nominally undoped zinc oxide (ZnO) single crystals exhibit intrinsic donor defects that influence their electrical properties.
• Understanding these native defects is critical for controlling ZnO's conductivity for various applications.

Purpose of the Study:

• To identify and characterize the nature of donor defects (D1 and D2) present in state-of-the-art ZnO single crystals.
• To confirm the role of hydrogen (H) as a donor species in ZnO.

Main Methods:

• Electron paramagnetic resonance (EPR) and Hall measurements were employed to detect and quantify donor species.
• Electron nuclear double resonance (ENDOR) was utilized to probe the microscopic structure and interactions of the D1 donor.

Main Results:

• Consistent evidence for two donor types (D1 and D2) was found in the ZnO crystals.
• The D1 donor exhibits extensive hyperfine interactions with numerous 67Zn nuclei, characteristic of a shallow, effective-mass-like donor.
• A distinct hyperfine interaction with a single hydrogen (H) nucleus was observed for D1, identifying H as the key constituent.
• The concentration of the D1 donor was determined to be 6x10^16 cm^-3.

Conclusions:

• Hydrogen (H) is definitively identified as the shallow effective-mass donor (D1) in ZnO, validating theoretical predictions.
• The significant concentration of D1 highlights its importance for carrier statistics and the practical applications of ZnO.