Passivation of aluminum nitride substrates
The present invention provides methods of protecting a surface of an aluminum nitride substrate. The substrate with the protected surface can be stored for a period of time and easily activated to be in a condition ready for thin film growth or other processing. In certain embodiments, the method of protecting the substrate surface comprises forming a passivating layer on at least a portion of the substrate surface by performing a wet etch, which can comprise the use of one or more organic compounds and one or more acids. The invention also provides aluminum nitride substrates having passivated surfaces.
1. A substrate comprising an aluminum nitride single crystal wafer with a polished surface that is at least partially covered with a passivating layer having a content of surface bound oxygen, wherein greater than 60% of the surface bound oxygen, on a molar basis, is in the OH − state, and wherein the passivating layer is stable at room temperature and humidity such that oxidation of the polished surface covered with the passivating layer is prevented under such conditions.
2. The substrate of claim 1 , wherein at least 70% of the surface bound oxygen is in the OH − state.
3. The substrate of claim 1 , wherein about 65% to about 90% of the surface bound oxygen is in the OH − state.
4. The substrate of claim 1 , wherein the substrate comprises a content of a further Group III element.
5. The substrate of claim 1 , wherein the polished surface is epiready.
6. The substrate of claim 1 , wherein the passivating layer has a thickness of less than about 2 nm.
7. The substrate of claim 6 , wherein the passivating layer has a thickness of less than about 1.5 nm.
8. The substrate of claim 1 , wherein the passivating layer exhibits a decreased surface molar fraction of oxygen and an increased surface molar fraction of both nitrogen and aluminum as compared to the substrate surface in the polished state prior to formation of the passivating layer.
9. The substrate of claim 1 , wherein the passivating layer exhibits a reduction in the difference between the molar fractions of nitrogen and aluminum (M Al -M N ) compared to the substrate surface in the polished state such that M Al -M N of the passivating layer is less than M Al -M N of the substrate surface in the polished state.
10. The substrate of claim 1 , wherein the passivating layer exhibits a reduced amount of aluminum that is bonded to oxygen compared to the amount of aluminum bonded to oxygen when the substrate surface is in the polished state prior to formation of the passivating layer.
11. The substrate of claim 1 , wherein the passivating layer is formed by applying a wet chemical etch to the substrate surface at a temperature of about 80° C. to about 120° C.
12. The substrate of claim 11 , wherein the wet chemical etch comprises an acid.
13. The substrate of claim 11 , wherein the wet chemical etch comprises a base.
14. The substrate of claim 1 , wherein the aluminum nitride single crystal wafer has a single crystal orientation.
15. The substrate of claim 14 , wherein the aluminum nitride single crystal wafer has an aluminum orientation.