Hayashi, Norihiko. A Phonological Sketch of Akha Buli: A Lolo-Burmese language of Luang Namtha, Laos. 2016. hh:phon:Hayashi:Akha-Buli
Hayashi analyzes creaky voice as a property of vowels, but since high tone and creaky voice can't co-occur, it's probably better analyzed as a property of tones.