to wake up means "일어나다"
It pronounced as "이러나다"
The reason of spelling of "일어나다" instead of "이러나다" is due to the The Korean Grammar in Hangeul Orthography about compound word.
It states that
합성어나 파생어와 같은 복합어의 경우, 앞말의 본뜻이 유지되는 경우에는 원형을 밝혀 적는다. 그러나 앞말의 본뜻이 유지되지 않는 복합어는 소리대로 적는다.
In case of compound word like composite word or derivative word, it should be written as an original form when the original meaning of the first word still retain. But, when the meaning of the first word is no longer remains, the compound word should be written as pronounced.
들어나다(X) 드러나다(O) is come from 들(다) + 어+ 나다.
The meaning of 들다 is not retained in that word. So it is written as pronounced.
졸음(O) 조름(X) is come from 졸다 + (으)ㅁ
The meaning of 졸다 is still retained in that word. So it is written as 졸음.
일어나다(O) 이러나다(X) is come from 일(다) (rise) + 어(and) + 나다(up,exit)
The meaning of 일다 is still retained in that word. So it is written as 일어나다.