Never write it
The word (actually phonetic spelling) of "got to" can be found in most dictionaries, however, it is not a proper word... it is simply a sound:
The use of got without 'have to' or 'has to' means “must” (I got to buy a new suit) is characteristic of the most relaxed, informal speech and does not occur in edited writing except in representations of speech. Gotta is a pronunciation spelling representing this use.
Why do people use 'gotta and haveta and gonna'?
It requires fewer muscles and less effort to make the 'gotta' sound when compared to the more strenuous 'go to' sound.
Don't, i.e., never use it in a job interview
'gotta/wanna etc' are informal sounds that could make one appear to have poor English pronunciation.
To see a previous discussion on this topic, go to: https://www.italki.com/discussion/81474
It's very easy: don't use it.
"Gotta" is not a word. It's two words said in a very lazy way. If you really want to use "gotta", then you'll just sound like someone who hasn't learnt English properly.
Do what native speakers do: speak English normally.