Is there a way I can wake up at morning without using an alarm.
I ask this because some of my roommates don't want to wake up early and I don't want to bother them.
I want to wake up at 4 a.m.
This may be based mostly on personal experience, but depending on your sense of responsibility and situation awareness, it may be enough to sit down at the evening and write down the time you want to wake up and why this is critical for you. You have to sign a contract with yourself in the most memorable way possible - but even then it may not work the first couple of times. It will also not work if you don't get enough sleep, keep an unhealthy diet or agitating thoughts bother you, before bed.
I have used a wearable vibrating alarm ($17) for a while. It's strapped to your soft noise-absorbing fleshy body as opposed to a vibrating phone on a hard surface.