Had it been a regular Rigidbody you would have changed the ForceMode to Impulse, but when using Rigidbody2D it seems that you have to calculate the force yourself.
To get the impulse effect this should work:
Vector2 force = (transform.up * force) / Time.fixedDeltaTime;
rigidbody2D.AddForce(force);
Then try fiddling around with the mass of your Rigidbody2D and the force applied to get the right jump height.