var allTeamMembers = from t in db.TeamMembers
	join ct in db.CaseTeamMembers on t.TeamMemberID equals ct.TeamMemberID into ctm
	from ct in ctm.DefaultIfEmpty()
	select new
	{
		CaseID = ct.CaseID == null ? 0 : ct.CaseID,
		t.TeamMemberID,
		CaseTeamMemberID = ct.CaseTeamMemberID == null ? 0 : ct.CaseTeamMemberID,
		t.Name,
		Photo = t.Photo ?? "default.gif"
	};

var allTeamMembers = from t in db.TeamMembers
									 join ct in db.CaseTeamMembers on t.TeamMemberID equals ct.TeamMemberID into ctm
									 from ct in ctm.DefaultIfEmpty()
									 select new
									 {
										 CaseID = ct.CaseID == null ? 0 : ct.CaseID,
										 t.TeamMemberID,
										 CaseTeamMemberID = ct.CaseTeamMemberID == null ? 0 : ct.CaseTeamMemberID,
										 t.Name,
										 Photo = t.Photo ?? "default.gif"
									 };

http://www.hookedonlinq.com/OuterJoinSample.ashx

NOTE: When you do an outer join, every column selected that could be null from the join must have a ternary operator in the select statement.

LINQ outer join

C#