Good source for representation of GL(n) over finite fields? I'd like to gain some understanding of unitary representations of GL(n) over finite fields. Any good source would be appreciated.
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My original question was ambiguous. Let me explain and give a few further details. 
I want to understand some combinatorial properties (expansion of some type) of the group $GL_{\mathbb{F}}(n)$, where the $\mathbb{F}$ is a finite field. One possible approach for doing that (that was successful in, e.g. understanding similar aspects of the permutation group) is through unitary representations of that group. As far as I can tell, most of the texts cover $GL(n)$ over fields of characteristic zero, which are not what I'm interested in. So I'm asking for sources for unitary representations of the linear group over finite fields..
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To clarify further, by unitary representations I mean homomorphisms of GL(n) of a finite fields, into the group of finite-dimensional unitary matrices over $\mathbb C$. As you might guess, I'm a cs/combinatorics person, and far from expert on representation theory -- please excuse my lack of verbal skills in this area and otherwise..
 A: Especially for combinatorialists, I found the book "Representations of finite classical groups. A Hopf algebra approach. Lecture Notes in Mathematics, 869" by Andrei Zelevinsky useful. It devolops a theory which covers both $S_n$ and $GL(n,\mathbb F_q)$. The  point of view is that representations of these groups should be studied simultaneously for all $n$.
A: I think the standard reference for representations over finite fields still is


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*J. L. Alperin, "Local Representation Theory" (1986)


I you want a much briefer introduction, the last chapters of Serre's book might be enough.
In fact, even if you want to study Alperin, Serre might be a good place to start.


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*Jean-Pierre Serre, "Linear Representations of Finite Groups" (1977)

A: I would highly recommend "Complex Representations of GL(2,K) for Finite Fields K" by Piatetski-Shapiro.  (I know you're interested in GL(n), but this book is a great place to start.)
A: All finite dimensional complex representations of finite groups are equivalent to unitary representations, so the requirement that the representations be unitary is not really a restriction.
The 1955 work of J.A. Green gives the definitive description of the complex characters of the groups ${\rm GL}(n,q)$ for q a prime power: see
http://www.ams.org/journals/tran/1955-080-02/S0002-9947-1955-0072878-2/S0002-9947-1955-0072878-2.pdf
Later work of Deligne-Lusztig studied the complex characters of other finite classical groups (and finite groups of Lie type), and the book of Digne and Michel mentioned by Neil Strickland is a good source of information.
A: On-line and a good starting point with GL(2, F_q):
Paul Garret's notes "Representations of GL2 and SL2 over finite fields"
http://www-users.math.umn.edu/~garrett/m/repns/notes_2014-15/04_finite_GL2.pdf
And also:
Amritanshu Prasad
"Representations of GL2(Fq) and SL2(Fq), and some remarks about GLn(Fq)"
http://www.imsc.res.in/~amri/html_notes/notes.html
or similar in arxiv:
https://arxiv.org/abs/0712.4051
PS
The bonus is that both authors are at MO so you might get answer if something is unclear.  
