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..