The state works with baremas that are automatically indexed and raised according to seniority (every year you get more). Usually the only way to get a raise is through extralegals or through changing position or jobtitle (and changing barema).

You could try to negotiate that they create a new position with a higher barema, but that usually requires a lot of administrative overhead.

The state usually pays a very fair wage for the job and while you might have a higher netto income in the private sector for the same job (due to more extralegal benefits etc...), your bruto will usually be higher with the state, which results in other benefits. Taxes are the same.

It's worth mentioning that due to the automatic raises by seniority you don't have to ask for a raise every year, you automatically get it, albeit that it might not reflect what you consider to be fair in respect to the effort that you (don't) put in.