How to increment a char value

Question

Does anyone know how can I auto-increment a char value in SQL Server?

If I have

create table mae_student (
    id_student char (3),
    First_Name varchar (75),
    Last_Name varcha (75)
)

Where the first row must be 001, the second 002 and so on until 999.

How can I handle this in a query, using Microsoft SQL Server?

Because in the query I have:

Create Procedure new_student(
-- user data
@par_id_student char (3),
@par_First_Name varchar (75),
@par_Last_Name varcha (75)
)
AS
BEGIN
SET NO COUNT ON

-- 1. Verify the id not come empty
If rtrim(ltrim(@par_cod_student))=''
    begin
        select @parretorno=-2,@parerrorstate='',@parerrormessage='The ID cannot be empty!';
        select @parretorno as retorno,@parerrorstate as estado,@parerrormessage as mensaje;
        return;
    end;

-- 2. Verify the par_First_Name not come empty
If rtrim(ltrim(@par_First_Name))=''
    begin
        select @parretorno=-2,@parerrorstate='',@parerrormessage='The First Name cannot be empty!';
        select @parretorno as retorno,@parerrorstate as estado,@parerrormessage as mensaje;
        return;
    end;

-- 3. Verify the par_Last_Name not come empty
If rtrim(ltrim(@par_Last_Name))=''
    begin
        select @parretorno=-2,@parerrorstate='',@parerrormessage='The Last Name cannot be empty!';
        select @parretorno as retorno,@parerrorstate as estado,@parerrormessage as mensaje;
        return;
    end;

-- 4. Verify the student does not Exist
if exists(select cod_student from mae_student where id_student=@par_id_student)
    begin
        select @parretorno=-6,@parerrorstate='',@parerrormessage='The ID Student is Already Register !';
        select @parretorno as retorno,@parerrorstate as estado,@parerrormessage as mensaje;
        return;
    end;


-- Transaction
begin transaction
    begin try
        -- Add the new student
        insert into erp.mae_student(cod_student,First_Name,Last_Name)
        values (@par_cod_student,@par_First_Name,@par_Last_Name);

        -- Comfirm the transaction
        commit;

        -- Message for user
        select @parretorno=1,@parerrorstate=@parcodigo,@parerrormessage='Success';
        select @parretorno as retorno,@parerrorstate as estado,@parerrormessage as mensaje;
    end try

end