Harrison's book is a good compromise between learning the full, formal maths approach to quantum mechanics and a pragmatic desire by engineering students to know enough to do useful work. It deprecates such ideas as operators in Hilbert spaces in favour of describing such practical implementations as quantum dots, quantum wires, tunnelling and other inherently quantum phenomena.

The intent is to expose the reader to current active areas of solid state research and engineering, at the microscopic level when quantum effects must be taken into consideration. There is not enough here to do serious band structure calculations, for example. But you gain enough knowledge to understand and use band structure results that are presented to you.