Embodiments of the present disclosure describe a method of fabricating spin qubit device assemblies that utilize dopant-based spin qubits, i.e. spin qubit devices which operate by including a donor or an acceptor dopant atom in a semiconductor host layer. The method includes, first, providing a pair of gate electrodes over a semiconductor host layer, and then providing a window structure between the first and second gate electrodes, the window structure being a continuous solid material extending between the first and second electrodes and covering the semiconductor host layer except for an opening through which a dopant atom is to be implanted in the semiconductor host layer. By using a defined gate-first process, the method may address the scalability challenges and create a deterministic path for fabricating dopant-based spin qubits in desired locations, promoting wafer-scale integration of dopant-based spin qubit devices for use in quantum computing devices.