Interface modulation and quantum well to quantum wire crossover in semiconductor heterostructures

We consider AlAs/GaAs/AlAs (001) quantum wells in which one of the interfaces is planar and the other is modulated by periodic steps. The systems are described theoretically within a real-space tight-binding approach, and the optical nature of the heterostructures is investigated through the calculated oscillator strength of the fundamental transition in the well. The interface profile amplitude and wavelength combined effects lead to distinct optical regimes, which are qualitatively summarized in a simple phase diagram. At short wavelengths, increasing the modulation amplitude causes a decrease in the oscillator strength and eventually a sharp direct-to-indirect gap transition takes place at a critical amplitude. For long enough wavelengths, the gap remains direct at all amplitudes: The oscillator strength decreases until it attains a minimum, and then it increases again as the interface modulation amplitude increases. The oscillator strength minimum in the second regime is a signature of a quantum well to quantum wire crossover in the optical behavior of the system.