Microscopic origin of compressive strain in hydrogen-irradiated dilute GaAs_{1−y}N_{y} alloys: Role of N-H_{n} centers with n>2 and their thermal stability

The addition of a small percent of nitrogen to GaAs causes a large reduction of the band gap energy and a tensile strain within the lattice. The further addition of H at 300 ◦C causes a recovery of the band gap of the N-free GaAs host. Concomitantly, tensile strain turns into compressive strain. Upon reduction of hydrogenation temperature, high-resolution x-ray diffraction studies show now a remarkable increase of compressive strain, while photoluminescence measurements show that the recovered band gap energy of GaAs does not change. Infrared measurements indicate that several N-Hn centers are formed in addition to the well-established H-N-H center (n = 2), which accounts for the band gap recovery. The vibrational properties of the corresponding deuterium centers provide clues to the microscopic structures of these centers. Furthermore, theory shows that the center with n = 2 is robust when additional H is added in its vicinity and remains as a core of likely N-Hn defects.