Optical properties of GaNAs samples with N concentration from N: 10¹⁸ cm^-3 to 0.62% are investigated by different optical techniques, including temperature dependent photoluminescence (PL), excitation dependent photoluminescence, photoluminescent excitation (PLE) and modulated photoreflectance (PR). The doped N induces two effects: First, even for very dilute doping (N: 10¹⁸ cm^-3) , the new band gap of GaNAs is already exhibited. The band gap energy decreases with increasing N concentration. Second, the N-related impurity states (NN pairs and N clusters) appear clearly at x=0.03% and persist as discrete levels below the band gap. Then they become a continuous spectrum that constitutes the tail of the band gap at x=0.62%....[ Read more ]

Optical properties of GaNAs samples with N concentration from N: 10¹⁸ cm^-3 to 0.62% are investigated by different optical techniques, including temperature dependent photoluminescence (PL), excitation dependent photoluminescence, photoluminescent excitation (PLE) and modulated photoreflectance (PR). The doped N induces two effects: First, even for very dilute doping (N: 10¹⁸ cm^-3) , the new band gap of GaNAs is already exhibited. The band gap energy decreases with increasing N concentration. Second, the N-related impurity states (NN pairs and N clusters) appear clearly at x=0.03% and persist as discrete levels below the band gap. Then they become a continuous spectrum that constitutes the tail of the band gap at x=0.62%.

From temperature dependent PL spectra, the peak related to GaNAs band gap appears at 40K in a sample with x=0.1%. At low temperatures, the N-related impurity states are dominant, while at high temperatures they are saturated due to thermal quenching of the localized state; the GaNAs band edge PL gradually appears and dominates. From the excitation dependent PL spectra, the PL peak related to the GaNAs band gap splits into two peaks corresponding to free and bound excitons under low excitation power and in lower N composition samples. All samples are investigated by PR technique at room temperature. The result is consistent with the PL spectra, showing that with N doping into GaAs, the new band gap of GaNAs is formed.