Terahertz pulse emission from strained GaN/GaInN quantum well structures

Efficient THz pulse generation from optically pumped InGaN/GaN multiple quantum well structures is demonstrated. Such structures incorporate strong electric fields of opposite directions - piezoelectric fields inside the quantum wells and in the barrier. Polarized states inside the quantum well and in the barrier give different contributions to the THz pulse, depending on whether the excitation is real or virtual. If the excitation energy is slightly below the e1-h1 transition in the quantum well, two-photon absorption in the barriers is observed to give the dominant contribution to the THz generation process at high pump fluence. At low pump fluence the virtual excitation of polarized states inside the quantum well dominates.