Efficient Terahertz Generation Within InGaN/GaN Multiple Quantum Wells

We have investigated terahertz (THz) generation from InGaN/GaN multiple quantum wells (QWs). For the laser pump power of 400 mW at 391 nm, the highest THz output power is nearly 1 mu W. Assuming that the output power quadratically scales up with the interaction length, such an output power corresponds to a normalized output power of 1.7 nW/nm(2). The normalized output power measured on the InGaN/GaN multiple quantum-well structures correspond to probably one of the highest values ever reported among all different semiconductor and nonlinear materials. Following our measurements of the output spectrum, power, and polarization angle as functions of average pump intensity, incident angle, and pump polarization angle, respectively, we have attributed the mechanism for the THz generation from the InGaN/GaN QWs to the radiation of the dipoles, following the generation of the spatially separated electrons and holes under the strong built-in electric fields inherently present in the nitride-based quantum-well structures.