Nitride semiconductors as terahertz sources based on spontaneous and piezoelectric polarization

We investigate the effects of internal polarization‐related drift and diffusion on the emitted THz radiation from m ‐plane (1$ \bar 1 $00), a ‐plane (11$ \bar 2 $0), and c ‐plane (0001) nitride semiconductors. Enhanced THz radiation is observed from c ‐plane InN/InGaN multiple quantum wells as compared to c ‐plane bulk InN at 800 nm excitation wavelength. THz generation in the quantum well structure is due to surface normal transport in electric fields due to the termination of spontaneous and piezoelectric polarization at the well/barrier interfaces. From high stacking fault density nonpolar GaN, we observe further enhanced THz emission as compared to stacking fault free m ‐plane GaN. THz generation from the high stacking fault density m ‐plane GaN is attributed to in‐plane transport in built‐in fields due to stacking fault‐terminated internal polarization. A similar effect is observed in m ‐plane as well as a ‐plane InN. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)