Nonpolar Nitride Semiconductor Optoelectronic Devices: a Disruptive Technology for next Generation Army Applications

Nonpolar nitride semiconductor materials containing a wide range of structural defects are studied. High quality InGaN quantum wells grown on bulk stacking fault (SF) -free GaN substrates show larger PL intensity and shorter PL lifetime with decreasing well width, indicating that the radiative lifetime is becoming smaller as the well narrows, consistent with the theoretically predicted increase in oscillator strength and associated exciton binding energy. Moreover, the fact that these phenomena are observable at room temperature is indicative of the suppression of defect-related nonradiative recombination for growth on bulk substrates, showing great promise for visible light emitters. We have also demonstrated enhanced THz emission from nonpolar GaN due to carrier transport in internal in-plane electric fields created by the termination of the in-plane polarization in wurtzite domains at zincblende stacking faults. The estimated, maximum average in-plane electric field of ~ 290 kV/cm in the wurtzite regions for an I1 type SF density of 1 X 10 cmis comparable to the bias fields applied to PC switches using low-temperature grown GaAs, one of the best PC materials, but does not require electrode processing or an external bias. Comparison with THz emission from SF-free m-GaN indicates that the THz signal from SF-related in-plane carrier transport dominates that usually observed from carrier diffusion or surface surge-currents normal to the sample surface, even for high excess electron energies and short absorption lengths favorable to diffusive transport. These results suggest that nonpolar nitride semiconductor devices are a potentially disruptive technology that may lead to leap-ahead advances in devices operating across the electromagnetic spectrum from UV to THz for future Army applications. Fig. 1. Comparison of band structure, electron and hole wave functions, and optical transitions in GaN/AlGaN single quantum wells grown along polar (left) and nonpolar directions.