10. Piezo-Phototronic Effect on Light-Emitting Diode

As a classical device, the performance of an LED is dictated by the structure of the p–n junction and the characteristics of the semiconductor materials. Once an LED is made, its efficiency is determined largely by the local charge carrier densities and the time at which the charges can remain at the vicinity of the junction. The latter is traditionally controlled by growing a quantum well or using a built-in electronic polarization for “trapping” electrons and holes in the conduction and valence bands, respectively. This is a rather complex and expensive process involving MBE and MOCVD, and more importantly, the width and potential well depth of the quantum well are fixed once the growth is complete. In this chapter, we describe the piezo-phototronic effect on the light emitting of a n-ZnO–p-GaN structure for illustrating its general impact to LED. The emission intensity and injection current at a fixed applied voltage have been enhanced by a factor of 17 and 4 after applying a 0.093 % compressive strain, respectively, and the corresponding conversion efficiency has been improved by a factor of 4.25 in reference to that without applying strain! The absolute external efficiency has reached 7.82 %. This hugely improved performance is suggested to arise from an effective increase in the local “biased voltage” as a result of the band shift caused by piezopotential and the trapping of holes/electrons at the interface region in a channel created by the piezopotential near the interface. The study shows that the piezo-phototronic effect can be very effectively used for enhancing the efficiency of energy conversion in today’s green and renewable energy technology without using the sophisticated nanofabrication procedures that are of high cost and complex. The physical model presented can be expanded to many other materials.