Piezoelectric effects on the optical properties of GaN/AlxGa1-xN multiple quantum wells

Piezoelectric effects on the optical properties of GaN/AlGaN multiple quant um wells (MQWs) have been investigated by picosecond time-resolved photolum inescence (PL) measurements. For MQWs with well thicknesses 30 and 40 Angst rom, the excitonic transition peak positions at 10 K in continuous wave (cw ) spectra are redshifted with respect to the GaN epilayer by 13 and 45 meV, respectively. The time-resolved PL spectra of the 30 and 40 Angstrom well MQWs reveal that the excitonic transition is in fact blueshifted at early d elay times due to quantum confinement of carriers. The spectral peak positi on shifts toward lower energies as the delay time increases and becomes red shifted at longer delay times. We have demonstrated that the results descri bed above are due to the presence of the piezoelectric field in the GaN wel ls of GaN/AlGaN MQWs subject to elastic strain together with screening of t he photoexcited carriers. By comparing experimental and calculation results , we conclude that the piezoelectric field strength in GaN/Al0.15Ga0.85N MQ Ws has a lower limit value of about 560 kV/cm. The electron and hole wave f unction distributions have also been obtained. The implication of our findi ngs on the practical applications of GaN based optoelectronic devices is al so discussed. (C) 1998 American Institute of Physics. [S0003-6951(98)04349- 6].