Emission mechanisms of bulk GaN and InGaN quantum wells prepared by lateral epitaxial overgrowth

The emission mechanisms of bulk GaN and InGaN quantum wells (QWs) were stud ied by comparing their optical properties as a function of threading disloc ation (TD) density, which was controlled by lateral epitaxial overgrowth. S lightly improved excitonic photoluminescence (PL) intensity was recognized by reducing TD density from 10(10) cm(-2) to less than 10(6) cm(-2). Howeve r, the major PL decay time was independent of the TD density, but was rathe r sensitive to the interface quality or material purity. These results sugg est that TDs simply reduce the net volume of light-emitting area. This effe ct is less pronounced in InGaN QWs where carriers are effectively localized at certain quantum disk size potential minima to form quantized excitons b efore being trapped in nonradiative pathways, resulting in a slow decay tim e. The absence of any change in the optical properties due to reduction of TD density suggested that the effective band gap fluctuation in InGaN QWs i s not related to TDs. (C) 1999 American Institute of Physics. [S0003-6951(9 9)01009-8].