Growth pressure dependence of optical and structural properties of a-plane InGaN/GaN multi-quantum wells on r-plane sapphire

We investigated the influence of growth pressure on the characteristics of a-plane InGaN based MQWs. Nonpolar a-plane GaN based MQW films were directly grown on r-plane sapphire by metalorganic chemical vapor deposition (MOCVD). The growth pressure for the MQWs was varied from 100 mbar to 400 mbar, while keeping other growth parameters constant. The polarity of a-plane InGaN/GaN grown on r-plane sapphire was determined by CBED (convergent-beam electron diffraction) measurements. The blue-shifted PL peak wavelength and decreased FWHM of the PL peak were observed as the growth pressure was increased from 100 mbar to 400 mbar. Meanwhile, the PL peak intensity for MQWs increased as the growth pressure increased. This result was explained by the variation of the wafer surface temperature, which was affected by the growth pressure in spite of being exposed to the same susceptor temperature. The increased growth pressure leads to increased gas conduction and, thereby, the wafer surface temperature increased. For MQWs grown at the same wafer surface temperature, the higher growth pressure led to increased In incorporation in a-plane InGaN/GaN MQWs.