Impurity doping effect on thermal stability of InGaN/GaN multiple quantum-well structures

Thermal stability of InGaN/GaN multiple quantum-well (MQW) structures grown by metalorganic vapor phase epitaxy on (0001) sapphire substrates was investigated. Samples were annealed under atmospheric nitrogen ambient at 1000°C after growth. The thermal stability of MQW structures was estimated by high-resolution x-ray diffraction. It was found that thermal annealing degraded MQW periodicity in an undoped sample. This was due to the thermal diffusion of indium atoms via Ga vacancies in the GaN barrier region. It was also found that both Si doping and Mg doping improved the thermal stability of MQW structures. This mechanism was considered that Si and Mg, which were incorporated into column-III sites, prevented formation of the Ga vacancies. Thus, the thermal diffusion of indium atoms was suppressed. Room temperature photoluminescence (PL) from the Si-doped MQWs retained intense emission after annealing, while the undoped and Mg-doped MQWs showed degradation of PL intensities after annealing. It was, therefore, found that Si was a desirable dopant to promote the thermal stability of InGaN/GaN MQWs.