Kyuhan Lee

Effects of barrier growth temperature on the properties of InGaN/GaN multi-quantum wells

The effects of the growth temperature and ambient of GaN quantum barriers on the characteristics of InGaN/GaN multi-quantum wells (MQWs) grown by a thermally pre-cracked ion-supplied metalorganic chemical vapor deposition (TPIS-MOCVD) system were investigated. The improvement of optical, structural properties and surface morphology in the MQWs with increasing the growth temperature of quantum barriers was found. Without a GaN capping layer, there were many pits and the thickness of quantum pair reduced by the thermal etching during the temperature-ramping process. Photoluminescence (PL) peaks showed a blue-shift and double peaks, but relative PL intensity abruptly increased due to the suppression of deep level related defects and smooth surface morphology caused by the increased surface mobility of adatom in the high temperature region. By using a GaN capping layer on the InGaN well layer, the thermal decomposition of the InGaN well layer was suppressed and pits on the surface abruptly reduced. A hydrogen carrier gas for the GaN barrier growth also improved the optical and structural properties of MQWs.

Growth of AlGaN epilayers related gas-phase reactions using TPIS-MOCVD

Abstract AlGaN epilayers on GaN/sapphire were successfully grown under various growth conditions using a thermally pre-cracked ion-supplied metalorganic chemical vapor deposition. The Al composition in the solid was affected by the gas-phase parasitic reaction between NH 3 and trimethylaluminum (TMAl). As the operating pressure decreased, the Al composition in the solid increased over the ideal incorporation efficiency. This is due to a scavenging effect and a site-blocking effect. As the TMAl flow rate increased with fixed flow rates of NH 3 and trimethylgallium (TMGa), the Al concentration in the solid increased but started to saturate. As the TMGa flow rate decreased, the solid Al composition increased linearly, which means different parasitic reactions between TMGa:NH 3 and TMAl:NH 3 . In addition, we found that the separating plate that was inserted to the reactor in front of the heated susceptor to separate ammonia gas flow from MO source input played an important role in the AlGaN growth. Particularly, the separating plate was more attractive under high operating pressure. When it was inserted, a white crystalline solid formed by the adduct (TMAl:NH 3 ) of parasitic reaction in the gas phase disappeared. It also increased the Al concentration in the solid. SEM images of AlGaN epilayer’s surface showed many small islands due to the lack of surface mobility of adatoms.

The influence of ammonia pre-heating to InGaN films grown by TPIS-MOCVD

Abstract The InGaN films on GaN layers using a thermally pre-cracked ion-supplied metalorganic chemical vapor deposition (TPIS-MOCVD) system were investigated by a high-resolution X-ray diffraction and the thermodynamic analysis was performed for an NH3 pre-heater by using the computational fluid-dynamic simulations. As the flow rates of NH3 increased, the In composition and the thickness of the InGaN films increased, which meant that the relative indium incorporation efficiency was dependent on the NH3 flow rate and affected by the growth rate. In a low NH3 flow condition, indium metal droplets appeared on the surface of the InGaN layer in a conventional MOCVD system and decreased the indium incorporation efficiency of the InGaN films. The thermodynamic model of the ammonia dissociation did not follow equilibrium conditions and adduct-driven species seemed the actual growth precursors in nitride. The catalyst effect of the NH3 pre-heater plays an important role in the mixing region and growing surface, resulting in the higher indium incorporation and droplet-free surface in a TPIS-MOCVD system.