Structural, electrical and optical characterization of MOCVD grown In-rich InGaN layers

We report on the growth of In-rich InGaN layers on GaN/sapphire templates. InGaN layers of various In contents were grown at a low temperature of 550 °C by varying the TMIn partial pressure. A thin InN interlayer was grown to enhance the In incorporation. About 11% absolute In content increase in InGaN was measured compared to a structure without InN interlayer. Low-temperature photoluminescence (PL) measurements were performed. Sufficiently strong PL was detected for InN and In-rich InxGa1-xN (x: 0.76-0.85) layers. An energy difference between the low-temperature PL peak energy and room temperature absorption edge was observed. The difference increases with decreasing In content below 76%, indicating a higher degree of localization of the photo-generated carriers. Surface electrical properties were studied by IR reflectance and X-ray photoemission spectroscopy. The amount of surface electron accumulation in connection with downward band bending decreased with increasing Ga content in the InGaN layer. The highest sheet carrier density was observed for InN with the highest band bending of 0.58 eV, whereas for the In0.20Ga0.80N sample, the band bending is much less (0.03 eV) and the surface carrier density is lower. A transition from an accumulation layer to an electron depletion layer was observed at an In content slightly less than 20%.