Influence of Buffer Layer And Growth Temperature on The Properties of An Undoped GaN Layer Grown on Sapphire Substrate by Metalorganic Chemical Vapor Deposition

The influence of low-temperature buffer layer thickness on the electrical properties of GaN film is investigated, and the surface morphology is also examined by atomic force microscopy. A best surface morphology does not show best electrical properties, which could be attributed to the usual growth mechanism for GaN film on sapphire substrate. The influence of the growth temperature for the final GaN layer is also investigated. When the growth temperature increases to 1100 °C, the mobility is greatly enhanced to 600 cm2/V s with a background carrier density of 3.3×1016/cm3 at room temperature. The emission energy of the near band gap exciton at a low temperature shows a blueshift with increasing growth temperature due to an enhanced thermal stress. The calculation based on a thermal stress model agrees very well with the photoluminescence measurement. This result could partly explain the reason that the previously published values for the near band gap exciton emission energy are scattered.

Epitaxial GaN layers grown on sapphire contain a very large density of defects (threading dislocations, stacking faults, inversion domain boundaries.Among these defects, we have performed the analysis of the basal stacking faults by high resolution transmission electron microscopy. Two faults, I1 and I2, were identified. The formation of the I1 fault is based on the climb-dissociation process of the (1/3)langle11-20rangle or of the perfect dislocations whereas the I2 fault is due to the shear of the structure leading to a partial dislocation loop.


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