Effect of Al Addition on Crystal Structure of AlGaN/GaN on GaAs (001) Substrate Grown by Metalorganic Vapor Phase Epitaxy

Abstract

Effects of Al addition on a structural phase modification in AlGaN/GaN films on GaAs  substrate grown by MOVPE have been investigated. To examine the effect of Al addition, AlGaN/GaN films were grown with varied a molar flow ratio of TMAl to the total group-III elements of 0, 0.15, and 0.30. Quantity of hexagonal phase incorporation was evaluated by the ratios of integrated XRD intensity of hexagonal  plane to cubic  plane from reciprocal space mappings. The diffraction geometry factor was considered in the calculation. The results suggest that GaN primarily contains a hexagonal phase with a small fraction of a cubic phase (15%). With Al addition, a hexagonal phase inclusion significantly decreased. The fraction of a cubic phase becomes dominant (66%) and overcomes a hexagonal phase inclusion. As a result, with an addition of Al, our result demonstrates a structural phase modification from hexagonal to cubic phases in the AlGaN/GaN films on GaAs . Besides, TEM image and selective area diffraction patterns indicated that the structural phase might transform through stacking faults. Moreover, the area of the flat surface seen from AFM images indicated a cubic  plane, therefore, can briefly comparatively predict the amount of cubic phase in the AlGaN/GaN films.