Nanoindentation of GaAs/AlAs distributed bragg reflector grown on GaAs substrate

Nanoindentation was used to investigate the mechanical parameters of GaAs/AlAs Distributed Bragg Reflectors. Such heterostructures are commonly employed in surface-emitting optoelectronic devices as LED or lasers. The investigation was carried for fully pseudomorphic AlAs/GaAs heterostructures and compared with bulk GaAs. The nanoindentation tests with sharp (Vickers) and spherical tip were conducted, and pop-in events were observed. We show that below pop-in load, the response of both materials is similar i.e., elastic parameters of the heterostructure and GaAs are practically the same. However, the pop-in events take place at higher loads for heterostructures than for GaAs. This in turn indicates that the heterostructure has a higher resistance to damage. For both materials, the pop-in load depends on loading rate. The possible mechanisms of pop-in are discussed. In the elastic-plastic stage (after pop-in), the heterostructure exhibits lower stiffness and lower hardness than GaAs does. The surface cracks that are generated in the heterostructure during the indentation test continue to grow even when the load is removed.