Semiconductor heterostructures are the core elements of electronic and especially opto-electronic semiconductor devices, such as light emitting diodes (LEDs) and laser diodes (LDs). Ideally it is the design of the structure that defines the properties of the device at hand, but in practice the structural quality of both the semiconductor materials themselves and the heterointerfaces between them often limit significantly the output. This is the case especially in device structures fabricated out of III-nitrides (AlN, GaN and InN) that are the material family of choice for blue and ultraviolet (UV) optoelectronics with a potential for covering the whole spectral range down to infrared (IR), due to the unfortunate aspect of having lattice constants that differ considerably one from another. Hence even if it was possible to grow the thin layers of materials, or more specifically their ternary alloys such as In_0.13Ga_0.87N, without defects in the bulk of the layer, the interface e.g. between the quantum well and the barrier in a LD is likely to have a complicated structure and will be prone to generate extended defects detrimental to the functioning of the device.

We explore the potential of positron annihilation spectroscopy in studying nitride heterostructures. In addition to the bandgap modulation that is essential for the electronic device, the use of different nitrides creates electric fields in the structure induced by spontaneous polarization due the non-inversionsymmetric wurtzite structure of the materials. We show that depending on the design of the heterostructure, both the interface regions and the defects inside the bulk materials in these structures can be studied with positrons. To this end we combine positron experiments in nitride materials and LED structures with state-of-the-art ab initio computational methods. without defects in the bulk of the layer, the interface between e.g. the quantum well and the barrier in a LD is likely to have a complicated structure and will be prone to generate extended defects detrimental to the functioning of the device.

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