Density Of V-pits Research Articles

Enhanced luminescence of InGaN/GaN multiple quantum wells by strain reduction

InGaN/GaN multiple quantum well (MQW) structures were grown by MOCVD. A strain-relief underlying layer was employed to reduce the strain in the InGaN well layers arising from the large lattice mismatch between InN and GaN. Samples were investigated by photoluminescence (PL), electroluminescence (EL) and atom force microscopy (AFM) to characterize their optical and morphological properties. By inserting an underlying layer, the PL intensity was increased more than three times. Under small injection current (1–15 mA), the blue-shift of EL peak wavelength was decreased from 8 to1.8 nm, the surface morphology was improved and the density of V-pits was reduced from 14–16 × 10 8 to 2–4 × 10 8/cm 2. Further, the 20-mA output power was increased by more than 50%.

Improved quality of InGaN/GaN multiple quantum wells by a strain relief layer

Different InGaN/GaN multi quantum wells (MQWs) structures were grown by metalorganic chemical vapor deposition (MOCVD). Samples were investigated by photoluminescence (PL), atom force microscopy (AFM) and double crystal X-ray diffractometry (DCXRD) to character their optical, morphological and crystal properties. By inserting the strain relief layer, the PL intensity was increased more than two times. The surface morphology was improved and the density of V-pits was reduced from 16–18×10 8 to 6–7×10 8/cm 2. Further, the interface abruptness was also improved. We attributed the improvements of the quality of InGaN/GaN MQWs to the relief of strain in the InGaN/GaN MQWs.

Strain relaxation due to V-pit formation in InxGa1−xN∕GaN epilayers grown on sapphire

Strain relaxation in semiconductor heterostructures generally occurs through the motion of dislocations that generates misfit dislocations above a critical thickness. However, majority of the threading dislocations in GaN-related materials have no driving force to glide, and those with a driving force are kinetically impeded even at a temperature of 1000 °C. In spite of this, the strain in InxGa1−xN∕GaN epilayers grown on c-plane sapphire substrates was observed to decrease as the InxGa1−xN layer becomes thicker. We have explored the possibility of V-pit formation at terminated dislocations as the predominant relaxation mechanism in highly mismatched systems such as InxGa1−xN∕GaN. We demonstrate that a driving force exists to nucleate V pits for strain relief. The formation of V pits was modeled through the energy balance between the strain energy in the InxGa1−xN epilayer, the destruction of dislocation energy to form V pits and the strain that is relieved due to the formation of edges during the process of nucleating V pits in thermal equilibrium. V-pit formation and growth lead to strain relief as the film becomes thicker. The model illustrates many features that correlate reasonably well with experimental observations; the most significant trends are a rise in V-pit density and a decrease in strain with increasing layer thickness.